Tsai M D, Byrn S R, Chang C, Floss H G, Weintraub H J
Biochemistry. 1978 Aug 8;17(16):3177-82. doi: 10.1021/bi00609a001.
The solution conformations of a series of pyridoxal-amino acid Schiff's bases were analyzed using 13C and 1H nuclear magnetic resonance techniques. The 13C--1H coupling constants were assigned based on model compounds and isotopic labeling. The predominant conformation of the the C4--C4' bond was found to be "cis" based on nuclear Overhauser effect (NOE) measurements and the "simultaneous" upfield shift of both H4' and H5' in the Schiff's bases of aromatic amino acids. Going from the monoanion (pD 8.2) to the dianion (pD 12.3), changes in these two effects suggested an increasing contribution of the "trans" conformer. The conformation of the N--Calpha bond was found to be approximately the same for all the Schiff's bases studied based on the long-range coupling constants 3J(C4'--Halpha) of these compounds, and the NOE studies indicate that there is a close spatial relationship between H4' and Halpha. The conformations of the Calpha--Cbeta bond of the Schiff's bases of aromatic amino acids were determined by stereospecific deuterium labeling at the beta position. A pi--pi interaction between the aromatic ring and the pi system of pyridoxal was observed which disappeared upon saturation of the aromatic ring.
使用碳-13和氢-1核磁共振技术分析了一系列吡哆醛-氨基酸席夫碱的溶液构象。基于模型化合物和同位素标记对碳-13-氢耦合常数进行了归属。基于核Overhauser效应（NOE）测量以及芳香族氨基酸席夫碱中H4'和H5'同时向高场位移，发现C4-C4'键的主要构象为“顺式”。从单阴离子（pD 8.2）转变为双阴离子（pD 12.3）时，这两种效应的变化表明“反式”构象体的贡献增加。基于这些化合物的远程耦合常数3J（C4'-Hα），发现所研究的所有席夫碱的N-Cα键构象大致相同，并且NOE研究表明H4'和Hα之间存在紧密的空间关系。通过在β位进行立体专一性氘代标记确定了芳香族氨基酸席夫碱的Cα-Cβ键构象。观察到芳香环与吡哆醛的π体系之间存在π-π相互作用，该相互作用在芳香环饱和后消失。
