A Review of Biologically Active Natural Products from a Desert Plant Cistanche tubulosa

An Orobanchaceae plant Cistanche tubulosa (SCHENK) WIGHT (Kanka-nikujuyou in Japanese), which is one of the authorized plant resources as Cistanches Herba in both Japanese and Chinese Pharmacopoeias, is a perennial parasitic plant growing on roots of sand-fixing plants. The stems of C. tubulosa have traditionally been used for treatment of impotence, sterility, lumbago, and body weakness as well as a promoting agent of blood circulation. In recent years, Cistanches Herba has also been widely used as a health food supplement in Japan, China, and Southeast Asian countries. Here we review our recent studies on chemical constituents from the stems of C. tubulosa as well as their bioactivities such as vasorelaxtant, hepatoprotective, and glucose tolerance improving effects.

Hepatoprotective Limonoids from Andiroba (Carapa guianensis)

Three gedunin-type limonoids, gedunin (1), 6α-acetoxygedunin (2), and 7-deacetoxy-7-oxogedunin (3), which were isolated from the seed and flower oils of andiroba (Carapa guianensis Aublet, Meliaceae), exhibited hepatoprotective effects at doses of 25 mg/kg, p.o. against d-galactosamine (d-GalN)/lipopolysaccharide (LPS)-induced liver injury in mice. To characterize the mechanisms of action of 1-3 and clarify the structural requirements for their hepatoprotective effects, 17 related limonoids (1-17) isolated from the seed and/or flower oils of C. guianensis were examined in in vitro studies assessing their effects on (i) d-GalN-induced cytotoxicity in primary cultured mouse hepatocytes, (ii) LPS-induced nitric oxide (NO) production in mouse peritoneal macrophages, and (iii) tumor necrosis factor-α (TNF-α)-induced cytotoxicity in L929 cells. The mechanisms of action of 1-3 are likely to involve the inhibition of LPS-induced macrophage activation and reduced sensitivity of hepatocytes to TNF-α; however, these compounds did not decrease the cytotoxicity caused by d-GalN. In addition, the structural requirements of limonoids (1-17) for inhibition of LPS-induced NO production in mouse peritoneal macrophages and TNF-α-induced cytotoxicity in L929 cells were evaluated.

Chemical structures and hepatoprotective effects of constituents from Cassia auriculata leaves

An 80% aqueous acetone extract of Cassia auriculata leaves was found to show a protective effect on D-galactosamine-induced cytotoxicity in primary cultured mouse hepatocytes. From the 80% aqueous acetone extract, we isolated a new benzocoumarin glycoside, avaraoside I (1), and a new flavanol dimer, avaraol I (2), together with 29 known constituents. The structures of the new compounds were elucidated on the basis of chemical and physicochemical evidence. In addition, three isolated compounds, pseudosemiglabrin (15, 0.0011%), (2S)-7,4'-dihydroxyflavan(4β→8)-catechin (22, 0.00075%), and (2S)-7,4'-dihydroxyflavan(4β→8)-gallocatechin (23, 0.092%), displayed hepatoprotective effects equivalent to that of the hepatoprotective agent, silybin.

Further acylated flavonol bisdesmosides from Sinocrassula indica

Further investigation on the whole herbs of Sinocrassula indica (Crassulaceae) led to the isolation of four new acylated flavonol bisdesmosides, sinocrassosides A₁₃, B₆, B₇, and D₄, together with kaempferol 3-O-β-D-(6-O-acetyl)glucopyranosyl-7-O-α-L-rhamnopyranoside. Their structures were established by spectral and chemical methods.

Grasshopper ketone 3-O-primveroside from Sinocrassula indica

A new megastigmane glycoside, grasshopper ketone 3-O-primveroside (1), was isolated from the methanolic extract of the whole herbs of Sinocrassula indica (Crassulaceae). Its structure was elucidated on the basis of spectral and chemical evidence.

Hepatoprotective amide constituents from the fruit of Piper chaba: Structural requirements, mode of action, and new amides

The 80% aqueous acetone extract from the fruit of Piper chaba (Piperaceae) was found to have hepatoprotective effects on D-galactosamine (D-GalN)/lipopolysaccharide-induced liver injury in mice. From the ethyl acetate-soluble fraction, three new amides, piperchabamides E, G, and H, 33 amides, and four aromatic constituents were isolated. Among the isolates, several amide constituents inhibited D-GalN/tumor necrosis factor-alpha (TNF-alpha)-induced death of hepatocytes, and the following structural requirements were suggested: (i) the amide moiety is essential for potent activity; and (ii) the 1,9-decadiene structure between the benzene ring and the amide moiety tended to enhance the activity. Moreover, a principal constituent, piperine, exhibited strong in vivo hepatoprotective effects at doses of 5 and 10 mg/kg, po and its mode of action was suggested to depend on the reduced sensitivity of hepatocytes to TNF-alpha.

Bioactive constituents from Chinese natural medicines. XXXIII. Inhibitors from the seeds of Psoralea corylifolia on production of nitric oxide in lipopolysaccharide-activated macrophages

The methanolic extract from the seeds of Psoralea corylifolia was found to inhibit production of nitric oxide (NO) in lipopolysaccharide-activated mouse peritoneal macrophages. Among the isolated compounds, bavachinin (IC(50)=26 microM), isobavachalcone (17 microM), neobavaisoflavone (ca. 29 microM), corylifol A (ca. 21 microM), and psoralidin (ca. 23 microM) significantly inhibited the accumulation of nitrite (NO(2)(-)) as a marker of production of NO. Bakuchiol, which is mainly contained in the extract, also showed weak activity at 10 microM, but cytotoxic effects were observed more than 30 microM.

Bioactive constituents from Chinese natural medicines. XXXII. aminopeptidase N and aldose reductase inhibitors from Sinocrassula indica: structures of sinocrassosides B(4), B(5), C(1), and D(1)-D(3)

From the methanolic extract of the whole plant of Sinocrassula indica (Crassulaceae), six new flavonol glycosides, sinocrassosides B(4) (1), B(5) (2), C(1) (3), D(1) (4), D(2) (5), and D(3) (6), were isolated together with 30 compounds. The structures of 1-6 were elucidated on the basis of chemical and physicochemical evidence. In addition, several constituents were found to show inhibitory effects on aminopeptidase N and aldose reductase.