Synthesis and Conformation of Aromatic Cyclic Dipeptides. Cyclo(phenylalanyl)<sub>2</sub>, Cyclo(1-naphthylalanyl)<sub>2</sub>, and Cyclo(2-naphthylalanyl)<sub>2</sub>
作者:Syun Egusa、Jun Takagi、Masahiko Sisido、Yukio Imanishi
DOI:10.1246/bcsj.59.2195
日期:1986.7
Cyclic dipeptides of aromatic amino acids, cyclo(l-phenylalanyl)2, cyclo(l-1-naphthylalanyl)2, and cyclo(l-2-naphthylalanyl)2 were synthesized and subjected to spectroscopic analyses using 1H NMR, absorption, circular dichroism (CD), fluorescence, and fluorescence-detected circular dichroism (FDCD). The 1H NMR data suggested that the 2,5-piperazinedione rings of the three cyclic dipeptides are in planar or nearly planar bowsplit boat-type conformation. The aromatic side groups of cyclo(1- and 2-naphthylalanyl)2’s were found to take asymmetric configurations, one naphthyl group being folded onto the 2,5-piperazinedione ring, the other being unfolded. Strong exciton couplet was observed in CD spectra of the three compounds. The signs of the exciton splitting were opposite in the two naphthyl cyclic dipeptides. Fluorescence spectra of the two naphthyl cyclic dipeptides showed no excimer emission. The absence of strong interchromophoric interaction in the lowest excited state was also suggested by the virtual coincidence of CD spectrum with FDCD spectrum. From the above spectroscopic data, probable conformations were proposed for the naphthyl cyclic dipeptides.
合成了芳香族氨基酸的环二肽cyclo(l-苯丙氨酰)2、cyclo(l-1-萘丙氨酰)2和cyclo(l-2-萘丙氨酰)2,并利用1H NMR、吸收光谱、圆二色谱(CD)、荧光光谱和荧光检测圆二色谱(FDCD)进行了光谱分析。1H NMR数据显示,这三种环二肽的2,5-哌嗪二酮环处于平面或近似平面的弓形分叉船式构象。cyclo(1-和2-萘丙氨酰)2的芳香侧基被发现采取不对称构型,一个萘基团折叠在2,5-哌嗪二酮环上,另一个则展开。在这三种化合物的CD光谱中观察到了强耦合分裂。两种萘基环二肽的耦合分裂符号相反。两种萘基环二肽的荧光光谱中未显示环二聚体发射。最低激发态中缺乏强烈的色素间相互作用,这也通过CD光谱与FDCD光谱的几乎重合得以表明。根据上述光谱数据,为萘基环二肽提出了可能的构象。