Inai Y, Ito T, Hirabayashi T, Yokota K
Department of Materials Science and Engineering, Nagoya Institute of Technology, Japan.
Biopolymers. 1993 Aug;33(8):1173-84. doi: 10.1002/bip.360330804.
Z-Dehydrophenylalanine (delta ZPhe) possessing four oligopeptides, Boc-(L-Ala-delta ZPhe-Aib)n-OCH3 (n = 1-4: Boc, t-butoxycarbonyl; Aib, alpha-aminoisobutyric acid), were synthesized, and their solution conformations were investigated by 1H-nmr, ir, uv, and CD spectroscopy and theoretical CD calculation. 1H-nmr (the solvent accessibility of NH groups) and ir studies indicated that all the NH groups except for those belonging to the N-terminal L-Ala-delta ZPhe moiety participate in intramolecular hydrogen bonding in chloroform. This suggests that the peptides n = 2-4 have a 4-->1 hydrogen-bonding pattern characteristic of 3(10)-helical structures. The uv spectra of all these peptides recorded in chloroform and in trimethyl phosphate showed an intense maximum around 276 nm assigned to the delta ZPhe chromophores. The corresponding CD spectra of the peptides n = 2-4 showed exciton couplets with a negative peak at longer wavelengths, whereas that of the peptide n = 1 showed only weak signals. Theoretical CD spectra were calculated for the peptides n = 2-4 of several helical conformations, on the basis of exciton chirality method. This calculation indicated that the three peptides form a helical conformation deviating from the perfect 3(10)-helix that contains three residues per turn, and that their side chains of delta ZPhe residues are arranged regularly along the helix. The center-to-center distance between the nearest phenyl pair(s) was estimated to be approximately 5.5 A. The chemical shifts of the delta ZPhe side-chain protons (H beta and aromatic H) for the peptides n = 2-4 indicated anisotropic shielding effect of neighboring phenyl group (s); the effect also supports a regular arrangement of the delta ZPhe side chains along the helical axis.
合成了含有四种寡肽的Z-脱氢苯丙氨酸（δZPhe），即Boc-(L-Ala-δZPhe-Aib)n-OCH3（n = 1 - 4：Boc，叔丁氧羰基；Aib，α-氨基异丁酸），并通过1H-核磁共振、红外光谱、紫外光谱和圆二色光谱以及理论圆二色计算研究了它们的溶液构象。1H-核磁共振（NH基团的溶剂可及性）和红外光谱研究表明，除了属于N端L-Ala-δZPhe部分的那些NH基团外，所有NH基团在氯仿中都参与分子内氢键形成。这表明n = 2 - 4的肽具有3(10)-螺旋结构特有的4→1氢键模式。在氯仿和磷酸三甲酯中记录的所有这些肽的紫外光谱在276 nm左右显示出一个强烈的最大值，归因于δZPhe发色团。n = 2 - 4的肽的相应圆二色光谱在较长波长处显示出具有负峰的激子偶合，而n = 1的肽的圆二色光谱仅显示出微弱信号。基于激子手性方法，对几种螺旋构象的n = 2 - 4的肽计算了理论圆二色光谱。该计算表明，这三种肽形成了一种偏离完美3(10)-螺旋（每圈包含三个残基）的螺旋构象，并且它们的δZPhe残基侧链沿螺旋规则排列。最近的苯基对之间的中心到中心距离估计约为5.5 Å。n = 2 - 4的肽的δZPhe侧链质子（Hβ和芳香族H）的化学位移表明相邻苯基的各向异性屏蔽效应；该效应也支持δZPhe侧链沿螺旋轴的规则排列。
