Towards a total synthesis of ustiloxins A and B. Stereocontrolled synthesis of (2S,4S,6S)-4-hydroxy-5-phenylsulfinylnorvaline

Abstract

A short, stereocontrolled synthesis of (2S,4S,6S)-4-hydroxy-5-phenylsulfinylnorvaline (8), an unusual amino acid component of ustiloxins A and B, has been achieved. Stereoselective bromolactonisation of N-Boc-(S)-allylglycine (3) is followed by substitution of the bromide 4a with thiophenol to give the corresponding sulfide 5. Highly stereoselective oxidation of the sulfide 5 gives the corresponding sulfoxide 6a. Removal of the Boc group and lactone ring opening then complete the synthesis of the unusual amino acid.