An efficient synthesis of all four optical isomers of nipradilol has been achieved. Thus, 8-methoxy-3-chromanone was reduced enantioselectively with baker's yeast to afford (3R)-8-methoxy-3-chromanol, which, after derivation to (3R)-8-acyloxy-3-chromanol, was led to (3S)- or (3R)-8-hydroxy-3-chromanyl nitrate (7 or 9) by selecting a reaction with retention (using acetyl nitrate) or inversion (using Bu4N+NO3-) of configuration. Futher, (3S)- and (3R)-8-methoxy-3-chromanol, prepared via chemical resolution of 8-methoxy-3-chromanyl N-mesyl-L-phenylalanylate, were also led to 7 or 9 in the same manner. Using 7 and 9, four optically active glycidyl ether derivatives (11-14) were synthesized by using a novel Me4N+Cl--catalyzed etherification reaction of phenol with (S)- and (R)-epichlorohydrin. Subsequent amination of 11-14 with isopropylamine afforded the four optical isomers of nipradilol.
聂拉地洛所有四种光学异构体的高效合成已经实现。因此,用面包酵母对映选择性地还原 8-甲氧基-3-苯并二氢
吡喃酮,得到 (3R)-8-甲氧基-3-苯并二氢
吡喃醇,在衍生为 (3R)-8- 乙酰氧基-3-苯并二氢
吡喃醇后,通过选择保留(使用
硝酸乙酰基)或反转(使用 Bu4N+
NO3-)构型的反应,得到 (3S)- 或 (3R)-8- 羟基-3-苯并二氢
吡喃
硝酸酯(7 或 9)。此外,通过对 N-甲砜基-L-苯丙
氨酰基 8-甲氧基-3-苯甲酰
化学分解制备的(3S)-和(3R)-8-甲氧基-3-
苯甲醇,也以同样的方式生成了 7 或 9。利用 7 和 9,通过新型 Me4N+Cl 催化
苯酚与 (S)- 和 (R)-
环氧氯丙烷的醚化反应,合成了四种光学活性
缩水甘油醚衍
生物(11-14)。随后用
异丙基胺对 11-14 进行胺化,得到了
尼普地洛的四种光学异构体。