The Early Stages of Alkaloid Biosynthesis

6 The Early Stages of Alkaloid Biosynthesis. — It is well established that L-lysine (13) is incorporated into some piperidine alkaloids by way of a symmetrical intermediate it is accepted that this symmetrical intermediate is cadaverine (17), which is also an alkaloid precursor. Lysine, however, is incorporated into other alkaloids, e.g. anabasine (12) (Section 1.5) and sedamine (18), without the intervention of any symmetrical intermediate. Cadaverine (17), although able to act as an alkaloid precursor. 

The decarboxylation by lysine decarboxylase of L-lysine (13) to give cadaverine (17) occurs with retention of configuration [protonation occurs on the a-face of the iraine (14)]. The oxidation of cadaverine (17) occurs with loss of the 1-pro-S proton, which is the proton originally sited at C-2 in L-lysine (13) c. Section 1.1). It follows that L-[2- H]lysine should 

If instead of protonation of the imine function in (14), in the lysine decarboxylase reaction, nucleophilic attack by the 6-amino-group of lysine [see (19)] occurs, (16) is obtained directly and independently of cadaverine, and without loss of the C-2 proton of lysine. This modified decarboxylase would function, it is suggested, for the biosynthesis of alkaloids such Lysine decarboxylase 

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Wang, J., Sheehan, M., Brookman, H., and Timko, M. P. (2000) Characterization of cDNAs differentially expressed in roots of tobacco (Nicotiana tabacum cv Burley 21) during the early stages of alkaloid biosynthesis. Plant Set. 158, 19-32. 

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