A straightforward approach to long forgotten acetophenone-derived bis-Mannich bases: synthesis, mechanistic studies, pharmacophore potential and unique trapping of N-nucleophiles

Abstract

Acetophenone-derived bis-Mannich bases, known for their bioactivity and potential to act as Michael acceptors via deamination and acrolein-type release, have historically suffered from low-yielding syntheses due to their instability. We report a simple, high-yielding (80–90% in most cases), scalable method using TMMDA and ZnCl₂ that eliminates the need for chromatographic purification. Mechanistic and DFT studies revealed that TMMDA functions as both a base and iminium precursor, while ZnCl₂ promotes acetophenone enolization and stabilizes the products. Notably, these bis-Mannich bases exhibit unprecedented reactivity with N-nucleophiles in aqueous media, forming hexahydropyrimidine and diazabicyclo[3.2.1]octane scaffolds. This transformation was successfully applied in the late-stage functionalization of erlotinib, including conjugation with the α_vβ₃-targeting cyclo(RGDfK) peptide. In vitro studies revealed enhanced nonspecific antiproliferative activity for erlotinib derivatives, likely driven by deamination and subsequent Michael addition to abundant nucleophiles in biomolecules. Overall, this work reestablishes bis-Mannich bases as versatile substrates for heterocycle synthesis and drug modification.