Synthesis and conformation of constrained peptides with hypoglycaemic activity derived from human growth hormone.
The alpha-aminosuccinimide (Asu11) octapeptide analogue of human growth hormone hGH[6-13] (Leu6-Ser-Arg-Leu-Phe-Asu-Asn-Ala13) has been reported [Robson et al. (1990) Biol. Chem. Hoppe Seyler 371, 423-431] to have hypoglycaemic activity whilst the corresponding peptide with Asp at position 11 is inactive. In order to determine whether this change in activity is caused by conformational and/or stereo-electronic effects, the incorporation of two different isomeric gamma-lactam structures at position 11 has been investigated. One lactam structure (i) is of the type developed by Freidinger and coworkers [Freidinger et al. (1982) J. Org. Chem. 47, 102-107], whilst the isomeric gamma-lactam structure (ii) represents a new type of constrained synthon for use in peptide synthesis. The chiral type-ii gamma-lactam was synthesized via a suitably protected desoxodipeptide prepared in several ways from L-aspartic acid. The solution conformations of the [Asu11]- and the [gamma-lactam11]-containing hGH[6-13] peptide analogues were investigated with the aid of two-dimensional NMR (COSY and NOESY) spectroscopy. Conformational similarities were found for these hGH[6-13] peptide analogues. For example, for all peptide analogues studied, weak NOEs were evident between the Phe10 ring protons and protons of the amino acid residues at the C-terminus. Overall, however, the NOESY NMR spectra of the [Asu11]- and the [gamma-lactam11]-containing peptides related to hGH[6-13] suggest the presence of an extended structure in solution with a possible weak type II' beta-turn at position 11. The extent of conformational constraint introduced into these hGH[6-13] peptide analogues by substitution of the Asu11 residue with either isomeric gamma-lactam structure was reflected as differences in their hypoglycaemic activity. In particular, the hGH[6-13] peptide analogue derived from the new chiral type-ii gamma-lactam exhibits both lower activity in intravenous insulin tolerance tests in vivo and weaker NOEs than the isomeric hGH[6-13] peptide analogue derived from the type (i) gamma-lactam structure. The relative change in blood glucose levels from 20 to 90 min for the racemic (R,S)-form of the type-ii gamma-lactam compared to the control values was approximately half that of the (S)-stereoisomer.
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Centre for Bioprocess Technology, Monash University, Clayton, Victoria, Australia.
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D000595:Amino Acid Sequence; D000818:Animals; D002240:Carbohydrate Sequence; D013006:Growth Hormone / Q000737:chemistry*; D006801:Humans; D007004:Hypoglycemic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010446:Peptide Fragments / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar
D007004:Hypoglycemic Agents; D010446:Peptide Fragments; D013006:Growth Hormone