A single crystal X-ray diffraction study of the tripeptide Boc-Phe-Aib-Leu-OMe (Aib =
α-aminoisobutyric acid) reveals that it forms structurally one of the best type II β-turns so far reported in tripeptides, stabilized by 10 atom intramolecular hydrogen bonding. In contrast, the isomeric tripeptide Boc-Phe-Leu-Aib-OMe adopts a β-strand like conformation. Interestingly, a previously reported structure of another isomeric tripeptide, Boc-Leu-Aib-Phe-OMe, shows a double bend conformation without any intramolecular hydrogen bonding. These results demonstrate an example of the creation of structural diversities in the backbone of small peptides depending upon the co-operative steric interactions amongst the amino acid residues.
三肽Boc-Phe-Aib-Leu-OMe(Aib为α-
氨基
异丁酸)的单晶X射线衍射研究表明,它形成了迄今为止在三肽中报道的最佳的II型β转角之一,由10原子内分子氢键稳定。相比之下,异构三肽Boc-Phe-Leu-Aib-OMe采取类似β链的构象。有趣的是,之前报道的另一种异构三肽Boc-Leu-Aib-Phe-OMe的结构显示为无内分子氢键的双弯构象。这些结果展示了小肽主链结构多样性的一个例子,取决于
氨基酸残基之间的协同空间相互作用。