O‐Heterocyclic Embeurekols from Embellisia eureka, an Endophyte of Cladanthus arabicus

Abstract

Three new polyketides ((-)-1, (+)-1, and 2) were isolated from the EtOAc extract of the fungus Embellisia eureka, an endophyte of the Moroccan plant Cladanthus arabicus (Asteraceae). The structures of these new compounds were determined on the basis of one- and two-dimensional NMR spectroscopy as well as by high-resolution mass spectrometry. The absolute configurations of (-)-1, (+)-1, and 2 were determined by TDDFT ECD calculations of solution conformers, online HPLC-ECD analysis, and the modified Mosher method.

Structure, absolute configuration, and conformational study of resorcylic acid derivatives and related congeners from the fungus Penicillium brocae

“…28,29 The ECD spectrum of 5 in acetonitrile showed a weak negative CE at 301 nm (p-p* transition) and a positive one at 269 nm (n-p* transition), the latter of which suggested that the major solution conformer had P helicity of the fused heteroring. 28 The P helicity of the heteroring and the axial orientation of the 8-OH implies (8R) absolute conguration, while the C-14 stereogenic centre of 5 corresponds to the (14R) stereogenic centre of 1-4, the absolute conguration of which must have preserved during the formation of the tetrahydro-2H-pyran ring by an intramolecular oxa-Micheal addition from the biosynthetic precursor (vide infra). In solution, the P helicity conformer is in equilibrium with the M helicity form, in which the 8-OH is equatorial (Fig.…”

Isolation, Stereochemical Study, and Antioxidant Activity of Benzofuranone Derivatives from a Mangrove‐derived Fungus Eurotium rubrum MA‐150

“…) were recorded by chiral HPLC‐ECD, and TDDFT‐ECD calculation was utilized to determine their absolute configurations. The HPLC‐ECD spectrum of the first‐eluting enantiomer with positive Cotton effect (CE) at 227 nm [(+CE) 227 nm ] showed a similar ECD pattern to that of embeurekol C having (3 R ) absolute configuration …”

“…The HPLC-ECD spectrum of the first-eluting enantiomer with positive Cotton effect (CE) at 227 nm [(+CE) 227 nm ] showed a similar ECD pattern to that of embeurekol C having (3R) absolute configuration. 21 DFT reoptimization of the initial seven MMFF geometries of (R)-1 resulted in two major conformers ( Fig. 4) above 1% Boltzmann population, which differed only in the orientation of the 13-OH.…”

Determination of the Absolute Stereochemistry of Two New Aristophyllene Sesquiterpenes: A Combined Theoretical and Experimental Investigation

“…Many successful applications of CD spectra prediction by TDDFT are being reported in the literature. [5][6][7][8][9][10] Aristophyllene sesquiterpenoids represent a very rare skeleton only found in the genus Aristolochia (Aristolochiaceae). They are structurally related to elemane-type sesquiterpenoids, 11 with the C 11 -C 12 -C 13 fragment in elemane being rearranged from C-7 to C-6 ( Fig.…”

“…Among them, DFT and TDDFT, which have proven to be reliable and feasible approaches, are perhaps the most widely used ab initio methodology in the field of chiroptical properties prediction, particularly for the prediction of ECD spectra. Many successful applications of CD spectra prediction by TDDFT are being reported in the literature …”