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A saponin fraction from the stems of Yucca schidigera (Mohave yucca) exhibited potent growth-inhibitory activities against certain food-deteriorating yeasts, film-forming yeasts, and dermatophytic yeasts and fungi. From this fraction, a number of new anti-yeast monodesmosidic spirostanol saponins, named schidigera-saponins A1 (1), A2 (2), A3 (3), B1 (4), C1 (5),C2 (6); 25(R and S) schidigera-saponins D1 (7), D2 (8), E1 (12), F1 (13); and 25(S) schidigera-saponins D3 (9), D4 (10), D5 (11), and F2 (14) were isolated, together with several related known saponins, and the structures were elucidated by spectroscopic methods (see Chart 1). The relationship between the antiyeast activities and the structures of these saponins is described.

A meroterpene and four flavonoids were isolated from the seeds of Psoralea corylifolia as antioxidative components. Their structures were elucidated by spectral data and identified as bakuchiol (1), bavachinin (2), bavachin (3), isobavachin (4) and isobavachalcone (5). In particular, meroterpene 1 and flavonoids 4 and 5 showed broad antioxidative activities in rat liver microsomes and mitochondria. They inhibited NADPH-, ascorbate-, t-BuOOH- and CCl(4)-induced lipid peroxidation in microsomes. They also prevented NADH-dependent and ascorbate-induced mitochondrial lipid peroxidation. Bakuchiol (1) was the most potent antioxidant in microsomes and the inhibition of oxygen consumption induced by lipid peroxidation was time-dependent. Furthermore, bakuchiol (1) protected human red blood cells against oxidative haemolysis. These phenolic compounds in P. corylifolia were shown to be effective in protecting biological membranes against various oxidative stresses.

A biphenyl compound, 3,4,3',4'-tetrahydroxy-5,5'-diisopropyl-2,2'-dimethylbiphenyl (1), and a flavonoid, eriodicytol (2), were isolated as antioxidative components from the leaves of Thymus vulgaris by bioassay-directed fractionation. These compounds inhibited superoxide anion production in the xanthine/xanthine oxidase system. Mitochondrial and microsomal lipid peroxidation induced by Fe(III)-ADP/NADH or Fe(III)-ADP/NADPH were also inhibited by these compounds. Compound 1 is an extremely potent antioxidant; complete inhibition was observed at 1 microM against both microsomal and mitochondrial peroxidation. Furthermore, compound 1 protected red cells against oxidative hemolysis. These phenolic compounds were shown to be effective to protect biological systems against various oxidative stresses.

Isoflavan derivatives, glabridin (1), hispaglabridin A (2), hispaglabridin B (3), 4'-Omethylglabridin (4) and 3'-hydroxy-4'-O-methylglabridin (5), isolated from Glycyrrhiza glabra, were investigated for their ability to protect liver mitochondria against oxidative stresses. Mitochondrial lipid peroxidation linked to respiratory electron transport and that induced non-enzymatically were inhibited by these isoflavans. Hispaglabridin A (2) strongly inhibited both peroxidations and 3'-hydroxy-4'-O-methylglabridin (5) was the most effective at preventing NADH-dependent peroxidation. 3'-Hydroxy-4'-O-methylglabridin (5) protected mitochondrial respiratory enzyme activities against NADPH-dependent peroxidation injury. Dihydroxyfumarate-induced mitochondrial peroxidation was also prevented by this isoflavan. Isoflavans from G. glabra were shown to be effective in protecting mitochondrial function against oxidative stresses.

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To improve the taste profile of glycyrrhizin (1, the saponin of licorice root, relative sweetness to sucrose: x170), a variety of 3-O-glycosides of glycyrrhetic acid were prepared and their sweetness evaluated. It was found that a significant enhancement of sweetness was observed for the 3-O-beta-D-xyloside and the 3-O-beta-D-glucuronide (MGGR). Especially, MGGR had a high sweetness relative to sucrose; x941, and would appear to be a new potent sweetener.