Absolute Configurations of Fungal and Plant Metabolites by Chiroptical Methods. ORD, ECD, and VCD Studies on Phyllostin, Scytolide, and Oxysporone

Abstract

The absolute configuration (AC) of the bioactive metabolites phyllostin (1) and scytolide (2), two hexahydro-1,4-benzodioxines produced by Phyllosticta cirsii, and oxysporone (3), a dihydrofuropyranone recently isolated from a strain of Diplodia africana, has been assigned by computational analysis of their optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra. Computational prediction of ORD, ECD, and VCD allowed us to assign (3S,4aR,8S,8aR) AC to naturally occurring (-)-1, while (4aR,8S,8aR) AC was assigned to (-)-2 employing only ECD and VCD, because in this case ORD analysis turned out to be unsuitable for AC assignment. Theoretical prediction of both ORD and ECD spectra of 3 led to assignment of (4S,5R,6R) AC to (+)-3. In this case a satisfactory agreement between experimental and calculated VCD spectra was obtained only after taking into account solvent effects. This study shows that in the case of flexible and complex natural products only a concerted application of more than a single chiroptical technique permits unambiguous assignment of absolute configuration.

Bioactive Diterpenoids from the Leaves of Callicarpa macrophylla

“…The absolute configuration was determined via experimental and calculated ECD data, a powerful tool to assign the absolute configuration of natural products. 29,30 Through systematic conformational search and geometry optimizations, 31−33 the ECD spectra were calculated at the CAM-B3LYP/SVP level with the conductor-like polarizable continuum model (CPCM) in acetonitrile. The calculated ECD spectrum of 1a (Supporting Information Figure S7) matched the experimental spectrum closely, which suggested an absolute configuration of 4R, 5R, 8S, 10S, 13S, and 14S.…”

Synthesis and L-type calcium channel blocking activity of new chiral oxadiazolothiazinones

“…We used density functional theory (DFT) computational simulations of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD) spectra [14] to assign the AC: although a single chiroptical property is enough to determine the AC, a higher degree of reliability arises from the concerted use of three properties [7,15].…”

Phytotoxins produced by Phoma chenopodiicola, a fungal pathogen of Chenopodium album

“…The IR spectrum of 4 showed the absence of any hydroxy group band while its 1 H NMR spectrum ( The absolute configuration of (À)-1 was determined by ab initio computational analyses of its ORD and ECD spectra (Autschbach, 2009(Autschbach, , 2012. This approach was demonstrated to be particularly straightforward and reliable for the absolute configuration assignment of natural products (Mazzeo et al, 2013;Santoro et al, 2013Santoro et al, , 2014. This allowed analyses in solution and sometimes on a microscale, using very diluted solutions (Berova et al, 2010).…”