CuBr-promoted domino Biginelli reaction for the diastereoselective synthesis of bridged polyheterocycles: Mechanism studies and in vitro anti-tumor activities

The low-cost CuBr-promoted domino Biginelli reaction among readily available ketones, salicylaldehyde derivatives and 3-amino-1,2,4-triazole was studied under solvothermal conditions, giving the novel bridged polyheterocycles bearing two or three stereocenters depending on the starting ketones. This multicomponent reaction proceeded with high diastereoselectivity (dr > 20:1) based on a combined 1H NMR, crystallographic and supercritical fluid chromatographic (SFC) analysis of the product. Time-dependent high-resolution mass spectrometry (HRMS) was performed to track the reaction process, and several key intermediates were identified, leading to the drawing of a plausible reaction mechanism. Density functional theory (DFT) calculation was supplemented, and two reaction pathways were differentiated. Moreover, in vitro antitumor activity was evaluated using HeLa and HepG2 cell lines, and two of these polyheterocycles demonstrated promising activities against HepG2 cells with EC50 down to 10 µmol/L. Additionally, ESI-MS/MS studies on all the polyheterocycles suggest a common fragmentation pathway (loss of one molecule of amino-triazole) they shared, providing the first-hand fragmentation rules for future rapid structural identification of them. The multicomponent domino reaction presented here may offer prospects for future design of more efficient strategies to access medicinally important bridged polyheterocycles.