STRUCTURAL AND CONFORMATIONAL STUDIES ON BIOACTIVE FLAVONOIDS - CRYSTAL AND MOLECULAR-STRUCTURE OF A COMPLEX FORMED BETWEEN 2',6'-DIMETHOXYFLAVONE AND ORTHOPHOSPHORIC ACID - A MODEL FOR FLAVONE-NUCLEOTIDE INTERACTIONS

In order to investigate mechanisms of action of flavones at the molecu lar level, we have prepared a complex between a flavone and orthophosp horic acid which can be considered as a simplest model of interaction between a flavone and a more complex biological phosphate such as nucl eotide, coenzyme or DNA. With orthophosphoric acid, the title flavone forms crystals which have 1:2 stoichiometry (C17H14O4.2H(3)PO(4)) This compound was found to be the 1:1 salt co-crystallized with the unioni zed molecular acid C17H15O4+.H2PO4-.H3PO4. The symmetry is monoclinic, space group P2(1)/n and unit cell dimensions a = 15.571(2), b = 7.369 (1), c = 17.837(2) A, beta = 100.84(1)degrees. One molecule of phospho ric acid is present as a solvate molecule of crystallization, but the other is ionized and protonates the carbonyl oxygen, introducing confo rmational and bond distance changes in the flavone. The dihedral angle between the benzopyrone and phenyl rings is 47 degrees. Complexes wit h phosphate groups involve strong hydrogen bonds and are expected to p lay important roles in biomolecular structures.