As a part of our study on the leguminous plants, we investigated the constituents of the aerial parts of Glycine soya. We isolated and identified four known saponins, soyasaponins I, II, III, and IV which have the same aglycone, soyasapogenol B. As a part of our studies concerning hepatoprotective drugs, we also examined the hepatoprotective actions of these saponins towards immunologically induced liver injury on primary cultured rat hepatocytes. The action of soyasaponin II was almost comparable with that of soyasaponin I, whereas those of soyasaponin III and IV were more effective than soyasaponins I and II. This means that the disaccharide group shows greater action than the trisaccharide group. Furthermore, the saponin having a hexosyl unit shows a slightly greater action than that of the pentosyl unit in each disaccharide group or trisaccharide group. Structure-activity relationships suggest that the sugar moiety linked at C-3 may play an important role in hepatoprotective actions of soybean saponins.

The antihepatotoxic activities of soyasaponin I and kaikasaponin III, triterpenoidal saponins isolated from Abri Herba, the whole plant of Abrus cantoniensis, were studied on liver injury induced by CCl4 in primary cultured rat hepatocytes. The antihepatotoxic activities of these saponins and glycyrrhizin (positive control) were demonstrated by measuring the levels of glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT). Soyasaponin I inhibited the elevation of GOT and GPT activities. The activities were comparable to those of glycyrrhizin. On the other hand, kaikasaponin III was more effective than soyasaponin I and glycyrrhizin. Kaikasaponin III showed the antihepatotoxic activity at less than 100 micrograms/ml. Furthermore, the highest activity was observed even in the lower doses (50, 100 micrograms/ml). However, soyasaponin I and kaikasaponin III showed some toxicity at the highest dose (500 micrograms/ml), though glycyrrhizin did not show toxicity at any dose.

The establishment of international monographs for herbs is in progress. Here, we propose both a marker compound and a method for its analysis for the identification of garlic bulbs and their products. The constituents in 26 kinds of fresh edible parts of Allium vegetables and three types of garlic preparations were analyzed. Sulfur compounds are the most characteristic constituents in garlic, but manufacturing processes of garlic products dramatically affect these constituents. Thus, no sulfur compound could be specified as a universal marker of identification applicable for any type of garlic. On the other hand, garlic contains other characteristic compounds, namely, saponins. After analyzing Allium vegetables and garlic preparations, we concluded that sapogenins, especially beta-chlorogenin, may be a viable candidate for identifying and distinguishing garlic from other Allium vegetables.

In the course of our research for biologically active constituents from coniferous plants, a chromone derivative (1) and an abietane derivative (2) were isolated along with several diterpenes from Chamaecyparis pisifera. Structures of the new compounds were determined to be 5,7-dihydroxy-2-(1-acetyl-2-methoxycarbonylethyl)-chromone and rel-(8R,10R,20S)-8,10,20-trihydroxy-9(10→20)-abeo-abieta-9,13-dien-12-one by means of spectral methods including two-dimensional NMR experiments. Some of these abietane-type compounds isolated from this plants showed antibacterial activity against the gram-positive bacteria Staphylococcus aureus and Bacillus subtilis.

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