In screening experiments for rat intestinal -glucosidase (sucrase and maltase) inhibitors in 325 plants cultivated in Japan's southern island, of Tanegashima, marked inhibition against both sucrase and maltase was found in the extract of the fruit of Solanum torvum. Enzyme-assay guided fractionation of the extract led to the isolation of methyl caffeate (1) as a rat intestinal sucrase and maltase inhibitor. We examined 13 caffeoyl derivatives for sucrase-and maltase-inhibitory activities. The results showed that methyl caffeate (1) had a most favorable structure for both sucrase and maltase inhibition, except for a higher activity of methyl 3,4,5-trihydroxycinnamate (14) against sucrase. Its moderate inhibitory action against -glucosidase provides a prospect for antidiabetic usage of S. torvum fruit.Key words: Solanum torvum; -glucosidase inhibitor; methyl caffeate; Tanegashima Diabetes mellitus is one of the most serious chronic diseases. It is caused by continual hyperglycemia and develops along with increases in obesity and aging in the general population. 1) One of the therapeutic approaches to decreasing postprandial hyperglycemia is to retard absorption of glucose by inhibition of carbohydrate hydrolyzing enzymes -amylase and -glucosidase in the digestive organs.2) In recent years, many efforts have been made to search for effective -glucosidase inhibitors from natural sources in order to develop a physiological functional food or to discover lead compounds for medicinal usage against diabetes.3) In the course of our search for rat intestinal -glucosidaseinhibiting principles from various plants, we have isolated and identified several active compounds from plants grown in Asian regions, including Japan, [4][5][6][7] Thailand, 8,9) China, 10,11) and Nepal. 12) In this paper, we present the results of a screening of plants cultivated in Tanegashima, a southern island of Japan, for rat intestinal -glucosidase inhibition. In the screening experiments for rat intestinal sucrase and/or maltase inhibitors in 325 plants, potent sucrase and maltase inhibiting activity was found in extract of the fruit of Solanum torvum (Solanaceae), an edible herbaceous perennial plant. There have been several reports on the chemical constituents of this plant, which include welldocumented steroidal compounds [13][14][15] and antiviral activities, 16) but no other biologically active compounds from this plant have been reported to date. Hence, the promising screening result prompted us to isolate and elucidate the structures of active compounds in this plant. Separation of S. torvum fruit extract using various column chromatographic techniques lead to the isolation of methyl caffeate (1) as one of active principles. Some -glucosidase inhibitors previously isolated from plants contain the caffeoyl moiety as the part of their structure and have been found to be important in exerting inhibitory activity, 3,7) but the contribution of an ester part to the -glucosidase-inhibitory activity of caffeic esters has not been studied. Hence ...