Design, Synthesis, In Vitro, and In Silico Studies of 5-(Diethylamino)-2-Formylphenyl Naphthalene-2-Sulfonate Based Thiosemicarbazones as Potent Anti-Alzheimer Agents

Abstract

Alzheimer's disease (AD) is known as one of the more devastating neurodegenerative diseases diagnosed in older people. Cholinesterase inhibitors (ChEI) can be used as an effective palliative treatment for AD. An extensive range of new biologically active 4-(diethylamino) salicylaldehyde-based thiosemicarbazone derivatives 5(a–u) was synthesized and evaluated as inhibitors of cholinesterase (ChE) and monoamine oxidase (MAO) enzymes. 2,3-Dichloro-substituted compound 5u was the most potent inhibitor of AChE and MAO-A with IC₅₀ values of 12.89 and 96.25 nM, respectively. In contrast, the 2,3-dichlorophenyl-substituted compound 5a was the most powerful inhibitor of BChE, with an IC₅₀ value of 124.72 nM. Structure–activity analysis revealed that the electron-withdrawing substituents on the phenyl ring play a crucial role in the inhibition potential of synthesized compounds. Compound 5a showed the strongest binding with 4BDS (−11.3 kcal/mol) via hydrogen bonds and π-interactions. Compound 5u exhibited high affinity with 1B41 (−8.2 kcal/mol), 2Z5X (−8.6 kcal/mol), and 2V5Z (−7.8 kcal/mol), forming key hydrogen bonds, salt bridges, and π-interactions, highlighting its multi-target potential. In silico ADME, pharmacokinetics, and drug-likeness studies were conducted and compared with the standard drugs galantamine and clorgyline.