Chemical constituents from the leaves of Hydrangea macrophylla var. thunbergii (III): Absolute stereostructures of hydramacrosides A and B, secoiridoid glucoside complexes with inhibitory activity on histamine release

Following the characterization of dihydroisocoumarin constituents, two seco iridoid glucoside complexes, called hydramacrosides A and B, were isolated from the leaves of Hydrangea macrophylla SERINGE var. thunbergii MAKINO. Th e absolute stereostructures of hydramacrosides A and B were elucidated on t he basis of chemical and physicochemical evidence, which included the appli cation of the C-13-NMR glycosylation shift rule of 1,1'-disaccharides and t he modified Mosher's method. Hydramacrosides A and B exhibited an inhibitor y effect on histamine release from rat mast cells induced by an antigen-ant ibody reaction.