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Title: Biosynthesis and conformational properties of the irregular sesquiterpenoids isothapsadiene and ¿-isothapsenol

item COOL, LAURENCE - Non ARS Employee
item Vermillion, Karl
item Takeoka, Gary
item WANG, SELINA - University Of California, Davis
item TANTILLO, DEAN - University Of California, Davis

Submitted to: Journal of Organic Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2018
Publication Date: 4/23/2018
Citation: Cool, L.G., Vermillion, K., Takeoka, G.R., Wang, S.C., Tantillo, D.J. 2018. Biosynthesis and conformational properties of the irregular sesquiterpenoids isothapsadiene and isothapsenol. Journal of Organic Chemistry. 83:5724-5730. https://doi.10.1021/acs.joc.8b00800.

Interpretive Summary: Terpenoids or isoprenoids are a large and highly diverse group of natural products encompassing flavors and fragrances, antibiotics, plant and animal hormones, membrane lipids, insect attractants and antifeedants. Our group recently identified a new sesquiterpene alcohol '-prethapsenol in Ligusticum grayi roots, which has been found to inhibit the growth of pathogenic mycobacteria. In this study we used quantum chemical calculations (density functional theory (DFT)) to postulate new biosynthetic routes to isothapsadiene and '-isothapsenol, new sesquiterpenoids that we identified in Ligusticum grayi roots. This knowledge is crucial for the synthesis of terpenoids with important biological functions.

Technical Abstract: A carbocation cyclization/rearrangement mechanism for the biosynthesis of isothapsadiene and '-isothapsenol is shown to be energetically viable on the basis of density functional theory (DFT) calculations. In addition, for both isothapsadiene and '-isothapsenol, variable-temperature NMR experiments reveal two equilibrium conformers that undergo hindered exchange. The identities of these conformers, which are related by a chair-flip, are confirmed by DFT calculations on their structures, energies, 1H and 13C chemical shifts and interconversion pathway.