Biosynthesis of the piperidine nucleus: The occurrence of two pathways from lysine

2-3H,6-14C-dl-Lysine was administered to the intact rat, to intact bean plants (Phaseolus vulgaris) and to excised shoots of Sedum acre. Pipecolic acid (IV), which was isolated from each of these tissues, contained 14C but was free of tritium. Since incorporation of label from 6-3H,6-14C-dl-lysine into pipecolic acid had previously been shown1 to take place specifically and to occur without change in 3H: 14C ratio in each of these systems, the evidence is now complete that conversion of lysine (I) into pipecolic acid (IV) proceeds via ϵ-amino-α-ketocaproic acid (II) and Δ1-piperideine-2-carboxylic acid (III) and not via α-aminoadipic-δ-semialdehyde (VI) and Δ1-piperideine-6-carboxylic acid (V). In S. acre, 2-3H,6-14C-dl-lysine was incorporated into sedamine (X) without change in 3H: 14C ratio. It follows that ϵ-amino-α-ketocaproic acid (II) cannot be an intermediate in the biosynthesis of sedamine from lysine, as had been previously suggested. Specific conversion of 6-3H,6-14C-dl-lysine into sedamine without change in 3H: 14C ratio had been demonstrated earlier. This and other evidence had been interpreted to show that α-aminoadipic-δ-semialdehyde (VI) is not an intermediate on the route from lysine to sedamine and other piperidine alkaloids. An alternative pathway, which invokes neither ϵ-amino-α-ketocaproic acid nor α-aminoadipic-δ-semialdehyde as intermediate, is now suggested.