CRYSTAL-STRUCTURE, CONFORMATIONAL-ANALYSIS, AND MOLECULAR-DYNAMICS OF TETRA-O-METHYL-(+)-CATECHIN

The structure of tetra-O-methyl-(+)-catechin has been determined in the crystalline state. Two independent molecules, denoted structure A and structure B, exist in the unit cell. Crystals are triclinic, space group P1, a = 4.8125(2) angstrom, b = 12.9148 (8) angstrom, c = 13.8862(11) angstrom, alpha = 86.962 (6)-degrees, beta = 89.120 (5)-degrees, gamma = 88.044(5)-degrees, Z = 2, D(c) = 1.336 g cm-3, R = 0.033 for 6830 observations. The heterocyclic rings o the crystal structures are compared to previous results tor 8-bromotetra-O-methyl-(+)-catechin, penta-O-acetyl-(+)-catechin, and (-)-epicatechin. One of the two molecules has a heterocyclic ring conformation similar to that observed previously for (-)-epicatechin, and the other has a heterocyclic ring conformation similar to one predicted earlier in a theoretical analysis of dimers of (+)-catechin and (-)-epicatechin. Both structure A and structure B in t he crystal have heterocyclic ring conformations that place the dimethoxyphenyl substituent, at C(2) in the equatorial position. However, this heterocyclic ring conformation does not explain the proton nmr coupling constant measured in solution. Molecular dynamics simulations show an equatorial half arrow left over half arrow right axial interconversion of the heterocyclic ring, which can explain the nmr results.