Nudicaulins, Yellow Flower Pigments of Papaver nudicaule: Revised Constitution and Assignment of Absolute Configuration

Abstract

The constitution of the aglycon of nudicaulin has been revised to be a pentacyclic indole alkaloid. The relative and absolute configurations of the two diastereomers, nudicaulins I (3a) and II (3b), have been assigned by NMR, conformational analyses, and interpretation of the experimental ECD spectra by quantum-chemical calculations.

Unprecedented Utilization of Pelargonidin and Indole for the Biosynthesis of Plant Indole Alkaloids

“…Shikimate also serves as the precursor of ring f( six carbon atoms, C-1' to C-6'), whereas phosphoenol pyruvate contributes three carbon atoms (C-3, C-11, C-12) throught he phenylpropanoid pathway. Ring a( C-4 to C-9) originates from three acetate/malonate units, which seem to be condensed to the polyketide starterp-coumaroyl-CoA-to form ac halcone-or flavonoid-typei nter-Scheme1.Isotopologue profiles of nudicaulin Io btained from 13 CNMR-based retro-biosynthetic experimentsw ith P. nudicaule.Full barsi nt he structures indicate doubly and triply 13 C-labeled isotopologues, and the widthsa nd numbers show their relative molar abundances (see also Table S3). Dashedb ars in ring a indicateisotopologues generated by alternativec losure of ring b.…”

“…The nudicaulins from Papavern udicauleL., [11] P. alpinum,a nd Meconopsis cambrica [12] also belong to the class of flavonoidal indole alkaloids. The diastereomerica glycones [13] of nudicaulins Ia nd II are each com-posed of an indole unit fused to ap olyphenolics caffold, and the molecules are each decorated with three partly malonylated b-glucose units.…”

“…Because of the unprecedented structures and obscured biosynthesis of the nudicaulins, the data mining of transcriptome databases for candidate biosynthetic genes and biochemical approaches to search for the enzyme(s)c atalyzingt heir formation was unfortunatelyn ot promising. Therefore, ar etro-biosynthetic study using 13 CO 2 as am etabolic tracer was performed. [14] In this recent work, both the indole and the phenolic parts of the nudicaulin molecule were shownt oo riginate from shikimate.…”

Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

“…[7,8] This problem is reflected in anumber of literature reports that have proposed NP structures in obvious violation of Bredts rule. [10] In order to provide clarity to this situation, we sought an ew criterion that could be used to determine whether aputative anti-Bredt NP structure would be capable of isolation. [10] In order to provide clarity to this situation, we sought an ew criterion that could be used to determine whether aputative anti-Bredt NP structure would be capable of isolation.…”

“…[9] In several of these cases,s ubsequent recognition of the anti-Bredt character led to structural reassignment. [10] In order to provide clarity to this situation, we sought an ew criterion that could be used to determine whether aputative anti-Bredt NP structure would be capable of isolation.…”