Agarsenone, a Cadinane Sesquiterpenoid from <i>Commiphora erythraea</i>

Agarsenone (<b>1</b>), a new cadinane sesquiterpenoid, was isolated from the resin of <i>Commiphora erythraea.</i> The structures of <b>1</b> and its decomposition products agarsenolides (<b>2a</b> and <b>2b</b>) and myrrhone (<b>3</b>) were established by extensive NMR spectroscopic analysis. The absolute configuration of <b>3</b> and the relative and absolute configurations of <b>1</b> were assigned by comparison of experimental and calculated optical rotatory dispersion and electronic circular dichroism spectra

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

The absolute configuration (AC) of the bioactive metabolites phyllostin (<b>1</b>) and scytolide (<b>2</b>), two hexahydro-1,4-benzodioxines produced by <i>Phyllosticta cirsii</i>, and oxysporone (<b>3</b>), a dihydrofuropyranone recently isolated from a strain of <i>Diplodia africana</i>, 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 (3<i>S,</i>4a<i>R,</i>8<i>S,</i>8a<i>R</i>) AC to naturally occurring (−)-<b>1</b>, while (4a<i>R,</i>8<i>S,</i>8a<i>R</i>) AC was assigned to (−)-<b>2</b> 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 <b>3</b> led to assignment of (4<i>S,</i>5<i>R,</i>6<i>R</i>) AC to (+)-<b>3</b>. 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

Helical Sense-Responsive and Substituent-Sensitive Features in Vibrational and Electronic Circular Dichroism, in Circularly Polarized Luminescence, and in Raman Spectra of Some Simple Optically Active Hexahelicenes

Four different hexahelicenes, 5-aza-hexahelicene (<b>1</b>), hexahelicene (<b>2</b>), 2-methyl-hexahelicene (<b>3</b>), and 2-bromo-hexahelicene (<b>4</b>), were prepared and their enantiomers, which are stable at r.t., were separated. Vibrational circular dichroism (VCD) spectra were measured for compound <b>1</b>; for all the compounds, electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) spectra were recorded. Each type of experimental spectrum was compared with the corresponding theoretical spectrum, determined via Density Functional Theory (DFT). Following the recent papers by Nakai et al., this comparison allowed to identify some features related to the helicity and some other features typical of the substituent groups on the helical backbone. The Raman spectrum of compound <b>1</b> is also examined from this point of view