Synthesis of the host-selective phytotoxin destruxin B. Avoiding diketopiperazine formation from an N-methyl amino acid dipeptide by use of the Boc-hydrazide derivative

Abstract

An efficient synthesis of the cyclic hexdepsipeptide destruxin B from its component residues is described that involves a [3+3] fragment coupling followed by cyclization via the azide method. A novel feature of the synthesis is the use of the Boc-hydrazide protecting group for the C-terminal N-methylalanine residue. This group serves both to inhibit facile diketopiperazine formation from the N-methylvalyl- N-methylalanine dipeptide and as a latent activating group for hexadepsipeptide cyclization.