A process is disclosed wherein an optically active .beta.-mercaptoalkanoic acid represented by formula (I): ##STR1## wherein R.sub.1 is lower alkyl having from 1 to 4 carbon atoms, is prepared by (1) reacting an optically active .beta.-hydroxyalkanoic acid represented by formula (II): ##STR2## wherein R.sub.1 is the same as defined above, with a halogenating reagent to prepare an optically active .beta.-haloalkanoyl halide represented by formula (III): ##STR3## wherein X is halogen and R.sub.1 is the same as defined above; (2) reacting the .beta.-haloalkanoyl halide with water or an aqueous alkaline solution to prepare an optically active .beta.-haloalkanoic acid represented by formula (IV): ##STR4## wherein X and R.sub.1 are each the same as defined above, or a salt thereof, respectively; and (3) reacting the .beta.-haloalkanoic acid or the salt thereof with a reagent capable of converting the halogen into the thiol group, the configuration of the compound (II), (III), and (IV) being retained throughout the process to prepare the compound represented by formula (I). The product of the present invention is useful as an intermediate for preparation of an antihypertensive agent such as N-(3-mercapto-2-D-methylpropanoyl)-L-proline.
本发明揭示了一种工艺,其中通过以下步骤制备了一种光学活性的β-巯基烷酸,其
化学式为(I):##STR1## 其中R.sub.1是具有1至4个碳原子的低级烷基,包括:(1)将
化学式为(II)的光学活性β-羟基烷酸与卤代试剂反应,以制备
化学式为(III)的光学活性β-卤代
酰卤,其中X为卤素,R.sub.1与上述定义相同;(2)将β-卤代
酰卤与
水或
水性碱性溶液反应,以制备
化学式为(IV)的光学活性β-卤代烷酸,其中X和R.sub.1分别与上述定义相同,或其盐;(3)将β-卤代烷酸或其盐与能够将卤素转化为巯基的试剂反应,化合物(II),(III)和(IV)的构型在整个过程中保持不变,以制备
化学式(I)所代表的化合物。本发明的产品用作抗高血压药物如N-(3-巯基-2-D-甲基丙酰基)-
L-脯氨酸的中间体。