Abstract
trans-Dehydrocrotonin (t-DCTN) a bioactive 19-nor-diterpenoid clerodane type isolated from Croton cajucara Benth, is one of the most investigated clerodane in the current literature. In this work, a new approach joining X-ray diffraction data, nuclear magnetic resonance (NMR) data and theoretical calculations was applied to the thorough characterization of t-DCTN. For that, the geometry of t-DCTN was reevaluated by X-ray diffraction as well as 1H and 13C NMR data, whose geometrical parameters where compared to those obtained from B3LYP/6-311G++(d,p) level of theory. From the evaluation of both calculated and experimental values of 1H and 13C NMR chemical shifts and spin-spin coupling constants, it was found very good correlations between theoretical and experimental magnetic properties of t-DCTN. Additionally, the delocalization indexes between hydrogen atoms correlated accurately with theoretical and experimental spin-spin coupling constants. An additional topological analysis from quantum theory of atoms in molecules (QTAIM) showed intramolecular interactions for t-DCTN.
Highlights
The clerodane group of diterpenes includes more than 800 isolated compounds and a significant number showed to have biological activity such as antimicrobial,[1] psychotropic,[2] antiulcer[3] and antitumor.[4]
A complete characterization of natural terpenoids compounds requires a large amount of work, in which 1D and 2D-nuclear magnetic resonance (NMR) techniques can be combined with X-ray diffraction analysis
In this work, aiming to describe the most stable conformational status of t-DCTN (Figure 1) more thoroughly, we have examined the combined set of X-ray data, NMR spectra and computational calculations using B3LYP/6-311G++(d,p) level of theory
Summary
The clerodane group of diterpenes includes more than 800 isolated compounds and a significant number showed to have biological activity such as antimicrobial,[1] psychotropic,[2] antiulcer[3] and antitumor.[4] the 19-nor-clerodane trans-dehydrocrotonin (t-DCTN), a furan clerodane skeleton type diterpene (Figure 1), is one of the most important bioactive clerodane reported in the current literature. This natural compound isolated from Croton cajucara Benth (Euphorbiaceae), a widely grown tree in the Amazonian region of Northern Brazil, became an important target for pre-clinical researches. The use of theoretical quantum chemistry methods becomes a complementary tool for structural analysis of organic compounds.[3,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
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