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Molecular conformation of ascidiacyclamide, a cytotoxic cyclic peptide from Ascidian : X‐ray analyses of its free form and solvate crystals
Author(s) -
Ishida Toshimasa,
In Yasuko,
Doi Mitsunobu,
Inoue Masatoshi,
Hamada Yasumasa,
Shiori Takayuki
Publication year - 1992
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360320204
Subject(s) - chemistry , crystallography , hydrogen bond , molecule , van der waals force , ring (chemistry) , crystal structure , stereochemistry , crystal (programming language) , x ray crystallography , aqueous solution , peptide , intramolecular force , diffraction , biochemistry , organic chemistry , computer science , programming language , physics , optics
In order to investigate the conformational variation of ascidiacyclamide, a cytotoxic cyclic peptide from marine tunicate Ascidian , single crystals were prepared from ethanol and aqueous ethanol solutions as its free form (crystal I) and H 2 O/0.5 C 2 H 5 OH solvate (crystal II), respectively, and were determined by the x‐ray diffraction method. Crystal I showed a pseudo C 2‐symmetric saddle‐shaped rectangular conformation. Similar conformations were also observed in crystal II, where there were two crystallographically independent C 2‐symmetric molecules (named Mol‐A and ‐B) per asymmetric unit. Mol‐A and ‐B included H 2 O and H 2 O/C 2 H 5 OH solvents within their ring structures, respectively. These water and ethanol molecules were located on the crystallographic dyad axes, and were stabilized by the van der Waals contacts (including hydrogen bonds) with the polar‐ring N atoms and nonpolar D ‐Val side‐chain atoms. The conformational characteristics of ascidiacyclamide and its fluctuation/variation were discussed based on the present and previously reported x‐ray results.