Conformations of cyclic octapeptides. 1

• Published in: Journal of the American Chemical Society 1984-11, Vol.106 (23), p.7212-7217
• Main Authors: Kopple, Kenneth D, Parameswaran, Kumarapuram N, Yonan, James P
• Format: Article
• Language: English
• Subjects: cyclic peptides; N.M.R
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00335a059

Four diastereoisomeric cyclic octapeptides, cyclo(L- or D-Ala-Gly-L-Pro-L- or D-Phe) sub(2), were synthesized and characterized, and NMR data bearing on their conformations in dimethyl sulfoxide solution were obtained. The most stable backbones of these peptides have trans Gly-Pro peptide bonds and C sub(2) symmetry in the NMR average. The populations of the all-trans C sub(2) form range between 50 and 98%. Likely solution conformations of all-trans cyclo(D-Ala-Gly-L-Pro-D-Phe) sub(2) and cyclo(L-Ala-Gly-L-Pro-L-Phe) sub(2) have turns at Pro-Phe. In both peptides two planes containing sequences of Gly, Pro, Phe, and Ala alpha -carbons are joined at roughly right angles along a line between the Ala alpha -carbons, and the Ala methyl groups are directed toward each other across the ring on the convex side of the fold. The proposed conformation for cyclo(L-Ala-Gly-L-Pro-L-Phe) sub(2) has two type I L-Pro-L-Phe beta turns and is similar in important respects to the backbone of the crystalline cyclic octapeptide beta -amanitin, except that beta -amanitin contains both type I and type II turns.