(IUCr) Crystallography Journals Online

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Acta Cryst. (2001). E57, o1019-o1021 [ doi:10.1107/S1600536801016129 ]

A folded conformation of an ascidiacyclamide derivative: 3-methoxysulfoxide-(2R,3R)-threoninyl desoxazoline-ascidiacyclamide

M. Doi, A. Asano, Y. Usami, Y. Katsuya, M. Nakai, M. Sasaki, T. Taniguchi and H. Hasegawa

Abstract: Ascidiacyclamide, cyclo(-Ile-Oxz-D-Val-Thz-)₂, has two methyl-oxazoline (Oxz) residues, and each Oxz residue has two chiral C atoms. In the present work, C₃₈H₆₀N₈O₁₂S₄, a chiral modification of these atoms was attempted. A total of ten diastereomers were considered, of which seven were synthesized. For the three remaining diastereomers, the reaction was incomplete or very much slowed down. These diastereomers had the D configuration for both Oxz residues. This result appeared to be related to the conformation of the reaction intermediates. Therefore, the intermediates were converted into stable forms and then isolated to confirm their structures. Crystals were obtained from one derivative and its structure was found to be of the folded form. In this form, the activated atoms were separated from the target atoms. It is suggested that this folded conformation hinders the completion of the reaction.

Online 6 October 2001