Biosynthesis of Nudicaulins: A 13CO2‐Pulse/Chase Labeling Study with Papaver nudicaule

Nudicaulins are unique alkaloids responsible for the yellow color of the petals of some papaveraceaous plants. To elucidate the unknown biosynthetic origin of the skeleton, a ¹³CO₂‐pulse/chase experiment was performed with growing Papaver nudicaule plants. ¹³C NMR analysis revealed more than 20 multiple ¹³C‐enriched isotopologues in nudicaulins from the petals of ¹³CO₂‐labeled plants. The complex labeling pattern was compared with the isotopologue composition of a kaempferol derivative that was isolated from petals of the same ¹³CO₂‐labeled plants. The deconvolution of the labeling profiles indicated that the nudicaulin scaffold is assembled from products or intermediates of indole metabolism, the phenylpropanoid pathway, and the polyketide biosynthesis. Naringenin‐type compounds and tryptophan/tryptamine are potential substrates for the condensation reaction finally generating the aglycone skeleton of nudicaulins.