Bioactive (3Z,5E)-11,20-Epoxybriara-3,5-dien-7,18-olide Diterpenoids from the South China Sea Gorgonian Dichotella gemmacea

Six new (3Z,5E)-11,20-epoxybriara-3,5-dien-7,18-olide diterpenoids, gemmacolides N–S (1–6), were isolated together with four known analogues, juncenolide D, and juncins R, S and U (7–10), from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by the detailed analysis of spectroscopic data in combination with the comparison with reported data. The absolute configuration of 1 was determined by a TDDFT calculation of its solution ECD spectrum, affording the determination of absolute configuration of other analogues by simply comparing their ECD spectra with that of 1. The cytotoxic and antimicrobial activities of these compounds were evaluated. In preliminary in vitro bioassays, compounds 4, 5, 6, 8 and 9 showed cytotoxicity against A549 and MG63, while compounds 1, 2, 4, 7–10 showed antimicrobial activity against the fungus Septoria tritici and the bacterium Escherichia coli

Absolute Configuration of Highly Flexible Natural Products by the Solid-State ECD/TDDFT Method: Ximaolides and Sinulaparvalides

The quantum-mechanical calculation of chiroptical properties such as electronic circular dichroism (ECD) is an increasingly popular tool for establishing the absolute configuration of organic compounds, including natural products. However, this approach is often limited by conformational flexibility, which can be overcome by considering the solid crystalline state instead of solution. By knowing the solid-state geometry, one may employ it as the input structure for ECD calculations and then comparing this with the ECD spectrum measured on a microcrystalline sample. We report here the application of this solid-state ECD approach to establish the absolute configuration of three natural products, namely ximaolide A, sinulaparvalide A and B; all display pronounced flexibility and belong to two families of compounds with remarkable biological activity. The present configurational assignment may also be extended to several analogues whose absolute configurations have not yet been reported

Circular Dichroism of Diglycosyl Dichalcogenides in Solution and Solid State

1,3-Dioxolane- and dioxane-type (1- and 2-naphthyl)ethylidene ketals of p-methoxyphenyl alpha-L-rhamnopyranoside and beta-D-glucopyranoside were prepared and their stereochemistry studied by solution and solid-state circular dichroism, X-ray diffraction, and coupled-oscillator CD calculations on the solid-state and MMFF-calculated geometries. Intermolecular exciton-coupled interactions between the nearby aromatic chromophores in the solid state and different conformers in solution and solid state could be identified as the main reason for the difference between solution and solid-state CDs