Conformational preferences of bicyclic proline analogues with induced chirality at the N atom

摘要

We are involved in a research project aimed at elucidating the conformational preferences of constrained analogues of proteinogenic amino acids when incorporated into a peptide chain.In this context,we have evaluated the relative stability of the beta I-and beta II-turns in model peptides RCO-L-Pro-L-Phe-NHR' when phenylalanine is replaced by different constrained derivatives.We report now the structural consequences arising from the replacement of proline(Pro)by two constrained analogues of bicyclic structure(Rb_7Pro)(Fig.1).In the proline surrogates studied,the flexibility of the pyrrolidine ring has been frozen by linking the a-and S-carbons through an ethylene bridge.Additionally,a phenyl(Phb_7Pro)or methyl(Meb_7Pro)substituent has been incorporated at the P-position.