Title of Invention

STREPTOGRAMINDERIVATIVES, THEIR PREPARATION AND COMPOSITIONS WHICH CONTAIN THEM

Abstract

The present invention relates to group A streptogramin derivatives of formula (I) wherein : R1 represents alkyl, alkenyl or alkynl which may be mono-fluorinated or poly-fluorinated, or cycloalkyl containing 3 to 6 carbon atoms, phenylmethyl or heterocyclmethyl whereof the heterocycyl part is aromatic; R2 represents hydrogen, methjyl or ethyl; the bond represents a single bond (stereochemistry 27R) or a double bond the alkyl radicals containing 1 to 6 carbon atoms in linear or branched chain and the alkenyl and/or alkenyl radicals containing 3 to 6 carbon atoms in linear or branched chain. Said derivatives are particularly interesting antibacterial agents.

Full Text

The present invention relates to group A streptogramin derivatives of general formula: which have particularly advantageous antibacterial activity. Among the known streptogramins, pristinamycin (RP 7293), an antibacterial agent of natural origin produced by Streptomyces pristinaespiralis, was isolated for the first time in 1955. The pristinamycin sold under the name Pyostacine® consists mainly of pristinamycin IIA combined with pristinamycin IA. Another antibacterial agent of the streptogramin class, virginiamycin, was isolated from Streptomyces virgxniae, ATCC 13161 [Antibiotics and Chemotherapy, 5, 632 (1955) ] . Virginiamycin (Staphylomycine®) consists mainly of factor M1 (VM1) combined with factor S (VS). F. Le Goffic et al., Eur. J. Med. Chem.-Chimica Therapeutica, 16(1), 69-72 (1981) have disclosed the preparation of dihydroxy derivatives of pristinamycin IIA. Patent application GB-A-2 206 879 discloses modified group A streptogramin derivatives of structure: however, these derivatives show no activity orally. It has now been found that the group A streptogramin derivatives of general formula (I) in which: - R1 represents alkyl, alkenyl or alkynyl radicals which may be mono- or polyfluoro radicals, or cycloalkyl radicals containing 3 to 6 carbon atoms, phenylmethyl radicals or heterocyclylmethyl radicals in which the heterocyclyl portion is aromatic, - R2 represents a hydrogen atom or a methyl or ethyl radical, and - the bond ---represents a single bond (27R stereo chemistry) or a double bond, the alkyl radicals containing 1 to 6 carbons in a straight or branched chain and the alkenyl and/or alkynyl radicals containing 3 to 6 carbons in a straight or branched chain, have particularly advantageous antibacterial activity, alone or combined with a group B streptogramin derivative. According to the invention, when R2 is a heterocyclylmethyl radical, the heterocyclyl radical is advantageously chosen from pyrrolyl, furyl, thienyl, imidazolyl and pyridyl. According to the invention, when R1 is alkyl mono- or polysubstituted with a fluorine atom, the alkyl radical preferably contains 1 or 2 carbon atoms; when R1 represents alkenyl, it preferably represents allyl, and when it represents alkynyl, it preferably represents propargyl. The streptogramin derivatives of general formula (I) may be prepared by the action of a derivative of general formula: for which R1 is defined as above and X represents a halogen atom or a methylsulphonyloxy, p-toluene-sulphonyloxy or trifluoromethylsulphonyloxy radical, in the presence of a phase-transfer agent, on a dibydroxy derivative of the streptogramin of general formula: in which R2 is defined as above, the bond represents a single bond (27R stereochemistry) or a double bond, and for which derivative the hydroxyl function in position 14 and/or the amide function in position 8 have been optionally protected beforehand, followed, where appropriate, by removal of the protecting radical(s). Preferably, when X is a halogen atom, a derivative of general formula (Ila) for which X is a bromine or iodine atom is reacted. The phase-transfer agent is advantageously chosen from quaternary ammonium derivatives (for example salts of tetraalkylammonium or trialkylbenzyl-ammonium such as the chloride, bromide or sulphate) . The reaction is generally carried out in basic medium, for example in the presence of sodium hydroxide or potassium hydroxide, or in the presence of potassium carbonate or caesium carbonate, at a temperature of between 10°C and 60°C, in aqueous-organic medium, for example in a hydrocarbon (for example toluene), a halogenated solvent (for example dichloromethane) or an ester (in particular ethyl acetate). The process is preferably performed at about 20°C. Preferably also, the process is performed in the presence of an excess of the derivative of general formula (Ila). The protection and deprotection of the hydroxyl radical in position 14 or of the amide radical in position 8 are carried out according to the usual methods which do not affect the rest of the molecule, in particular by applying the methods described by T.W. Greene and P.G.M. Wuts, Protective Groups in Organic Synthesis (2nd edition), A. Wiley - Interscience Publication (1991) or by Mc Omie, Protective Groups in Organic Chemistry, Plenum Press (1973). For example, the protection of the hydroxyl radical is carried out with an allyl radical which is installed and removed by analogy with the methods described below in the examples. The protection of the amide may be carried out in particular with the t-butoxycarbonyl radical. When the reaction leads to a mixture of the 14- and 16-0-alkyl isomers, these isomers may be separated according to the usual methods which do not affect the rest of the molecule, in particular by chromatography [high performance liquid chromatography (HPLC) on a normal or reverse phase, on a chiral or non-chiral phase, or by flash chromatography] or by crystallization. According to the invention, the streptogramin derivatives of general formula (I) may also be prepared by desilylation and then 37-O-alkylation using a derivative of general formula (Ila), of a silyl and 14-0-allyl derivative of general formula: in which R2 is defined as above, the bond represents a single bond (27R stereochemistry) or a double bond, and the radical R3 represents a protecting radical and R4 represents a silyl radical, followed by removal of the allyl radical and the protecting radical R3 according to the known methods which do not affect the rest of the molecule. The protecting radical R3 is advantageously t-butoxycarbonyl. The silyl radical R4 may be chosen in particular from trialkylsilyl, dialkylphenylsilyl and alkyldiphenylsilyl (for example t-butyldiphenylsilyl or t-butyldimethylsilyl). The desilylation is carried out according to the usual methods which do not affect the rest of the molecule. The process is performed in particular in the presence of a source of fluoride ions such as tetra-n-butylammonium fluoride or a hydrofluoric acid/amine complex, the amine possibly being, for example, triethylamine or pyridine. The reaction is carried out in a chlorinated solvent (for example dichloromethane) or in an ether (for example tetrahydrofuran) at a temperature of between 20°C and 80°C. The 37-O-alkylation reaction is carried out by the action of a derivative of general formula (Ila) as defined above, on the desilylated streptogramin of general formula (III). Preferably, the process is performed under an inert atmosphere (for example under nitrogen or argon) in basic medium, for example in the presence of sodium hydride, alkali metal (lithium, sodium or potassium) hexamethyldisilylamide or in the presence of an organolithium reagent (for example n-butyllithium) or alternatively in the presence of an amide (for example lithium diisopropylamide) , in an inert solvent such as an amide (for example dimethyl-formamide) or an ether (for example tetrahydrofuran) , at a temperature of between -20°C and 60°C. The removal of the allyl radical is carried out, for example, in the presence of a proton donor such as 4-methylphenylsulphinic acid, in the presence of a palladium catalyst (for example tetrakis(triphenyl-phosphine)palladium) , in a chlorinated solvent (for example dichloromethane), at a temperature of between 0°C and 60°C. It is also possible to perform the process according to the methods described in the references cited above. The t-butoxycarbonyl radical is removed according to the methods which do not affect the rest of the molecule, in particular in a solvent such as dimethyl sulphoxide, dimethylformamide or diphenyl ether, at a temperature of between 130°C and 170°C. The streptogramin derivative of general formula (III) may be prepared by 36-O-allylation and then 37-O-silylation and protection of the amide in position 8 with a radical R3. The allylation is carried out according to the usual methods as cited in the above references. In particular, it is carried out by the action of an allyl halide (preferably bromide) or of a methylsulphonyloxy, p-toluenesulphonyloxy or trifluoromethylsulphonyloxy derivative in the presence of a base such as a carbonate (in particular potassium carbonate or caesium carbonate), in a solvent such as a ketone (for example methyl ethyl ketone), a nitrile (for example acetonitrile) or a hydrocarbon (in particular toluene), at a temperature of between 40°C and 80°C, preferably 70°C. The silylation is carried out according to the methods which do not affect the rest of the molecule, in particular using a halide (preferably a chloride) of the silyl radical R4. For example, the process is performed using trialkylsilyl chloride, dialkylphenylsilyl chloride or alkyldiphenylsilyl chloride (for example t-butyldiphenylsilyl chloride or t-butyldimethylsilyl chloride), working in a solvent such as a chlorinated solvent (for example dichloro-methane) , an amide (for example dimethylformamide) , an ether (for example tetrahydrofuran) or a nitrile (for example acetonitrile) , at a temperature of between 0°C and 60°C, and preferably at room temperature. The installation of the protecting radical R3 is carried out according to the methods mentioned above. For example, it is carried out in the presence of an excess of di-t-butyl dicarbonate, a base (triethylamine or pyridine) and optionally a catalyst such as 4-dimethylaminopyridine, in a chlorinated solvent (dichloromethane) or an ether (tetrahydrofuran) at a temperature of between 0°C and 80°C. The dihydroxylated group A streptogramin derivative of general formula (II) may be obtained by selective reduction of the natural pristinamycin component of general formula: in which R2 is defined as above and the bond represents a single bond (27R stereochemistry) or a double bond, followed by separation of the 16S epimer form. The reduction is advantageously carried out in the presence of a reducing agent such as an alkali metal borohydride, for example sodium borohydride or sodium triacetoxyborohydride, in an organic solvent chosen from chlorinated solvents (for example dichloro-methane, dichloroethane or chloroform), tetrahydro-furan, acetic acid and alcohols such as methanol, ethanol or 2-propanol, at a temperature of between -78°C and 40°C. The separation of the 16R epimer form and of the 16S epimer form is carried out according to the 11 usual methods; for example, the separation of the epimer forms may be carried out by chromatography, flash chromatography, high performance liquid chromatography (HPLC), on a chiral or non-chiral phase, or centrifugal partition chromatography (CPC), starting with the mixture of the 16R and 16S epimers. Alternatively, the separation may be carried out by crystallization. The pristinamycin derivatives of general formula (IV) correspond, respectively, to pristinamycin IIA (PIIA) , pristinamycin IIB (PUB) , pristinamycin IIC (PIIC) , pristinamycin I ID (PIID), pristinamycin IIF (PIIF) and pristinamycin IIG (PIIG), which are known components of natural pristinamycin. The components PIIF and PIIG have been disclosed in European patent EP-A-0 614 910- Pristinamycin IIC (PIIC) and pristinamycin IID (PIID) may be obtained as described by J.C. Barriere et al. , Expert- Opin. Invest. Drugs, 3(2), 115-31 (1994). The pristinamycin derivatives of general formula (III) are novel products. The preparation and separation of the natural group A streptogramin components [streptogramins of general formula (IV)] is carried out by fermentation and isolation of the constituents from the fermentation must according to or by analogy with the method described by J. Preud'homme et al. , Bull. Soc. Chim, Fr., vol. 2, 585 (1968) or in European patent EP-A-0 614 910. Alternatively, the preparation of the natural group A components may be carried out by specific fermentation, as disclosed in patent application FR-A-2 689 518. The streptogramin derivatives of general formula (I) may be purified, where appropriate, by physical methods such as crystallization, chromatography or CPC. The streptogramin derivatives according to the present invention have antibacterial properties and synergistic properties with respect to the antibacterial activity of the group B streptogramin derivatives- They are particularly advantageous on account of their powerful activity alone or in combination. When they are combined with a group B streptogramin component or derivative, this component or derivative may be chosen, depending on whether it is desired to obtain a form for oral or parenteral administration, from the following natural components: pristinamycin IA, pristinamycin IB, pristinamycin IC, pristinamycin ID, pristinamycin IE, pristinamycin IF, pristinamycin IG, virginiamycin S1, S3 or S4, vernamycin B or C, etamycin or from semisynthetic derivatives as disclosed in patents or patent applications US-A-4 618 599, US-A-4 798 827, US-A-5 326 782, EP-A-0 772 630 or EP-A-0 770 132, in particular streptogramin derivatives of general formula: in which: 1. Rb, Rc, Re and Rf are hydrogen atoms, Rd is a hydrogen atom or a dimethylamino radical, and Ra is a radical of structure -CH2R'a for which R'a is pyrrolidinyl-3-thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, alkylthio substituted with 1 or 2 hydroxy sulphonyl, alkylamino or dialkyl-amino (which itself may optionally be substituted with mercapto or dialkylamino) , or substituted with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl or 2- or 3-pyrrolidinyl rings (which may be substituted with alkyl), or alternatively Ra is a radical of structure =CHR'a for which R'a is pyrrolidinyl-3-amino, piperidyl-3- (or -4-)amino, pyrrolidinyl-3-oxy, piperidyl-3- (or -4-)oxy, pyrrolidinyl-3~thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, or R'a is alkylamino, alkyloxy or alkylthio which is substituted with 1 or 2 hydroxy-sulphonyl, alkylamino or dialkylamino (which is itself optionally substituted with dialkylamino) , or with trialkylammonio, 4- or 5-imidazolyl, or with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl, or 2- or 3-pyrrolidinyl rings (which may be substituted with alkyl), or Ra is a quinuclidinyl-3- (or -4-)thiomethyl radical, or alternatively 2 . Ra is a hydrogen atom and a) either Rb, Re and Rf are hydrogen atoms, Rd is an -NHCH3 or -N(CH3)2 radical and Re is a chlorine or bromine atom, or represents an alkenyl radical containing 3 to 5 carbon atoms [if Rd is -N(CH3)2], b) or Rb, Rd, Re and Rf represent a hydrogen atom and Re is a halogen or an aminomonoalkyl, aminodialkyl, alkyloxy, trifluoromethyloxy, thioalkyl, Ci to C3 alkyl or trihalomethyl radical c) or Rb, Rc, Re and Rf represent a hydrogen atom and Rd is a halogen or an ethylamino, diethylamino or methylethylamino, alkyloxy or trif luoromethyloxy, thioalkyl, C1 to C6 alkyl, aryl or trihalomethyl radical, d) or Rb, Rc and Rf represent a hydrogen atom and Re is halogen or an aminomonoalkyl or aminodialkyl, alkyloxy or trifluoromethyloxy, thioalkyl or C1 to C3 alkyl radical, and Rd is halogen or an amino, amino monoalkyl or aminodialkyl, alkyloxy or trifluoro methyloxy, thioalkyl, C1 to C6 alkyl or trihalomethyl radical, e) or Rc, Re and Rf represent a hydrogen atom and Rb and Rd represent a methyl radical; or alternatively from the semisynthetic derivatives of the group B streptogramins of general formula: R1 is a hydrogen atom, an alkyl radical (1 to 8 carbons) , alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 8 carbons) , saturated or unsaturated heterocyclyl radical (3- to 8-membered), phenyl radical, substituted phenyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkyl- sulphinyl, alkylsulphonyl, amino, alkylamino or dialkyl- amino radicals] or a radical NR'R", R' and R", which may be identical or different, possibly being hydrogen atoms or alkyl radicals (1 to 3 carbons) or possibly forming, together with the nitrogen atom to which they are attached, a 3- to 8-membered heterocycle optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons) , cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-meiribered), benzyl radical, phenyl radical or substituted phenyl radical as defined above for the definition of Ri] , or alternatively, when Y is a radical =CR3-, R1 may also be halomethyl, hydroxymethyl, alkyloxymethyl, alkyl- thiomethyl in which the alkyl portion is optionally substituted with NR'R", alkylsulphinylmethy1, alkyl- sulphonylmethyl, acyloxymethyl, benzoyloxymethyl, cyclopropylaminomethyl or -(CH2)nNR'R" (n being an integer from 1 to 4 and R' and R" being defined as above) , or alternatively, if R3 is a hydrogen atom, R1 may also be formyl, carboxyl, alkyloxycarbonyl or -CONR'R" for which R' and R" are defined as above, or alternatively, when Y is a nitrogen atom, R1 may also be a radical -XR° for which X is an oxygen or sulphur atom, a sulphinyl or sulphonyl radical, or an NH radical and R° is an alkyl radical (1 to 8 carbons) , cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (3- to 8-membered), heterocyclylmethyl radical (3- to 8-membered) in which the heterocyclyl portion is attached to the methyl radical via a carbon atom, phenyl radical, substituted phenyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkyl sulphinyl, alkyl sulphonyl, amino, alkylamino or dialkylamino radicals] or a radical -(CH2)nNR'R" for which R' and R" are defined as above and n is an integer from 2 to 4, or alternatively, if X represents NH, R° may also represent a hydrogen atom, R2 is a hydrogen atom or an alkyl radical (1 to 3 carbons), R3 is a hydrogen atom or an alkyl, carboxyl, alkyloxycarbonyl or carbamoyl radical of structure -CO-NR'R" in which R' and R" are defined as above, Ra is a methyl or ethyl radical, and Rb, Rc and Rd have the definitions below: Rb and Rc are hydrogen atoms and Rd is a hydrogen atom or a methylamino or dimethyl ami no radical, Rb is a hydrogen atom, Re is a hydrogen, chlorine or bromine atom, or represents an alkenyl radical (3 to 5C) , and Rd is a radical -NMe-R"' for which R'" represents an alkyl radical, hydroxyalkyl radical (2 to 4C) or alkenyl radical (2 to 8C) optionally substituted with phenyl, cycloalkyl(3 to 6C)methyl radical, benzyl radical, substituted benzyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkylsulphinyl, alkyl sulphonyl, amino, alkylamino or dialkylamino radicals], heterocyclylmethyl radical or hetero- cyclylethyl radical in which the heterocyclyl portion is saturated or unsaturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-membered), phenyl radical, substituted phenyl radical as defined above for the definition of R1 or benzyl radical], or alternatively R'" represents a cyanomethyl radical or a radical -CH2CORe for which either Re is -OR'e, R'e being hydrogen, alkyl (1 to 6 carbons), alkenyl (2 to 6 carbons), benzyl or heterocyclylmethyl in which the heterocyclyl portion is 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen, or Re is an alkylamino, alkylmethylamino, heterocyclylamino or heterocyclylmethylamino radical in which the heterocyclyl portion is saturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted with an alkyl, benzyl or alkyloxycarbonyl radical, 3) Rb is a hydrogen atom, Rd is an -NHCH3 or -N(CH3)2 radical and Re is a chlorine or bromine atom or represents an alkenyl radical (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are hydrogen atoms and Re is a halogen atom or an alkylamino or dialkylamino, alkyloxy, trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 5) Rb and Re are hydrogen atoms and Rd is a halogen atom or an ethylamino, diethylamino or methylethyl-amino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkylsulphonyl, alkyl (1 to 6C) , phenyl or trihalomethyl radical, 6) Rb is a hydrogen atom and Re is a halogen atom or an alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) radical and Rd is a halogen atom or an amino, alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Re is a hydrogen atom and Rb and Rd represent a methyl radical, as well as the salts thereof, or alternatively from the semisynthetic derivatives of the group B streptogramins of general formula: in which R represents a radical -NRiR2 or -SR3 [for which Ri and R2, which may be identical or different, represent H, alkyl (1 to 8C) optionally substituted with OH, alkenyl (3 to 8C), cycloalkyl (3 to 8C), alkyloxy (1 to 8C) , dialkylamino, phenylalkyl which is optionally substituted [with one or more halogen or alkyl, hydroxyalkyl, alkyloxy or dialkylamino], saturated or unsaturated heterocyclylalkyl (3- to 8-membered) containing one or more hetero atoms chosen from N, S and 0, or altera tively R1 and R2 form, manner: 0.20 cm3 of triethylamine and 0.12 g of 4-N,N- dimethylaminopyridine are added to a solution of 1 g of (161?) -14-0-allyl-16- (tert-butyldimethylsilyloxy) -16- deoxopristinainycin IIB and 3.4 g of di-tert-butyl dicarbonate in 30 cm3 of dichloromethane, at 25°C. The reaction mixture is stirred for 16 hours at room temperature, diluted with 30 cm3 of dichloromethane and then poured into 60 cm3 of saturated aqueous sodium chloride solution. The organic phase is separated out after settling has taken place, dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa) to give 1.65 g of a yellow oil, which is purified by flash chromatography on silica [eluent: cyclohexane/ethyl acetate (60/40 by volume)]. -After concentrating the fractions containing the expected product, 0.71 g of (16.R) -14-0-allyl-16- (tert-butyldimethylsilyloxy) -8-N-tert-butyloxycarbonyl-16-deoxopristinamycin IIB is obtained in the form of a (16R) -14-O-Allyl-16- (tert-butyldimethyl-silyloxy) -16-deoxopristinamycin IIB may be prepared in the following manner: 3.06 cm3 of diisopropylethylamine and 0.43 g of 4-N,N-dimethylaminopyridine are added, at 20°C and under an argon atmosphere, to a solution of 2 g of (16J?) -14-0-allyl-16~hydroxypristinamycin IIB and 2 . 64 g of tert-butyldimethylchlorosilane in 15 cm3 of dichloro-methane. After stirring for 17 hours, the reaction mixture is diluted with 50 cm3 of dichloromethane and then poured into 50 cm3 of saturated aqueous sodium chloride solution. The organic phase is separated out after settling has taken place, dried over magnesium sulphate, filtered and then concentrated to dryness under reduced pressure (2.7 kPa) to give a residue which is stirred for 2 hours in 30 cm3 of diisopropyl ether. After filtering and drying under reduced pressure (2.7 kPa) , 1.57 g of (16J?) -14-0-allyl-16- (tert-butyldimethylsilyloxy) -16-deoxopristinamycin IIB are obtained in the form of a white powder. 1.5 Hz : 1H); 5.19 (broad d, J = 9 Hz : 1H); 5.23 (dd, J = 17.5 and 1.5 Hz : 1H); 5.71 (ddd, J =16-8.5 and 5 Hz : 1H); 5.81 (dd, J = 16.5 and 1.5 Hz : 1H); 5.88 (mt : 1H); 6.20 (d, J = 16 Hz : 1H) ; 6.28 (mt : 1H) ; 6.49 (dd, J = 16.5 and 5 Hz : 1H); 8.05 (s : 1H) . (16R)-14-0-Allyl-16-deoxo-16-hydroxy-pristinamycin IIB may be prepared in the following manner: 36.57 g of potassium carbonate and 65.35 cm3 of allyl bromide are added to a solution of 20 g of (16R) -16-deoxo-16-hydroxypristinamycin IIB in 450 cm3 of 2-butanone, at 20°C. The reaction mixture is refluxed for 76 hours. After cooling to 20°C and filtering, the reaction mixture is concentrated under reduced pressure (2.7 kPa)- The residue is taken up in 200 cm3 of dichloromethane and then washed successively with twice 100 cm3 of water and 300 cm3 of saturated aqueous sodium chloride solution. The organic phase is dried over magnesium sulphate and then concentrated to dryness under reduced pressure (2.7 kPa) to give 27.8 g of a yellow foam, which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/ methanol (94/3/3 by volume)]. After concentrating the fractions containing the expected product, 7.80 g of (16R) -14-0-allyl-16-deoxo-16-hydroxypristinamycin IIB are obtained in the form of a yellow foam. XH NMR spectrum (400 MHz, CDC13, 5 in ppm) : 0.96 (d, J = 6.5 Hz : 3H); 1.00 (d, J = 6.5 Hz : 3H); 1.10 (d, J = 6.5 Hz : 3H) ; from 1.70 to 2.05 (xnt : 6H) ; 1.80 (s : 3H) ; 2.12 (mt : 1H) ; 2.74 (mt : 1H) ; 2.79 (dd, J = 16.5 and 5.5 Hz : 1H) ; 2.99 (dd, J = 16.5 and 7 Hz : 1H) ; (16.R) -16-Deoxy-16-hydroxypristinamycin IIB may be prepared in the following manner: A suspension of 11.35 g of sodium borohydride in 550 cm3 of dichloromethane is refluxed for 20 minutes. 68.6 cm3 of acetic acid are then added dropwise over about 30 minutes, followed by addition of a solution (predried over sodium sulphate) of 52.75 g of pristinamycin IIB in 230 cm3 of dichloromethane, over about 45 minutes. The reaction mixture is stirred for 4.5 hours at reflux and then for 16 hours at 20°C. 500 cm3 of dichloromethane and 1500 cm3 of water are then added to the reaction mixture. The organic phase is separated out after settling has taken place and the aqueous phase is extracted with 500 cm3 of methylene chloride. The organic phases are combined and the pH is adjusted to 8 by slow addition of 1000 cm3 of saturated aqueous sodium bicarbonate solution. The resulting organic phase is washed successively with 1000 cm3 of water and 1000 cm3 of saturated aqueous sodium chloride solution and then treated with 3S vegetable charcoal, dried over sodium sulphate, filtered through Celite® and concentrated to dryness under reduced pressure (2.7 kPa) to give 50 g of a pale yellow solid. 378 cm3 of aqueous 0.5 M ammonium hydroxide solution are added to a solution of the above solid in 900 cm3 of methylene chloride, at 20°C. After stirring for 16 hours at 20°C, the organic phase is separated out after settling has taken place, washed with 1000 cm3 of water and then with 1000 cm3 of saturated aqueous sodium chloride solution, dried over sodium sulphate, filtered and concentrated to dryness under reduced pressure (2.7 kPa) to give 46 g of a pale yellow solid, which is purified by flash chromatography on silica [eluent: methylene chloride/ methanol gradient (98/2 and 97/3 by volume)]. After concentrating the fractions containing the expected product, 8.57 g of (16R) -16-deoxy-16-hydroxy- Example 2 (16R) -16-Deoxo-16-methoxypristinamycin IIB 1.2 g of sodium hydroxide, 0.50 g of tetra-n-butylammonium bromide and 4.7 0 cm3 of iodomethane are added to a solution of 8 g of (16R) -16-deoxo-16-hydroxypristinamycin IIB (prepared as described in Example 1) in 40 cm3 of dichloromethane and 40 cm3 of water, at 25°C. The reaction mixture is stirred for 24 hours at room temperature and the phases are then separated after settling has taken place. The organic phase is washed with 3 times 100 cm3 of saturated aqueous sodium chloride solution and then dried over magnesium sulphate, filtered and concentrated under reduced pressure (2.7 kPa) to give 10.7 g of a cream-coloured foam which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/ methanol (95/2.5/2.5 by volume)]. After concentrating the fractions containing the expected product, 1.2 g of a pale yellow foam are obtained, which product is recrystallized from 7 cm3 of hot acetonitrile to give 1.15 g of (16R) -16-deoxo-16-methoxypristinamycin IIB in the form of white crystals melting at about 125°C Example 3 (161?) -16-Allyloxy-16-deoxopristinamycin IIB 1.06 g of sodium hydroxide, 0.40 g of tetra- n-butylammonium bromide and 11.49 cm3 of allyl bromide are added to a solution of 7 g of (16.R) -16-deoxo-16- hydroxypristinamycin IIB (prepared as described in Example 1) in 50 cm3 of dichloromethane and 50 cm3 of water, at 25°C. The reaction mixture is stirred for 24 hours at room temperature and the phases are then separated once settling has taken place. The organic phase is washed with twice 100 cm3 of saturated aqueous sodium chloride solution and then dried over magnesium sulphate, filtered and concentrated under reduced pressure (2.7 kPa) to give 7.15 g of a yellow foam, which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/methanol (95/2.5/2.5 by volume)]. After concentrating the fractions containing the expected product, 1.2 g of a white foam are obtained, which product is recrystallized from 5 cm3 of hot acetonitrile to give 0.68 g of (16J?)-16-allyloxy-16-deoxopristinamycin IIB in the form of white crystals melting at about 114°C Example 4 (16J?) -16-Deoxo-16- (prop-2-ynyloxy)pristinamycin IIB Working in a similar manner to that described in Example 2, but starting with 7 g of {16R) -16-deoxo- 16-hydroxypristinamycin IIB dissolved in 40 cm3 of dichloromethane, 1.7 g of tetra-n-butylammonium bromide, 1.06 g of sodium hydroxide, 40 cm3 of water and 5 cm3 of propargyl bromide are added, at 20°C and under an argon atmosphere. After stirring for 18 hours and work-up, 7.23 g of an orange solid are obtained, which product is purified by flash chromatography on silica [eluent: dichloromethane/methanol/acetonitrile (95/2.5/2.5 by volume)]. After concentrating the fractions containing the expected product, 1.58 g of a yellow solid are obtained, which product is recrystallized from 40 cm3 of hot acetonitrile. After filtering off the crystals through a No. 4 sinter funnel with 40 cm3 of acetonitrile and drying under reduced pressure (2.7 kPa), 1.36 g of (16R)-16-deoxo-16-(prop-2-ynyloxy)pristinamycin IIB are obtained in the form of white crystals melting at about 112°C with decomposition. Example 5 {16R)-16-Deoxo-16-methoxypristinamycin IIA Working in a manner similar to that described in Example 2, but starting with a solution of 8 g of (16R) -16-deoxo-16-hydroxypristinamycin IIA in 40 cm3 of dichloromethanhe and 40 cm3 of water, 1.2 g of sodium hydroxide, 0.49 g of tetra-n-butylammonium bromide and 4.7 cm of methyl iodide are added, at 25°C. After stirring for 96 hours and work-up, and after purification by flash chromatography on silica [eluent: dichloromethane/acetonitrile/methanol (96/2/2 by volume)] and concentrating the fractions containing the expected product, 0.38 g of a foam is obtained, which is diluted in 40 cm3 of ethyl acetate and then washed successively with 20 cm3 of 0.1 N hydrochloric acid solution, 20 cm3 of water and 20 cm3 of saturated aqueous sodium chloride solution. The organic phase is dried over magnesium sulphate, filtered and concentrated under reduced pressure (2.7 kPa) to give 0.15 g of (16J?)-16-deoxo-16-methoxypristinamycin IIA in the form of a white powder melting at about 151 °C with (t, J = 3 Hz : 1H); 6.62 (dd, J = 16.5 and 7.5 Hz : 1H); from 7.25 to 7.40 (mf : 1H) ; 7.89 (s, 1H) . {16R)-16-Hydroxypristinamycin IIA may be prepared according to F. Le Goffic: M-L. Capmau, J. Abbe, L. Charles and J. Montastier; EUR. J. MED. -CHIMICA THERAPEUTICA: JANUARY - FEBRUARY, 1981 - 16, No. 1, pp. 69-72. The present invention also relates to pharmaceutical compositions containing at least one streptogramin derivative according to the invention, in pure form, combined with at least one group B streptogramin derivative, . where appropriate in the form of a salt, and/or in the form of a combination with one or more compatible and pharmaceutically acceptable diluents or adjuvants. The compositions according to the invention may be used orally, parenterally, topically, rectally or as aerosols. Solid compositions for oral administration which may be used include tablets, pills, gel capsules, powders and granules. In these compositions, the active product according to the invention, generally in the form of a combination, is mixed with one or more inert diluents or adjuvants, such as sucrose, lactose or starch. These compositions may comprise substances other than diluents, for example a lubricant such as magnesium stearate or a coating intended for controlled release. Liquid compositions for oral administration which may be used include pharmaceutically acceptable solutions, suspensions, emulsions, syrups and elixirs containing inert diluents such as water or liquid paraffin. These compositions may also comprise substances other than diluents, for example wetting, sweetening or flavouring products. The compositions for parenteral administration may be sterile solutions or emulsions. Solvents or vehicles which may be used include propylene glycol, a polyethylene glycol, plant oils, in particular olive oil, and injectable organic esters, for example ethyl oleate. These compositions may also contain adjuvants, in particular wetting agents, isotonic agents, emulsifiers, dispersants and stabilizers. The sterilization may be carried out in several ways, for example using a bacteriological filter, by irradiation or by heating. The compositions may also be prepared in the form of sterile solid compositions which may be dissolved at the time of use in sterile water or any other injectable sterile medium. The compositions for topical administration may be, for example, creams, ointments, lotions or aerosols. The compositions for rectal administration are suppositories or rectal capsules which contain, besides the active principle, excipients such as cocoa butter, semisynthetic glycerides or polyethylene glycols. The compositions may also be aerosols. For use in the form of liquid aerosols, the compositions may be stable sterile solutions or solid compositions dissolved at the time of use in apyrogenic sterile water, in saline or any other pharmaceutically acceptable vehicle. For use in the form of dry aerosols for direct inhalation, the active principle is finely divided and combined with a solid water-soluble diluent or vehicle with a particle size of from 30 to 80 µm, for example dextran, mannitol or lactose. In human therapy, the novel streptogramin derivatives according to the invention are particularly useful for treating infections of bacterial origin. The doses depend on the desired effect and the duration of the treatment. The doctor will determine the dosage he considers to be most suitable depending on the treatment, as a function of the age, weight, degree of infection and the other factors specific to the individual to be treated. Generally, the doses are between 0,5 and 3 g of active product in 2 or 3 administrations per day, via the oral or parenteral route for an adult. The example which follows illustrates a composition according to the invention. EXAMPLE Tablets containing a 250 mg dose of active product and having the composition below are prepared according to the usual technique: (16R) -16-Deoxo-16-methoxy- pristinamycin lis 175 mg Pristinamycin IB 75 mg Excipient: starch, hydrated silica, dextrin, gelatin, magnesium stearate: qs 500 mg 0 together with the nitrogen atom, a saturated, partially saturated or unsaturated mono- or polycyclic heterocycle (3- to 12-membered) optionally containing another hetero atom chosen from N, S and 0, and optionally substituted [with one or more OH, alkyl, phenyl which is optionally substituted with a halogen atom, phenylalkyl, phenyl-alkenyl (alkenyl containing 2 to 4C) , hydroxyalkyl, acyl, alkyloxycarbonyl or heterocyclyl or heterocyclyl-carbonyl in which the heterocyclyl portion is saturated or "unsaturated (4- to 6-membered) and contains one or more hetero atoms chosen from N, S and 0] , R3 is alkyl (1 to 8C) or cycloalkyl (3 to 8C) substituted with -NR1R2 for which R1 and R2, which may be identical or different, are H or alkyl or form, together with the nitrogen atom to which they are attached, a heterocycle as defined above, or alternatively R3 is saturated or unsaturated heterocyclyl or heterocyclylmethyl (3- to 7-membered) optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen and optionally substituted with an alkyl radical; 1) Rb and Rc are H and Rd is H or an MeNH or NMe2 radical, 2) Rb is H, Rc is H, Cl or Br, or alkenyl (3 to 5C), and Rd is -NMe-R'", R'" being alkyl, hydroxyalkyl (2 to 4C) or alkenyl (2 to 8C) , phenylalkenyl, cycloalkyl(3 to 6C)methyl, benzyl, substituted benzyl, heterocyclylmethyl or heterocyclylethyl, or alternatively R'" is -CH2CN, -CH2COOH or -CORe or -CH2CORe for which either Re is -OR'e or Re is alkylamino, alkylmethylamino, heterocyc lylamino or heterocyclylmethylamino, 3) Rb is H, Rd is an -NHCH3 or -N(CH3)2 radical and Re is CI or Br or alkenyl (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are H and Re is halogen or alkylamino or dialkylamino, alkyloxy, trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl, 5) Rb and Re are H and Rd is halogen or ethylamino, diethylamino or methylethylamino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkyl-sulphonyl, alkyl (1 to 6C), phenyl or trihalomethyl, 6) Rb is H and Re is halogen or alkylamino or dialkyl- amino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) and Rd is halogen or an amino, alkyl amino or dialky lamino, alkyloxy or trif luoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Rc is H and Rb and Rd are CH3, as well as the salts thereof, when they exist. It is -understood that the combinations formed from the derivatives according to the invention and from the group B streptogramins also fall within the context of the present invention. The group B streptogramin derivatives of structure (B) may be prepared according to the methods disclosed in International patent application PCT/FR 99/00409. The group B streptogramin derivatives of structure (C) may be prepared according to the methods disclosed in International patent application PCT/FR 00/02146. In vitro on Staphylococcus aureus IP8203, the streptogramin derivatives according to the invention have been shown to be active at concentrations of between 0.06 and 32 µg/ml alone or combined with a group B derivative such as pristinamycin IB; in vivo, they synergise the antimicrobial activity of pristinamycin Ib on experimental infections of mice with Staphylococcus aureus IP8203 at doses of between 32 and 150 mg/kg orally (DC5o) - Finally, the products according to the invention are particularly advantageous on account of their low toxicity. None of the products has shown any toxicity at doses of 150 mg/kg on Staphylococcus aureus IP8203, twice a day subcutaneously or orally in mice. The streptogramin derivatives of general formula (I) for which: R1 represents an alkyl, alkenyl or alkynyl radical, R2 represents a methyl radical, and The bond represents a single bond (27R stereochemistry) or a double bond, are of particular interest. And among these products more particularly the products described hereinbelow in the examples. Among the group A streptogramin derivatives according to the invention, mention will also be made • (16R) -16-deoxo-16- (2-fluoropropen-3-yloxy) -pristinamycin IIA. The examples which follow, given without any implied limitation, illustrate the present invention. In the examples which follow, the 16-deoxo-pristinamycin IIA (or IIB) nomenclature indicates the replacement of the ketone function in position 16 with 2 hydrogen atoms. As the chromatography proceeds, all the fractions are analysed by thin layer chromatography (TLC) on Merck 60F254 silica plates. The fractions corresponding to the same spot on TLC are combined and then concentrated to dryness, under reduced pressure (30°C; 2.7 kPa) . The residues thus obtained are analysed by the usual spectroscopic techniques (NMR; IR; MS), allowing the expected product to be identified. Example 1 (16R) -16-Deoxo-16-methoxypristinamycin IIB A solution of 0.6 g of (16R) -8-N-tert-butyl- oxycarbonyl-16-deoxo-16-methoxypristinamycin IIB in 15 cm3 of N,N-dimethylformamide is boiled for 2.5 hours. The reaction mixture is poured into 200 cm3 of ice-cold water and the aqueous phase is then extracted with 3 times 100 cm3 of ethyl acetate. The organic phases are combined, washed with 3 times 2 00 cm3 of saturated aqueous sodium chloride solution, dried over magnesium sulphate, filtered and then concentrated to dryness under reduced pressure (2.7 kPa) to give 0.65 g of a yellow oil, which is purified by flash chromatography on silica on silica [eluent: dichloromethane/methanol/-acetonitrile (90/5/5 by volume)]. After concentrating the fractions containing the expected product, 0.16 g of a yellow foam is obtained and is recrystallized from 3 cm3 of hot acetonitrile to give 0.13 g of (161?) -16-deoxo-16-methoxypristinamycin IIB, in the form of a white powder melting at about 124°C (dec). (16R)-8-N-tert-Butyloxycarbonyl-16-deoxo~ 16-methoxypristinamycin IIB may be prepared in the following way: 2.4 cm3 of 1N hydrochloric acid are added, at 0°C under an argon atmosphere, to a solution of 0.41 g of sodium p-toluenesulphinate in 14 cm3 of dichloro-methane, and the mixture is then allowed to warm to room temperature over 15 minutes. This solution is dried over magnesium sulphate, filtered and then poured at 20°C, under an argon atmosphere, into a solution of 0.93 g of (16l?)-14-0-allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-methoxypristinamycin IIB and 0.31 g of tetrakis(triphenylphosphine)palladium in 18 cm3 of dichloromethane. After stirring for 30 minutes at room temperature, the reaction mixture is poured into 100 cm3 of water and the phases are then separated by settling. The organic phase is dried over magnesium sulphate, filtered and then concentrated to dryness under reduced pressure' (2.7 kPa) to give 1.66 g of a yellow oil which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/methanol (95/2.5/2.5 by volume)]. After concentrating the fractions containing the expected product, 0.63 g of a yellow foam is obtained and is stirred in 5 cm3 of pentane and then filtered and dried under reduced pressure (2.7 kPa) to give 0.6 g of (16R) -8-N-tert-butyloxycarbonyl-16-deoxo- (16i?)-14-0-Allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-methoxypristinamycin IIB may be prepared in the following way: 0.19 cm3 of iodomethane and 0.043 g of 50% sodium hydride in petroleum jelly are added, at 25°C under an argon atmosphere, to 0.4 g of (161?)-14-0- allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-hydroxy- pristinamycin IIB dissolved in 5 cm3 of N,N-dimethyl- formamide. After stirring for 4 hours, the reaction mixture is diluted with 20 cm3 of ethyl acetate and then poured into 40 cm3 of water. The organic phase is separated out after settling has taken place, and then washed with 40 cm3 of saturated aqueous sodium chloride solution, dried over magnesium sulphate, filtered and then concentrated to dryness under reduced pressure (2.7 kPa) to give 0.31 g of a yellow oil, which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/methanol (95/2.5/2.5 by volume)]. After concentrating the fractions containing the expected product, 0.06 g of (16R)-14-O-allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-methoxy-pristinainycin IIB is obtained in the form of a white solid. (16R)-14-0-Allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-hydroxypristinamycin IIB may be prepared in the following way: 90 cm3 of triethylamine trihydrofluoride are added to 16.05 g of (16R) -14-0-allyl-16- (tert-butyl- dimethylsilyloxy-8-N-tert-butyloxycarbonyl-16-deoxo-pristinainycin IIB dissolved in 80 cm3 of dichloro-methane. After stirring for 17 hours at 40°C, the reaction mixture is diluted with 100 cm3 of dichloro-methane and then poured into 300 cm3 of water. The pH of the aqueous phase is adjusted to 8 by slow addition of sodium bicarbonate. The organic phase is separated out after settling has taken place and then dried over sodium sulphate, filtered and concentrated to dryness under reduced pressure (2.7 >Pa) to give 16.5 g of a yellow oil, which is purified by flash chromatography on silica [eluent: dichloromethane/acetonitrile/ methanol (93/3.5/3.5 by volume)]. After concentrating the fractions containing the expected products, 10.23 g of (16i?) -14-0-allyl-8-N-tert-butyloxycarbonyl-16-deoxo-16-hydroxypristinamycin IIB are obtained in the form of a yellow foam. 1. Group A streptogramin derivative of general formula: in which: - R1 represents alkyl, alkenyl or alkynyl radicals which may be mono- or polyfluoro radicals, or cycloalkyl radicals containing 3 to 6 carbon atoms, phenylmethyl radicals or heterocyclylmethyl radicals in which the heterocyclyl portion is aromatic, - R2 represents a hydrogen atom or a methyl or ethyl radical, and - the bond represents a single bond (27R stereo chemistry) or a double bond, the alkyl radicals containing 1 to 6 carbons in a straight or branched chain and the alkenyl and/or alkynyl radicals containing 3 to 6 carbons in a straight or branched chain. 2. Streptogramin derivative according to Claim 1, characterized that R2 represents a methyl radical, and the bond represents a single bond (27R stereochemistry) or a double bond. 3 . Process for preparing group A streptogramin derivative according to Claim 1, characterized in that a derivative of general formula: R1-X (Ha) for which R1 is defined as in Claim 1 and X represents a halogen atom or a methylsulphonyloxy, p-toluene-sulphonyloxy or trifluromethylsulphonyloxy radical, is reacted, in the presence of a phase-transfer agent, with a dihydroxy derivative of the streptogramin of general formula: in which R2 is defined as in Claim 1, the bond represents a single bond (27R stereochemistry) or a double bond, and for which derivative the hydroxyl function in position 14 and/or the amide function in position 8 have optionally been protected beforehand, followed, where appropriate, by removal of the protecting radicals. streptogramin derivative according to Claim 1, characterized in that the process is performed by desilylation and then 37-O-alkylation of a silyl and 14-0-allyl derivative of general formula: in which R2 is defined as in Claim 1, the bond represents a single bond (27R stereochemistry) or a double bond, and the radical R3 represents a protecting radical and R4 represents a silyl radical, by means of a derivative of general formula (Ila) as defined in Claim 2, followed by removal of the allyl radical and the protecting radical R3 according to the known methods which do not affect the rest of the molecule. 5. Preparation process according to Claim 3, characterized in that the radical R3 is a t-butoxycarbonyl radical. 6. Group A streptogramin derivative, characterized in that it corresponds to the general formula: in which the bond , R2, R3 and R4 are defined as in Claim 3. 7. Pharmaceutical composition comprising a group A streptogramin derivative according to Claim 1, in pure form or in the form of a combination with at least one group B streptogramin derivative, and/or in the form of a combination with one or more compatible and pharmaceutically acceptable diluents or adjuvants. 8. Pharmaceutical composition according to Claim 7, characterized in that the group B streptogramin derivative is chosen from the following natural components: pristinamycin IA, pristinamycin IB, pristinamycin IC, pristinamycin ID, pristinamycin IE, pristinamycin IF, pristinamycin IG, virginiamycin SI, S3 or S4, vernamycin B or C, etamycin or from semi- /%$b synthetic derivatives of general formula: in which: 1) Rb, Re, Re and Rf are hydrogen atoms, Rd is a hydrogen atom or a dimethylamino radical, and Ra is a radical of structure -CH2R'a for which R'a is pyrrolidinyl-3-thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, alkylthio substituted with 1 or 2 hydroxysulphonyl, alkylamino or dialkyl-amino (which itself may optionally be substituted with mercapto or dialkylamino) , or substituted with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl or 2- or 3-pyrrolidinyl rings (which may be substituted with alkyl), or alternatively Ra is a radical of structure =CHR'a for which R'a is pyrrolidinyl-3-amino, piperidyl-3- (or -4-)amino, pyrrolidinyl-3-oxy, piperidyl-3- (or -4-)oxy, pyrrolidinyl-3-thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, or R'a is-alkylamino, alkyloxy or sulphonyl, alkylamino or di a lky 1 amino (which is itself optionally substituted with dialkylamino), or with trialkylammonio, 4- or 5-imidazolyl, or with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl, or 2- or 3-pyrrolidinyl rings (which may be substituted with jalkyl), or Ra is a quinuclidinyl-3- (or -4-) thiomethyl radical, or . alternatively 2) Ra is a hydrogen atom and a) either Rb, Re and Rf are hydrogen atoms, Rd is an -NHCH3 or -N(CH3)2 radical and Rc is a chlorine or bromine atom, or represents an alkenyl radical containing 3 to 5 carbon atoms [if Rd is -N(CH3)2], b) or Rb, Rd, Re and Rf represent a hydrogen atom and Re is a halogen or an aminomonoalkyl, aminodialkyl, alkyloxy, trifluoromethyloxy, thioalkyl, Ci to C3 alkyl or trihalomethyl radical c) or Rb, Re, Re and Rf represent a hydrogen atom and Rd is a halogen or an ethylamino, diethylamino or methylethylamino, alkyloxy or trif luoromethyloxy, thioalkyl, C1 to C6 alkyl, aryl or trihalomethyl radical, d) or Rb, Re and Rf represent a hydrogen atom and Rc is halogen or an aminomonoalkyl or aminodialkyl, alkyl radical, and Rd is halogen or an amino, amino- monoalkyl or aminodialkyl, alkyloxy or trifluoro- methyloxy, thioalkyl, Ci to C6 alkyl or trihalomethyl radical, e) or Re, Re and Rf represent a hydrogen atom and Rb and Rd represent a methyl radical; or alternatively from the semisynthetic derivatives of i cjen^ral formula: in which: Y is a nitrogen atom or a radical =CR3~, Ri is a hydrogen atom, an alkyl radical (1 to 8 carbons) , alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 8 carbons) , saturated or unsaturated heterocyclyl radical (3- to 8-membered) , phenyl radical, substituted phenyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkyl- sulphinyl, alkylsulphonyl, amino, alkylamino or dialkyl- may be identical or different, possibly being hydrogen atoms or alkyl radicals (1 to 3 carbons) or possibly forming, together with the nitrogen atom to which they are attached, a 3- to 8-membered heterocycle optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-membered), benzyl radical, phenyl radical or substituted phenyl radical as defined above for the definition of R1] , or alternatively, when Y is a radical =CR3~, R1 may also be halomethyl, hydroxymethyl, alkyloxymethyl, alkyl- thiomethyl in which the alkyl portion is optionally substituted with NR'R", alkylsulphinylmethyl, alkyl- sulphonylmethyl, acyloxymethyl, benzoyloxymethyl, cyclopropylaminomethyl or - (CH2)nNR'R/' (n being an integer from 1 to 4 and R' and R" being defined as above) , or alternatively, if R3 is a hydrogen atom, R1 may also be f ormyl, carboxyl, alkyloxycarbonyl or -CONR'R" for which R' and R" are defined as above, or alternatively, when Y is a nitrogen atom, R1 may also be a radical -XR° for which X is an oxygen or sulphur atom, a sulphinyl or sulphonyl radical, or an NH radical and R° is an alkyl radical (1 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or heterocyclylmethyl radical (3- to 8-membered) in which the heterocyclyl portion is attached to the methyl radical via a carbon atom, phenyl radical, substituted phenyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkylsulphinyl, alkylsulphonyl, amino, alkylamino or dialkylamino radicals] or a radical -(CH2)nNR'R" for which R' and R" are defined as above and n is an integer from 2 to 4, or alternatively, if X represents NH, R° may also represent a hydrogen atom, R2 is a hydrogen atom or an alkyl radical (1 to 3 carbons), R3 is a hydrogen atom or an alkyl, carboxyl, alkyloxy- carbonyl or carbamoyl radical of structure -CO-NR'R" in which R' and R" are defined as above, Ra is a methyl or ethyl radical, and Rb, Rc and Rd have the definitions below: 1) Rb and Re are hydrogen atoms and Rd is a hydrogen atom or a methylamino or dimethylamino radical, 2) Rb is a hydrogen atom. Rc is a hydrogen, chlorine or bromine atom, or represents an alkenyl radical (3 to 5C) , and Rd is a radical -NMe-R'" for which R'" represents an alkyl radical, hydroxyalkyl radical (2 to 4C) or alkenyl radical (2 to 8C) optionally substituted with phenyl, cycloalkyl(3 to 6C)methyl radical, benzyl radical, substituted benzyl radical hydroxyl, alkyl, alkyloxy, alkylthio, alkylsulphinyl, alkylsulphonyl, amino, alkylamino or dialkylamino radicals], heterocyclylmethyl radical or hetero- cyclylethyl radical in which the heterocyclyl portion is saturated or unsaturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-membered), phenyl radical, substituted phenyl radical as defined above for the definition of R^ or benzyl radical], or alternatively R'" represents a cyanomethyl radical or a radical -CH2CORe for which either Re is -OR'e, R'e being hydrogen, alkyl (1 to 6 carbons), alkenyl (2 to 6 carbons), benzyl or heterocyclylmethyl in which the heterocyclyl portion is 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen, or Re is an alkylamino, alkylmethylamino, heterocyclylamino or heterocyclylmethylamino radical in which the heterocyclyl portion is saturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted with an alkyl, benzyl or alkyloxycarbonyl radical, radical and Rc is a chlorine or bromine atom or represents an alkenyl radical (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are hydrogen atoms and Rc is a halogen atom or an alkylamino or dialkylamino, alkyloxy, trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 5) Rb and Rc are hydrogen atoms and Rd is a halogen atom or an ethylamino, diethylamino or me thy 1 ethyl-amino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkylsulphonyl, alkyl (1 to 6C) , phenyl or trihalomethyl radical, 6) Rb is a hydrogen atom and Re is a halogen atom or an alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) radical and Rd is a halogen atom or an amino, alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Rc is a hydrogen atom and Rb and Rd represent a , methyl radical, as well as the salts thereof, or alternatively from the semisynthetic derivatives of general formula: in which R represents a radical -NR1R2 or -SR3 [for which R1 and R2, which may be identical or different, represent H, alkyl (1 to 8C) optionally substituted with OH, alkenyl (3 to 8C) , cycloalkyl (3 to 8C) , alkyloxy (1 to 8C) , dialkylaminc, phenylalkyl which is optionally substituted [with one or more halogen or alkyl, hydroxyalkyl, alkyloxy or dialkylamino], saturated or unsaturated heterocyclylalkyl (3- to 8-membered) containing one or more hetero atoms chosen from N, S and 0, or alternatively R1 and R2 form, together with the nitrogen atom, a saturated, partially saturated or unsaturated mono- or polycyclic heterocycle (3- to 12-membered) optionally containing another hetero atom chosen from N, S and 0, and optionally substituted [with one or more OH, alkyl, phenyl which is optionally substituted with a halogen atom, phenylalkyl, phenyl-alkenyl (alkenyl containing 2 to 4C), hydroxyalkyl, acyl, alkyloxycarbonyl or heterocyclyl or heterocyclyl-carbonyl in which the heterocyclyl portion is saturated more hetero atoms chosen from N, S and 0] , R3 is alkyl (1 to 8C) or cycloalkyl (3 to 8C) substituted with -NR1R2 for which R1 and R2, which may be identical or different, are H or alkyl or form, together with the nitrogen atom to which they are attached, a heterocycle as defined above, or alternatively R3 is saturated or unsaturated heterocyclyl or heterocyclylmethyl (3- to 7-membered) optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen and optionally substituted with an alkyl radical; 1) Rb and Re are H and Rd is H or an MeNH or ]SJMe2 radical, 2) Rb is H, Re is H, CI or Br, or alkenyl (3 to 5C), and Rd is -NMe-R"', R'" being alkyl, hydroxyalkyl (2 to 4C) or alkenyl (2 to 8C), phenylalkenyl, cycloalkyl(3 to 6C)methyl, benzyl, substituted benzyl, heterocyclylmethyl or heterocyclylethyl, or alternatively R'" is -CH2CN, -CH2C00H or -CORe or -CH2C0Re for which either Re is -OR'e or Re is alkylamino, alkylmethylamino, heterocyclylamino or heterocyclylmethylamino, 3) Rb is H, Rd is an -NHCH3 or -N(CH3)2 radical and Rc is CI or Br or alkenyl (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are H and Re is halogen or alkylamino or dialkylamino, alkyloxy, trif luoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl, 5) Rb and Re are H and Rd is halogen or ethylamino, diethylamino or methylethylamino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkyl-sulphonyl, alkyl {1 to 6C) , phenyl or trihalomethyl, 6) Rb is H and Re is halogen or alkylamino or dialkyl-amino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) and Rd is halogen or an amino, alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Rc is H and Rb and Rd are CH3, as well as the salts thereof, when they exist. WE CLAIM : 1. Group A streptogramin derivative of general formula: in which: - R1 represents alkyl, alkenyl or alkynyl radicals which may be mono- or polyfluoro radicals, or cycloalkyl radicals containing 3 to 6 carbon atoms, phenylmethyl radicals or heterocyclylmethyl radicals in which the heterocyclyl portion is aromatic, - R2 represents a hydrogen atom or a methyl or ethyl radical, and - the bond represents a single bond (27R stereochemistry) or a double bond, the alkyl radicals containing 1 to 6 carbons in a straight or branched chain and the alkenyl and/or alkynyl radicals containing 3 to 6 carbons in a straight or branched chain. 2 - Streptogramin derivative according to Claim 1, characterized in that - R1 represents an alkyl, alkenyl or alkynyl radical, - R2 represents a methyl radical, and the bond represents a single bond (27R stereochemistry) or a double bond. 3. Process for preparing a group A streptogramin derivative according to Claim 1, characterized in that a derivative of general formula: R1-X (Ha) for which R1 is defined as in Claim 1 and X represents a halogen atom or a methylsulphonyloxy, p-toluene-sulphonyloxy or trifluromethylsulphonyloxy radical, is reacted, in the presence of a phase-transfer agent, with a dihydroxy derivative of the streptogramin of general formula: in which R2 is defined as in Claim 1, the bond represents a single bond (27R stereochemistry) or a double bond, and for which derivative the hydroxyl function in position 14 and/or the amide function in position 8 have optionally been protected beforehand, followed, where appropriate, by removal of the protecting radicals. 4. Process for preparing a group A streptogramin derivative according to Claim 1, characterized in that the process is performed by desilylation and then 37-O-alkylation of a silyl and 14-0-allyl derivative of general formula: in which R2 is defined as in Claim 1, the bond represents a single bond (27R stereochemistry) or a double bond, and the radical R3 represents a protecting radical and R4 represents a silyl radical, by means of a derivative of general formula (IIa) as defined in Claim 2, followed by removal of the allyl radical and the protecting radical R3 according to the known methods which do not affect the rest of the molecule. 5. Preparation process according to Claim 3, characterized in that the radical R3 is a t-butoxycarbonyl radical, 6. Group A streptogramin derivative, characterized in that it corresponds to the general formula: in which the bond ---,R2,R3 and R4 defined as in Claim 3. 7. Pharmaceutical composition comprising a group A streptogramin derivative according to Claim 1, in pure form or in the form of a combination with at least one group B streptogramin derivative, and/or in the form of a combination with one or more compatible and pharmaceutical!:/ acceptable diluents or adjuvants. 8. Pharmaceutical composition according to Claim 7, characterized in that the group 3 streptogramin derivative is chosen from the following natural components: pristinamycin IA, pristinamycin 13, pristinamycin IC, pristinamycin ID, pristinamycin IE, pristinamycin IF, pristinamycin IG, virginiamycin Si, 33 or S4, vernamycin 3 or C, etamycin or from semi synthetic derivatives of general formula: in which: 1) Rb, Rc, Re and Rf are hydrogen atoms, Rd is a hydrogen atom or a dimethylamino radical, and Ra is a radical of structure -CH2R'a for which R'a is pyrrolidinyl-3-thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, alkylthio substituted with 1 or 2 hydroxysulphonyl, alkylamino or dialkyl-amino (which itself may optionally be substituted with mercapto or dialkylamino), or substituted with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl or 2- or 3-pyrrolidinyl rings (which may be substituted with alkyl), or alternatively Ra is a radical of structure =CHR'a for which R'a is pyrrolidinyl-3-amino, piperidyl-3- (or -4-)amino, pyrrolidinyl-3-oxy, piperidyl-3- (or -4-)oxy, pyrrolidinyl-3-thio, piperidyl-3- (or -4-)thio which may be substituted with alkyl, or R'a is alkylamino, alkyloxy or alkylthio which is substituted with 1 or 2 hydroxy-sulphonyl, alkylamino or dialkylamino (which is itself optionally substituted with dialkylamino), or with trialkylammonio, 4- or 5-imidazolyl, or with 1 or 2 piperazine rings, optionally substituted, morpholino, thiomorpholino, piperidino, 1-pyrrolidinyl, 2-, 3- or 4-piperidyl, or 2- or 3-pyrrolidinyl rings (which may be substituted with lalkyl), or Ra is a quinuclidinyl-3- (or -4-)thiomethyl radical, or . alternatively 2) 'Ra is a hydrogen atom and a) either Rb, Re and Rf are hydrogen atoms, Rd is an -NHCH3 or -N(CH3)2 radical and Rc is a chlorine or bromine atom, or represents an alkenyl radical containing 3 to 5 carbon atoms [if Rd is -N(CH3)2] b) or Rb, Rd, Re and Rf represent a hydrogen atom and Re is a halogen or an aminomonoalkyl, aminodialkyl, alkyloxy, trifluoromethyloxy, thioalkyl, C1 to C3 alkyl or trihalomethyl radical c) or Rb, Re, Re and Rf represent a hydrogen atom and Rd is a halogen or an ethylamino, diethylamino or methylethylamino, alkyloxy or trifluoromethyloxy, thioalkyl, C1 to C6 alkyl, aryl or trihalomethyl radical, d) or Rb, Re and Rf represent a hydrogen atom and Rc is halogen or an aminomonoalkyl or aminodialkyl, alkyloxy or trifluoromethyloxy, thioalkyl or C1 to C3 alkyl radical, and Rd is halogen or an amino, amino-monoalkyl or aminodialkyl, alkyloxy or trifluoromethyloxy, thioalkyl, C1 to C6 alkyl or trihalomethyl radical, e) or Rc, Re and Rf represent a hydrogen atom and Rb and Rd represent a methyl radical; or alternatively from the semisynthetic derivatives of 1 general formula: in which: Y is a nitrogen atom or a radical =CR3~, R1 is a hydrogen atom, an alkyl radical (1 to 8 carbons), alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 8 carbons), saturated or unsaturated heterocyclyl radical (3- to 8-membered), phenyl radical, substituted phenyl radical (substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkyl- sulphinyl, alkylsulphonyl, amino, alkylamino or dialkyl- amino radicals] or a radical NR'R", R' and R", which may be identical or different, possibly being hydrogen atoms or alkyl radicals (1 to 3 carbons) or possibly forming, together with the nitrogen atom to which they are attached, a 3- to 8-membered heterocycle optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-membered), benzyl radical, phenyl radical or substituted phenyl radical as defined above for the definition of R1] , or alternatively, when Y is a radical =CR3-, R1 may also be halomethyl, hydroxymethyl, alkyloxymethyl, alkyl-thiomethyl in which the alkyl portion is optionally substituted with NR'R", alkylsulphinylmethyl, alkyl-sulphonylmethyl, acyloxymethyl, benzoyloxymethyl, cyclopropylaminomethyl or -(CH2)nNR'R" (n being an integer from 1 to 4 and R' and R" being defined as above) , or alternatively, if R3 is a hydrogen atom, R1 may also be formyl, carboxyl, alkyloxycarbonyl or -CONR'R" for which R' and R" are defined as above, or alternatively, when Y is a nitrogen atom, R1 may also be a radical -XR° for which X is an oxygen or sulphur atom, a sulphinyl or sulphonyl radical, or an NH radical and R° is an alkyl radical (1 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (3- to 8-membered), heterocyclylmethyl radical (3- to 8-membered) in which the heterocyclyl portion is attached to the methyl radical via a carbon atom, phenyl radical, substituted phenyl radical [substituted with one or more halogen , atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkylsulphinyl, alkylsulphonyl, amino, alkylamino or dialkylamino radicals] or a radical -(CH2)nNR'R" for which R' and R" are defined as above and n is an integer from 2 to 4, or alternatively, if X represents NH, R° may also represent a hydrogen atom, R2 is a hydrogen atom or an alkyl radical (1 to 3 carbons), R3 is a hydrogen atom or an alkyl, carboxyl, alkyloxy-carbonyl or carbamoyl radical of structure -CO-NR'R" in which R' and R" are defined as above, Ra is a methyl or ethyl radical, and Rb, Rc and Rd have the definitions below: 1) Rb and Rc are hydrogen atoms and Rd is a hydrogen atom or a methylamino or dimethylamino radical, 2) Rb is a hydrogen atom, Rc is a hydrogen, chlorine or bromine atom, or represents an alkenyl radical (3 to 5C), and Rd is a radical -NMe-R"' for which R'" represents an alkyl radical, hydroxyalkyl radical (2 to 4C) or alkenyl radical (2 to 8C) optionally substituted with phenyl, cycloalkyl(3 to 6C)methyl radical, benzyl radical, substituted benzyl radical [substituted with one or more halogen atoms or hydroxyl, alkyl, alkyloxy, alkylthio, alkylsulphinyl, alkylsulphonyl, amino, alkylamino or dialkylamino radicals], heterocyclylmethyl radical or hetero-cyclylethyl radical in which the heterocyclyl portion is saturated or unsaturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted [with an alkyl radical, alkenyl radical (2 to 8 carbons), cycloalkyl radical (3 to 6 carbons), saturated or unsaturated heterocyclyl radical (4- to 6-membered), phenyl radical, substituted phenyl radical as defined above for the definition of R1 or benzyl radical], or alternatively R'" represents a cyanomethyl radical or a radical -CH2C0Re for which either Re is -OR'e, R'e being hydrogen, alkyl (1 to 6 carbons), alkenyl (2 to 6 carbons), benzyl or heterocyclylmethyl in which the heterocyclyl portion is 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen, or Re is an alkylamino, alkylmethylamino, heterocyclylamino or heterocyclylmethylamino radical in which the heterocyclyl portion is saturated and 5- or 6-membered and contains 1 or 2 hetero atoms chosen from sulphur, oxygen and nitrogen which is optionally substituted with an alkyl, benzyl or alkyloxycarbonyl radical, 3) Rb is a hydrogen atom, Rd is an -NHCH3 or -N(CH3)2 radical and Rc is a chlorine or bromine atom or represents an alkenyl radical (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are hydrogen atoms and Rc is a halogen atom or an alkylamino or dialkylamino, alkyloxy, trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 5) Rb and Rc are hydrogen atoms and Rd is a halogen atom or an ethylamino, diethylamino or methylethyl-amino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkylsulphonyl, alkyl (1 to 6C) , phenyl or trihalomethyl radical, 6) Rb is a hydrogen atom and Rc is a halogen atom or an alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) radical and Rd is a halogen atom or an amino, alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Rc is a hydrogen atom and Rb and Rd represent a , methyl radical, as well as the salts thereof, or alternatively from the semisynthetic derivatives of general formula: in which R represents a radical -NR1R2 or -SR3 [for which R1 and R2, which may be identical or different, represent H, alkyl (1 to 8C) optionally substituted with OH, alkenyl (3 to 8C), cycloalkyl (3 to 8C), alkyloxy (1 to 8C) , dialkylamino, phenylalkyl which is optionally substituted [with one or more halogen or alkyl, hydroxyalkyl, alkyloxy or dialkylamino], saturated or unsaturated heterocyclylalkyl (3- to 8-membered) containing one or more hetero atoms chosen from N, S and 0, or alternatively R1 and R2 form, together with the nitrogen atom, a saturated, partially saturated or unsaturated mono- or polycyclic heterocycle (3- to 12-membered) optionally containing another hetero atom chosen from N, S and 0, and optionally substituted [with one or more OH, alkyl, phenyl which is optionally substituted with a halogen atom, phenylalkyl, phenyl-alkenyl (alkenyl containing 2 to 4C), hydroxyalkyl, acyl, alkyloxycarbonyl or heterocyclyl or heterocyclyl-carbonyl in which the heterocyclyl portion is saturated or unsaturated (4- to 6-membered) and contains one or more hetero atoms chosen from N, S and 0], R3 is alkyl (1 to SC) or cycloalkyl (3 to 8C) substituted with -NR1R2 for which R1 and R2 which may be identical or different, are H or alkyl or form, together with the nitrogen atom to which they are attached, a heterocycle as defined above, or alternatively R3 is saturated or unsaturated heterocyclyl or heterocyclylmethyl (3- to 7-membered) optionally containing another hetero atom chosen from oxygen, sulphur and nitrogen and optionally substituted with an alkyl radical; below: 1) Rb and Rc are H and Rd is H or an MeNH or NMe2 radical, 2) Rb is H, Rc is H, Cl or Br, or alkenyl (3 to 5C), and Rd is -NMe-R'", R'" being alkyl, hydroxyalkyl (2 to 4C) or alkenyl (2 to 8C), phenylalkenyl, cycloalkyl(3 to 6C)methyl, benzyl, substituted benzyl, heterocyclylmethyl or heterocyclylethyl, or alternatively R'" is -CH2CN, -CH2C00H or -CORe or -CH2C0Re for which either Re is -OR'e or Re is alkylamino, alkylmethylamino, heterocyclylamino or heterocyclylmethylamino, 3) Rb is H, Rd is an -NHCH3 or -N(CH2)2 radical and Rc is Cl or Br or alkenyl (3 to 5C) [if Rd is -N(CH3)2], 4) Rb and Rd are K and Rc is halogen or alkylamino or dialkylamino, alkyloxy, trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl, 5) Rb and Rc are H and Rd is halogen or ethylamino, diethylamino or methylethylamino, alkyloxy or trifluoromethoxy, alkylthio, alkylsulphinyl, alkyl-sulphonyl, alkyl (1 to 6C), phenyl or trihalomethyl, 6) Rb is H and Rc is halogen or alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl or alkyl (1 to 3C) and Rd is halogen or an amino, alkylamino or dialkylamino, alkyloxy or trifluoromethoxy, thioalkyl, alkyl (1 to 6C) or trihalomethyl radical, 7) Rc is H and Rb and Rd are CH3, as well as the salts thereof, when they exist.

Documents:

5185-che-2007-abstract.pdf

5185-che-2007-claims.pdf

5185-che-2007-correspondnece-others.pdf

5185-che-2007-description(complete).pdf

5185-che-2007-form 1.pdf

5185-che-2007-form 26.pdf

5185-che-2007-form 3.pdf

5185-che-2007-form 5.pdf

5185-che-2007-pct.pdf

5185-CHENP-2007 AMENDED PAGES OF SPECIFICATION 14-03-2012.pdf

5185-CHENP-2007 AMENDED CLAIMS 07-12-2012.pdf

5185-CHENP-2007 AMENDED CLAIMS 14-03-2012.pdf

5185-CHENP-2007 CORRESPONDENCE OTHERS 02-08-2011.pdf

5185-CHENP-2007 CORRESPONDENCE OTHERS 07-12-2012.pdf

5185-CHENP-2007 CORRESPONDENCE OTHERS. 23-11-2012.pdf

5185-CHENP-2007 OTHERS 07-12-2012.pdf

5185-CHENP-2007 EXAMINATION REPORT REPLY RECEIVED 14-03-2012.pdf

5185-CHENP-2007 FORM-3 14-03-2012.pdf