Conformational Studies of Bis(cyclic tetrapeptide),<i>S</i>,<i>S</i>′-Bis[cyclo(Gly–L-hemiCys–Sar–L-Pro)]. A Proposed Castanet-type Structure in a Dimethyl Sulfoxide Solution
作者:Toshimi Shimizu、Yoshio Tanaka、Keishiro Tsuda
DOI:10.1246/bcsj.55.3808
日期:1982.12
A bis(cyclic tetrapeptide), S,S′-bis[cyclo(Gly–l-hemiCys–Sar–l-Pro)] (BCGCSP), was prepared by coupling two homodetic cyclotetrapeptide. The conformations of BCGCSP in solutions were investigated by means of NMR, Raman, and CD spectroscopy. The 1H-NMR data in dimethyl-d6 sulfoxide (Me2SO-d6) demonstrated that the two cyclic skeletons of BCGCSP take the same conformations as that of an authentic cyclic tetrapeptide, cyclo[Gly–l-Cys(Bzl(OMe))–Sar–l-Pro] (CGCSP). The 1H-NMR spectrum of CGCSP contains three sets of resonances, corresponding to three different molecular conformations. From the Raman lines of BCGCSP at 529 cm−1 and 683 cm−1 in Me2SO-d6, it is deduced that the two HCα-CβS dihedral angles are 180°(trans), while one of the SS–CβCα dihedral angles is 20–30° and the other is either near 90° or near 180°. In addition, the values of two Raman lines predict that the CβS–SCβ dihedral angle is in the range of near 90°. Such a conformation around the CβS–SCβ bond is also reasonable in the light of the presence of a CD transition (CS–SC) at λ>250 nm in water. By combining the above data, the CPK molecular model of BCGCSP was constructed. An inspection of the model reveals that this bis(cyclic tetrapeptide) is likely to adopt a “castanet-type” structure in Me2SO-d6. At the same time the individual cyclic skeleton is considered to take three different ring conformations in equilibrium.
一种双(环状四肽)--S,S′-双[环(Gly-l-hemiCys-Sar-l-Pro)](BCGCSP)--是由两个同位环四肽偶联制备而成的。通过核磁共振、拉曼和 CD 光谱研究了 BCGCSP 在溶液中的构象。二甲基-d6 亚砜(Me2SO-d6)中的 1H-NMR 数据表明,BCGCSP 的两个环状骨架与真正的环状四肽--环[Gly-l-Cys(Bzl(OMe))-Sar-l-Pro](CGCSP)的构象相同。CGCSP 的 1H-NMR 光谱包含三组共振,分别对应三种不同的分子构象。从 BCGCSP 在 Me2SO-d6 中 529 cm-1 和 683 cm-1 处的拉曼线推断,两个 HCα-CβS 二面角为 180°(反式),而其中一个 SS-CβCα 二面角为 20-30°,另一个接近 90°或接近 180°。此外,根据两条拉曼线的值推测,CβS-SCβ 二面角的范围接近 90°。鉴于在水中 λ>250 nm 处存在一个 CD 转变(CS-SC),围绕 CβS-SCβ 键的这种构象也是合理的。综合上述数据,我们构建了 BCGCSP 的 CPK 分子模型。通过对模型的检验发现,这种双环四肽在 Me2SO-d6 中很可能采用 "蓖麻瓣型 "结构。同时,单个环状骨架被认为在平衡状态下具有三种不同的环状构象。