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A new Stemona alkaloid glycoside derivative, 6-hydroxy-5,6-seco-stemocurtisinoside (4), was isolated from the ethanolic extract of the aerial parts of Stemona curtisii Hook.f., together with stemocurtisine (1), (11Z)-1',2'-didehydrostemofoline (2) and 6-hydroxy-5,6-seco-stemocurtisine (3).Whereas, stemocurtisine (1), stemocurtisinol (5) and oxyprotostemonine (6) were isolated from the roots. Their structures were elucidated using 1D and 2D NMR spectroscopy as well as MS experiments. The extract and the pure isolated compounds were evaluated for their cytotoxicities and larvicidal activities against the dengue vector, Aedes aegypti. The alkaloid 2 showed the strongest larvicidal activity with a LC 50 value of 2.44 µM. While the alkaloid 3 exhibited cytotoxicity against MCF-7 and KB cells (IC 50 values of 62.52 and 18.82 µM, respectively) and showed no significant cytotoxicity against Vero cells. Additionally, quantitative analysis of the most active compounds; 2 and 3 in the crude extracts was also performed by HPLC.

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Biotransformations of stemofoline (1a), (2 0 S)-hydroxystemofoline (2a), (11Z)-1 0 ,2 0-didehydrostemofoline (3a) and stemocurtisine (4) were studied through fermentation with Cunninghamella elegans TISTR 3370. Three new stemofoline derivatives; 6 R-hydroxystemofoline (1b), (2 0 S, 6 R)-dihydroxystemofoline (2b) and (11Z,6R)-1 0 ,2 0-didehydro-6-hydroxystemofoline (3b), together with the known compound 1 0 ,2 0didehydrostemofoline-N-oxide (3c), were produced by C-hydroxylation and N-oxidation reactions. Stemocurtisine was not biotransformed under these conditions. The transformed product 1b was four times more potent (IC 50 ¼ 11.01 ± 1.49 mM) than its precursor 1a (IC 50 ¼ 45.1 ± 5.46 mM) as an inhibitor against acetylcholinesterase.