CYCLOLEONURIPEPTIDE-D, A NEW PROLINE-RICH CYCLIC DECAPEPTIDE FROM LEONURUS-HETEROPHYLLUS

A new proline-rich cyclic decapeptide, cycloleonuripeptide D (1), cycl e (-Ser-Pro-Pro-Pro-Tyr-Phe-Gln-Thr-Pro-Ile-), was isolated from the f ruits of Leonurus heterophyllus and the structure was elucidated by ex tensive 2D NMR, chemical and enzymatic degradation studies, and tandem MS method. The solid state conformation of cycloleonuripeptide D was clarified by X-ray diffraction study. The cyclic decapeptide backbone of 1 contained two beta-turns, one type I beta-turn at Pro-Ile and one type III beta-turn at Pro-Tyr. A transannular 4 --> 1 backbone hydrog en bond between Ser-NH and Thr-CO, and a 5 --> 1 hydrogen bond between Phe-NH and Pro-CO encompassing Pro-Pro-Tyr, in which the peptide link age between the two proline residues was shown to be in the cis confor mation, were observed. (C) 1997, Elsevier Science Ltd.