Restriction of a peptide turn conformation and conformational analysis of guanidino group using arginine-proline fused amino acids: application to mini atrial natriuretic peptide on binding to the receptor.

Compounds (2S,4S)- and (2S,4R)-4-(2'-guanidinoethyl)proline have been synthesized as a conformationally restricted arginine. Their backbones fit the i + 1 position in a turn, and the side chains are restricted compared to that of arginine. These analogues were incorporated into mini atrial natriuretic polypeptide, which has an important turnlike conformation at Gly(6)-Arg(7)()-Met(8)-Asp(9). Structural analysis revealed that the size of the conformational space of Arg(7) on binding to the receptor was approximately one-third of the entire conformational space.