SYNTHESIS OF THE FIRST TRICYCLIC HOMODETIC PEPTIDE - USE OF COORDINATED ORTHOGONAL DEPROTECTION TO ACHIEVE DIRECTED RING-CLOSURE

The discovery of somatostatin antagonists at one or more receptor subt ypes remains an important goal. We therefore undertook the synthesis o f the homodetic tricyclic peptide (1) hoping to cause conformational d istortion and thereby achieve this biological goal. The synthetic stra tegy called for five dimensional orthogonal amino protection. The carb oxyl and amino protecting groups were selected to assure the desired s elective ring closures. The amino protecting groups were also chosen t o permit differentiation between the two lysine epsilon-amino groups. An improved general cyclization procedure was achieved, which provided the complex c-octapeptide 13 in 93% yield. Biological assay results f or 1 are also presented. (C) 1998 Elsevier Science Ltd. All rights res erved.