The cleavage of glucosinolates by myrosinase to produce toxic breakdown products is a characteristic insect defense of cruciferous plants. Although green peach aphids (Myzus persicae) are able to avoid most contact with myrosinase when feeding from the phloem of Arabidopsis thaliana, indole glucosinolates are nevertheless degraded during passage through the insects. A defensive role for indole glucosinolates is suggested by the observation that atr1D mutant plants, which overproduce indole glucosinolates, are more resistant to M. persicae, whereas cyp79B2 cyp79B3 double mutants, which lack indole glucosinolates, succumb to M. persicae more rapidly. Indole glucosinolate breakdown products, including conjugates formed with ascorbate, glutathione and amino acids, are elevated in the honeydew of M. persicae feeding from atr1D mutant plants, but are absent when the aphids are feeding on cyp79B2 cyp79B3 double mutants. M. persicae feeding from wild-type plants and myrosinase-deficient tgg1 tgg2 double mutants excrete a similar profile of indole glucosinolate-derived metabolites, indicating that the breakdown is independent of these foliar myrosinases. Artificial diet experiments show that the reaction of indole-3-carbinol, a breakdown product of indol-3-ylmethylglucosinolate, with ascorbate, glutathione and cysteine produces diindolylmethylcysteines and other conjugates that have antifeedant effects on M. persicae. Therefore, the post-ingestive breakdown of indole glucosinolates provides a defense against herbivores such as aphids that can avoid glucosinolate activation by plant myrosinases.

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The methanol extract of Sophora flavescens showed a potent glycosidase inhibitory activity. Active components were identified as well-known flavonoid antioxidants: kushenol A (1), (؊)-kurarinone (2), sophoraflavanone G (3), 2-methoxykurarinone (4), kurarinol (5), 8-prenylkaempferol (6), isoxanthohumol (7), kuraridin (8) and maackian (9). All flavonoids were effective inhibitors of a a -glucosidase and b b -amylase. Interestingly, lavandulylated flavanones 1-5 had strong a a -glucosidase inhibitory activities, with IC 50 values of 45 m mM, 68 m mM, 37 m mM, 155 m mM and 179 m mM, respectively. Kushenol A (1) which does not bear a 4-hydroxy group showed selective a a -glucosidase inhibitory activity. Lavandulylated chalcone, kuraridine (8), exhibited IC 50 value of 57 m mM against b b -glucosidase, which is the first report of a chalcone displaying glycosidase inhibition. Results showed that 8-lavandulyl group in B-ring was a key factor of the glycosidase inhibitory activities. The inhibition pattern was noncompetitive for a a -glucosidase, whereas mixed inhibition was observed for b b -amylase.

The organic extract of the roots of Broussonetia papyrifera showed extremely high alpha-glucosidase inhibitory activity with an IC50 of around 10 microg/mL. Due to its potency, subsequent bioactivity-guided fractionation of the chloroform extract led to 12 polyphenols, 1-12, 4 of which were identified as chalcones (1-4), another 4 as flavans (5-8), 2 as flavonols (9 and 10), and 2 others as the novel species benzofluorenones (11 and 12). Broussofluorenone A (11) and broussofluorenone B (12) emerged as new compounds possessing the very rare 5,11-dioxabenzo[b]fluoren-10-one skeleton. These compounds (1-12) were evaluated for alpha-glucosidase inhibitory activity to identify their inhibitory potencies and kinetic behavior. The most potent inhibitor, 10 (IC50=2.1 microM, Ki=2.3 microM), has an inhibitory activity slightly higher than that of the potent alpha-glucosidase inhibitor deoxynojirimycin (IC50=3.5 microM). The novel alpha-glucosidase inhibitors 11 (IC50=27.6 microM) and 12 (IC50=33.3 microM) are similar in activity to sugar-derived alpha-glucosidase inhibitors such as voglibose (IC50=23.4 microM). Interestingly, major constituents (1, 2, 6, 7, 9, and 10) of B. papyrifera displayed significant inhibitory activity with IC50 values of 5.3, 11.1, 12.0, 26.3, 3.6, and 2.1 microM, respectively. In kinetic studies, chalcones (1-4) exhibited noncompetitive inhibition characteristics, whereas the others (5-12) showed mixed behavior.

The antioxidative properties of five prenylated flavonoids, including new flavanone (2), from the root bark of Cudrania tricuspidata were examined against the ABTS, DPPH, and hydroxyl radicals. In most of the assays to determine their antioxidative properties, the ABTS activity was strongly correlated with DPPH because both methods are responsible for the same chemical property of hydrogen- or electron-donation to the antioxidant. On the other hand, the prenylated flavonoids (1-5) acted differently with both methods; namely, all the prenylated flavonoids strongly scavenged the ABTS radical (IC(50) < 10 microM), while they were inactive against the DPPH radical (IC(50) > 300 microM). Even though isolated 5,7,2',4',-tetrahydroxy-6,5'-diprenylflavanone (3) showed weak reducing power (746 mV) by cyclic voltammetry when compared to quercetin (394 mV), both had similar ABTS activity (IC(50) < 5 microM).

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