Celogentin K, a new cyclic peptide from the seeds of Celosia argentea and X-ray structure of moroidin

A new cyclic peptide with a 3-hydroxyoxindole ring, celogentin K (1), has been isolated from the seeds of Celosia argentea and the structure including its absolute stereochemistry was assigned by using extensive NMR, MS/MS, and CD spectra. The stereostructure of a known related bicyclic peptide, moroidin (2), was confirmed by a single crystal X-ray diffraction analysis. (C) 2004 Elsevier Ltd. All rights reserved.