Patent ID: 8329150

Claim:
A method for producing suplatast tosilate crystals exhibiting evenness in optical purity and exhibiting peaks at diffraction angles (2θ±0.1°) in the vicinity of 6.7°, 13.3°, 19.0°, 20.0°, 21.7°, and 22.6° as measured through powder X-ray diffractometry, the method comprising stirring suplatast tosilate crystals in a solvent to thereby induce transition of the crystals, and collecting crystals which exhibit an optical purity of less than 2% ee as measured in each of the suspension supernatant and the solution when subjected to optical purity measurement by a method for evaluating evenness in the crystallinity of suplatast tosilate crystals, comprising: (a)(i) adding a solvent to suplatast tosilate crystals to thereby dissolve 3% or less of the crystals in the solvent and form a suspension, and (ii) subjecting a portion of the supernatant of the resultant suspension to an optical purity measurement; (b)(i) adding a solvent to the remaining suspension to thereby dissolve the entirety of the suplatast tosilate crystals in the suspension in the solvent, and (ii) subjecting a portion of the resultant solution to an optical purity measurement; and (c) comparing the optical purity measurement (a)(ii) to the optical purity measurement (b)(ii).