Journal of Natural Products Vol. 47, No. 5 , pp. 775-780, Sep-Ort 1984
775
DIPHENYLAMINE, AN ANTIHYPERGLYCEMIC AGENT FROM ONION AND TEA M.S. K A U W Y A , S.M. ABDELWAHAB, Department of Pharmarognosy, Faculty of Pharmacy, Cairo University, Cairo, Egypt
M . M . EL-OLEMY~ Faculty of Pharmacy, Tanta University, Tanta, Egypt and N.M. FARUG
National Organization fw Drug Control and Resemrb, Pyramid Ave., Giza, Egypt ABSTRACT.-Diphenylamine has been isolated as one of the active antihyperglycemic agents of onion. It was identified by ir, uv, cmr, pmr, and mass spectra. It attained the highest percentage in mature onion bulbs; other onion organs contained diphenylamine in lower percentages. Green and black teas were found to contain relatively high percentages of diphenylamine, being higher in the former. Cooking was found to decrease the diphenylamine content.
Antihyperglycemic agents, especially those of plant origin, have received much attention recently. Many plants and plant products ( 1) were claimed to have certain beneficial effects on diabetes in folk medicine. Onion (2) and a number of its extracts (3) have been reported to possess hypoglycemic activity. Allylpropyldisulfide, a component of the volatile oil of onion, has been found to produce hypoglycemia and to effect a rise in serum insulin in normal fasting human subjects (4).SeveraI reviews have appeared on the subject (5-8). Upon the oral administration of crude onion juice reduction of the blood-sugar level, in cases of induced hypoglycemia, has been reported, both in laboratory animals and in human volunteers (9- 11). These observations support the presence of a potent hypoglycemic principle in onion, which has not been isolated previously. Mathew and Augusti (12), Augusti (13), and Georgy (14) have pointed out that such antihyperglycemic agents are chiefly extracted with Et20. Tea, the most popular hot drink in Asia, Africa, and Europe, has also been claimed to possess a hypoglycemic activity (15). In the course of an investigation of tea flavor, Nose et al. (16) identified diphenylamine as one of the major constituents in green tea leaves, using gc-ms. Diphenylamine has also been identified in citrus fruit rind oils by gc (17). The present study (18) is directed towards the isolation and identification of the antihyperglycemic agent(s) of onion and tea. RESULT AND DISCUSSION The petroleum ether extract, the E t 2 0 extract, and the CHCl, extract produced a marked reduction in the blood-sugar level of 50.6, 58.0, and 33.7 percent, respectively. Thus, the maximum hypoglycemic activity was contained in the E t 2 0 extract. These findings coincide with those reported by Augusti (13) and Mathew and Augusti (12), while Gupta et al. (9) stated that the CHC1, extract was most effective. The latter findings, however, do not seem contradictory, since Gupta et al. utilized CHC1, before E t 2 0 in the order of extraction. The petroleum ether-soluble fraction of the E t 2 0 extract of onion was chromatographed on one of two columns: either silica gel/,-heptane-diisopropyl ether (1: 1) or aluminahsooctane.
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fVol. 47, No. 5
Journal of Natural Products
Chemical Shift (pprn)
Carbon No.
c, 1 , l '
Found value
Calculated value"
143.2 117.9 129.3 121.0
144.8 124.1 129.1 122.6
. . . . . . . .
C,2, 2',6,6' . . . . . . C,3,3,'5,5' . . . . . C,4,4' . . . . . . . . 'According to Pretsch et af. (19).
The mass spectrum of the isolated compound showed a molecular ion peak (M+) at
mlz 169(loo%, base peak) and corresponded in all details with those reported in the literature for diphenylamine (16). In view of this compound being an unusual plant constituent, the assignment of structure as diphenylamine was confirmed by undepressed mmp with authentic material, cochromatography, and superimposable ir spectra with authentic diphenylamine. Further, both isolated and authentic material reacted with HC1 in the presence of HNO,, turning blue (20). When tested for hypoglycemic activity in hyperglycemic rabbits' (Table 2), TABLE2.
Average Blood-Sugar Level (rng %)^ after Administration of Isolated Substance as Cornpared to Tolbutamide 25 g k g body weight)
Fasting
Control Diphenylamine . . . . . 10 rnglkg body weight
102.0 f5.1 102.2 20.86
at2h
%h
lh
162 k4.1 140.2 f7.8
180 k15.4 154.6 f1.7
l%h
2h 186 212.1 71.8 k6.2
P
