Phytochemical Studies on the Tobacco Alkaloids. XII. Identification of γ-Methylaminobutyraldehyde and Its Precursor Role in Nicotine Biosynthesis

γ-Methylaminobutyraldehyde (N-methylpyrroline) labeled with 14C was isolated from tobacco roots which had metabolized ornithine-2-14C. It was labeled most strongly 4 hours after adding ornithine-2-14C to the root, also labeled by putrescine-1,4-14C and methionine-^{14}\text{C}{}_{3}$, and observed in the root but not in the aerial portions of tobacco plants. γ-Methylaminobutyraldehyde when added back to the root was an efficient precursor of nicotine. Identity of γ-methylaminobutyraldehyde from tobacco roots was confirmed by comparison with the authentic compound. The existence of γ-methylaminobutyraldehyde (N-methylpyrroline) in the biosynthetic pathway of nicotine indicates that the methyl group must be introduced before condensation of the pyridine moiety with the pyrrolidine moiety.