Unprecedented diterpene skeletons isolated from vascular plants in the last twenty years (2001-2021).

Every year there are hundreds of reports about the isolation of undescribed terpenoids based on novel functionalizations of known carbocyclic skeletons series. However, on some occasions the compounds obtained have a carbocyclic skeleton that does not correspond with the series established, in these peculiar opportunities, in addition to finding an undescribed natural product, is obtained an unprecedented carbocyclic skeleton, whose biogenesis must necessarily involve other additional steps that explain its formation. This review accounts for the reports of seventy-nine unprecedented diterpene skeletons (corresponding to one-hundred-three undescribed diterpenoids) isolated from vascular plants in the last two decades.

Preparation of a ε-caprolactonic diterpenoid derivate by unexpected oxidative cleavage/lactonization of 2-oxoaustroeupatol.

From aerial parts of Austroeupatorium inulifolium was isolated the ent-nor-furano triol labdane austroeupatol 1. The compound 1 was treated with IBX showing an unexpected selectivity at the potentially oxidizable sites of the substrate yielding the 2-oxoaustroeupatol (2) and 2,19-dioxoaustroeupatol (3). The treatment of 2 with sodium periodate yields a heterocyclic derivative (ε-caprolactone derivate 4) formed by oxidative cleavage and unexpected intramolecular attack of the hydroxymethylene (C-19) oxygen to the ketonic carbon (C-2).

Helenin from . The first report of this natural eudesmanolide mixture in Eupatorieae tribe.

From aerial parts of Lagasca was isolated the natural mixture of isomeric eudesmanolides helenin. The identification and quantification of the constituents of helenin (alantolactone and isoalantolactone , ratio 3:7) was performed through the quantitative analysis of its 1D and 2D NMR spectra.

Structure Determination and Mechanism of Formation of a seco-Moreliane Derivative Supported by Computational Analysis.

Basic hydrolysis of a dichloromethane extract of Stevia lucida yielded (4R,5S,7R,9R,10R,11R)-7,9-dihydroxylongipin-2-en-1-one (1), which was oxidized and subjected to acidic conditions to generate the new seco-moreliane derivative 3. The structure of 3 was established based on NMR data interpretation and confirmed computationally. A plausible mechanism for the carbocationic rearrangement of the trione 2 to the seco-moreliane 3 was supported by DFT computations.