Flavones Occurring in Green Tea (Part 1)

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The occurrence of flavonols and their glycosides in tea and tea leaves, has been reported in many papers but there are no previous references to flavone. Three yellow pigments, however, were isolated and other seventeen ones detected on the paperchromatogram from the green tea infusion, and eighteen of them were identified as flavones. Ultraviolet absorption spectra of these three pigments, designated pigment I, II, and III as shown in Figure 1, were similar to those of apigenin family, especially to saponarin, saponaretin and vitexin. Moreover, as the results of studies on the spectral characteristics, alkaline degradation products and color reactions, it was concluded that these pigments belonged to flavone and seemed to have the same skeleton as apigenin (5, 7, 4'-trihydroxy flavone). Especially pigment III may be one of the important constituents related to the color of green tea infusion, for its high water solubility and a deep greenish yellow color in aqueous solution. As the results of spectral studies, fifteen of seventeen spots detected on the two-way paper chromatogram, as shown in Figure 5, were identified as flavones, which had the similar structure to the pigment I, II, and III, but two of them did not. Because the pigments were proved not to be hydrolyzed under such condition that flavonol glycosides were completely hydrolyzed, removal of them from the fraction which was precipitated with lead acetate and ammonia water from green tea infusion, was carried out by treatment with 3.5% hydrochloric acid on a boiling water bath for an hour. After hydrolysis, only the spots of these pigments remained as before, and those of kaempferol, quercetin and myricetin resulted from their glycosides came out. Gallic acid, probably its parent compound occurred in this fraction, was also detected. The hydrolyzate was first fractionated by shaking with ethyl ether, ethylacetate and n-buthanol. Then further fractionations were carried out by the column chromatography using silica gel or cellulose powder. Pigment I and If were obtained in small quantities, and seventeen minor pigments were isolated by the preparative paper chromatography, so that the works on them were only performed by absorption spectral studies and paper chromatography. Pigment III was finally purified as an amorphous yellow powder. Yield : about 420 mg. from 2 kg, of green tea. m. p. more than 300°C (begin to change color at about 258°C). acetate : white opaque granules, m. p. 151°C. Solubilities : very easily soluble in cold water, soluble in hot methanol and insoluble in ethanol, ethylacetate, acetone and ether. Color reactions of them on the paper chromatograms were as follows ; pale yellow in visible light, reddish brown in ultraviolet light and change to yellow when fumed with ammonia, yellow with alkalis and aluminum chloride, and brown with ferric chloride. Reaction of these pigments with magnesium or zinc and conc. hydrochloric acid in ethanol gave pink color. Pigment III on the chromatograms developed with 2% acetic acid and n-buthanol-acetic acidwater gave distinctly a single spot, but when developed with 75% phenol a tailing spot. After division by preparative paper chromatography, pigment III proved to be a mixture of IIIa and IIIb, which had quite similar spectra as shown in Figure 2c and 2d. But it will be discussed in the following paper. These pigments exihibited high intensity absorptions at 333-5mμ region (Band I) and 270-3 mμ region (Band II ). From the absorption spectral studies on the aluminum chloride complex and sodium acetate shifts of these pigments, it came to the conclusion that fourteen of eighteen tea flavones had to belong to apigenin family, and had free hydroxyl groups in 5, 7, and 4' positions, and four had no free hydroxyl group in 7-position (Table 2 and Table 6).
日本茶業技術協会の論文

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坂本裕
農林省茶業試験場

Flavones Occurring in Green Tea (Part 1)

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