Ede N J, Rae I D, Hearn M T
Centre for Bioprocess Technology, Monash University, Clayton, Victoria, Australia.
Int J Pept Protein Res. 1994 Dec;44(6):568-81. doi: 10.1111/j.1399-3011.1994.tb01146.x.
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.
据报道，人生长激素hGH[6 - 13]（Leu6 - Ser - Arg - Leu - Phe - Asu - Asn - Ala13）的α - 氨基琥珀酰亚胺（Asu11）八肽类似物具有降血糖活性，而在第11位为天冬氨酸的相应肽则无活性。为了确定这种活性变化是由构象和/或立体电子效应引起的，研究了在第11位引入两种不同的异构γ - 内酰胺结构的情况。一种内酰胺结构（i）是由Freidinger及其同事开发的类型[Freidinger等人（1982年）《有机化学杂志》47卷，102 - 107页]，而异构γ - 内酰胺结构（ii）代表一种用于肽合成的新型受限合成子。手性ii型γ - 内酰胺是通过由L - 天冬氨酸以几种方式制备的适当保护的脱氧二肽合成的。借助二维NMR（COSY和NOESY）光谱研究了含[Asu11]和含[γ - 内酰胺11]的hGH[6 - 13]肽类似物的溶液构象。发现这些hGH[6 - 13]肽类似物具有构象相似性。例如，对于所有研究的肽类似物，在Phe10环质子与C末端氨基酸残基的质子之间都有明显的弱核Overhauser效应（NOE）。然而，总体而言，与hGH[6 - 13]相关的含[Asu11]和含[γ - 内酰胺11]的肽的NOESY NMR光谱表明，在溶液中存在伸展结构，在第11位可能有弱的II'型β - 转角。用异构γ - 内酰胺结构取代Asu11残基引入到这些hGH[6 - 13]肽类似物中的构象限制程度反映在它们的降血糖活性差异上。特别是，源自新型手性ii型γ - 内酰胺的hGH[6 - 13]肽类似物在体内静脉胰岛素耐量试验中的活性较低，并且与源自（i）型γ - 内酰胺结构的异构hGH[6 - 13]肽类似物相比，NOE较弱。与对照值相比，ii型γ - 内酰胺的外消旋（R，S）形式在20至90分钟内血糖水平的相对变化约为（S） - 立体异构体的一半。
