CRYSTAL AND SOLUTION FORMS OF A CYCLIC HEPTAPEPTIDE, PSEUDOSTELLARIN-D

Crystal and solution forms of a cyclic heptapeptide, pseudostellarin D , cyclo(Gly-Tyr-Gly-Pro-Leu-Ile-Leu), were examined by spectroscopic e vidences. A single crystal X-ray analysis showed that a revised struct ure, pseudostellarin D possesses a type II beta-turn between Leu(7) an d Gly(1), and a type I beta-turn between Pro(4) and Leu(5). One transa nnular 4-->1 hydrogen bond between Ile(6)-NH and Gly(3)-CO and two bif urcated hydrogen bonds between Tyr(2)-NH and Ile(6)-CO, and Gly(3)-NH and Ile(6)-CO were observed, forming a classical beta-bulge unit in th e crystal. The dominant solution conformation analyzed by high field N MR employing vicinal coupling constant, temperature dependence of NH p rotons, and POESY spectrum was, on the whole, homologous to that obser ved in the solid state.