Tyrosinase inhibitory activity of ethanol extracts from medicinal and edible plants cultivated in okinawa and identification of a water-soluble inhibitor from the leaves of Nandina domestica.

The tyrosinase inhibitory activity of the extracts of 53 parts of 36 plant species cultivated for edible and medicinal use in Okinawa was investigated. The extract of Nandina domestica showed potent activity among these. The inhibitor in the extract was purified by assay-guided fractionation to give a simple phenol glucoside. Although it was a known compound (4-beta-D-glucopyranosyloxybenzoic acid), its inhibitory activity toward tyrosinase is revealed for the first time in this work.

Screening for tyrosinase inhibitors among extracts of seashore plants and identification of potent inhibitors from Garcinia subelliptica.

The tyrosinase inhibitory activity of methanol extracts of the leaves of 39 plant species growing on the seashore of Iriomote island (Okinawa, Japan) was investigated. The extracts of Hibiscus tiliaceus, Carex pumila, and Garcinia subelliptica showed potent activity among them. The inhibitors in the extract of Garcinia subelliptica were purified by assay-guided fractionation to give two biflavonoids. These were known compounds (2R,3S-5,7,4',5'',7'',3''',4'''-heptahydroxy flavanone[3-8''] flavone and 5,7,4',5'',7'',3''',4'''-heptahydroxy[3-8''] biflavanone), although their strong inhibitory activity toward tyrosinase is revealed for the first time in this work. One of these biflavonoids (2R,3S-5,7,4',5'',7'',3''',4'''-heptahydroxy flavanone[3-8''] flavone) showed much stronger activity (IC50 2.5 microM) than that of kojic acid (IC50 9.1 microM) when L-tyrosine was used as the substrate.

Cytotoxic activity of maytanprine isolated from Maytenus diversifolia in human leukemia K562 cells.

We examined the cytotoxic effect of maytanprine isolated from the methanol extract of Maytenus diversifolia on human leukemia K562 cells using a flow cytometer and compared its cytotoxicity with that of maytansine, a potent cytotoxic maytansinoid. Maytanprine at concentrations of 0.03 nM or more (up to 1 nM) attenuated cell growth with decreasing cell viability and increased the population of shrunken cells in a concentration-dependent manner. Complete inhibition of growth by maytanprine was observed at concentrations of 0.3 nM or more. The compound at 0.03 nM markedly decreased the population at G0G1 phase in the cell cycle, but only slightly decreased that in the G2M phase, suggesting the possibility that it inhibits or delays cell division, and increased the population of cells with hypodiploidal DNA (apoptotic cells). The potency of maytanprine in inhibiting cell growth was greater than that of maytansine, although the inhibitory action of maytanprine was similar to that of maytansine. The results suggest that maytanprine exerts a potent inhibitory action on the growth of human leukemia K562 cells. M. diversifolia is one natural source of maytanprine, which is more cytotoxic than maytansine.

Flow cytometric estimation on cytotoxic activity of leaf extracts from seashore plants in subtropical Japan: isolation, quantification and cytotoxic action of (-)-deoxypodophyllotoxin.

The cytotoxic activity of methanol extracts of leaves collected from 39 seashore plants in Iriomote Island, subtropical Japan was examined on human leukaemia cells (K562 cells) using a flow cytometer with two fluorescent probes, ethidium bromide and annexin V-FITC. Five extracts (10 microg/mL) from Hernandia nymphaeaefolia, Cerbera manghas, Pongamia pinnata, Morus australis var. glabra and Thespesia populnea greatly inhibited the growth of K562 cells. When the concentration was decreased to 1 microg/mL, only one extract from H. nymphaeaefolia still inhibited the cell growth. A cytotoxic compound was isolated from the leaves by bioassay-guided fractionation and was identified as (-)-deoxypodophyllotoxin (DPT). The fresh leaves of H. nymphaeaefolia contained a remarkably high amount of DPT (0.21 +/- 0.07% of fresh leaf weight), being clarified by a quantitative HPLC analysis. DPT at 70-80 pM started to inhibit the growth of K562 cells in an all-or-none fashion and at 100 pM or more it produced complete inhibition in all cases. Therefore, the slope of the dose-response curve was very steep. DPT at 100 pM or more decreased the cell viability to 50%-60% and increased the number of cells undergoing apoptosis (annexin V-positive cells). The results indicate that DPT contributes to the cytotoxic action of the extract from the leaves of H. nymphaeaefolia on K562 cells.

Chemistry of Zerumbone. 1. Simplified Isolation, Conjugate Addition Reactions, and a Unique Ring Contracting Transannular Reaction of Its Dibromide.

Zerumbone (1) was isolated from fresh rhizomes of Zingiber zerumbet Smith in yields of 0.3-0.4% by simple steam distillation and recrystallization. 1 accepted 2 equiv of hydrogen cyanide at the C6 and C9 double bonds of the cross-conjugated dienone system to give a mixture of diastereomers 3a-d. In the presence of potassium cyanide, the dominant isomer 3a was isomerized to a mixture of 3a-d. Under controlled conditions, 1 added one mole of methanol regio- and stereoselectively at the C6 double bond to give adduct 4a. With potassium cyanide, 4a was transformed to the mixture of 3a-d. 1 took up one mole of bromine at C6 double bond to give a diastereomeric mixture of adducts 5a and 5b. Treatment of 5a with potassium cyanide gave a mixture of cyclopropanecarboxylic acid 6a and 6b. This unique ring-contracting cyclopropane formation is pictured as a sequential Favorskii type reaction. alpha-Cyclodextrin improved the selectivity and yields of the reactions conducted in an aqueous medium.