Methyl 2-[ Isomer by Inversion Method

We report an efficient protocol for synthesis of methyl 2-[(tert-butoxycarbonyl) amino]-3-hydroxy-3-phenylpropanoate (Erythro (±)) by simple reduction and methyl 2-[(tert-butoxycarbonyl) amino]-3-hydroxy-3-phenylpropanoate (Threo (±)) by inversion method. The erythro (±) isomer has been obtained in excellent yield (93%) using sodium borohydride in methanol at -40°C. The erythro isomer has been effectively converted into its threo (±) with 100% efficiency, by inversion, using methanesulfonyl chloride, cesium acetate and crown ether-18-6. The salient features of this method include cost effectiveness, excellent yields and scope for large-scale synthesis, which makes the method an attractive addition to the applicable methodologies.