Regio- and stereo-selective biotransformation of 2α,5α,10β,14β-tetra-acetoxy-4(20), 11-taxadiene by Ginkgo cell suspension cultures

Ginkgo biloba cell suspension cultures were used to bioconvert sinenxan A, 2alpha,5alpha, 10beta, 14beta-tetra-acetoxy-4(20), 11-taxadiene, a taxoid isolated from callus tissue cultures of Taxus spp. Besides two major products, 9alpha-hydroxy-2alpha,5alpha,10beta,14beta-tetra-acetoxy-4(20), 11-taxadiene 1 and 9alpha,10beta-dihydroxy-2alpha,5alpha,14beta-triacetoxy-4(20), 11-taxadiene 2, additional six minor products were obtained and five of them identified as new compounds. On the basis of chemical and spectral data, their structures were identified as 9alpha,14beta-dihydroxy-2alpha,5alpha,10beta-triacetoxy-4(20), 11-taxadiene 3, 6alpha,10beta-dihydroxy-2alpha,5alpha,14beta-triacetoxy-4(20), 11-taxadiene 4, 6alpha,9alpha,10beta-trihydroxy-2alpha,5alpha,14beta-triacetoxy-4(20), 11-taxadiene 5, 9alpha,10beta-O-(propane-2,2-diyl)-2alpha,5alpha,14beta-triacetoxy-4(20), 11-taxadiene 6, 9alpha-hydroxy-2alpha,5alpha,10beta,14beta-tetra-acetoxy-4(20), 11-taxadiene formate 7, 10beta-hydroxy-2alpha,5alpha,9alpha,14beta-tetra-acetoxy-4(20), 11-taxadiene formate 8, respectively. Investigation of the properties of the enzymes responsible for the biocatalysis process of sinenxan A to I and 2 revealed that the enzymes were extracellular and constitutive. Using sinenxan A and the two major products (1 and 2) as indicators, the stage and concentration of sinenxan A added and the kinetics of the biotransformation reaction were investigated. The results showed that: (1) the optimal stage for sinenxan A addition was the logarithmic phase of the cell growth period, in which sinenxan A was almost completely bioconverted, and the biotransformation rates were up to 60 and 20% for 1 and 2, respectively; (2) the optimal concentration of sinenxan A added was 60 mg/L; (3) the substrate was mainly converted into 1 and 2 in the first 48 h after addition and then into the minor products. (C) 2002 Elsevier Science Ltd. All rights reserved.