Bioactive Constituents from Chinese Natural Medicines . XXIV . 1 ) Hypoglycemic Effects of Sinocrassula indica in Sugar-Loaded Rats and Genetically Diabetic KK-Ay Mice and Structures of New Acylated Flavonol Glycosides

tributed on the mountain areas in China (e.g., Yunnan, Guangxi, Sichuan, Guizhou, and Hunan provinces). The whole plant of S. indica has been used for the treatment of hepatitis and otitis media in Chinese traditional medicine. This plant also has been used as a vegetable and a herbal tea in Chinese local areas such as Guangxi province. However, chemical constituents from this herbal medicine were left uncharacterized. During the course of our studies on bioactive constituents from Chinese natural medicines, we found that the methanolic extract of the whole plant of S. indica inhibited the increase in serum glucose levels in both sucroseand glucose-loaded rats. From the methanolic extract, four new acylated flavonol glycosides, sinocrassosides A1 (1), A2 (2), B1 (3), and B2 (4), were isolated together with 11 flavonoids (5—15) and 2 megastigmanes (16, 17). This paper deals with antidiabetic activities of the methanolic extract from S. indica as well as the isolation of the constituents from this extract including the structure elucidation of 1—4. Hypoglycemic Effects of the Methanolic Extract from S. indica The dried whole plant of S. indica was extracted with methanol to give a methanolic extract (7.7% from the dried plant). As shown in Tables 1 and 2, the methanolic extract significantly inhibited the increase in serum glucose levels after oral administration of sucrose and glucose in rats at doses of 250 and 500 mg/kg (p.o.). However, the extract did not show significant effect on increase of these levels after intraperitoneal administration of glucose. These findings suggested that the absorption of glucose in the intestinal tract was suppressed by the extract. The delay of sugar absorption after ingesting a meal has recently been found to be effective for type 2-diabetic patients, and the speed of gastric emptying is important in the regulation of glucose homeostasis. The effect of the above extract on gastric emptying (GE) after administration of 10% glucose in rats was examined. As shown in Table 3, the inhibitory effect of the extract was observed, but it was weaker than the effects of lowering of blood glucose levels. These findings indicated that the extract inhibited not only gastric emptying but also glucose absorption via Na /glucose cotransporter, although more detailed examination is needed. The effect of the extract on serum glucose levels in KK-A mice, a genetically type II diabetic mice, was also examined. The extract (250 and 500 mg/kg/d, p.o.) significantly inhibited these levels and tended to reduce TG levels, but not serum T-Cho or FFA levels, after administration for 2 weeks under non-fasted conditions (Table 4). On the other hand, serum glucose levels were lowered to normal (from ca. 530 to ca. 150 mg/dl) after the fasting, which was also reported previously, and the extract did not affect blood glucose levels, body weight, weights of visceral fats (epididymal, mesenteric, and paranephric fats) and liver, TG, T-Cho, and FFA and L-TG or L-T-Cho levels in the fasted mice (Tables 5, 6). These results of experiments using diabetic mice as well as the results of experiments using rats described above suggested that inhibition or delay of sugar absorption is involved in the hypoglycemic effect of the extract, at least in part. The mechanism of action of the extract, however, requires further study. Next, the methanolic extract was partitioned into an EtOAc–H2O (1 : 1, v/v) mixture to furnish an EtOAc-soluble fraction (2.5%) and an aqueous phase. The aqueous phase was further extracted with n-BuOH to give an n-BuOH-soluble fraction (1.7%) and an H2O-soluble fraction (3.4%). As shown in Table 7, the EtOAcand n-BuOH-soluble fractions inhibited the increase in serum glucose levels in sucroseloaded rats at a dose of 500 mg/kg (p.o.). Isolation of Sinocrassosides (1—4) and Known Constituents To elucidate the constituents from the active fractions, the EtOAcand n-BuOH-soluble fractions of the methanolic extract were subjected to normaland reversedphase column chromatographies, and finally to HPLC to give 1 (0.0013%), 2 (0.0012%), 3 (0.0009%), and 4 (0.0002%) together with 11 flavonoids, kaempferol (5, 0.0026%), 1308 Vol. 55, No. 9