Biosynthesis of morphine alkaloids in Papaver bracteatum Lindl

Administration of 1-3H-N-methyl-14C-(+/-)-reticuline to Papaver bracteatum gave good incorporation of carbon-14 into thebaine and a decrease in the tritium to carbon-14 ratio indicative of racemization. The incorporation of carbon-14 and the extent of tritium loss were the same whether reticuline was administered to the intact plant or to isolated leaves. Carrier dilution with cold codeine, codeinone, and morphine showed only insignificant incorporation of radioactivity into codeine and none at all into codeinone and morphine. When codeinone was administered to the living plant, it was converted to codeine rapidly and efficiently, but no O-demethylation to morphine could be detected. The experimental data indicate that the biosynthesis of thebaine in P. bracteatum proceeds by the same pathway as in the opium poppy. The limiting step in the sequence is the demethylation of the enol ether group of thebaine to neopinone.