Synthesis of Enniatin-like Cyclic Depsipeptides via ‘Direct Amide Cyclization’

✍ Scribed by Peter Köttgen; Anthony Linden; Heinz Heimgartner

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: German
• Weight: 190 KB
• Volume: 89
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200690069

✦ Synopsis

Abstract

The synthesis of several 18‐membered cyclodepsipeptides with an alternating sequence of α,α‐disubstituted α‐amino acids and α‐hydroxy acids (compounds 14a–14e) is described. The ring closure via macrolactonization was accomplished by treatment of a diluted suspension of the corresponding linear precursors 12a–12e in toluene with HCl gas, i.e., the so‐called ‘direct amide cyclization’. The incorporation of the α,α‐disubstituted α‐amino acids was achieved via the ‘azirine/oxazolone method’ with 2__H__‐azirin‐3‐amines of type 6 and 9 as building blocks. The structure of the cyclic depsipeptide 14a was established by X‐ray crystallography.