NOVEL MOLECULAR-CONFORMATION OF (R,S)-HESPERETIN IN ANHYDROUS CRYSTAL

Novel molecular conformation of racemic hesperetin, ydro-5,7,-dihydrox y-2-(3-hydroxy-4-methoxy-phenyl) 4H-1-benzopyran-4-one, was determined by X-ray analysis. A new form was crystallized from ethanol solution and its molecular conformation is quite different from that of monohyd rate crystal (Acta Crystallogr., C43,1946 (1987)). The aromatic ring p art of benzopyrone and the phenyl ring form the twist orientation (dih edral angle of two rings, Phi is 53.1(3)degrees), in contrast to the p arallel arrangement in the moaohydrate form (Phi = 0.6 degrees). The p yrone ring forms a slightly flattened sofa conformation, where C(2) is displaced by 0.40(2) Angstrom A from the pyrone plane, in contrast to the large displacement in the monohydrate form (0.54 Angstrom A). The re is a strong intramolecular hydrogen bond between keto O(4) atom and hydroxy H(05)-O(5) group which forms a six-membered ring conjugated w ith benzopyrone rings. The degree of conjugation is also slightly diff erent of the two forms and may relate to the difference of hydrogen bo nding network and stacking mode of aromatic rings.