Synthesis of 14,15-Dehydroerythromycin A Ketolides: Effects of the 13-Substituent on Erythromycin Tautomerism.
作者:MARIA FARDIS、GARY W. ASHLEY、JOHN R. CARNEY、DANIEL T. CHU
DOI:10.7164/antibiotics.54.278
日期:——
A ketolide was prepared from 14, 15-dehydroerythromycin A by two different routes. The first approach involving oxidation of the 3-OH of 3-descladinosyl-14, 15-dehydroerythromycin A 2'-O-acetate gave unexpectedly high levels of 3, 11-double oxidation. This may be due to greater formation of the 9, 12-hemiketal in 14, 15-dehydroerythromycin A and concomitant exposure of the 11-OH group for oxidation. NMR studies of 14, 15-dehydroerythromycin A support this hypothesis, revealing a 9:1 ratio of 9-ketone to 9, 12-hemiketal in CDC13 and a 1: 1 ratio in CD3OD as contrasted with the corresponding tautomer ratios of 30:1 in CDC13, and 6:1 in CD3OD with erythromycin A. Alteration of the 13-substituent on the erymronolide A ring from ethyl to vinyl thus favors formation of the 9, 12-hemiketal. A second route to the ketolides was developed based on these findings, in which the 11-OH is eliminated prior to oxidation of the3-OH.
通过两种不同的路线从14, 15-脱氢红霉素A制备了酮类化合物。第一种方法涉及对3-脱落氨基-14, 15-脱氢红霉素A 2'-O-醋酸酯的3-OH进行氧化,意外地产生了高水平的3, 11-双氧化。这可能是由于在14, 15-脱氢红霉素A中9, 12-半缩酮的形成增加,同时11-OH基团暴露于氧化反应中。对14, 15-脱氢红霉素A的核磁共振(NMR)研究支持了这一假设,显示在CDC13中的9-酮与9, 12-半缩酮的比例为9:1,而在CD3OD中则为1:1,与红霉素A在CDC13和CD3OD中对应的量子异构体比例30:1和6:1形成对比。将红霉素A环上的13-取代基从乙基更改为乙烯基,从而有利于9, 12-半缩酮的形成。基于这些发现,发展了第二种制备酮类化合物的路线,其中在氧化3-OH之前先消除11-OH。