Abstract
Leucine, intermediates of glycolysis and of the Krebs cycle, and two-carbon compounds labelled at C-1 are poor precursors of the C 9–10 unit of cephaeline. Although acetate was a specific precursor of a typical steroid sitosterol, and showed significant incorporation into cephaeline, neither it nor glycolic acid labelled at C-2 were specific precursors of the C 9–10 unit of cephaeline in Cephaelis acuminata. Neither was acetate a specific precursor of ajmaline or reserpine in Rauwolfia serpentina. Glycine-2- 14C was a specific precursor of ajmaline and reserpine in Rauwolfia serpentina, and of cephaeline in 4–5-yr-old Cephaelis acuminata plants fed in summer, but a poor precursor of β-sitosterol in the latter system. However, neither glycine-2- 14C nor glyoxalate-2- 14C incorporated activity into the C 9–10 unit of cephaeline or ipecoside in 2-yr-old plants fed in winter. In all cases where ipecoside or emetine were isolated their activities paralleled that of cephaeline. The results suggest that the monoterpene unit of alkaloids is formed by a pathway different from that utilized for sterols, and that the oxidation state of a two carbon compound may exert an effect on whether it is capable of being a specific precursor of a particular monoterpene unit.
Published Version
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