Keywords: allelopathy, leaf litter leacheate, plant species, sandwich method. time-consuming bioassay method and could be used to screen a large number of samples.

In the screening experiments for rat intestinal alpha-glucosidase inhibitors in 218 plants cultivated in the Japanese temperate region, potent maltase-inhibiting activity was found in the extract of flowers of Spiraea cantoniensis. The enzyme assay guided fractionation of the extract led to the isolation of three flavonol caffeoylglycosides, quercetin 3- O-(6- O-caffeoyl)-beta-galactoside ( 1), kaempferol 3- O-(6- O-caffeoyl)-beta-galactoside ( 2), and kaempferol 3- O-(6- O-caffeoyl)-beta-glucoside ( 3), as rat intestinal maltase inhibitors. This is the first report on the alpha-glucosidase-inhibitory activity of those flavonol caffeoylglycosides. Comparison in the activity of the isolates indicated the importance of caffeoyl substructures in the molecule for the alpha-glucosidase-inhibiting activity. The relatively high contents of the active isolates in the plant suggest that S. cantoniensis could be physiologically useful for treatment of diabetes.

Genetic identification among cinnamon species was studied by analyzing nucleotide sequences of chloroplast DNA from four species (Cinnamomum cassia, C. zeylanicum, C. burmannii and C. sieboldii). The two regions studied were the intergenic spacer region between the trnL 3'exon and trnF exon (trnL -trnF IGS) and the trnL intron region. We found nucleotide variation at one site in the trnL-trnF IGS, and at three sites in the trnL intron. With the sequence data from analysis of these regions, the four Cinnamomum species used in this study were correctly identified. Furthermore, single-strand conformation polymorphism (SSCP) analysis of PCR products from the trnL-trnF IGS and the trnL intron resulted in different SSCP band patterns among C. cassia, C. zeylanicum and C. burmannii.

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 ...