Approaches to phomactin A: Unexpected late-stage observations

A dihydroxyepoxide analogous to that proposed as a late intermediate in the biosynthesis of phomactin A was prepared by reduction of the corresponding ketoaldehyde. The structure of the dihydroxyepoxide, specifically its configuration at C14, was confirmed by the X-ray crystal structure of its diacetate. The stereoselectivity of reduction of the ketoaldehyde would appear to be influenced by the presence of a remote phenylsulphonyl moiety at C10. Of interest in the context of the biosynthesis of phomactin A was the observation that this dihydroxyepoxide did not rearrange into the isomeric hydroxytetrahydropyran despite having the configuration at C14 required for this rearrangement.