Biosynthesis of hermidin from Mercurialis annua: A retrobiosynthetic study

Cut seedlings of Mercurialis annua L. were supplied with solutions containing [1-¹³C₁]glucose or [U-¹³C₄,¹⁵N₁]aspartate. After 5-7 days, the pyridinone-type chromogen, hermidin, was isolated and analyzed by NMR spectroscopy. In the experiment with [1-¹³C₁]glucose, five single-labelled isotopomers of hermidin were detected at high abundances (2.7-1.8 mol%). In the experiment with [U-¹³C₄,¹⁵N₁]aspartate, contiguous labelling was observed for carbon atoms 2 and 3 and the nitrogen atom in hermidin. The labelling patterns of hermidin and of amino acids from the same experiments rule out predominant formation of the pyridinone by pathways resembling the biosyntheses of vitamin-B₆, anabasine, or polyketides, but suggest a pathway by condensation of aspartate and dihydroxyacetone phosphate affording nicotinate as a precursor of hermidin.