R-(−)-carnitine is prepared by (a) conversion of (S)-3-hydroxy-4-butyrolactone [1] to alkyl (S)-4-halogen-3-hydroxy-butyrate [2] by reaction with a linear or branched C
1
-C
7
alcohol (b), substitution of a CN group for the halogen of compound [2] to yield the alkyl ester of (R)-4-cyano-3-hydroxybutyric acid [3], (c) conversion of alkyl ester [3] to yield (R)-4-cyano-3-hydroxybutyramide [4], (d) cyclization of compound [4] to yield (R)-5-(cyanomethyl)-2-oxazolidone [5] via conversion of the amide function to isocyanate, (e) hydrolysis of compound [5] to yield (R)-4-amino-3-hydroxybutyric acid [6], and finally (f) methylation of the amino group of compound [6] to yield the end product (R)-carnitine.
(R)-(−)-肉碱的制备方法:(a)将(S)-3-羟基-4-
丁酸内酯[1]与一种直链或支链的C1-C7醇[b]反应,得到烷基(S)-4-卤代-3-羟基
丁酸酯[2],(b)将化合物[2]的卤素替换为CN基,得到(R)-4-
氰基-3-羟基
丁酸酯[3],(c)将烷基酯[3]转化为(R)-4-
氰基-3-羟基丁酰胺[4],(d)通过将酰胺功能团转化为
异氰酸酯,使化合物[4]环化,得到(R)-5-(
氰甲基)-
2-噁唑烷酮[5],(e)
水解化合物[5],得到(R)-
4-氨基-3-羟基丁酸[6],最后(f)将化合物[6]的
氨基甲基化,得到最终产物(R)-肉碱。