Synthetic studies on the azinothricin family of antitumour antibiotics. 5. Asymmetric synthesis of two activated esters for the northern sector of A83586C

Abstract An asymmeric synthesis of the activated esters 20 and 21 is reported. Both molecules equate with the C(28)–C(47) region of A83586C, and contain functionality appropriate for future unification with the hexapeptide unit. A useful new reaction is described for converting a methyl ester directly into a thioethyl or HOBT ester that operates under very mild conditions.