Iridoids and secoiridoids from Guettarda platypoda

A reinvestigation of the roots of Guettarda platypoda afforded in addition to morronoside and sweroside isolated previously further two iridoids, loganic acid and loganin and a rare secoiridoid, secoxyloganin. The structures were elucidated by NMR techniques. This is the first report of the isolation of such compounds from G.platypoda. Some chemotaxonomic conclusion can be drawn.

A spectrophotometric assay for strictosidine synthase

A spectrophotometric assay for strictosidine synthase is described. Strictosidine is extracted with ethyl acetate and, where high substrate concentrations are used, the organic extract is washed with dilute ammonia to remove coextracted secologanin; after evaporation of the solvent, the residue is heated with 5 M H2SO4 for 45 min and the A348 value is measured. Strictosidine production is calculated from the response of similarly treated standards. A minimum production of 10-25 nmol of strictosidine may be determined. The assay is demonstrated using extracts of cultured Cinchona ledgeriana cells.

Aucubin: potential antidote for alpha-amanitin poisoning

Aucubin, an iridoid glucoside isolated from Aucuba japonica (Cornaceae), exhibited significant protective activity against alpha-amanitin intoxication in mice. When a single dose of aucubin was administered intraperitoneally, a 50% survival rate was obtained even when the treatment was withheld for 12 hr after alpha-amanitin administration. A possible mechanism of protective activity is partly due to a competitive effect of aucubin on alpha-amanitin inhibition of liver RNA biosynthesis.

Protective activities of aucubin against carbon tetrachloride-induced liver damage in mice

An iridoid glucoside, aucubin was isolated from Aucuba japonica leaves and its protective activities against CCl4-induced hepatotoxicity were evaluated by measuring the duration of hypnosis induced by hexobarbital after CCl4 challenge (0.2 ml/kg/day, po) and the levels of serum glutamic-oxalacetic (GOT) and serum glutamic-pyruvic transaminase (GPT). The duration of hypnosis for the saline control group, the CCl4 alone treated group and the aucubin plus CCl4 treated group was 24.8 +/- 8.5, 60.5 +/- 9.5 and 28.0 +/- 3.2 min, respectively. Treatment of mice with aucubin also effectively protected against CCl4-induced increased serum GOT and GPT activities. It was found that aucubin inhibited hepatic RNA and protein syntheses in vivo. Such inhibitory effects of aucubin might be responsible for protective activities against CCl4-induced liver damage.

Purification and properties of strictosidine synthetase (an enzyme condensing tryptamine and secologanin) from Catharanthus roseus cultured cells

Strictosidine synthetase, which catalyzes the condensation of tryptamine with secologanin to form strictosidine (isovincoside), was purified 740-fold to homogeneity from cultured cells of Catharanthus roseus in 10% yield. The specific activity is 5.85 nkat/mg. The molecular weight as estimated by gel filtration is 38,000. The isoelectric point is 4.6. Apparent Km values for tryptamine and secologanin are 0.83 and 0.46 mM, respectively. The enzyme shows a broad pH optimum between 5.0 and 7.5. The product of the enzymic reaction is exclusively strictosidine, while no trace of its epimer vincoside can be detected. Sulfhydryl inhibitors have no effect on the enzyme. End products in the biosynthetic pathway of indole alkaloids such as ajmalicine, vindoline, and catharanthine do not inhibit the activity of strictosidine synthetase.

Chemical constituents of Gentianaceae XIX: CNS-depressant effects of swertiamarin

CNS activity of swertiamarin, a secoiridoid glucoside from Swertia chirata, was evaluated. An apparent anomaly, associated with the unanticipated finding that the alcoholic extracts (excluding mangiferin) of S. chirata significantly reversed the mangiferin-induced CNS-stimulating effects in albino mice and rats, was resolved. The results indicate that swertiamarin and mangiferin antagonize each other in vivo and thereby reverse their CNS effects.