Patent ID: 7351869

Claim:
A method of crystallizing calcipotriene comprising the steps of: a) providing a solution of a starting calcipotriene in a first solvent selected from: lower alkyl alcohols, lower aliphatic ketones, alkyl esters of lower carboxylic acids, and cyclic ethers, b) combining, with agitation, the provided solution with from about 1 to about 100 volumes of a second solvent, c) cooling the combination to a temperature of less than about −10° C., and d) isolating calcipotriene from the resulting suspension, wherein when the first solvent is a cyclic ether the second solvent is methyl formate, when the first solvent is a lower alkyl alcohol the second solvent is a lower hydrocarbon, and when the first solvent is a lower dialkyl ketone, the second solvent is methyl formate.