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[摘要]：Hybrid peptides are prepd. from a C-linked carbo-b-amino acid ester (R-b-Caa) and an a-aminoxy acid (R-Ama) derived from S-lactic acid. Extensive NMR (in CDCl3 soln.), CD, and MD studies on the tetra- and hexapeptides led to identification of robust 12/10-mixed helixes. The dipeptide repeat having an R-b-Caa and an R-Ama thus provides a "new motif" to realize a 12/10-mixed helix, for the first time, in oligomers contg. R-Ama. To understand the impact of side chains in and S-b-hAla/R-Ama oligomers were investigated. NMR studies revealed the existence of 12/10-helixes in these hybrid peptides, and the side chains of monomers were found to have a profound influence on their stabilities. These observations imply that the propensity of b-amino acid to prefer a mixed 12/10-helix governs the structural behavior in these peptides. The structural consequences of the lone-pair repulsion between nitrogen and oxygen atoms result in a new and interesting structural motif which behaves like "pseudo" b3,b2-peptides in generating 12/10-mixed helixes. |
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