Studies on the resolution of racemic gossypol. II. By chiral alpha-methylphenethylamine and alpha-methylbenzylamine

A simplified and more practical method for the resolution of racemic gossypol was developed by quick chromatographing the condensation products of either (S) or (R)-alpha-methylphenethylamine and alpha-methylbenzylamine with racemic gossypol on a silica column using diethylether/light petroleum as eluent. The optically active gossypol thus obtained showed specific rotation [alpha]D of (+) or (-)370 +/- 10 degrees, with ee% 96.8 and 98.8 respectively and chemical purity greater than 99% by HPLC. Isomerization of the amino condensates of optically active gossypol through the racemization of the binaphthalene moiety of gossypol was observed, though gossypol itself is optically stable in such condition. The rate of racemization varied with the structure of the amine moiety and solvent present and was increased by light and free radical initiator.