Tuzi A, Ciajolo M R, Picone D, Crescenzi O, Temussi P A, Fissi A, Pieroni O
Department of Chemistry, University of Naples, Italy.
J Pept Sci. 1996 Jan-Feb;2(1):47-58. doi: 10.1002/psc.47.
The pentapeptide Boc-Val-delta Phe-Gly-delta Phe-Val-OME, containing two dehydro-phenylalanine (delta Phe) residues, has been synthesized and its structure investigated. In the crystalline state, the molecule adopts a right-handed 3(10)-helical conformation stabilized by two intramolecular hydrogen bonds between CO of Val1 and NH of delta Phe4, and between CO of delta Phe2 and NH of Val5, respectively. NMR measurements are consistent with the presence of 3(10)-helical structures also in acetonitrile and dimethylsulphoxide solution: the distances between backbone protons estimated from NOE connectivities are in overall agreement with those observed in the solid state; the chemical shifts of the amide protons show the smaller temperature coefficients for the NHs that in solid state are involved in intramolecular hydrogen bonds. The CD spectra in acetonitrile, chloroform, methanol and dimethylsulphoxide display exciton couplets of bands corresponding to the delta Phe electronic transition at 280 nm; the sign of the bands is consistent with the presence of helical structures having a prevalent left-handed screw sense. Addition of 1,1,1,3,3,3-hexafluoro-propan-2-ol gives rise to the gradual appearance of a couplet of opposite sign, suggesting the helix reversal from left-handed sense to right-handed sense. The conformational behaviour is discussed on the basis of the specific sequence of the peptide.
已合成了含有两个脱氢苯丙氨酸（δPhe）残基的五肽Boc-Val-δPhe-Gly-δPhe-Val-OME，并对其结构进行了研究。在晶体状态下，该分子呈现右手3(10)-螺旋构象，分别通过Val1的羰基与δPhe4的氨基之间以及δPhe2的羰基与Val5的氨基之间的两个分子内氢键得以稳定。核磁共振测量结果表明，在乙腈和二甲亚砜溶液中也存在3(10)-螺旋结构：根据核Overhauser效应（NOE）连接性估算的主链质子间距离与固态中观察到的总体一致；酰胺质子的化学位移显示，在固态中参与分子内氢键的NHs具有较小的温度系数。在乙腈、氯仿、甲醇和二甲亚砜中的圆二色光谱显示出与280 nm处δPhe电子跃迁相对应的激子偶合带；这些带的符号与普遍具有左手螺旋方向的螺旋结构的存在一致。添加1,1,1,3,3,3-六氟-2-丙醇会导致逐渐出现一对符号相反的偶合带，表明螺旋方向从左手向右手反转。基于肽的特定序列对构象行为进行了讨论。
