Computation-Assisted Structural Elucidation of Epoxyroussoeone and Epoxyroussoedione Isolated from <i>Roussoella japanensis</i> KT1651

The structures of epoxyroussoenone (<b>1</b>) and epoxyroussoedione (<b>3</b>) isolated from a culture broth of <i>Roussoella japanensis</i> KT1651 were determined. Although NMR spectra provided insufficient structural information, computation of the theoretical chemical shifts with DFT EDF2/6-31G* enabled us to elucidate not only the planar structure, but also the relative configuration. Their ECD (electric circular dichroism) spectra suggested the absolute configurations, which were confirmed with time-dependent DFT calculations employing BHandHLYP/TZVP. The ECD calculations for other stereoisomers yielded obviously different spectral profiles, thus confirming the relative structures of <b>1</b> and <b>3</b>

Neomacrophorin X, a [4.4.3]Propellane-Type Meroterpenoid from <i>Trichoderma</i> sp. 1212-03

Neomacrophorin X (<b>1</b>) was isolated from <i>Trichoderma</i> sp. 1212-03. Heteronuclear multiple bond correlation (HMBC) spectral analysis indicated a unique [4.4.3]­propellane framework, which was verified by the ¹H and ¹³C chemical shift calculations based on density functional theory (DFT) and subsequent comparison with experimental data obtained in CDCl₃. The DFT-based electronic circular dichroism (ECD) calculations were effective in not only determining the absolute configuration but also confirming the relative structure. The predominant conformation of <b>1</b> was found to be solvent-dependent, with different conformations presenting different NMR and ECD profiles. Introduction of <i>J</i>-based analysis with a <i>J</i>-resolved HMBC aided in this investigation. This conformational alternation was reproduced by considering the solvation with the SM5.4 model in the calculation, although it was not sufficiently quantitative. Although the calculations without solvent effects suggested a conformer that satisfies the spectral profiles in CDCl₃, postcalculations with the SM5.4 solvation protocol stabilized the second major conformer, which reproduces the NMR and ECD profiles in polar solvents. Neomacrophorin X (<b>1</b>) is assumed to be biosynthesized by a coupling between the reduced form of anthraquinone and a neomacrophorin derivative. This hypothesis was supported experimentally by the isolation of pachybasin and chrysophanol, as well as acyclic premacrophorin (<b>2</b>), from the same fungus. Some biological properties of <b>1</b> are described

Cyclohelminthol X, a Hexa-Substituted Spirocyclopropane from <i>Helminthosporium velutinum</i> yone96: Structural Elucidation, Electronic Circular Dichroism Analysis, and Biological Properties

<i>Helminthosporium velutinum</i> yone96 produces cyclohelminthol X (<b>1</b>), a unique hexa-substituted spirocyclopropane. Although its molecular formula and NMR spectral data resemble those of AD0157, being isolated from marine fungus <i>Paraconiothyrium</i> sp. HL-78-gCHSP3-B005, our detailed analyses disclosed a totally different structure. Chemical shift calculations and electronic circular dichroism spectral calculations were quite helpful to establish the structure, when those were performed based on density functional theory. The carbon framework of cyclohelminthols I–IV is found at the C1–C8 propenylcyclopentene substructure of <b>1</b>. Thus, <b>1</b> is assumed to be biosynthesized by cyclopropanation between an oxidized form of cyclohelminthol IV and a succinic anhydride derivative <b>4</b>. Cytotoxicity for two cancer cell lines and proteasome inhibition efficiency are measured