Utility of the Cleavage of Nitrosamides for the Preparation of Chiral Acids after Chromatographic Separation of their Diastereomeric Amides

A m ethod for optical resolution of chiral acids is described. I t consists o f the conversion of racemic acids to diastereomeric amides, their chromatographic separation and sub­ sequent deam idation via the nitrosamide route. Reaction conditions for cleavage of amide derivatives of phenylalanine and m ethylbenzylam ine are given. No or only negligible racem ization o f carboxylic acids, chiral in a-position takes place under those conditions. The exten t o f E,Z-isom erization of double bonds is very sm all, as is the ex ten t o f double bond m igration from the Zl3-position into conjugation w ith the carboxyl function. Enantiom erically pure Ror S[2-3H]2-m ethylbutanoic acid and (-)methyl-3(p-chlorophenyl)2-chloropropionate (Bidisin®) were prepared by this procedure.