Biocatalysis of precursors to new-generation SB-T-taxanes effective against paclitaxel-resistant cancer cells

A 10-O-deacetylbaccatin III 10-O-acetyltransferase biocatalyst from Taxus plants was expressed in bacteria whole-cells that were fed 10-O-deacetylbaccatin III and cyclopropane carboxylic acid. Product analysis by qualitative LC/ESI-MS suggested that the C10-acylated products baccatin III, 10-O-n-propionyl-10-O-deace-tylbaccatin III, and 10-O-cyclopropanecarbonyl-10-O-deacetylbaccatin III were made in vivo. The results implied that the cells provided non-natural cyclopropanecarbonyl CoA, from a broad-specificity CoA ligase, and natural products, acetyl CoA and n-propionyl CoA, from reserves in the bacteria for use by acyltransferase to acylate 10O-deacetylbaccatin III in vivo. The 10-acyl-10-O-deacetylbaccatin III are precursors used to synthesize new generation paclitaxel analogs SB-T-1214 and SB-T-121303, which are effective against cancer cells resistant to paclitaxel and its drug derivatives. The k(cat) and K-M of the acyltransferase for cyclopropanecarbonyl CoA (0.83 s(-1), 0.15 M) and n-propionyl CoA (1.2 s(-1), 0.15 M) guided scale-up efforts. The 10-acyl-10-O-deacetylbaccatin III analogs (similar to 45 mg each) were made in vitro by the acyltransferase when incubated with the commercial taxane 10-O-deacetylbaccatin III and synthesized cyclopropanecarbonyl or n-propionyl CoA. The structures of the 10acyl products were verified by NMR analyses that confirmed C10 acylation of the taxane substrate. LC/ESI-MS/MS analysis also supported the identities of the biocatalyzed products. This effort provides a biocatalysis framework to produce new-generation taxane precursors.