Leucoflavonine, a new bioactive racemic flavoalkaloid from the leaves of Leucosceptrum canum.

A new flavoalkaloid racemate, leucoflavonine (1), together with its flavonoid precursor pectolinarigenin (2), was isolated from the leaves of Leucosceptrum canum collected from Tibet. Its structure was established by comprehensive spectroscopic analysis. Chrial separation of the enantiomers of 1 was achieved, and their absolute configurations were determined as S-(+)- and R-(-)-leucoflavonines ((+)-1a and (-)-1b) by comparison of their computational and experimental optical rotations. Biological assays indicated that both (+)-1a and (-)-1b exhibited inhibitory activity against acetylchlorinesterase (AChE) in vitro (IC50 = 68.0 ±â€¯8.6 and 18.3 ±â€¯1.8 µM, respectively). Moreover, (-)-1b displayed cytotoxicity against human hepatoma cells HepG2 (IC50 = 52.9 ±â€¯3.6 µM), and inhibited the production of interleukelin-2 (IL-2) in Jurkat cells (IC50 = 16.5 ±â€¯0.9 µM), while (+)-1a showed no obvious activity in these assays.

Biologically active dichapetalins from Dichapetalum gelonioides.

A phytochemical investigation of the toxic tropical plant Dichapetalum gelonioides led to the isolation and identification of 14 new dichapetalins (1-14) and the known dichapetalins A (15) and K (16). The structures of the new compounds were determined by analyses of their NMR, MS, electronic circular dichroism, and X-ray diffraction data. The esterification at C-25 by 4-hydroxyphenylpropanoic acid and the hydroxylation at C-2' are unique in this unusual class of natural products. In addition to the known cytotoxicity, an array of biological activities, including antifeedant, nematicidal, antifungal, and NO and AChE inhibitory activities, were observed for this class of compounds. These findings suggested that dichapetalin hybrid triterpenoids as a class have broad biologically active cellular functions including defense against insect herbivores and pathogens.

Antifeedant and Antiviral Diterpenoids from the Fresh Roots of Euphorbia jolkinii.

ABSTRACT: The perennial herbaceous plant Euphorbia jolkinii (Euphorbiaceae) is a noxious weed widely distributed in the grasslands of northwestern Yunnan and has greatly threatened the local biodiversity. Phytochemical investigation on the fresh roots of E. jolkinii afforded six new diterpenoids 1, 2, 4-6, and 8, together with fifteen known diterpenoids. Their structures were elucidated on the basis of 1D and 2D NMR and other spectroscopic methods. Casbane, lathyrane, abietane, and ent-kaurane diterpenoids were reported from this plant for the first time. Selected compounds were evaluated for their antifeedant and anti-RSV (respiratory syncytial virus) activities. Compound 2 and ingenol (3) exhibited moderate antifeedant activity against a generalist insect herbivore, Spodoptera exigua, with EC50 values of 17.88 and 17.71 µg/cm(2) respectively. Compound 19 showed significant anti-RSV activity, with 50 % inhibition (IC50) value of 10.0 µM and selective index of 8.0. Compounds 1 and 2 were less active against RSV virus, both with IC50 value of 25 µM, and with selective indices of 1.0 and 3.2 respectively. These findings provided new evidence for the biological functions and utilization of the diversified diterpenoid metabolites in the roots of this rich but harmful plant.