STRUCTURE-FUNCTION-RELATIONSHIPS OF DES-(B26-B30)-INSULIN

In order to study the role of the amino acid in position B25 and its e nvironment in shortened insulins, a series of analogues was prepared w ith the following modifications: 1, Stepwise shortening of the B-chain including replacements of Tyr(B26) and Thr(B27) by glycine; 2, substi tutions at the carboxamide nitrogen of des-(B26-B30)-insulin-B25-amide by apolar, polar or charged residues of various chain lengths; 3, rep lacement of Phe(B25) by asparagine-amide, phenylalaninol or a series o f alkyl and aralkyl residues. Trypsin-catalyzed semisyntheses were per formed with Boc-protected or unprotected des-octapeptide-(B23-B30)-ins ulin and synthetic peptides. Relative receptor binding and in vitro bi oactivity of [Asn(B25)]-des-(B26-B30)-insulin-B25-amide was 227 and 29 2% (on insulin), other activities ran ed between 1 and ca. 200%. We ma ke the following conclusions. An L-amino acid is essential in position B25. The B25-carbonyl and NH groups favour high binding and ''superpo tency'', but are not indispensible for receptor contacts. For high aff inity receptor interaction, the planarity at the C-gamma-atom and the distance of B25-side-chain branching in position B25 are important, bu t an aromatic ring is not necessary. (C) Munksgaard 1995.