摘要:
Amino acids (Val, Phe) are combined with two rigid spacers phenoxathiin-4,6-dicarboxylic acid (5) and 2,8-dimethyl-4,6-bis(aminomethyl)phenoxathiin-10,10-dioxide (6) to synthesize the cyclic structures 1 (5-Val/Val-6) and 2 (5-Phe/Phe-6). The diacid and diamino spacers 5 and 6 provide a distance between the attached short peptides which allows hydrogen bonding similar to that found in a parallel beta-sheet. The beta-sheet conformation of 1 and 2 is proved by NMR measurements at low temperatures. The derived dihedral angles and NOE distances are compared to the most stable conformations of 1 calculated with MM3 and AM1.