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

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 ver y much slowed down. These diastereomers had the D configuration for both Ox z residues. This result appeared to be related to the conformation of the r eaction intermediates. Therefore, the intermediates were converted into sta ble forms and then isolated to confirm their structures. Crystals were obta ined from one derivative and its structure was found to be of the folded fo rm. In this form, the activated atoms were separated from the target atoms. It is suggested that this folded conformation hinders the completion of th e reaction.