Cadinane Sesquiterpenoids and Their Glycosides from Alangium chinense That Inhibit Spontaneous Calcium Oscillations

Nine new cadinane sesquiterpenoids, alanenses A-I (1-9), were isolated from the leaves of Alangium chinense together with three previously reported analogues (10-12). The structures of these molecules were elucidated by interpretation of spectroscopic and spectrometric data. Absolute configurations were established by the comparison of experimental and calculated ECD data, chemical degradation studies for sugar moieties, and a single-crystal X-ray diffraction analysis. Compounds 1 and 2 were isolated as racemates, and enantiopurification was achieved by chiral HPLC. Compounds 3-5 are glycosylated cadinanes bearing a β-d-glucose unit, while compounds 6-9 incorporate a hydroxymethyl group in either the free form or additional ring fusion. The structure of compound 11 was originally misassigned and later revised using additional NMR data. The corrected structure is here supported by X-ray single-crystal analysis. Compounds 1 and 2 inhibit spontaneous calcium channel oscillations at low micromolar concentrations.

Photochemical reactions as key steps in natural product synthesis

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.