Configurational and conformational analyses by theoretical methods of pentacyclic triterpenes isolated from Myricaria elegans

Triterpenes are a large group of natural products widely distributed in the plant kingdom. These natural products exhibit a variety of pharmacological activities, such as anti-microbial, cytotoxic, hepatoprotective, and anti-inflammatory activities, making it a natural resource of great importance for the development of new drugs. The pentacyclic triterpenes eleganene-A and eleganene-B were isolated from aerial parts of Myricaria elegans Royle (Tamariscineae) and their structures were proposed through spectroscopic data of IR and NMR (1H and 13C) and mass spectrometry. The proposed structure of the phytoconstituents isolated of M. elegans indicates configuration 5S,9R for eleganene-A and configuration 5R,9R for eleganene-B (ring junctions A/B and B/C in cis form) which is in disagreement with the biosynthesis reported in the literature for these compounds. The configurational and conformational analyses of the triterpenes isolated from M. elegans were based on correlations between values of calculated carbon chemical shift (sC) and experimental data of 13C NMR (?C). As result, the correlations indicated stereochemistry 5R,9S for eleganene-A and 5S,9S for eleganene-B. Both the configurations show the slowest electronic-nuclear energies and ring junctions A/B and B/C in trans geometries, being in agreement with the biosynthesis proposed to these compounds.The structural analysis of eleganene-B also evaluated the stereochemical variations on centers which have substitutions by hydroxyl groups. Correlations between the values of sC and ?C show the best value of R2 for the structure with configuration 1R,2S,3S,6S.