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Keywords:

  • biosynthesis;
  • indole alkaloids;
  • isotopic labeling;
  • nudicaulin;
  • Papaver nudicaule

Abstract

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.