Title of Invention

A PROCESS FOR THE PREPARATION OF THE POLYCYCLITOLS

Abstract

Disclosed herein is a process for preparation of novel polycyclitols of the formula I wherein R1 and R2 may be same or different and independently represent hydrogen, (C1-C6) alkyl or (C2-C4) acyl group: R3 represents hydrogen, hydr4oxy group or both the R3 groups may from a double bond; r4 and R5 may be same or different and independently represent hydrogen, or OR1 group; n represents an integer in the range of 1 to 6, the groups OR1, OR2, R3, R4 and R5 may either be alpha or beta oriented, A represents a cyclohexyl ring and B represents a 5 to 8 membered carbocyclic

Full Text

This invention relates to a process for the preparation of novel polycyclitols. This is a divisional out of Indian Patent Application No. 859/MAS/2000, wherein the novel polycyclitols have been folly described and claimed. Polycyclitols are a new class of compounds having polycyclic (carbo- and/or hetero¬cyclic) framework and endowed with a dense array of hydroxyl fonctionalities and in some ways mimics naturally occurring cyclitols (hydorxylated biomolecules like inositols, conduritols, carbasugars). Field of the Invention The present invention relates to novel compounds of the formula 1, their stereoisomers, their derivatives, their analogs. The present invention more particularly relates to novel polycyclitols of the formula 1, their stereoisomers, their derivatives, their analogs. The compounds of the present invention are glycosidase inhibitors, which are used as potential candidates for the treatment of a variety of carbohydrate mediated diseases. For example, the novel polycyclitols of the formula 1 are usefol as antidiabetic, antiviral and anticancer agents. Background of the Invention Several publications recently have reported polyhydroxylated pyrrolizidines, indolizidines and quinolizidine alkaloids having wide ranging biological activities of these compounds, important being anti-viral, anti-cancer and anti-HIV. Some examples are alexine 2a (Tetrahedron Lett.,29, 2487, 1988), australin 2b {J. Nat. Prod., 51, 1198, 1988), casuarine 3 (Tetrahedron Lett, 35, 7849, 1994), castanospermine 4 (Arch. Biochem. Biophy., 221, 593, 1983 ) and many of their synthetic analogues. Many of these polyhydroxylated compounds have been found to be potent glycomimics. The glycosidase-inhibitory action of these compounds largely depends on the hydroxyl substitution pattern. Recent literature references also report few more examples of polycyclic structures such as the tricyclic conduritol derivative 6 which has been shown to modulate the insulin release from isolated pancreatic islet cells (Bioorg. Med. Chem. Lett, 4, 2307-2312, 1994). Balci and co-worker in Tetrahedron Lett., 35, 3349-3352, 1994, have synthesised the conduritol analog 7. The group of Hudlicky have reported in J. Chem. Soc, Perkin Trans. 1, 621-628, 1999, the compounds 8 which have been tested for enzymatic inhibition against some of the common glycosidases. Inhibitors of glycosidases have received considerable focus of attention in the past few decades as they are potential candidates for the treatment of a variety of carbohydrate mediated diseases. Therefore, the development of new glycosidase inhibitors is of considerable interest to synthetic chemists. The main objective of the present invention is therefore to provide novel polycyclitols of the formula 1 which have very good glycosidase inhibition and have beneficial effects in the treatment of a variety of carbohydrate mediated diseases such as antidiabetic, antiviral and anticancer agents. Another objective of the present invention is to provide novel polycyclitols of the formula1, which have close structural as well as functional group resemblance to the corresponding carbo-sugars. Detailed Description of the Invention Accordingly, the present invention provides novel polycycUtols of the formula 1, wherein R1 and R2 may be same or different and independently represent hydrogen, (Ci-C6)alkyl or (C2-C4) acyl group; R3 represents hydrogen, hydroxy group or both the R3 groups may form a double bond; R4 and R5 may be same or different and independently represent hydrogen, or OR1 group; n represents an integer in the range of 1 to 6, the groups 0R1 OR2 , R3 R4 and R5 may either be a or P oriented, A represents a cyclohexyl ring and B represents a 5 to 8 membered carbocyclic structure, their stereosiomers, their derivatives and their analogs, and in particular compound of the formula 1, wherein the bicyclic structure represented by A and B is represented by structure I in which the substituents at C4, C5 atoms are in α-orientation, C6, C7 are in β -orientation or structure II in which the substituents at C5, C6 atoms are in a-orientation, C7, C8 are in P-orientation; R4and R5 is OR1 wherein R1 is as defined above,. The term alkyl as used herein above may be selected from methyl, ethyl, propyl, butyl and the like. The term acyl group as used herein above may be selected from ethanoyl, propanoyl and the like. Suitable bicyclic structures formed by A and B together may be selected from any of the structures I to IV The groups ORl, 0R2, R3, R4 and R5 may either be oriented a or p. According to another embodiment of the present invention there is provided a process for the preparation of the novel polycyclitols of the formula 1, wherein the bicyclic structure represented by A and B is represented by structure I in which the substituents at C4, C5 atoms are in a-orientation, C6, C7 are in P-orientation or structure II in which the substituents at C5, C6 atoms are in a-orientation, C7, C8 are in P-orientation; R4 and R5 is OR'. The process is as shown in Scheme-1. The compoxind of formula 10 wherein R' represents alkyl group or both the R' groups together form cycUc ketal, may be prepared by a process described in Tetrahedron Le«., 40,9137, 1941,1999 The compound of formula 11 may be prepared from the compound of the formula 10 in solvent like acetone in presence of the acid catalyst like Amberlyst-15, p-toulenesulphonic acid at ambient or the reflux temperature. The decarbonylation of the compound of formula 11 to produce a compound of formula 12 may be carried out in the presence of solvents such as nitrobenzene, toluene. The reaction may be carried out at a temperature in the range of 110°C to 160°C. The compound of formula 12 may be oxidised to a compound of formula 1 using oxidising agents such as OSO4, KMn04. The reaction may optionally be carried out in the presence of reoxidants such as N-Methylmorpholine N-oxide (NMMO), tert-butylhydroperoxide. The reaction may be carried out in the presence of mixture of solvents such as acetone/water, ter/-butanol/water or acetone/water/ teri-hxAano\. According to yet another embodiment of the present invention there is provided a process for the preparation of the novel polycyclitols of the formula 1, wherein the bicyclic structure represented by A and B is represented by structure I in which the 6 substituents at C4, C5, C6, C7 are in p-orientation or structure II in which the substituents at C5, C6, C7, C8 are in p-orientation; R4 and R5are different and independently represent -OR1 or CH2-0R\ The process is as shown in Scheme-2 and the same is described and claimed in the divisional application NO. The compound of formula 13 wherein R' represents alkyl group or both the R' groups together form cyclic ketal, may be prepared by a process described in Tetrahedron Lett., 40,9137, 1941,1999 The simultaneous protection and deprotection of the compound of formula 13 to produce a compound of formula 14 may be carried out using Amberlyst-15 resin (catalytic) in moist acetone at ambient temperature for about 2 -3h. The oxidation of the compound of formula 14 to produce a compound of formula 15 may be carried out using oxidising agents such as meta-chloroperbenzoic acid, tert-butylhydroperoxide. The reaction may be carried out in the presence of suitable solvents selected from dry chloroform or dichloromethane. The reaction is carried out in the presence of buffers such as NaaCOs, NaHCOs, or Na2HP04. 7 The lactone of the formula 15 is reduced to a compound of formula 16 using LiAlH4. The reaction may be carried out in the presence of solvents such as THF or diethyl ether. The compound of the formula 16 is hydrolysed to produce a compound of formula 1 using acids such as dil. hydrochloric acid, dil. sulphuric acid or trifluoroacetic acid at ambient temperature. According to still another embodiment of the present invention there is provided a process for the preparation of the novel polycyclitols of the formula 1, wherein the bicyclic structure represented by A and B is represented by structure I in which the substituents at C4, C7 are in p-orientation; R^ and R^ are same and independently represent 0R\ The process is as shown in Scheme-3. Scheme 3 The peroxide of the formula 17 may be obtained from the diene of the formula 12 by bubbling oxygen through a solution of diene in chloroform, using sensitiser like methylene blue , Rose Bengal and irradiation from the light source like a 500W tungsten lamp. The peroxide of the formula 17 may be reduced to a compound of formula 18 using LiAlH4 or thiourea. The reaction may be carried out in the presence of solvents such as THF, diethylether or methanol respectively. The compound of formula 18 may be oxidised using oxidising agents such as OSO4, KMn04. The reaction may optionally be carried out in the presence of reoxidants such as N-Methylmorpholine N-oxide (NMMO), tertbutylhydroperoxide. The reaction may be carried out in the presence of mixture of solvents such as acetone/water, tert-butanol/water or acetone/water/ fer^butanol. The intermediate acetonide polyol obtained above may be hydrolysed to a compound of formula 1 using acids such as dil. hydrochloric acid, dil. sulphuric acid or trifluoroacetic acid at ambient temperature The compound of formula 1 wherein R' represents ethanoyl may be hydrolysed to a compound of formula 1 wherein R' represents hydrogen using aqueous base such as NaOH, KOH and the like. The compound of formula 1 wherein any of the two adjacent R' groups form an acetonide may be hydrolysed to a compound of formula 1 wherein R' represents hydrogen using acids such as dil. hydrochloric acid, dil. sulphuric acid or trifluoroacetic acid at ambient temperature. The present invention is described in the examples given below which are provided by way of illustration only and does not limit the scope of the invention. 9 The diol was prepared by the procedure described in Tetrahedron Lett., 1, 9141-9144, 1999. m.p.: 210-212 °C IR (Nujol): 3260, 1600,1260 cm-^ 'H NMR (300 MHz, CDCI3): 6 4.43(s, 2H), 4.29 (s, 2H), 3.79 (s, 3H), 3.57 (S, 3H), 3.04 (s, 2H), 1.45 (s, 3H), 1.34 (s, 3H) '^C NMR (75 MHz, CDCI3): 5 129.4 (2C), 114.7, 108.4, 76.7 (2C), 75.6 (2C), 65.1 (2C), 53.1, 51.7,46.3,26.1,23.3 MS (70 eA^, EI) : m/e 451 (M++1). Liquid ammonia was distilled into a three-necked round bottom flask equipped with a condenser, KOH guard tube and septum. The tetrachloro compound obtained in preparative example 1, in dry THF and dry EtOH was added. Small pieces of freshly cut sodium were introduced to the reaction mixture with stirring till the blue color persisted. The mixture was stirred for 30 min and soUd NH4CI was added. The excess ammonia was allowed to evaporate and cold aqueous saturated NH4CI solution was added and was extracted with ethyl acetate. The combined organic layer was washed with water, brine and dried over anhydrous sodium sulphate. Removal of the volatiles, followed by purification of the residue by silica gel colunrn chromatography gave the dechlorinated product. m.p.: 200-202 °C To a stirred solution of the olefin obtained in preparative example 2 in acetone, water and tert-butyl alcohol (5:5:2) solvent system, N-Methylmorpholine N-oxide (1.2 mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (Na2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with ethylacetate-hexane as eluent to furnish the ketal-diol. The ketal-diol was stirred with Amberlyst-15 resin (catalytic) in moist acetone at ambient temperature for about 2 -3h. The resin was filtered out and the filtrate on concentration under vacuum gave the ketone-bisacetonide. To an ice-cold solution of the ketone (Immol) obtained in preparative example 3, in dry chloroform, NaHCO3 (l.lmmol) and 70% meta-chloroperbenzoic acid (1.2 mmol) was added and reaction mixture was stirred at ambient temperature. After completion of the reaction (TLC), the reaction mixture was cooled to 0°C and excess peracid was quenched by addition of the aqueous saturated solution of NaiSOs. After usual workup and evaporation of the solvent gave a residue, which on silica gel column chromatography with ethylacetate-hexane as the eluent gave the lactone. LiAlHU (1.2mmol) was added to the ice-cold solution of lactone obtained in preparative example 4 in THF and reaction mixture was stirred at room temperature till all of the starting material had been consumed. The excess LiAlH4 was quenched with cold ethyl acetate followed by treatment with cold saturated sodium sulphate solution to liberate the free alcohol. After usual workup with ethylacetate and removal of the solvent under vacuum gave a residue, which was charged on a silica gel column, to furnish the diol. The stirred solution of the ketal in moist acetone was refluxed for 3h. After the reaction, the reaction mixture was cooled and filtered. The filtrate on concentration under vacuum, followed by silica gel column chromatography of the residue obtained furnished the ketone The ketone obtained in preparative example 7, was taken in nitrobenzene and heated to about 160°C for 4h. The nitrobenzene was removed imder vacuum at a temperature of about 80-90°C. The residue obtained was chromatographed through a sihca gel column to furnish the diene 15 To a stirred solution of the diene obtained in preparative example 8 in acetone, water and tert-butyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1 to 1. mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (NaaSjOs) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with ethylacetate-hexane or chloroform-methanol as eluent to furnish the polyol. solution to liberate the free alcohol. The resulting mixture was extracted with ethylacetate and combined organic layer was washed with water, brine and dried over anhydrous sodium sulphate. Removal of the solvent under vacuum gave a residue, which was charged on a silica gel column, to furnish the diol. The ketal was stirred with Amberlyst-15 resin (catalytic) in moist acetone at ambient temperature for about 2 -3h. The resin was fitered out and the filtrate on concentration under vacuum gave the ketone The ketone obtained in preparative example 13, was taken in nitrobenzene and heated to about 160°C for 3-6h. The nitrobenzene was removed under vacuum at a temperature of about 80-90°C. The residue obtained was chromatographed through a silica gel column to furnish the diene. The ketal obtained in peparative example 2, was stirred with Amberlyst-15 resin (catalytic) in moist acetone at ambient temperature for about 2 -3h. The resin was filtered out and the filtrate on concentration imder vacuum gave the ketone The ketone obtained in preparative example 15, was taken in nitrobenzene and heated to about 160°C for 5-6h. The nitrobenzene was removed under vacuum at a temperature of about 80-90°C. The residue obtained was chromatographed through a sihca gel colunrn to fumish the diene. To a stirred solution of the diene obtained in preparative example 16 in acetone, water and tert-butyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1.2. mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite CNa2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with chloroform-methanol as eluent to furnish the polyol. The diol was prepared by the procedure described in Tetrahedron Lett., 1, 9141-9144, 1999. Liquid ammonia was distilled into a three-necked round bottom flask equipped with a condenser, KOH guard tube and septum. The tetrachloro compound obtained in preparative example 18, in dry THF and dry EtOH was added. Small pieces of freshly cut sodium were introduced to the reaction mixture with stirring till the blue color persisted. The mixture was stirred for 30 min and solid NH4CI was added. The excess ammonia was allowed to evaporate and cold aqueous saturated NH4CI solution was added and was extracted with ethyl acetate. The combined organic layer was washed with water, brine and dried over anhydrous sodium sulphate. Removal of the volatiles, followed by purification of the residue by silica gel column chromatography gave the dechlorinated product. The ketal was stirred with Amberlyst-15 resin (catalytic) in moist acetone at ambient temperature for about 3h. The resin was filtered out and the filtrate on concentration under vacuum gave the ketone IR (KBr): 3269,1777,1375, 1208 cm'-1 The ketone obtained in preparative example 20, was taken in nitrobenzene and heated to about 160°C for 3h. The nitrobenzene was removed under vacuum at a temperature of about 80-90°C. The residue obtained was chromatographed through a silica gel column to furnish the diene. To a stirred solution of the diene obtained in preparative example 21, in acetone, water and tert-hutyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1.2 mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (Na2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with ethylacetate-hexane or chloroform-methanol as eluent to furnish the polyol. The acetonide obtained in preparative example 9, was taken in 30% trifluoroacetic acid and stirred at ambient temperature for about Ih followed by removal of the volatiles under vacuum to furnish the polyol To a stirred solution of the olefin obtained in preparative example 11 in acetone, water and tert-butyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1.2 mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (Na2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography with chloroform-methanol as eluent to furnish the polyol-acetonide. This on treatment with 30% trilfluoroacetic acid at ambeint temperature, furnished the polyol To a stirred solution of the olefin obtained in preparative example 11 in acetone, water and tert-hutyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1.2 mmol per double bond) followed by OSO4 (0.5 mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (Na2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with chloroform-methanol as eluent to furnish the polyol-acetonide. This on treatment with 30% trilfluoroacetic acid at ambeint temperature, furnished the polyol To a stirred solution of the diene obtained in preparative example 14 in acetone, water and tert-butyl alcohol (5:5:2) solvent system, N-Methylmorphiline N-oxide (1.2. mmol per double bond) followed by OSO4 (0.5mol%) was added at ambient temperature. The reaction mixture was stirred for 10-15h at the same temperature. After the reaction time, the OSO4 was quenched by addition of saturated solution of sodium metabisulphite (Na2S205) at 0°C. The resulting mixture was extracted with ethyl acetate (3 times). The organic layer was washed with brine and dried over anhydrous sodium sulphate. Evaporation of the volatiles gave a residue, which was subjected to silica gel column chromatography, with ethylacetate-hexane or chloroform-methanol as eluent to furnish the polyol. The triacetate obtained in example 5 was stirred with 10% aqueous NaOH at ambient temperature for 2h. The reaction mixture was concentrated under vacuum and residue obtained was passed through a acidc as well basic ion exchanger resin to furnish the polyol The acetonide obtained in preparative example 17, was taken in 30% trifluoroacetic acid and stirred at ambient temperature for about l-2h followed by removal of the volatiles under vacuum to furnish the polyol The acetonide obtained in preparative example 22 was taken in 30% trifluoroacetic acid and stirred at ambient temperature for about l-2h followed by removal of the volatiles under vacuum to furnish the polyol The novel polycyclitols of the present invention were tested for their glycosidase inhibition activity against the enzymes, a-glucosidase (Baker's yeast), p-glucosidase (Almonds), a-galactosidases (green coffee beans) and p- galactosidases (Escherichia coli) and p-mannosidase (snail acetone powder) with corresponding o- or p-nitrophenylglycoside as the substrates. A typical enzymatic assay (final volume 1ml) contained 1 to 0.1 units/ml of the enzyme and corresponding nitrophenyl glycopyranoside as substrate buffered to the pH optimum fpr the enzyme. The enzyme and the inhibitor were preincubated for about 5 min at temperature optimum for the enzyme and the reaction was started by the addition of the substrate. After incubating for 30 min at the optimum temperature, the reaction was terminated by the addition of borate buffer (pH 9.8). The nitrophenolate released was estimated by visible absorbance spectroscopy at about 410 nm. Example 5 and Example 7 showed very specific inhibition for a-glucosidase with Ki of 84 and 12 μM. respectively. We claim 1. A process for the preparation of Novel polycyclitols of the formula 1 wherein R1 and R2 may be same or different and independently represent hydrogen, (C1-C6)alkyl or (C2-C4) acyl group; R3 represents hydrogen, hydroxy group or both the R3 groups may form a double bond; R4 and R5 may be same or different and independently represent hydrogen, or OR1 group wherein R1 is as defined above; A represents cyclohexyl ring and B represents a 5 to 8 membered carbocyclic structure; n represents an integer in the range of 1 to 6, their stereosiomers, their derivatives and their analogs, and in particular compound of the formula 1, wherein the bicychc structure represented by A and B is rq)resented by structure I in which the substituents at C4, C5 atoms are in α-orientation, C6, C7 are in P-orientation or structure II in which the substituents at C5, C6 atoms are in α-orientation, C7, C8 are in β-orientation; R4 and R5 is OR1 wherein R1 is as defined above, which comprises: (i) converting the compound of the formula 10, wherein R' represents an alkyl group or both the R' groups together form a cyclic ketal; to a compound of formula 11, (ii) decarbonylating the compound of formula 11 to produce a compound of formula 12, (iii) oxidising the compound of fonnula 12 to a compound of formula 1 using oxidising agents, (iv) hydrolysing the compound of formula 1 wherein R1 represents ethanoyl to a compound of formula 1 wherein R1 represents hydrogen using aqueous base, (v) hydrolysing the compound of formula 1 wherein any of the two adjacent R1 groups form an acetonide to a compound of formula 1 wherein R1 represents hvdrosen using acids. usins acids.

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