Pyrrolidine and Tropane Alkaloids

Simple pyrrolidine-containing alkaloid structures are exemplified by hygrine and cuscohygrine, found in those plants of the Solanaceae that accumulate medicinally valuable tropane alkaloids such as hyoscyamine or cocaine (see Figure 6.3). The pyrrolidine ring system is formed initially as a A^pyrrolinium cation (Figure 6.2). PLP-dependent decarboxylation (see page 20) of ornithine gives putrescine, which is then methylated to N-methylputrescine. Oxidative deamina-tion of N-methylputrescine by the action of a diamine oxidase (see page 28) gives the aldehyde, and Schiff base (imine) formation produces the N-methyl-Ax-pyrrolinium cation. Indeed, the aminoaldehyde in aqueous solution is known to exist as an equilibrium mixture with the

h2n n"

urea cycle (animals)

ho2c

CO2H plants

L-Glu

L-Arg

,co2h plp nh2

arginase urea

,co2h nh2

L-Orn

Schiff base formation

W-methyl-A1-pyrrolinium cation

NH O

agmatine O 1

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