Triazole-isatin hybrids as potential dual cholinesterase inhibitors for Alzheimer’s disease: synthesis, structure-activity relationships, molecular docking and in silico ADME profiling

Abstract

Alzheimer's disease (AD) is the most common cause of dementia worldwide, and cholinesterase inhibition remains the principal strategy for its symptomatic treatment. Because BuChE progressively compensates for the loss of AChE activity as the disease advances, dual AChE/BuChE inhibitors continue to attract attention. Twenty-one new hybrid molecules (6–8a-g) were synthesised by reacting 4-amino-3-substituted-4,5-dihydro-1H-1,2,4-triazol-5-ones (3a-g) with isatin-3-imine benzoyl chlorides (5a-c), and their structures were confirmed by 1H NMR and 13C NMR spectroscopy and corroborated by elemental analysis. Cholinesterase inhibition was measured by Ellman's method against galantamine. Twenty of the twenty-one derivatives inhibited AChE more strongly than galantamine (IC50 = 72.21 ± 0.87 µM), and thirteen of the fifteen hybrids for which BuChE IC50 could be quantified were also more potent than the reference. Compound 7 g was the most potent AChE inhibitor, while 7b gave the most potent BuChE inhibition and the best balance across the two enzymes (7b: AChE IC50 = 23.97 ± 0.22 µM; BuChE IC50 = 32.69 ± 0.44 µM; 7g: AChE IC₅₀ = 21.60 ± 0.28 µM), ahead of 8d (25.87 ± 0.10 µM). Structure-activity analysis identified the triazolone C-3 substituent as a major determinant of activity, with the isatin halogen modulating the magnitude of those substituent effects. Molecular docking provided a qualitative structural rationale for the experimental findings: 7b and 7g gave highly favourable AChE docking scores (−13.85 and −13.67 kcal mol⁻¹, respectively) with hydrogen-bonding and π-π stacking interactions, while 7b also scored more favourably than galantamine against BuChE (−8.75 versus −8.22 kcal mol⁻¹). In silico ADME profiling predicted high gastrointestinal absorption but poor blood-brain barrier permeation, and only the non-benzylic methyl and phenyl derivatives satisfied every druglikeness filter, with 7b combining full compliance with the best balanced AChE/BuChE inhibition profile.