NMR investigation and theoretical calculations of the effect of solvent on the conformational analysis of 4',7-di-hydroxy-8-prenylflavan

Abstract

Recebido em 12/2/03; aceito em 10/11/03 NMR INVESTIGATION AND THEORETICAL CALCULATIONS OF THE EFFECT OF SOLVENT ON THE CONFORMA-TIONAL ANALYSIS OF 4',7-DI-HYDROXY-8-PRENYLFLAVAN. The NMR conformational study of 4',7-di-hydroxy-8-prenylflavan 1 was carried out in acetone-d6, DMSO-d6 and CDCl 3 which enabled the proposition of three conformations, namely 1a, 1b and 1c, differing in the position of the prenyl group. Geometry optimizations performed using AM1 method showed that 1a (∆H f = -86.2 kcal/mol) is as stable as 1b (∆H f = -85.1 kcal/mol) and 1c (∆H f = -85.4 kcal/mol). When the solvent was included, the calculations showed that the solute-solvent interactions could be explained either in the light of the electronic intermolecular delocalization or the electrostatic character between solute and solvent. Theoretical calculations (HF/6-31G*, DFT/BLYP/6-31G*, and DFT/B3LYP/6-31G*) showed that the combination of these types of interactions present in each solute-solvent system, dependent on the chemical properties of the solvent, lead to different spatial arrangements of the prenyl group, which in turn determined the conformation of 1.

Comparisons between Crystallography Data and Theoretical Parameters and the Formation of Intramolecular Hydrogen Bonds: Benznidazole

“…In 1T, however, the C-H d¨¨¨Ob =N and C-H e¨¨¨Ob =N hydrogen bonds were considered, but their lengths of 2.347 Å and 2.562 Å are longer than those results of 1C. From a structural viewpoint, this discovery provides solid evidence about the preferential conformation of 1C, s-cis, as has already been demonstrated in many similar works [21,[44][45][46][47]. Regarding 1K and 1W (see Figures 3 and 4), B3LYP/6-311++G(d,p) calculations revealed that 1K presents the same intramolecular C-H c¨¨¨Ob =N hydrogen bond of 1C, once the distance values of 2.340 Å (1K) differ slightly from the value of 2.287 Å (1C).…”

Validation of Computational Methods Applied in Molecular Modeling of Caffeine With Epithelial Anticancer Activity: Theoretical Study of Geometric, Thermochemical and Spectrometric Data

“…Already for 13 C the best matches were verified in HF/3-21G*, HF/6-311G* and HF/6-311G** for C2, DFT/B3LYP -3-21G* for C4, DFT/B3LYP -6-311G** for C5, DFT/B3LYP -3-21G* and DFT/B3LYP -3-21G** for C6 and HF/STO-3G* and DFT/B3LYP -6-31G** for C8. A general analysis of table 8 Good results for NMR data calculated with the DFT/B3LYP method have been also obtained, such as reported in works with 4', 7-dihydroxy-8-prenylflavan, 38 as well as 1-methylpyrrolidine-2-one-3-Halo-derivatives. 39 Here, the HF method used with basis set 6-31G** has also shown good results for NMR data prediction, with B classification.…”

Correlations among experimental and theoretical NMR data to determine the absolute stereochemistry of darcyribeirine, a pentacyclic indole alkaloid isolated from Rauvolfia grandiflora

“…In these cases, the solvent effect is not significant to electronic polarization of occupied frontier molecular orbitals of the isomers. In other cases, contributions of solvent atoms (DMSO, acetone, and chloroform) were observed to formation of the frontier molecular orbitals of a prenylflavan [45]. As result, van der Waals forces between polar groups of the alkaloid and DMSO can induce electronic polarizations on the alkaloid, contributing to the carbon chemical shift value.…”