Biocatalytic and Regioselective Exchange of 2‐O‐Benzoyl for 2‐O‐(m‐Substituted)Benzoyl Groups to Make Precursors of Next‐Generation Paclitaxel Drugs

A taxane 2‐O‐benzoyltransferase (mTBT, derived from Accession: AF297618) biocatalyzed the dearoylation and rearoylation of next‐generation taxane precursors of drugs effective against multidrug‐resistant cancer cells. Various taxanes bearing an acyl, hydroxyl, or oxo group at C13 were screened to assess their turnover by mTBT catalysis. The 13‐oxotaxanes were the most productive, where 2‐O‐debenzoylation of 13‐oxobaccatin III was turned over faster compared to 13‐oxo‐10‐O‐(n‐propanoyl)‐10‐O‐deacetylbaccatin III and 13‐oxo‐10‐O‐(cyclopropane carbonyl)‐10‐O‐deacetylbaccatin III, yielding ~20 mg of each. mTBT catalysis was likely affected by an intramolecular hydrogen bond with the C13−hydroxyl. Oxidation to the 13‐oxo recovered catalysis. The experimental data for the debenzoylation reaction was supported by Gaussian‐accelerated molecular dynamics simulations that evaluated the conformational changes caused by different functional groups at C13 of the substrate. These findings also helped postulate where the 2‐O‐benzoylation reaction occurs on the paclitaxel pathway in nature. mTBT rearoylated the debenzoylated 13‐oxobaccatin III acceptors fastest with a non‐natural 3‐fluorobenzoyl CoA among the other aroyl CoA thioesters evaluated, yielding ~10 mg of each with excellent regioselectivity at laboratory scale. Reducing the 13‐oxo group to a hydroxyl yielded key modified baccatin III precursors (~10 mg at laboratory scale) of new‐generation taxoids. A Taxus 2‐O‐benzoyltransferase (mTBT), assisted by CoA, is used to biocatalytically deconstruct older‐generation paclitaxel precursors by removing the 2‐O‐benzoyl group from baccatin III or one of its 10‐O‐acyl analogs. mTBT then appends various non‐natural (m‐substituted)benzoyl groups, transferring them from CoA thioesters to the debenzoylated intermediates to make pharmacologically more potent, newer‐generation paclitaxel precursors.