Study on the spatial structure of brachystemin C, a new cyclic peptide from Brachystemma calycinum

A new cyclic octapeptide, brachstemin C (the molecular formula: C38H56N8O9), was isolated from the root of Brachystemma calycinum. The types and sequence of the amino acids of the title compound were confirmed by spectral analyses and X-ray diffraction. The stereochemistry of the title cyclic octapeptide was clarified by X-ray crystallographic study. The cyclic octapeptide backbone contains three b-turns. Two of them are type I b-turns and one is type III b-turn (right-handed 310 helix). There are intermolecular hydrogen bonds between the cyclic peptide and the solvent molecules which maintained the steady spatial arrangement in crystal. q 2003 Elsevier B.V. All rights reserved