Substrate specificity for the hydroxylation of polyoxygenated 4(20),11-taxadienes by Ginkgo cell suspension cultures

Three C-14 oxygenated taxanes isolated from callus cultures of Taxus spp., 2α,5α,10β,14β-tetra-acetoxy-4(20),11-taxadiene 3, 2α,5α,10β-triacetoxy-14β-propionyloxy-4(20),11-taxadiene 4, 2α,5α,10β-triacetoxy-14β-(2-methylbutyryl)-oxy-4(20),11-taxadiene 5, and three deacetylated derivatives of 3, 10β-hydroxy-2α,5α,14β-triacetoxy-4(20),11-taxadiene 6, 14β-hydroxy-2α,5α,10β-triacetoxy-4(20),11-taxadiene 7, 10β,14β-dihydroxy-2α,5α-diacetoxy-4(20),11-taxadiene 8, could all be regio- and stereo-selectively hydroxylated at the 9α-position by Ginkgo cell suspension cultures to yield a series of new 9α,14β-dihydroxylated taxoids. The effects of functional groups, especially at C-14 of the substrates, on the biotransformation were also investigated. The results revealed that substrates with an acetoxyl group at C-14 could be more efficiently 9α-hydroxylated than those with a longer ester chain or a hydroxyl group at C-14. An acetoxyl or hydroxyl group at C-10 had no effect on the conversion rates of the substrates, but substrates with the hydroxyl group (compared with the acetoxyl analogues) could be converted into 9α-hydroxylated products more easily.