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 evidences. A single crystal X-ray analysis showed that a revised structure, pseudostellarin D possesses a type II beta-turn between Leu(7) and Gly(1), and a type I beta-turn between Pro(4) and Leu(5). One transannular 4-->1 hydrogen bond between Ile(6)-NH and Gly(3)-CO and two bifurcated 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 the crystal. The dominant solution conformation analyzed by high field NMR employing vicinal coupling constant, temperature dependence of NH protons, and POESY spectrum was, on the whole, homologous to that observed in the solid state.