Optical resolution by the replacing crystallization of DL-threonine with L-alanine as an optically active cosolute

DL-Threonine (DL-Thr) was optically resolved by replacing crystallization with L-alanine (L-Ala) as an optically active cosolute. D-Thr was preferentially crystallized from a supersaturated aqueous solution of DL-Thr in the presence of L-Ala. Optical resolution was successfully achieved to afford D-Thr with an optical purity of 96-98% and L-Thr of 91-95%. The partially resolved D- and L-Thr were recrystallized from water, taking account of the solubility of DL-Thr, to efficiently yield both enantiomers in an optically pure form.