Synthesis of a New Dual Metalloprotease Inhibitor. I. Diastereoselective Alkylation of Protected 6-Oxopipecolic Acid Esters.
作者:Kozo AKASAKA、Hiroshi AKAMATSU、Yuichi KIMOTO、Yuki KOMATSU、Toshikazu SHIMIZU、Naoyuki SHIMOMURA、Katsuya TAGAMI、Shigeto NEGI
DOI:10.1248/cpb.47.1525
日期:——
Diastereoselective methylation of the enolate generated from various protected 6-oxopipecolic acid esters (3aa-3cd) was studied. The protecting groups on the carboxylic acid and amino groups significantly influenced the trans/cis selectivity in the methylation reaction. The optimal substrate (3ca), bearing benzhydryl ester and carbobenzyloxy moieties gave a trans/cis isomer ratio of ca. 4 : 1. Investigation of the reaction conditions revealed that the reaction solvent, alkylating reagent, and base employed to generate the enolate, were decisive factors for diastereoselectivity. Further optimization of reaction conditions, including the amounts of the reagents and their addition sequence enabled maximization of reaction conversion and minimization of by-products to produce the trans rich 5-methyl-6-oxopipecolic acid ester (4ca) on a large scale.
研究了各种受保护的 6-氧代联哌啶酸酯(3aa-3cd)生成的对映体的非对映选择性甲基化反应。羧酸和氨基上的保护基团对甲基化反应的反式/顺式选择性有显著影响。带有苄基酯和苄氧基的最佳底物(3ca)的反式/顺式异构体比率约为 4 :1.对反应条件的研究表明,生成对映体所使用的反应溶剂、烷基化试剂和碱是影响非对映选择性的决定性因素。进一步优化反应条件,包括试剂用量和加成顺序,可以最大限度地提高反应转化率,减少副产物,从而大规模生产出富含反式的 5-甲基-6-氧代联哌啶酸酯 (4ca)。