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, 2α,5α,10β,14β-tetra-acetoxy-4(20), 11-taxadiene, a taxoid isolated from callus tissue cultures of Taxus spp. Besides two major products, 9α-hydroxy-2α,5α,10β,14β-tetra-acetoxy-4(20), 11-taxadiene and 9α,10β-dihydroxy-2α,5α,14β- triacetoxy-4(20), 11-taxadiene , 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 9α,14β-dihydroxy-2α,5α,10β-triacetoxy-4(20), 11-taxadiene , 6α,10β-dihydroxy-2α,5α,14β-triacetoxy-4(20), 11-taxadiene , 6α,9α,10β-trihydroxy-2α,5α,14β-triacetoxy-4(20), 11-taxadiene , 9α,10β-O-(propane-2,2-diyl)-2α,5α,14β-triacetoxy-4(20), 11-taxadiene , 9α-hydroxy-2α,5α,10β,14β-tetra-acetoxy-4(20), 11-taxadiene formate , 10β-hydroxy-2α,5α,9α,14β-tetra-acetoxy-4(20), 11-taxadiene formate , respectively. Investigation of the properties of the enzymes responsible for the biocatalysis process of sinenxan A to and revealed that the enzymes were extracellular and constitutive. Using sinenxan A and the two major products ( and ) 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 and , respectively; (2) the optimal concentration of sinenxan A added was 60 mg/L; (3) the substrate was mainly converted into and in the first 48 h after addition and then into the minor products.