Stemona

Abstract: Stemona alkaloids represent a unique class of natural products exclusively isolated from the monocotyledonous family Stemonaceae comprising three genera mainly distributed in southeast Asia Structurally the alkaloids are characterised by a pyrrolo[1,2- a]azepine nucleus usually linked with two carbon chains mostly forming terminal lactone rings Based on biosynthetic considerations and their various distribution the present review describes 82 Stemona alkaloids grouped into three skeletal types Due to different carbon chains attached to C-9 of the pyrroloazepine nucleus they were classified into stichoneurine-, protostemonine- and croomine-type alkaloids The genera Croomia and Stichoneuron only accumulate croomine or stichoneurine derivatives, respectively, whereas the genus Stemona produces all three types of alkaloids However, species-specific accumulation trends towards certain structural types represent valuable chemosystematic criteria Bioassays with larvae of Spodoptera littoralis exhibited very high insect toxicity for the roots of Stemona species containing certain protostemonine derivatives, especially didehydrostemofoline, whereas those with dominating stichoneurine or croomine derivatives showed low toxicity but sometimes remarkable repellence due to an accumulation of tuberostemonine Tuberostemonine also showed effects on the motility of helminth worms and reduced the excitatory transmission at the crayfish neuromuscular junction Significant antitussive activity was shown for the stereoisomeric neotuberostemonine in guinea-pig after cough induction by citric acid aerosol stimulation Studies on structure-activity relationship with seven related compounds revealed that the saturated tricyclic pyrrolobenzazepine nucleus of tuberostemonines is the prerequisite for antitussive activity

Abstract: Bioactivity-directed fractionation of the crude extract of Stemona tuberosa led to the isolation and characterization of four new stenine-type Stemona alkaloids, namely tuberostemonine J ( 2), tuberostemonine H ( 3), epi-bisdehydrotuberostemonine J ( 4) and neostenine ( 5), together with the known neotuberostemonine ( 1). These five isolated alkaloids were examined for antitussive activity in guinea pig after cough induction by citric acid aerosol stimulation. In this report, we demonstrated, for the first time, that compounds 1 and 5 showed significant antitussive activities. Further study of the structure-activity relationship on these isolated alkaloids and two synthetic analogues revealed that the saturated tricyclic pyrrolo[3,2,1- jk] benzazepine nucleus is the primary key structure contributing to the antitussive activity and all cis configurations at the three ring junctions are the optimal structure for the antitussive activity of stenine-type Stemona alkaloids.

Abstract: On the basis of chronic feeding bioassays with neonate larvae of Spodoptera littoralis reared on an artificial diet, the methanolic leaf and root extracts from Stemona collinsae displayed very high insect toxicity compared to those of two Aglaia species, a commercial Pyrethrum extract, and azadirachtin, whereas S. tuberosa extracts demonstrated low activity in roots and no activity in leaves. Beyond that, in leaf disk choice tests against fifth instar larvae, S. collinsae showed strong antifeedant activity, whereas S. tuberosa was characterized by remarkable repellency. The anti-insect properties of both species were based on pyrrolo[1,2-a]azepine alkaloids, from which didehydrostemofoline (asparagamine A) was the major compound of the roots of S. collinsae, exhibiting the highest toxicity in feeding assays. Saturation and hydroxylation of the side chain in the co-occurring stemofoline and 2'-hydroxystemofoline, respectively, led to an increasing loss of activity. Contact toxicity tests with stemofoline and didehydrostemofoline exhibited even higher activities than those of Pyrethrum extract. Tuberostemonine was the dominating alkaloid in the roots of S. tuberosa, showing outstanding repellency but no toxic effects.