Structural hybridization as a tool for developing novel biologically active analogues of protulactone A.

The study described in the manuscript includes the synthesis of twelve novel hybrid analogues of protulactone A and the evaluation of their antiproliferative activity against a panel of ten tumour and one normal human cell line (foetal lung fibroblasts, MRC-5). The key step in the synthesis was the Grignard addition of PhMgBr to the aldehyde derived from d-galactose, followed by removal of the 1,2-O-isopropylidene protecting group and cyclocondensation of the resulting lactols with Meldrum's acid to build the [3.3.0]furofuranone core. After routine manipulation with present functional groups, the natural product protulactone A and several new hybrid analogues were obtained, ready for biological testing. Several analogues, particularly compounds 9, 13, and 16, showed IC₅₀ values below 10 μM against leukaemia (K562, HL-60), breast (MCF-7, MDA-MB-231), and cervical (HeLa) cancer cells. Selected derivatives (3, 8, 11) further reduced MRP1 levels and induced apoptosis through Caspase-3 activation in K562 cells, indicating their potential as modulators of multidrug resistance. Structure-activity relationship analysis revealed that the introduction of a phenyl group at the C-7 position and specific stereochemical configurations significantly enhanced cytotoxic potency. Importantly, none of the analogues displayed antibacterial or antifungal activity, underscoring their selectivity for tumour cells. Cellular LC-MS/MS profiling revealed that compound 11 achieves uniform high uptake but remains non-toxic to normal cells, demonstrating true pharmacodynamic cancer selectivity. These findings highlight the structural hybridization of protulactone A and styryl lactone as a rational strategy for designing novel anticancer agents with selectivity and relevance in drug resistance contexts.