CONFIGURATIONAL AND CONFORMATIONAL-ANALYSES OF A CYCLIC OCTAPEPTIDE, LYCIUMIN-A, FROM LYCIUM-CHINENSE MILL

Configurational and conformational analysis of a unique cyclic octapep tide, lyciumin A, showing an inhibitory activity on angiotensin-conver ting enzyme, was made by the spectroscopic and computational chemical methods. The homo- and heteronuclear 2D NMR analysis at 600 MHz in pyr idine-d(5) enable us to determine the complete stereostructure of lyci umin A, which agrees with the structure obtained by the Monte Carlo (M C) and restrained molecular dynamics (MD) calculation using AMBER for ce field. A major solution form of lyciumin A in pyfidine-d(5), analyz ed by NH-C alpha H coupling constants, temperature dependence on NH pr otons, and NOE constrained MD calculations, was shown to have a type I I beta-turn-like conformation between the Val and Gly residues constit uting the cyclic backbone.