Synthesis of a Novel Class of Peptides: Dilactam-Bridged Tetrapeptides

Article abstract of DOI:10.1021/jo00233a006

As model compounds for the study of constrained peptides, the following lactam-bridged derivatives were synthesized: Ac-L--D--NHMe (I), Ac-L--L--NHMe (II), Ac-L--NHMe (III), Ac-L--D--NHMe (IV), Ac-L--L--NHMe (V), and Ac-L--NHMe (VI).Benzyloxycarbonyl and tert-butyloxycarbonyl groups were employed for amine protection and the benzyl and methyl esters for carboxyl protection.Coupling reactions were carried out by the use of active esters or through azide activation.Cyclization reactions were carried out by adding the active ester hydrochlorides into large volumes of pyridine at elevated temperatures.The cyclic intermediates were obtained in yields of 45-50percent.Fragment condensation of the cyclic dipeptides yielded the corresponding dilactam-bridged tetrapeptides.