Determination of absolute configuration of photo‐degraded catechinopyranocyanidin A by modified Mosher's method
Determination of absolute configuration of photo‐degraded catechinopyranocyanidin A by modified Mosher's method
复制标题
改良Mosher法测定光降解儿茶素吡喃花青素A的绝对构型
作者：
Oyama Kin‐ichi;Kondo Tadao;Shimizu Toshimichi;Yoshida Kumi
儿茶素吡喃花色素A和B（cpcA和cpc B）是红赤豆（Vigna angularis）种皮中存在的两种紫色色素，其中cpcA是主要色素，在儿茶素部分含有两个手性碳。通过比较它们的实验和量子化学计算的电子圆二色性（ECD），确定了它们的绝对构型。这些紫色色素在光照射下不稳定，容易分解为光降解的儿茶素吡喃花青素A和B（pdcpcA和pdcpc B），同时保留儿茶素残基的立体结构。我们应用改进的Mosher方法测定pdcpcA中仲醇的手性。用重氮甲烷对pdcpcA进行六甲基化，然后用（S）-和（R）-MTPAC 1进行酯化，分别得到（R）-和（S）-MTPA酯。通过对（R）-和（S）-MTPA四甲基儿茶素酯的NMR谱分析，确定pdcpcA的手性为2 R，3S，与cpcA的绝对构型相同。
Catechinopyranocyanidins A and B (cpcA and cpcB) are two purple pigments present in the seed‐coat of red adzuki bean,Vigna angularis, of which cpcA is the major pigment, containing two chiral carbons in the catechin part. Their absolute configurations were determined by comparison of their experimental and quantum chemical calculated electronic circular dichroisms (ECDs). These purple pigments are labile on light irradiation and easily decompose to photo‐degraded catechinopyranocyanidins A and B (pdcpcA and pdcpcB), while retaining the stereostructure of the catechin residue. We applied modified Mosher's method for determining the chirality of the secondary alcohol in pdcpcA. Hexamethylation of pdcpcA by diazomethane followed by esterification using (S)‐ and (R)‐MTPACl gave (R)‐ and (S)‐MTPA esters, respectively. By analysis of the NMR spectra of (R)‐ and (S)‐MTPA esters of tetramethylated (+)‐catechin, the chirality of pdcpcA was determined to be 2R, 3S, same as the absolute configuration of cpcA.