OPTICAL RESOLUTION BY PREFERENTIAL CRYSTALLIZATION AND REPLACING CRYSTALLIZATION OF DL-ALLOTHREONINE

The ternary solubility diagram, X-ray diffraction pattern, and infrare d spectra have suggested that DL-allothreonine [DL-aThr] exists as a c onglomerate. The optical resolution by successive preferential crystal lization gave both D- and L-aThr of 95% optical purities in 9-13% degr ees of resolution. The successive replacing crystallization was more s uccessfully achieved by the coexisting 4-hydroxy-L-proline, as an opti cally active cosolute, in a racemic supersaturated solution. D-aThr of 94% optical purity was allowed to crystallize preferentially without seeding D-aThr in 24% degree of resolution, whereas L-aThr of 81% opti cal purity from the mother liquor was allowed to crystallize by seedin g L-aThr in 22% degree of resolution. Recystallization of the obtained D- and L-aThr from water gave an optically pure form.