Studies in Polyphenol Chemistry and Bioactivity. 1. Preparation of Building Blocks from (+)-Catechin. Procyanidin Formation. Synthesis of the Cancer Cell Growth Inhibitor, 3-<i>O</i>-Galloyl-(2<i>R</i>,3<i>R</i>)-epicatechin-4β,8-[3-<i>O</i>-galloyl-(2<i>R</i>,3<i>R</i>)-epicatechin]
作者:Werner Tückmantel、Alan P. Kozikowski、Leo J. Romanczyk
DOI:10.1021/ja993020d
日期:1999.12.1
The additive diminishes the extent of ketone enolization while maintaining a stereoselectivity of ≥200:1. Oxidation of 14 with DDQ was performed best from the standpoint of product purification if ethylene glycol was used as the nucleophilic trapping agent. The resulting ether 19 was condensed with 14 using TiCl4 to give a good yield of benzyl-protected epicatechin-4β,8-epicatechin (octa-O-benzylprocyanidin
已启动一个项目来合成可可中发现的原花青素低聚物。天然的、容易获得的 (+)-儿茶素通过 (a) 酚氧的苄基化转化为 5,7,3',4'-四-O-苄基-(-)-表儿茶素 (14);(b) Dess-Martin periodinane 将 3-醇氧化成酮;(c) 在 LiBr 存在下用三仲丁基硼氢化锂 (l-Selectride) 还原。该添加剂降低了酮烯醇化的程度,同时保持了≥200:1 的立体选择性。如果使用乙二醇作为亲核捕集剂,从产物纯化的角度来看,用 DDQ 氧化 14 的效果最好。所得醚 19 使用 TiCl4 与 14 缩合,得到良好收率的苄基保护的表儿茶素-4β,8-表儿茶素(octa-O-benzylprocyanidin B2, 20)作为唯一的二聚产物。