Synthesis and assignment of stereochemistry of the antibacterial cyclic peptide xenematide

The synthesis of the antimicrobial cyclic peptide xenematide was accomplished by Fmoc solid phase peptide synthesis and the key esterification reaction was achieved using a modified Yamaguchi esterification. Comparison of the optical rotation and NMR data of the synthesized diastereomers to that of the natural product confirmed the structure of xenematide to be PA-L-[Thr-L-Trp-D-Trp-β-Ala]. (PA = phenylacetyl).