Configurational studies of complexes of tea catechins with caffeine and various cyclodextrins.
A suspension of an equimolecular amount of ENT-gallocatechin-3-O-gallate ( ENTGCg) and caffeine in water afforded two kinds of crystals, which were 1 : 2 and 2 : 2 complexes of ENTGCg and caffeine. The stereochemical structures and intermolecular interactions between ENTGCg and caffeine were determined by X-ray crystallographic analysis. The crystal structure of ENTGCg was determined and compared with those of the 1 : 2 and 2 : 2 complexes. Epigallocatechin-3-O-gallate (EGCg) formed a 1 : 1 complex with β-cyclodextrin (CD), in which the aromatic A ring and a part of the heterocyclic C ring were included from the wide secondary hydroxyl group side of the β-CD cavity in aqueous solution, while the B rings and 3-O-gallate groups (B' rings) were left outside the cavity. In contrast, ENTGCg formed a 1 : 2 complex with β-CD, in which the aromatic A and B rings of ENTGCg were included by two molecules of β-CD.
Inactivation Effect of Tea Leaf Catechins on Human Type-A Influenza Virus.
The effects of catechins obtained from the hot water extract of green tea leaves on two human type-A influenza virus strains of Aichi/2/68 and PR/8/34 were studied. In this study, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), (-)-epigallocatechin gallate (EGCg), the crude catechins containing these catechins and (+)-catechin were used. Consequently it was observed that catechins used in this study had an inhibitory effect on the hemolytic activity to red blood cells induced by these two type-A virus strains under acidic conditions (pH 5.1 or 5.4) although they did not have an influence on the agglutination activity to red blood cells induced by the same virus strains. After incubation of (-)-ECg and (-)-EGCg with A/Aichi/2/68 virus, MDCK cells, virus-sensitive cells, were infected with the virus and the ability of virus proliferation was measured in terms of an index of the agglutination activity of the virus to red blood cells. The used two catechins, (-)-ECg and (-)-EGCg, inhibited the virus proliferation at concentrations of 100μg/ml and 50μg/ml, respectively. Furthermore, at a concentration of 2.0 mg/ml these two catechins were found to inhibit the activity of neuraminidase on the surface of the virus membrane by 71.3% and 60.8%, respectively. From the above-mentioned results, it is considered that among the catechins contained in green tea leaves, such two catechins as (-)-ECg and (-)-EGCg inhibit the activity of neuraminidase present on the surface of human influenza virus in order to block the invasion of the influenza virus into virus-sensitive cells.
Molecular association of barbital and caffeine in 2:1 crystalline complex.
The crystal structure of the 2:1 complex of barbital with caffeine has been determined by X-ray diffraction methods.The crystals are triclinic, space group P1, with a= 14.627, b= 14.160, c= 6.902 A, α = 95°15′, β = 92°48′, and γ = 100°45′, and with four barbital and two caffeine molecules in the cell.The block-diagonal least-squares refinement of 496 atomic positional and thermal parameters, based on 4665 X-ray intensity data, gave a final Rfactor of 0.05.The structure consists of ribbons of barbital molecules linked by NH...O=C hydrogen bonds.Caffeine molecules are bound to the ribbon by an NH...N(9) hydrogen bond and by an unusual interaction involving C(8)H with two barbital oxygen atoms.Weak interactions of nonhydrogen-bonded caffeine carbonyl groups with barbital carbonyl groups may also be important in this crystal.There is minimal overlap of the flat ring systems of the component molecules.