Patent ID: 6921650

Claim:
A method to prepare an epothilone D derivative with a methyl group at C-12 and a double bond between C-12 and C-13, which method comprises providing substrates including extender units to a non- S. cellulosum host cell that expresses a modified functional epothilone PKS comprising (a) the proteins encoded by the Sorangium cellulosum epoA, epoB, epoC, epoE, and epoF genes and (b) a modified functional epoD protein that lacks a β-carbonyl modifying activity encoded by a Sorangium cellulosum epoD gene, wherein said activity is selected, from the group consisting of a ketoreductase (KR) activity encoded by module 4, a dehydratase (DH), enoylreductase (ER) or KR activity encoded by module 5, or an ER or KR activity encoded by module 6.