Cysteic- and homocysteic acid-S-(aminoiminomethyl) amides: a new class of modified arginines useful in peptide synthesis

A novel, practical synthesis of the title compounds and their derivatives are described. The protecting groups for amino, guanidino and carboxylic functions of substituted amides of cysteic and homocysteic acid were selected with the aim of making the amino acid derivatives synthons for peptide synthesis both in solution and by the solid phase method. Studying the structure-activity relationship some new kyotorphin, [Leu(1)] kyotorphin and MIF-1 analogues, containing the unusual amino acid cysteic acid-S-(aminoiminomethyl) amide (sArg) in position two, have been prepared. It is a very promising compound, a structural analogue of arginine and an efficient antagonist in its metabolism.