Biosynthesis of panaxynol and panaxydol in Panax ginseng

The natural formation of the bioactive C17-polyacetylenes (−)-(R)-panaxynol and panaxydol was analyzed by 13C-labeling experiments. For this purpose, plants of Panax ginseng were supplied with 13CO2 under field conditions or, alternatively, sterile root cultures of P. ginseng were supplemented with [U-13C6]glucose. The polyynes were isolated from the labeled roots or hairy root cultures, respectively, and analyzed by quantitative NMR spectroscopy. The same mixtures of eight doubly 13C-labeled isotopologues and one single labeled isotopologue were observed in the C17-polyacetylenes obtained from the two experiments. The polyketide-type labeling pattern is in line with the biosynthetic origin of the compounds via decarboxylation of fatty acids, probably of crepenynic acid. The 13C-study now provides experimental evidence for the biosynthesis of panaxynol and related polyacetylenes in P. ginseng under in planta conditions as well as in root cultures. The data also show that 13CO2 experiments under field conditions are useful to elucidate the biosynthetic pathways of metabolites, including those from roots

Biosynthesis of panaxynol and panaxydol in Panax ginseng

The natural formation of the bioactive C17-polyacetylenes (−)-(R)-panaxynol and panaxydol was analyzed by 13C-labeling experiments. For this purpose, plants of Panax ginseng were supplied with 13CO2 under field conditions or, alternatively, sterile root cultures of P. ginseng were supplemented with [U-13C6]glucose. The polyynes were isolated from the labeled roots or hairy root cultures, respectively, and analyzed by quantitative NMR spectroscopy. The same mixtures of eight doubly 13C-labeled isotopologues and one single labeled isotopologue were observed in the C17-polyacetylenes obtained from the two experiments. The polyketide-type labeling pattern is in line with the biosynthetic origin of the compounds via decarboxylation of fatty acids, probably of crepenynic acid. The 13C-study now provides experimental evidence for the biosynthesis of panaxynol and related polyacetylenes in P. ginseng under in planta conditions as well as in root cultures. The data also show that 13CO2 experiments under field conditions are useful to elucidate the biosynthetic pathways of metabolites, including those from roots

Isotopologue Profiling of Triterpene Formation under Physiological Conditions. Biosynthesis of Lupeol-3-(3′‑<i>R</i>‑hydroxy)-stearate in <i>Pentalinon andrieuxii</i>

The biosynthesis of lupeol-3-(3′<i>R</i>-hydroxy)-stearate (procrim b, <b>1</b>) was investigated in the Mexican medicinal plant <i>Pentalinon andrieuxii</i> by ¹³CO₂ pulse-chase experiments. NMR analyses revealed positional enrichments of ¹³C₂-isotopologues in both the triterpenoid and the hydroxystearate moieties of <b>1</b>. Five of the six isoprene units reflected a pattern with [1,2-¹³C₂]- and [3,5-¹³C₂]-isotopologues from the respective C₅-precursors, IPP and DMAPP, whereas one isoprene unit in the ring E of <b>1</b> showed only the [3,5-¹³C₂]-connectivity of the original C₅-precursor, due to rearrangement of the dammarenyl cation intermediate during the cyclization process. The presence of ¹³C₂-isotopologues was indicative of [¹³C₂]­acetyl-CoA being the precursor units in the formation of the fatty acid moiety and of the triterpene via the mevalonate route. The observed labeling pattern was in agreement with a chair-chair-chair-boat conformation of the (<i>S</i>)-2,3-oxidosqualene precursor during the cyclization process, suggesting that the lupeol synthase from <i>P. andrieuxii</i> is of the same type as that from <i>Olea europea</i> and <i>Taraxacum officinale</i>, but different from that of <i>Arabidopsis thaliana</i>. The study shows that ¹³CO₂ pulse-chase experiments are powerful in elucidating, under <i>in vivo</i> conditions and in a single experiment, the biosynthesis of complex plant products including higher terpenes