Enantioselective Total Synthesis of Cepharatines via Bioinspired Ring Reconstruction

We describe enantioselective total syntheses of cepharatines A-D, members of the hasubanan alkaloid family, which feature an unusual tetracyclic skeleton including an azabicyclo[3.3.1]nonane motif. A key reaction is a regio-divergent oxidative phenolic coupling reaction that affords the tricyclic core structure of hasubanan with different substitution patterns on the A-ring, including the all-carbon quaternary stereogenic center at C13, in a single step. The characteristic tetracyclic azabicyclo[3.3.1]nonane motif was constructed by means of a bioinspired cascade reaction involving the retro-aza-Michael reaction/hemiaminal formation.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Antiproliferative activity of O4-benzo[c]phenanthridine alkaloids against HCT-116 and HL-60 tumor cells

The O4-benzo[c]phenanthridine alkaloids exhibit potent antiproliferative activity against cancer cells, which is derived from their ability to inhibit of topoisomerase I and II. It has been reported that in the alkaloids a cationic quaternary ammonium atom, which results in resonance effects between ring A and B, is necessary for increased antiproliferative activity. These findings indicate the role of their substituents at ring A on inhibition of tumor cell proliferation. In the present study, we systematically assessed the cytotoxic activities of naturally occurring alkaloids and their derivatives containing various ring A substituents against two tumor cell lines, HCT-116 colon tumor cells and HL-60 promyelocytic leukemia cells. Among the cationic iminium alkaloids, which displayed more potent activity than the corresponding neutral derivatives, and the 7,8-oxygenated benzo[c]phenanthridine alkaloids, chelerythrine and NK109, exhibited stronger antiproliferative activity than the 8,9- and 9,10-oxygenated alkaloids. The activity of cationic iminium alkaloids could be correlated with the bond lengths of their ring A substituents and the electrostatic potentials of their ammonium molecules by DFT calculation.