u03b1 24 s dihydroxyvitamin d 2 product represents a valuable purification method which can remove products derived from the synthetic path including its concomitant 24 epimeric compound namely 1 u03b1 24 r dihydroxyvitamin d 2 such impurity is a result of the nonstereospecific construction of the side chain u s pat no 5 786 348 and 5 789 397 in such case the separation of both epimeric vitamins is necessary and it is usually performed during the last stage of the synthesis however column chromatography and straight phase separation of the 24 epimers is practically impossible due to their similar chromatographical properties and larger scale separation is also difficult by reverse phase hplc a 1 u03b1 24 s dihydroxyvitamin d 2 product 25 mg m p 136 142 5 u00b0 c was dissolved in boiling acetone 0 18 ml fisher scientific under argon atmosphere and hexane 0 72 ml burdick amp jackson was added the solution was left at room temperature 68 u00b0 f for a few hours and then in a refrigerator 35 45 u00b0 f overnight the precipitated crystals were filtered off washed with a small volume of a cold hexane and dried the yield of crystalline material was 15 mg 60 hplc profiles of crystals and mother liquor are shown in fig3 a 3 b b these crystals of 1 u03b1 24 s dihydroxyvitamin d 2 12 mg were recrystallized from acetone 0 07 ml and hexane 0 3 ml as described in example 1 a and the precipitated crystals 9 mg 75 m p 146 5 151 u00b0 c were observed under a microscope fig5 a and analyzed by.