Biosynthesis of the Pyrrolidine Ring in Plants

Abstract

<p>DL-[5-³H,5-¹⁴C]ornithine and DL-[2-³H,5-¹⁴C]ornithine were administered to intact tobacco plants (Nicotiana tabacum) in separate experiments. Proline, ornithine and nicotine were isolated. The ³H:¹⁴C ratio in proline derived from DL-[5-³H,5-¹⁴C]ornithine was the same as that in the reisolated ornithine, whereas proline derived from DL-[2-³H,5-¹⁴C]ornithine contained ¹⁴C but lost almost all tritium relative to ¹⁴C. This evidence definitely excludes 5-oxo-2-aminopentanoic acid and Δ¹-pyrroline-5-carboxylic acid as intermediates on the route from ornithine to proline. These results together with earlier work are interpreted to show that proline is derived from ornithine via 2-oxo-5-aminopentanoic acid and Δ¹-pyrroline-2-carboxylic acid. The ³H:¹⁴C ratios found in nicotine samples isolated from experiments using DL-[5-³H,5-¹⁴C]ornithine and DL-[2-³H,5-¹⁴C]ornithine are consistent with the accepted route from ornithine via 1,4-diaminobutane, mono-N-methyl-1,4-diaminobutane, 4-methylaminobutanal, and N-methylpyrrolinium ion. The ³H:¹⁴C ratio found in nicotine derived from DL-[5-³H,5-¹⁴C]ornithine is interpreted as showing that oxidation of mono-N-methyl-1,4-diaminobutane to 4-methylaminobutanal proceeds with loss of the 4(S)-hydrogen.</p>