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

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.

Abstract

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.

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