Enzymatic formation of the sarpagan-bridge: a key step in the biosynthesis of sarpagine- and ajmaline-type alkaloids.

The glucoalkaloid strictosidine has been converted under cell-free conditions into 10-deoxysarpagine (= normacusine B) in the presence of a crude soluble enzyme extract and microsomal protein isolated from cell suspensions of Rauwolfia serpentina. The enzymatic formation of this alkaloid bearing the C-5/C-16 bond (sarpagan-bridge), which is characteristic for all sarpagine- and ajmaline-type alkaloids, is dependent on NADPH and oxygen. Inhibition studies indicate that for the synthesis of 10-deoxysarpagine a cytochrome P450 dependent monoxygenase is necessary.