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New isoconessimine derivatives were synthesized from conessine (1) and evaluated as acetylcholinesterase (AChE) inhibitors. The derivatives were prepared via two reaction steps, N-demethylation and nucleophilic substitution. All of the synthesized derivatives exhibited more potential anti-acetylcholinesterase activities than conessine (1) (IC50=16 mu molL(-1)) and isoconessimine (2) (IC50>300 mu molL(-1)). Compound 7b (3-[methyl-[2-(4-nitrophenoxy)ethyl]amino]con-5-enine) showed the most potent inhibitory activity with an IC50 of 110 nmol/L which is close to that of reference compound huperzine A (IC50=70 nmol/L). The mode of AChE inhibition by 7b was reversible and non-competitive. In addition, molecular modeling was performed to explore the binding mode of inhibitor 7b at the active site of AChE and the results showed that 7b could be docked into the acetylcholinesterase active site and compound 7b had hydrophobic interactions with Trp279 and Leu282.

Precursor feeding strategy for increasing the yield of conessine, a steroidal alkaloid of Holarrhena antidysenterica, was established in cell suspension culture. A total of 50 mg/L added cholesterol was converted into 43 mg/L of alkaloid, 90% of which constituted the conessine. By applying the precursor feeding policy to the cell suspension culture in modified Murashige and Skoog (MS) medium, a total of 143 mg/L of alkaloid was produced in 8 days. In this way the alkaloid content of the cells was increased more than six times compared to that obtained in the standard MS medium. The steps leading to biotransformation of cholesterol into alkaloids were unaffected by phosphate. The shake flask data were successfully transferred to a bench scale 6-L stirred tank bioreactor in which the specific biosynthetic rate of alkaloid production was 110 mg/100 g dry cell weight per day, about 160 times higher than that of whole plant.

The effect of major nutrients on growth and alkaloid production by plant cell culture of Holarrhena antidysenterica was studied with a view to increasing the yield of the alkaloid conessine, a therapeutic drug used for treatment of dysentery and helminthic disorders. The studies resulted in development of a modified Murashige and Skoog (MS) medium that contained 60 mM total nitrogen with a NH(4) (+)-to-NO(3) (-) ratio of 5:1, 0.25 mM phosphate, and 40 g/L sucrose. The growth regulators 2,4-dichlorophenoxy acetic acid (2,4-D) and kinetin (Kn) were also found to affect the synthesis of alkaloid. Using an optimal level of inoculum (3 g/L), the modified medium resulted in alkaloid synthesis of 0.66 g/100 g dry cell weight, which represented a 4.25-fold increase over that obtained in standard MS medium.

Chemical investigations on the stem bark of Holarrhena antidysenterica resulted in the isolation of a new steroidal alkaloid designated as holadysenterine (1), together with three known steroidal alkaloids, conessine (2), isoconessimine (3) and kurchessine (4). Their structures were elucidated on the basis of 1D- and 2D-NMR techniques and high-resolution mass spectrometry.

The degradation of the Holarrhena alkaloid conessine (V) to 18-hydroxy-progesterone (Xa, resp. Xb) is described.