Title of Invention	A PROCESS FOR PREPARATION OF TAXANES
Abstract	A process for preparation of taxanes of formula 10, wherein R is phenyl or tertiary butoxy and R1 is hydrogen, acetyl or chloroacetyl comprising the steps of: i) reacting compound of formula 6, wherein R1is hydrogen, acetyl or chloroacety"

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TITLE Method of preparation of anticancer taxanes using 3- [(substituted-2-trialkylsilyl)ethoxycarbonyl]-5-oxazolidine carboxylic acids. The present invention relates to the process for the preparation of taxanes such as paclitaxel, docetaxel and their structural analogs using a novel oxazoiidine carboxylic acid side chain. FIELD OF THE INVENTION The present invention relates to a novel oxazoiidine carboxylic acid and a process for its preparation. The invention further relates to a process for the preparation of paclitaxel, docetaxel and their structural analogs using such oxazoiidine carboxylic acid. BACKGROUND OF THE INVENTION Paclitaxel is a diterpene taxane found in very low concentration in the bark of Pacific yew tree Taxus brevifoiia. Therefore, a number of semi-synthetic strategics have been developed for its synthesis from more readily available 1O-DAB. However, the taxane nucleus is highly prone to degradation and semisynthetic crude materials are often produced contaminated with structurally similar impurities, thereby necessitating elaborate purification procedure using HPLC. In view of the above facts, it becomes highly desirable to develop alternative routes for synthesis of paclitaxel which involves minimal degradation along the synthetic pathway. Any synthetic protocol for the semi-synthesis of paclitaxel/ docetaxel generally consists of a. selective acylation/protection at similarly reactive C-7 and C-10 hydroxyl groups. Among the 1,7,10 and 13-hydroxyl groups in 10- DAB, the order Of reactivity is 7>10>13>1. Therefore, selective esterification of 13-hydroxyl group requires prior protection of both 7 and iO-hydroxyl groups. Furthermore, if acetyl group is required in the final product, as in the case of paclitaxel, then 7- hydroxyl is to be protected first followed by acetylation of 10- hydroxyl. This requires selection of appropriate protecting groups, which can be put selectively and removed selectively under mild condition. Recently, we have explored the use of haloalkyl acid chlorides as protecting groups (US Provisional Patent Application 60/311077). These haloalkonoyl groups undergo hydrolysis faster than unsubstituted alkonoyl groups and their deprotection causes minimum degradation. We have found that such haloalkyl acid chlorides specifically 2-halo/2,2-dihaloalkyl acid chlorides can be used for selective protection in taxanes and can be selectively deprotected, selective esterificatioa of 13-hydroxyI group with a suitably protected N-ben.zoylphenylisoserine. It has been found that a- hydroxy-P-amidoaryl moiety at the 13-hydroxyl of the taxane moiety is essential for its anti-cancer activity (Wani et al J Am Chem Soc 93, pp 2325, 1971). Esterification at 13-hydroxyi of taxane is very siuggisi due to its stereo-electronic disposition. It is known that the esterification step proceeds to completion with cyclic forms of a-hydroxy-p-amidoarylcarboxylic acids. Furthermore, when cyclic forms of C-13 side chain are used, no 2- epimers are obtained as side product. Therefore, new cyclic forms of side chains, which undergo facile coupling with suitably protected 10-DAB in high yield under simple reaction condition without their use in large excess, are required for developing better and more efficient alternative routes for synthesis of paclitaxel and its analogs, conversion of side chain precursor part into side chain and removal of the protecting groups from baccatin part. These reaction conditions should be tnild in nature to afford final material in high yield with very few side products. For successful commercial production, it is desirable that the crude semi-synthetic taxane is produced with such purity that it could easily be purified into pharmaceutical grade material. Most of the nitrogen protecting groups used so far in oxazolidine carboxylic acid require either harsh acidic condition or hydrogenolysis for their removal. Thus, eg. US Patent 5476954 to Bourzat et ai describes an oxazolidine side chain having a terf-butoxy carbonyl protecting group on the t itrogen atom. After coupling with suitably protected 10-DAB, this protecting group is removed by treating the coupled product in an acidic medium to obtain an amine which is then converted into the corresponding benzoyl derivative. Also, Mas et al in the US Patent 5616739 describes a process in which the coupled product, obtained from coupling of an oxazolidine carboxylic acid and a protected 10-DAB, is treated in an acidic medium to achieve simultaneous removal of side chain protecting groups and 10- hydroxyl protecting group. The resultant amine is then suitably protected to obtain the taxane. On the other hand, US Patent 5637723 issued to Rhone Poulenc Rorer S A in 1997 described an oxazolidine carboxylic acid, which incorporated benzoyl group as the nitrogen-protecting groupx Consequently, the coupled product obtained from the oxazolidine carboxylic acid and protected 10-DAB, upon deprotection did not require to be protected by a benzoyl group. Again this procedure requires deprotection of th; coupled product in an acidic medium. With a view to develop side chain precursor which can be processed to paclitaxei/docetaxel after coupling with suitably protected taxane under very mild and preferably neutral condition, the applicants have SUMMARY OF THE INVENTION The present investigation relates to synthesis of taxanes comprising i. subjecting 5-oxazolidine carboxyiic acid of general structure 1 to the step of coupling with 7-0-(2-haloacyJ)-baccatin III 6c or 7,10-O-di- (2-haloacyl)-10-deacetylbaccatin III 6b in the presence of a condensation agent and an activating agent in an aromatic hydrocarbon at a temperature between 0-100°C to obtain 7-0-[2-(haIoacyI)J-13-[(4S> 5R) -4-aryl -3-(2- unsubstituted /substituted-2-trialkylsilyl)ethoxycarbonyl -1, 3- oxazoiidinyl-5-carbonyl]baccatin III 7a (from 6c) and 7,10-0- di-[2-(haloacyl)]-l 3-[(4S, 5R) -4-aryi -3-(2-unsubsti-tuted /substituted -2-trialkylsily)ethoxycarbonyl-l, 3-oxazolidinyl-5- carbonyl]-10-baccatin III 7b (from 6b); ii. subjecting the coupled product 7 to opening of the oxazolidme ring aiongwith Jeprotection of (2-substituted-2-trialkylsilyl) ethoxycarbonyl group by treatment with a source of fluoride ions to lead to free amines 8; iii. converting the resultant free amines 8 into the corresponding amides by known literature procedure, comprising treating the amines with acid chlorides or acid anhydrides in the presence of a base in a hetero geneous phase to obtain the interm ediate 9; iv. subjecting the intermediate 9 to selective deprotection of 2- hatoacyl/2>2-dih loacyl group under mitd alkaline condition at -20 to +40°C fo>- 6-24h in the presence of ammonia or aliphatic amines or aromatic amines or their combination to afford paclitaxel or docetaxel. The complete reaction scheme is shown in Scheme I, where Ra is alkyl found the following oxazolidine carboxylic acid of general structure 1. It has a (2-trialkylsilyl) ethoxycarbonyl/(2-alkyl/aryl-2-trialkylsilyl) ethoxycarbonyl group as nitrogen protecting group, which can be cleaved under very mile, condition, and therefore degradation of tax an e nucleus can be avoided. The other N,0-bifunctional protecting group then undergoes ckavage very fast without degradation under mild condition. Therefore, these oxazolidine carboxylic acids have emerged as new type of side chain precursor for the synthesis of paclitaxel and docetaxel. Herein, the applicants have described new intermediates for taxoid anticancer drugs, their process of synthesis and process for synthesis of paclitaxel and similar analogs using them (Scheme-I). OBJECTS OF THE INVENTION The object of this indention is to propose a novel oxazolidine carboxylic acid. Another object of this invention is to propose a novel process for the preparation of anticancer taxanes. Another object of the present invention is to propose a new process for the preparation of intermediates of taxanes. Yet another object of this invention is to propose a process for preparation of paclitaxel, docetaxel and their analogs using intermediates, which minimise degradation during the process and thereby increase the purity of the target product. Rb, is selected from hydrogen, alkyl and aryl Rc and Rd are in dep en deftly selected from hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, alkoxy, alkenyloxy, alkynloxy, aryloxy and heteroaryloxy, Re and Rf are independently selected from hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, alkoxy, alkenyloxy, alkynyloxy, aryloxy and heteroaryloxy. In the preferred structure, Re is hydrogen and Rf is aryl, more preferably p-methoxyplienyl or both Re and Rf are methyl, Rg is (substituted-2-trialiiy lsily )ethoxy preferably 2-(phenyl-2- trim ethy lsily l)ethoxy. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a process for the preparation of paclitaxel, docetaxel and their structural analogs. In this process (4R, 5S)-4-phenyl-2-substituted-3-[(2-unsubstituted /substituted -2-trialkyl- silyl)ethoxycarbonyl]-l,3-oxazoIidine-5-carboxylic acids 1 is coupled with 7-0-(2-ha!oacyi)baccatin III 6c or 7,10-O-di(2-haloacyl)-10- deacetylbaccatin III 6b in the presence of a condensation agent and an activating agent in an arcmatic hydrocarbon as solvent to obtain 7-0- [2-(haloacyl)]-13-[(4S, 5R)-4-phenyl-2-substituted -3-(2-unsubsti- tuted/substituted-2-trialky lsily l)ethoxycarbonyl-l, 3-oxazolidinyl-5- carbonyl]baccatin III or 7,10-O-di-[2-(haloacyl)]-13-[(4S, 5R)-4- phenyl-2-substituted-3-(2 -unsubstitu ted/substituted-2-trialky lsily 1) ethoxycarbonyl-1, 3oxazolid.inyl-5-carbonyl]-10-baccatin III respectively. The reaction is carried out at a temperature between 0- 100°C, more preferably it 40-80°C, most preferably at 60°C. Among aromatic hydrocabrons, toluene is found most suitable. Opening of the oxazolidine ring in the coupled product 7 alongwith simultaneous deprotection of the nitrogen protecting (2- trialkylsilyl)ethoxycarbonyl group was found to be structure dependent; the determ iniitg factor being the nitrogen-protecting group. In case of a (2-substitutec-2-trialkylsilyl)ethoxycarbonyl group eg. (2- phenyl-2-lrimethylsilyl)elhoxycarbonyl group as the nitrogen protecting group in the coupled product, the desired protection could be achieved by fluoride induced fragmentation leading to fewer side reaction. Among the sources of fluoride ion, tetraalkylammonium fluoride is preferable. The reaction is carried out by treating the coupled product 7 with two equivalents of tetraalkylammonium fluoride, preferably tetrabutylammonium fluoride in a haloalkane, preferably dichloromethane for 15-120 mins., preferably 30 mins. at 0-40°C, preferably at 25oC to obtain the corresponding free amine 8. Alternatively, deprotection of (2-trialkylsilyl)ethoxycarbonyl group eg. (2-trimethylsilyl)ethoxycarbonyl group or (2-substituted-2- triaIkylsilyl)ethoxycarbonyl group eg. (2-phenyl-2-trimethyl- silyl)ethoxycarbonyl gnup, the nitrogen protecting group in the coupled product 7 can be achieved by using acidic medium. Treating coupled product 7 with 60% aqueous trifluoroacetic acid (10 times) and then mixing at a temperature between 18-25°C, preferably 22°C for 3-6h, preferably 4.5 hrs. effects deprotection alongwith desired opening of the oxazolidme ring. This is followed by usual work-up to obtain free amines 8. The yields obtained by using acidic medium to obtain free amines 8 are more or less comparable to those obtained by using tetrabutylammonium fluoride. However, the latter method provides final product eg. pacbtaxel or docetaxel which are comparatively easier to purify to pharmaceutical grade material. The free amines 8 are treated with acid chlorides or acid anhydrides in the presence of a base in a heterogeneous phase to obtain intermediates 9. The intermediale 9, under mild alkaline condition, in the presence of ammonia or aliphatic amines or aromatic amines or their combination, preferably ammonia and pyridine (2:10) undergoes selective deprotection of 2-haloacyl groups without any appreciable degradation. The reaction is carried out at 0-5°C, preferably 2°C under stirring for 6-24h, preferably 1Oh to obtain paclitaxel or docetaxel. According to this invention is provided a process for the preparation of 4-phenyl-3-[(2-uni5ubstituted/substituted-2-trialkylsily) ethoxy- carbonyl]-2-substituted 1, 3-exazoliduine-5-carboxylic acids 1 comprising i. subjecting a haloformate such as a (2-unsubstituted/substi- tuted-2-triaIkylsily)ethyl haloformate to the step of condensa- tion with arylisoerine 2 eg. phenylisoserine in the presence of a base such as alkali hydroxide or carbonate or bicarbonate or any other acid neutralising chemical; ii. converting the isoserine 3 thus obtained into the corresponding ester 4 in the presence of an alcohol, preferably methanol and an activating agent such as dicyclohexylcarbodiimide or carbonyldiimidazdle. The methyl ester 4 is alternatively prepared by condensing the intermediate 3 with diazom ethane or treating it with alkyl halide in the presence of a base such as potassium bicarbonate iu acetone, iii. converting the isoserine ester 4 into 3-[(2- uttsubstttuted/substituted-2 trialkylsilyl) ethoxycarbonylj-5- oxazoiidine carbosylic ester 5 in the presence of chemicals such as alkoxyalkane ot gem-dialkoxylkane or 1,1,1-trialkoxyaIkane. The reaction is oatalysed by p-arylsulfonic acids or their pyridinium salt, iv. converting the 5-oxazolidine carboxylic ester 5 into the corresponding add 1 by hydrolysis with alkali hydroxide or carbonate followed by treatment with mineral acid. The invention will now be explained in greater details with the help of the accompanying expe iments. EXPERIMENTAL Synthesis of 7-O-chloroacetyl-1O-deacetylbaccatin III (6a) A mixture of 10-deaceiylbaccatin III (250 gm, 0.46 mole), pyridine (150 gm) and 4-DMAP (5.6 gm, 46 mmol) is dissolved in dichloromethane (2.0L) The reaction mixture is stirred for 10 mins. Chloroacetylchloride (75 gm, 0.66 mole) dissolved in dichlorom eft an e (1.5L) is then slowly added to the reaction mixture at 25-30°C. The whole m xture is stirred for 20 mins. and then excess reagent is decomposed by adding 100 gm ice water, and acidified with 5% hydrochloric acid. The organic layer thus obtained is successively washed with aqueous sodium bicarbonate, sodium chloride solution, dried over anhydrous sodium sulfate and then distilled under reduced pressure. The residue is dissolved in toluene (1.5L) at 70-80°C and then cooled down to 0 5°C. The resulting fine solid is filtered and then washed with 1000 til of hexane to obtain the pure title compound 6a (250 gm, 0.40 mole, yield 87%). Synthesis of 7-O-chloroacetylbaccatin III (6c) 7-O-Chloroacetyl-10-deacetylbaccatin III (250gm, 0.40 mole) is dissolved in pyridine (2.5L). The reaction mixture is cooled to 0-5°C. 190gm (2.42 mole) of acetyl chloride is slowly added to the reaction mixture at 0-5°C over a period of 40-50 min. Then the resulting mixture is further stirred 0-5°C for 3 h. The excess reagent is decomposed by adding 200 ml water maintaining internal temperature 0-5°C. The solvent is then removed under reduced pressure and the residual mass is extracted with 2.5L of ethyl acetate. The organic layer thus obtained is wasted with aqueous hydrochloric acid, sodium bicarbonate and sodium chloride solution. The organic layer is evaporated under reduced pressure. The residue is dissolved in toluene (1.5L) at 70-80°C and them cooled down to 0°C. The resulting fine solid is filtered and then washed with 800 ml of hexane to obtain the pure title compound 6c (249.1 gm, 0.376 mole, yield 94%). Synthesis of 7,10- di-O-chloroacelyl-10-deacetylbaccatin III (6b) A mixture of 10-deacetylbaccatin III (250 gm,0.46 mole), pyridine (300gm) and 4- DMAP (11.2 gm, 92 mmol) is dissolved in 2.0L of dichloromethane. The reaction mixture is stirred for 10 minutes.150 gm (1.33 mole) of chloroacetyl chloride dissolved in 1.5 L dichlorom ethane is slowly added to the reaction mixture at 25 -30oC. Then, the whole mixture is stirred for 20 minutes. 150gm Ice water is added to decompose the excess reagent, and then the reaction mixture is acidified with 5% hydrochloric acid. The organic layer thus obtained is successively washed with aqueous sodium-bicarbonate, sodium chloride solution, dried over anhydrous sodium sulfate, and then distilled under reduced pressure. The residue is d ssolved in toluene (1.5 L) at 70-80°C and then cooled down to 0-5°C. The resulting fine solid is filtered and then washed with 1000 ml of hexane to obtain of the pure title compound 6b(304.6 gm ,0.437 mole, yield 95%). 7-0-[2-(Chloroacetyl)]-13-l(4S, 5R) -2-p-methoxyphenyl-4-phenyl-3-(2-phenyl-2- trimethyisHyi-)ethoxycarbonyl] —1, 3-oxazotidinyt-5-carbonyl] baceatin III (7a) A mixture of 7-0-(2-chloroacetyl}baccatin III (6c, 100 gm, 0.15 mole), (4S, 5R) -2-p- methoxyphe.nyl-3-[(2-phenyl-2-triniethylsilyl)ethoxycarbonyl]-4-phenyl-l, 3- oxazolidine-5-carboxylic acid (la, 83 gm, 0.16 mole) and 4-dimethylaminopyridine (5.0 gm, 40.9 mmol) is dissolved in toluene (0.8 L) under nitrogen atmosphere. The temperature of the reaction mixture is raised to 50 C under stirring and then a solution of DCC (45 gm,0.22 mole) in toluene (0.2 L) is added to it. Exotherm occurs and the temperature of the reaction mixture automatically.rises to 60°C and that temperature is maintained for 30 minutes. The reaction mixture is then cooled to 25 -3Q°C, diluted with ethyl acetate (2.5 L) and kept under stirring for 15 minutes. The reaction mixture is then filtered under suction. The residue is extracted with ethyl acetate (2 x 1.0 L). The combined organic layer is washed successively with 25% ammonium chloride solution, 5 % aqueous sodium bicarbonate, water, and brine and then dried over anhydrous sodium sulfate. Evaporation of the organic layer under reduced pressure affords the crude product, which is then precipitated with DCM/Hexane (1:10) to obtain compound 7a (164 gm, 0.14 mole, 93.3%). 7, 10-Di-O-l2-(Chloroacetyl)J 13-[(4S, 5R)-2-p-methoxyphenyl-4-phenyl-3-(2- phenyl-2-triinethylsayl)ethoxycarbonyi]-l,3-oxazolidinyl-5-carbonyl]-10- deacetylbaccatin III (7b) The compound 7b is obtained from 7, 10-di-O-(2-chloroacetyl)-10-deacetylbaccatin III (6b, 110 gm, 0.158 mole), (4S, 5R) -2-p-methoxyphenyl-3-[(2-phenyl-2- trimethylsilyl)ethoxycarbonylJ-4-phs;nyl-l, 3-oxazolidine-5-carboxylic acid (In, 88.6 gm, 0.17 mole) and 4-dimethylaminopyiidine (5.27 gm, 43.1 mmol) and DCC (47.8 gm, 0.23 mole) in toluene (1.1 L)by following the protocol described above for the compound 7a. Yield: 178gm, 0.148 mole, 94%). 7-0-[2-(ChloroacetyI)]-13-l(4S, 5R)-2-p-inethoxyphenyl-4-phenyl-3-(2- trimethylsilyl)ethoxy-carbonyl]-l,3- oxazolidlinyi-5-carbonyl] baccatin III (7c) The compound 7c is obtained from 7-0-(2-chloroacety!) baccatin III (6c, 100 gm, 0.15 mole), (4S,5R)-2-p-methoxyphenyl-4-phenyl-3-[(2-trimethylsilyl)ethoxycarbonyl3-l,3- oxazolidine-5-carboxylic acid (lb,7 gm,0.16 mole) and 4-dimethyiaminopyridine (5.0 gm,40.93 mole) and DCC (45 gm,0.12 mole) in toluene (1.0 L) by following the protocol described above for the compound 7a. Yield: 155 gm, 0.14 mole, 94.4% 7, 10-Di-O-[2-(ChIoroacetyl)]-13-f(4S, 5R)-2-p-methoxyphenyl-4-phenyl-3-(2- trimethyisayl)-ethoxycarbonyiJ-5-oxazoBdinyl carbonyi]-10-decaetyibaccatin III (7b) The compound 7d is obtained from 7, 10-di-O-(2-chloroacetyl)-10-deacetylbaceatin 111 (6b, 100 gm, 0.14 mole), (4S, 5R)-2p-methoxyphenyl-4-phenyl- 3-[(2- trimethylsilyl)ethoxycarbonyl]4,3-oxazolidine-5-carboxylic acid (lb,66.2 gm, 0.149 mole) and 4-dimethylaminopyridine (4.67 gm, 38.2 mmol) and DCC (42.4 gm, 0.205 mole) in toluene(1.0 L) by following the protocol described above for the compound 7a. Yield:149.5 gm, 0.133 mole, 95% 7-Chloroacetyl - 13-[(4S, 5R)-2,2'-dimethyl-4-phenyl -3-12- (trimethylsilyl)ethoxyarbonyl] -l,3-oxazolidinyl-5-carbonyl ] baccatin III (7e) The compound 7c is obtained from 7-0-(2-chloroacetyl)baccatin III (6c,100 gm,0.15 mole), (4S,5R)- 2,2-dimethyl-]-4-phenyl-3-[(2-trimethylsilyl)ethoxycarbonyl-l 3- oxazolidine -5-carboxylic acid (ld,58.5 gm, 0.16 mole) and 4- dimethylam in opyridine(5.0 gm, 40.9.': mmol) and DCC(45 gm, 0.22 mole) in toluene (1.0 L) by following the protocol described above for the compound 7a. Yield: 144 gm, 0.14 mole, 94.5%. 7,10-Dichloroacetyl-13-[(4S, 5R)-2,2-dimethyl-4-phenyl -3-12- (trimethyIsflyI)ethoxyarbonyl]-l,3-osazolidinyl-5-carbonyl]-1O-baccatin III (7f) The compound 7f is obtained from 7,10-O-di-(2-chloroacetyl)baccatin III (6b, 100 gm, 0.14 mole), (4S, 5R)- 2,2-dimethyl-]-4-phenyl-3-[(2-trimethylsilyl)ethoxycarbonyl-l, 3- oxazolidine -5- carboxylic acid (1d 54.8 gm, 0.15 mole) and 4-dim ethy lamiaopyridine (4.68 gm, 38.3 mmol) and DCC (42 4 gm, 0.205 mole) in toluene.(1.0 L) by following the protocol described above for the compound 7a. Yield: 136 gm, 0.13 mole, 92.8%. 7-0-(2-Chlroacetyl)paditaxel (9a) 7-0-[2-(Chloroacetyl)]-13-[(4S, 5R)-2-p-methoxyphenyl-4-plienyl-3-(2-phenyl-2- trimethylsilyl)- ethoxycarbonyl]-l, 3-oxazolidmyl-5-carbonyl] baccatin III (7a, 116.4 gm, 0.1 mole) is suspended in dichloromethane(l.17 L) at 25 - 30°C. To the stirred solution is added 2 equivalents of tetrabutylam monium fluoride trihydrate (63.1 gm, 0.2 mole). Stirring is continued for 30 minutes at 25°C and then 5% aqueous sodium bicarbonate (11.8 gm, 0.14 mole, 236 ml) is addtd. The reaction mixture is cooled to 0 -5°C and then a solution of benzoyl chloride (17 4 ml, 0.149 mole) in dichloromethane (350 ml) is added at the same temperature ovei a period of 20 minutes. After the addition is over, stirring is continued for 15 minutes. The organic layer is separated, washed with brine, and dried over anhydrous sodium sulfate. The solvent is evaporated under reduced pressure and the residue is subjected to column chromatography (eluent: ethylacetate/hexane, 2/5, v/v) to obtain the title compound 9a (77 gm, 0.083 mole, 83%). Alternative method: 7-0-[2-(Chbroacetyl)]-13-[(4S, 5R)-2-p-methoxyphenyl-4- phenyl-3-(2-trimethylsilyl) ethoxyearbonyl]-l, 3-oxazolidinyl-5-carbonyl]baccatin III (7c, 110 gm, 0.1 mol) is suspended in 60% aquoeous trifluoroacetic acid (1.1 L, 10 times) and then stirred at 18 -22°C for 4.5 h, when TLC indicates completion of the reaction. The reaction mixture is then dilutee with dichloromethane and poured into a solution of sodium hydrogen phosphate (2.5 Kg) in water (5 0 L) under stirring. The organic layer is cooled to 0-5°C and then a preceded solution of 5% aqueous sodium bicarbonate (11 8 gm, 0.14 mole, 236 ml) is added under stirring. A solution of benzoyl chloride (17.4 ml. 0.149 mole) in dichlorom ethane (350 ml) is added slowly over a period of 20 minutes to the above reaction mixture at the sime temperature. After the addition is over, stirring is continued for 15 minutes. The organic layer is then separated, washed with brine, and dried over anhydrous sodium sulfate. The solvent is evaporated under reduced pressure- and the residue is subjected to column chromatography (eluent: ethyl acetate/hexane, 2/5. v/v) to obtain the title compound 9a (74.5 gm, 0.08 mole, 80%) Alternative method: 7-Chloroacetyl - 13-[(4S, 5R)-2,2,-dimethyl-4-phenyl -3-[2- (trimethylsilyl)ethoxyarbonyl] -l,3-oxazolidinyl-5-carbonyl]baccatin III (7e, 101 gm, 0.1 mole) is dissolved in 1.0L of 60% aqueous TFA-waler and the mixture is stirred at 18- 22DC temperature for 4 h. After completion of reaction the reaction mixture is diluted with dichloro methane (2.0 L) and thsn poured into a solution of disodium hydrogenphosphate (2.5 Kg) in wai.er (5.0) under stirring. The dichlorom ethane layer is separated and sodium bicarbonate (.1.8 g 0.14 mole in 1000 ml of water) was added to the mixture, cooled to 0-2°C and then benzoyl chloride (17.4 ml, 0.149 mole) dissolved in dichloromethane (350 ml) is added dropwise thereto. After addition the reaction mixture is stirred at 28-32°C for 2 h. The organic layer is separated and washed with brine and then dried over anhydrous sodium sulfate. The solvent is evaporated under reduced pressure and the residue is subjected to column chromatography (eiuent: ethylacetate/hexane, 2/5, v/v) to obtain the title compound 9a (75.0 gm, 0.08 mole, 80%) as a white solid. 7,10-Di-0-(2-chlroacetyl)docetaxe] (9b) ?, 10-Di-O-[2-(Chloroacetyl)]-13-[(4S, 5R)-2-p-methoxyphenyl-4-phenyl-3-(2-phenyl- 2-trimethylsiiyl)ethoxycarbotiyl]-l, 3-oxazolidmyl-5-carbonyl] - 10-deacetylbaccatin HI (7b, 120 gm, 0.1 mole) is suspended in dichlorom ethane (1.2 L) at 25 - 30°C. To the stirred reaction mixture is added 4 equivalents of tetrabutylammonium fluoride trihydrato (126.21 gm, 0.4 mole). Stirring is coitinued for 30 minutes at 25°C and the reaction is monitored by TLC. After the react on is over dichlorom ethane is evaporated under reduced pressure. The residue is taken in toluene (2.0 L) and stirred at 25 - 30°C. To the stirred solution is added sodium bicarbonate (11.8 gm), followed by ditertbutyl dicarbonate (30.55 gm, 0.14 mole) inder stirring. The reaction mixture is stirred for further 3 h and then sodium bicarbonate is removed by filtration. The organic layer is evaporated under reduced pressure at 35 - 40°C. The residue is taken in ethyl acetate (2.4 L), washed with brine and dried over anhydrous sodium sulfate. Evaporation of the organic layer under reduced pressure affords the compound 9b (78.8 gm, 0.082 mole, 82%). Alternative Procedure: 7, 10-Di-O-[2-(Chloroacetyl)]-13-l(4S, 5R)-2-p- methoxyphenyl-4-phenyl-3-(2-tnmethylsilyl)ethoxycarbonyl]- 5-oxazolidinyl carbonylj - 10-decaetylbaccatin III (7d, 112 gn, 0.099 mole) is suspended in 60% aqueous trifluoroacetic acid (1.12 L, 10 times) aid then stirred at 18 - 22°C for 4.5 h, when TLC indicates completion of the reaction. The reaction mixture is then diluted with dichloromethane (2.0 L) and poured into a solution of sodium hydrogen phosphate (2.5 Kg) in water (5.0 L). The organic layer is separated, washed with water, brine and dried over anhydrous sodium sulfate. Evaporation of the organic layer affords the corresponding free amine 8b, The latter is taken in tetrahydrofuran (2.0 L) and then sodium bicarbonate (11.6 gm,0.H8 mole) followed by di-tert-butyl dicarbonate (30.55gm, 0.14 mole) is added under stirring. After the addition is over, stirring is continued for 3 h and then sodium bicarbonate is removed by filtration. The organic layer is evaporated under reduced pressuie at 35 -40°C. The residue is laker, in ethyl acetate (2.5 L), washed with brine and dried over anhydrous sodium sulfate. Evaporation of the organic layer under reduced pressure affords the compound 9b (76 gm, 0.079 mole, 79%). Paclitaxel (10a) To aprecooled solution (0 -5°C) of 25% ammonia (150 ml) in pyridine (750ml) is added 7-0-(2-chloroacetyl)paclitaxel (9a,75 gm,80.6 mmol) and then stirred at this temperature for 12 h. The reaction is monitorec by TLC. After the reaction is over, ammonia and pyridine is removed under low pressure. The resultant gum is dissolved in ethyl acetate (1.5L). The organic layer is washed successively with 2% hydrochloric acid, 5% sodium bicarbonate solution, and brine and then stored over anhydrous sodium sulfate. Evaporation of the organic layer under reduced pressure affords crude paclitaxel. The latter is on column chromatography on silica 60 with ethyl acetate/hexane (6/4) affords paclitaxel (57.8 gm, 67.69 mmol, S4%) as a white solid. Docetaxel is obtained from 7, 10-O-(2-chloroacetyl)docetaxel (9b„ 75 gm, 0.078 mole) using 25% ammonia (300 ml) in pyridine (1500 ml) and by following the protocol described above for paclitaxel. After column chromatography on silica 60 with ethyl acetate/hex ane (6/4) docetaxel is obtained as a white solid. Yield: 50.5 gm, 0.0625 mole, 80.1 %. WE CLAIM: 1. A process for preparation of taxanes of formula 10: wherein R is phenyl or tertiary butoxy and R1 is hydrogen, acetyl or chloroacetyl, wherein the pracess comprises the steps of: i) reacting compound of formula 6, wherein R1 is hydrogen, acetyl or chloroacetyl with (4S,5R)-3-[(2'-substitutecl or unsubstituted-2'-trialkylsilyl) ethoxy-carbonyl]-4-phenyl-2-mono or di-substituted-1,3- oxazolidine-5-carboxylic acid of formula 1, wherein R2 is hydrogen or phenyl, R3 is alkyl (C1 to C4) or p- methoxy phenyl and R4 is hydrogen or alkyl (C1 to C4) in the presence of 4-dimethylaminopyridine, dicyclohexylcarbodiimide (DCC) and an aromatic hydrocarbon solvent to give compound of formula 7, wherein R1 is hydrogen, acetyl or chloroacetyl, R2 is hydrogen or phenyl, R3 is alkyl (C1 to C4) or p-methoxy phenyl and R4 is hydrogen or alkyl (C1 to C4); ii) reacting compound of formula 7 with a tetra alkyl ammonium halide in the presence of a haloalkane solvent to give compound of formula 8, wherein R1 is hydrogen, acetyl or chloroacetyl; iii) reacting the solution of corr pound of formula 8 in the haloalkane solvent with an acid chloride or acid anhydride in the presence of an aqueous solutic n of a base to give compound of formula 9, wherein R is phenyl or tertiary butoxy and R1 is hydrogen; acetyl or chloroacetyl; and iv) treating the compound of formula 9 with aqueous ammonia in the presence of pyridine at a temperature of between -20° to +40° C. to give taxane compound of formula 10. 2. A process as claimed is clairi 1, wherein the aromatic hydrocarbon solvent is toluene 3. A process as claimed in claim 1, wherein step-i) is carried out at a temperature of between 0- 100°C. 4. A process as claimed in clairi 1, wherein the tetraalkylammonium halide is.etrabutyl ammonium fluoride. 5. A process as claimed in claim 1, wherein the haloalkane solvent is dichloromethane. 6. A process as claimed in claim 1, wherein, the ratio of aqueous ammonia and pyridine is 1:10 weight by weight. 7. A compound of formula 8, wherein R1 is acetyl or chloroacetyl. 8. A compound of formula 9 A process for preparation of taxanes of formula 10, wherein R is phenyl or tertiary butoxy and R1 is hydrogen, acetyl or chloroacetyl comprising the steps of: i) reacting compound of formula 6, wherein R1is hydrogen, acetyl or chloroacety"

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