Three known compounds, stemofoline (1), (2'S)-hydroxystemofoline (2), and (11Z)-1',2'-didehydrostemofoline (3), along with two new alkaloids, stemaphylline (4) and stemaphylline-N-oxide (5), have been isolated from a root extract of Stemona aphylla. The structures of these alkaloids were determined on the basis of their spectroscopic data. The analysis of the crude dichloromethane extract by GC-MS in the EIMS mode showed the presence of alkaloids 1-4, the alkaloid 11, and stilbostemin R (12). The crude dichloromethane extract and 4 were tested for their comparative biological activities. The results of their acetylcholinesterase (AChE) inhibitory activities showed that the crude extract had higher activity than that of 4. The insecticidal properties of the crude extract and 4, using a topical application, showed that 4 had an activity similar to the positive control, methomyl, whereas the crude extract had much lower activity. Their antimicrobial activity against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Pseudomonas auruginosa ATCC 27853, and Candida albicans ATCC 90028 was weak (MIC 62.5-125 microg/mL, MBC 125-250 microg/mL, MFC 125 microg/mL) but much higher than that of the crude extract.

The isolation of two new Stemona alkaloids, 1-hydroxyprotostemonine and stemocurtisine N-oxide, and a new benzofuran, stemofuran L, from the root extracts of Stemona curtisii is reported. The major known alkaloids from this plant extract, stemocurtisine, stemocurtisinol, and oxyprotostemonine, were also isolated along with oxystemokerrine N-oxide. The nonalkaloid components of this extract included a new benzofuran derivative, stemofuran L, the known stemofurans F, J, and K, dihydro-γ-tocopherol, and stigmasterol. Stemocurtisine and stemocurtisinol were converted to their respective N-oxides by oxidation. Stemocurtisine was converted to a tetracyclic derivative by oxidative cleavage of the γ-butyrolactone ring, while stemocurtisinol gave a novel lactam derivative by oxidative cleavage of the C-4 side chain under basic conditions. The acetylcholinesterase inhibitory activities of some known and new alkaloids and their derivatives are also reported. All were 10-20 times less active as acetylcholinesterase inhibitors than the pyrrolo[1,2-a]azepine Stemona alkaloids stemofoline and 1',2'-didehydrostemofoline. None of the stemofuran compounds showed significant antibacterial or antifungal activities.

A new stemofoline alkaloid, (2'S)-hydroxy-(11S,12R)-dihydrostemofoline (3), new stemofurans M-R (8-13), and known compounds stemofoline (1), (2'S)-hydroxystemofoline (2), stemofuran E (4), stemofuran F (5), stemofuran J (6), and stilbostemin F (7) have been isolated from the root extracts of Stemona aphylla. The structures and relative configurations of these new compounds have been determined by spectroscopic data interpretation and from semisynthetic studies. These natural and semisynthetic alkaloids were tested for acetylcholinesterase inhibitory activities and were found to be 10-20 times less active than 1',2'-didehydrostemofoline itself. Stemofurans 4, 6, 8, 11, and 13 were tested for their antibacterial and antifungal activities. Three of these showed antibacterial activities against MRSA with MIC values of 15.6 μg/mL.

This report is an overview of our research on phytochemical, synthetic and biological studies of the Stemona and Stichoneuron species of plants.