Vibrational circular dichroism behavior of quinol cacalolides from Psacalium aff. sinuatum

• Published in: Journal of molecular structure Vol. 1224; p. 128987
• Main Authors: del Río, Rosa E., Pardo-Novoa, Julio C., Cerda-García-Rojas, Carlos M., Joseph-Nathan, Pedro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2021
• Subjects: Absolute configuration; Cacalolides; Psacalium; Vibrational circular dichroism; Cacalolides; Vibrational circular dichroism; Psacalium; Absolute configuration
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2020.128987

•Psacalium aff. sinuatum yielded 4 furotetralin derivatives to achieve a DFT/VCD study.•DFT/VCD calculations of furotetralin derivatives were carried out at several levels.•Isomeric quinols gave good calculated spectra at the B3PW91/DGDZVP2 level of theory.•Dihydronaphthofuran required the PBEPBE/DGDZVP level to be modeled satisfactorily.•Preparation of acetyl derivatives is relevant to minimize intermolecular interactions. In search to find levels of density functional theory (DFT) for the accurate prediction of vibrational circular dichroism (VCD) spectra of cacalolides, we undertook the evaluation of isomeric quinols. To gain compounds that provide experimental VCD spectra for comparative purposes to the calculated spectra, we prepared the hexanes extracts of the roots of Psacalium aff. sinuatum (Cerv.) H. Rob. & Brettell. They afforded the known furotetralin cacalol (1a), the isomeric quinols cacalone (2a) and epi‑cacalone (3a), and the furodehydrotetralin cacalohastine (4). In an earlier work we found that the absolute configuration (AC) determination of 1a by VCD required the study of its acetyl derivative 1b when comparing the experimental data with DFT spectra calculated at the commonly used B3LYP/DGDZVP level of theory. Herein the AC of acetylcacalone (2b) and of non-acetylated 3a were addressed using the same VCD methodology for which it is difficult to predict which DFT level of theory would provide satisfactory results for the uncommon quinol chromophores. It turned out that epi‑cacalone (3a) required the B3PW91/DGDZVP2 level of theory, while in the case of natural occurring 2a it was necessary, as in the case of 1a, to study the acetyl derivative 2b since in 2a the tertiary hydroxy group is prone to intermolecular associations in solution. In addition, the dihydronaphthofuran 4 required the PBEPBE/DGDZVP level of theory, mainly used for aromatic compounds, to be modeled satisfactorily. [Display omitted]