Herbicidal and Fungicidal Activities of Lactones in Kava (Piper methysticum).

This is the first report showing that kava lactones are plant and plant fungus growth inhibitors. Aqueous extract of kava roots showed high allelopathic potential and strongly suppressed germination and growth of lettuce, radish, barnyardgrass, and monochoria. Nine kava lactones were detected using GC-MS including desmethoxyyagonin, kavain, 7,8-dihydrokavain, hydroxykavain, yagonin, 5,6,7,8-tetrahydroxyyagonin, methysticin, dihydromethysticin, and 11-hydroxy-12-methoxydihydrokavain. Quantities of desmethoxyyagonin, kavain, 7,8-dihydrokavain, yagonin, methysticin, and dihydromethysticin detected were 4.3, 6.9, 18.6, 5.7, 1.4, and 5.4 mg/g of dry weight, respectively. These six major lactones in kava roots showed great herbicidal and antifungal activities. Growth of lettuce and barnyardgrass were significantly inhibited at 1-10 ppm, and four plant fungi including Colletotrichum gloeosporides, Fusarium solani, Fusarium oxysporum, and Trichoderma viride were significantly inhibited at 10-50 ppm. The biological activities of kava lactones were characterized by different double-bond linkage patterns in positions 5,6 and 7,8. The findings of this study suggest that kava lactones may be useful for the development of bioactive herbicides and fungicides.

Inhibitory effects of Alpinia speciosa K. SCHUM on the porphyrin photooxidative reaction.

It is thought that the beta-carotene defense mechanism against photosensitivity involves the inhibition of singlet oxygen formation, a kind of active oxygen. When we screened chemical substances obtained from plants indigenous to Okinawa, known to have residents with the longest life span in Japan, we found that Alpinia speciosa K. SCHUM (Japanese name: gettou), which is used as a food preservative, has an activity similar to that of beta-carotene. We measured the amount of lipid peroxide (LPO) formed from a hematoporphyrin-containing rat liver microsomal suspension irradiated with visible light. The inhibitory effect of Alpinia speciosa on LPO formation was confirmed when the addition of increasing concentrations of Alpinia speciosa extract led to a decrease in the amount of LPO formed. Moreover, the reaction mechanism that affects the amount of singlet oxygen formed was measured, and the effect of the extract was determined by the ESR trapping technique. It was found that the extract effectively inhibited the formation of singlet oxygen. The extract of Alpinia speciosa contains dihydro-5,6-dehydrokawain. It was confirmed that dihydro-5,6-dehydrokawain, which is a water-soluble compound, has singlet oxygen quenching activity. We synthesized five derivatives of kawain and found that dimethyl [6-(2-phenylethyl)-2-oxo-2H-pyran-4-yl] phosphorothionate has the strongest singlet oxygen quenching activity. The use of the compound from Alpinia speciosa that exhibits singlet oxygen quenching activity as an inhibitory agent of the phototoxic reaction in porphyria is expected.

Syntheses and biological activities of dihydro-5,6-dehydrokawain derivatives.

The syntheses and biological activities of dihydro-5,6-dehydrokawain derivatives against plant pathogenic fungi and termites were investigated. Dihydro-5,6-dehydrokawain was isolated by a simple method without chromatography from the leaves of Alpinia speciosa K. SCHUM. The white crystalline compound obtained was identified as dihydro-5,6-dehydrokawain (1) by instrumental analyses. 4-Hydroxy-6-(2-phenylethyl)-2H-pyran-2-one (3) was prepared by hydrolyzing dihydro-5,6-dehydrokawain. Three dihydro-5,6-dehydrokawain derivatives were synthesized by reacting 3 with phosphoric agents. Among the synthesized compounds, dimethyl [6-(2-phenylethyl)-2-oxo-2H-pyran-4-yl]phosphorothionate (4) had the strongest antifungal activity of 91% at 100 ppm against Corticium rolfsii.

Synthesis and antifungal activity of cinnamic acid esters.

Cinnamic, p-coumaric and ferulic acids were isolated from pineapple stems (Ananas comosus var. Cayenne). Twenty-four kinds of esters were prepared from these acids, alcohols and the components of Alpinia. Isopropyl 4-hydroxycinnamate (11) and butyl 4-hydroxycinnamate (12) were found to have almost the same effectiveness in antifungal activity against Pythium sp. at 10 ppm as that of the commercial fungicide iprobenfos (kitazin P).