An Efficient Synthesis of OpticallyActivetrans-2-Aryl-2,3-dihydrobenzofuran-3-carboxylicAcid Esters via C-H Insertion Reaction

Total Synthesis of Sophoraflavanone H and Confirmation of Its Absolute Configuration

Sophoraflavanone H (1) is a polyphenol with a hybrid-type structure containing 2,3-diaryl-2,3-dihydrobenzofuran and flavanone ring moieties. This compound and related analogues are promising leads for antimicrobial and antitumor drug development. Here we describe a total synthesis of 1 and its diastereomer. The dihydrobenzofuran and flavanone rings were constructed by a Rh-catalyzed asymmetric C-H insertion reaction and selective oxy-Michael reaction. The absolute configuration of 1 was established by X-ray crystallographic analysis and CD spectral investigation of synthetic derivatives.

Gardenifolins A-H, Scalemic Neolignans from Gardenia ternifolia: Chiral Resolution, Configurational Assignment, and Cytotoxic Activities against the HeLa Cancer Cell Line

From the tropical plant Gardenia ternifolia Schumach. and Thonn. (Rubiaceae), eight stereoisomeric 2,3-dihydrobenzo[b]furan neolignans, named gardenifolins A-H (1a-d and 2a-d), were isolated and fully structurally characterized. Reversed-phase chromatography of a stem bark extract afforded two peaks, viz. mixtures I and II, each one consisting of two diastereomers and their respective enantiomers. They were resolved and stereochemically analyzed by HPLC on a chiral phase coupled to electronic circular dichroism (ECD) spectroscopy, giving single ECD spectra of all eight stereoisomers. The double-bond geometries (E or Z) of the gardenifolins A-H and their relative configurations (cis or trans) at the stereogenic centers C-7 and C-8 in the dihydrofuran ring system were assigned by 1D and 2D NMR methods, in particular, using NOE difference experiments, whereas the absolute configurations of the isolated enantiomers were established by ECD spectroscopy by applying the reversed helicity rule. The individual pure gardenifolin isomers A-H showed the most different cytotoxic effects against the human cancer HeLa cell line, with 1d and 2a displaying the highest activities, with IC₅₀ values of 21.0 and 32.5 μM, respectively. Morphological experiments indicated that gardenifolin D (1d) induces apoptosis of HeLa cells at 25 μM.