作者:Anindita Sengupta、Rituparna S. Roy、Varatharajan Sabareesh、Narayanaswamy Shamala、Padmanabhan Balaram
DOI:10.1039/b516088j
日期:——
The crystal structures of four protected β-amino acid residues, Boc-(S)-β3-HAla-NHMe (1); Boc-(R)-β3-HVal-NHMe (2); Boc-(S)-β3-HPhe-NHMe (3); Boc-(S)-β3-HPro-OH (6) and two β-dipeptides, Boc-(R)-β3-HVal-(R)-β3-HVal-OMe (4); Boc-(R)-β3-HVal-(S)-β3-HVal-OMe (5) have been determined. Gauche conformations about the CβâCα bonds (θ
â¼
±60°) are observed for the β3-HPhe residues in 3 and all four β3-HVal residues in the dipeptides 4 and 5. Trans conformations (θ
â¼ 180°) are observed for β3-HAla residues in both independent molecules in 1 and for the β3-HVal and β3-HPro residues in 2 and 6, respectively. In the cases of compounds 1â5, molecules associate in the crystals via intermolecular backbone hydrogen bonds leading to the formation of sheets. The polar strands formed by β3-residues aggregate in both parallel (1, 3, 5) and antiparallel (2, 4) fashion. Sheet formation accommodates both the trans and gauche conformations about the CβâCα bonds.
四种保护的β-氨基酸残基的晶体结构被确定,包括Boc-(S)-β3-HAla-NHMe (1);Boc-(R)-β3-HVal-NHMe (2);Boc-(S)-β3-HPhe-NHMe (3);Boc-(S)-β3-HPro-OH (6),以及两个β-二肽,Boc-(R)-β3-HVal-(R)-β3-HVal-OMe (4);Boc-(R)-β3-HVal-(S)-β3-HVal-OMe (5)。在3中观察到β3-HPhe残基及在二肽4和5中的所有四个β3-HVal残基围绕Cβ-Cα键呈现出偏斜的构象(θ ≈ ±60°)。在1中的两个独立分子及在2和6中的β3-HAla、β3-HVal和β3-HPro残基分别观察到反式构象(θ ≈ 180°)。在化合物1–5的情况下,分子通过分子间骨架氢键在晶体中结合,形成层状结构。由β3-残基形成的极性链条以平行(1、3、5)和反平行(2、4)的方式聚集。层的形成容纳了围绕Cβ-Cα键的反式和偏斜构象。