The final step of the semisynthetic route to paclitaxel involves cleavage of the triethylsilyl (TES) protecting group from the C-7 hydroxyl group. Paclitaxel is an extremely complex molecule, and standard deprotection conditions led to formation of several impurities. Trifluoroacetic acid in aqueous acetic acid was found to be very effective in the cleavage of the TES group without compromising the quality of the product.

alpha-(3-Chloropropyl)-4-fluorobenzenemethanol, a possible intermediate for synthesis of a potential anti-psychotic agent alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMS 181100), was resolved by acetylation using isopropenyl acetate and lipase PS-30 in heptane. S-alcohol was obtained in 42% yield with >99% optical purity. R-acetate was obtained with 92.6% optical purity by stopping the reaction after 46% conversion. The enzymatically produced acetate was hydrolyzed by lipase PS-30 to give R-alcohol with >99% optical purity after 62-72% conversion. BMS 181100 acetate ester was treated with lipase GC-20 in buffer containing 10% toluene to give the R-alcohol with 97.9% optical purity after 47.6% conversion. The rate and enantioselectivity of hydrolysis by lipase GC-20 were very dependent on the organic solvent. E values ranged from 1 in the absence of organic solvent to >100 with dichloromethane and toluene.

A key chiral intermediate [(3R-cis)-3-(acetyloxy)-4-phenyl-2-azetidinone (2)] for the semi-synthesis of paclitaxel (taxol; 5), an anti-cancer compound, was prepared by an enzymic process. The stereoselective enzymic hydrolysis of cis-3-(acetyloxy)-4-phenyl-2-azetidinone (1) to the corresponding (S)-(-)-alcohol (3) was carried out using various lipases. Lipase PS-30 (Pseudomonas cepacia) and BMS (Bristol-Myers Squibb) lipase (Pseudomonas sp. SC13856) catalysed hydrolysis of the undesired enantiomer of racemic compound 1, producing the (S)-(-)-alcohol (3) and the desired (R)-(+)-acetate (2). Reaction yields of > 96% and optical purities of > 99.5% were obtained. For a very efficient enzyme source (BMS lipase), a lipase fermentation using Pseudomonas sp. SC13856 was developed. In a fed-batch process using soybean oil, the fermentation resulted in 1500 units of extracellular lipase activity/ml. Crude BMS lipase (1.7 kg, containing 140,000 units/g) was recovered from the filtrate by ethanol precipitation. BMS lipase and commercially available lipase PS-30 were independently immobilized on Accurel polypropylene. These immobilized lipases were re-used (ten cycles) without loss of enzyme activity, productivity or optical purity of the product. The enzymic reaction process was scaled up to 75 and 150 litres using immobilized BMS lipase and lipase PS-30 respectively. From the reaction mixture, compound 2 was isolated in 88-90 mol% yield and 99.5% optical purity. A purity of 99.9 (area %) was demonstrated by g.c. for isolated compound 2.

An isolate ofM roridum (ATCC 52485) which is a potent pathogen to muskmelon was shown to produce a series of macrocyclic trichothecenes, the myrotoxins, heretofore found to be produced only by an. isolate ofM roridum which is a pathogen to tomato. The fact that these two isolates are virulent pathogens and both produce the same potent mycotoxins suggests that these novel trichothecenes may play an important role in the pathogenicity of the fungi.