Studies on the Polar Constituents from Psidium guajava L. and Euphorbia tirucalli L.
Tannins are polyphenolic compounds which widely exist in plant kingdom. Recently, their characteristics have been realized together with developmentof chromatography techniques and spectrascopic analysis. The bioactivitiesof polyphenolic compounds also have been reported successively. Thus, tanninchemistry is a new research field of natural products. Red guava, a variant of Psidium guajava L. (Myrtaceae), was originated fromtropic America and have been naturalized in Taiwan for a long time. The immat-ure fruit of red guava have been used as a folk medicine for treatment of hyp-perglycemia and diarrhea. However, the active chemical constituents and relatedpharmacological activities are still remained to be explored. The immature fruitwere extracted with 70 % aqueous acetone. By means of various column chromatog-raphies, 12 compounds were isolated and purified. The chemical structures of these compounds were elucidated as gallic acid (1), castalagin (2), vescalagin (3), pedunculagin (4), casuarinin (5), (+)-catechin (6), (+)-gallocatechin (7),procyanidin B-1 (8), quercetin (9), quercetin-3-O-galactoside (10), D-threo-1-C- guaiacylglycerol 3-O--D-glucopyranoside (11), D-erythro-1-C- guaiacylglycerol 3-O--D-glucopyranoside (12). Among them, castalagin and (+)-catechin are majorcomponents. D-threo-1-C- guaiacylglycerol 3-O--D-glucopyranoside (11) andD-erythro-1-C- guaiacylglycerol 3-O--D-glucopyranoside (12) were characterizedfor thr first time from plant source. Euphorbia tirucalli L., an Euphorbiaceous plant, widely distribute in tropics. There are cultivated plants in Taiwan and Pen-huo islands. It has been used asa folk medicine in treatment of dermatosis, paralysis, and pain of human body.However, the active chemical constituents and related pharmacological activitiesare still remained to be explored. Euphorbia tirucalli were extracted with 60%aqueous acetone. By means of various column chromatographies, 14 compounds wereisolated and characterized. The chemical structures of these compounds wereelucidated as gallic acid (1), 1-O-galloyl--D-glucose (13), 1,2,3-tri-O- galloyl--D-glucose (14), pedunculagin (4), corilagin (15), casuariin (16), 5-desgalloylstachyurin (17), 2,3-(S)- HHDP-D-glucose (18), putranjivain A (19), putranjivain B (20), quercitrin (21), rutin (22) , 3,3'-di-O-methyl-ellagic acid(23) , 3,3',4-tri-O-methyl-4'-O-rutinosyl-ellagic acid (24) . Among them, cori-lagin and putranjivain B (1C4 type ellagitannins) are major components. Compound 11 and compound 12 are isolated from plant source and elucidated their chemical structures for the first time and the NMR characteristics of compound 24 are characterized by 2D-NMR technologies in this investigation.