In vitro, in vivo, and in silico profiling of optimized hydrazide-hydrazone indole congeners as multi-faceted AChE, BACE1, and MAO-B inhibitors for Alzheimer's disease therapy.

Contemporary evidence indicates that Alzheimer's disease (AD) is characterized by two convergent levels of pathological alteration. The first involves neurochemical downregulation, whereas the second encompasses broader neuropathological changes. Together, these findings underscore the need for multifaceted therapeutic strategies, such as multi-target-directed ligands (MTDLs). In this study, hydrazide-hydrazone based derivatives 3a-l and 5a-c were rationally optimized from previously synthesized compounds Ia-o to address multiple AD-related targets. Structural elongation was approached by introducing a glycyl fragment into the hydrazinylidene side chain of the indole scaffold. The new derivatives were subjected to a sequential biological evaluation pipeline to identify the most promising candidates. Preliminary in vitro screening against AChE and BChE highlighted compounds 3c, 3f, and 3 k, each exhibiting >80% inhibition of AChE. Further in vitro profiling demonstrated their inhibitory potencies across additional AD-relevant enzymes, including AChE, BChE, BACE-1, MAO-A, MAO-B, and COX-2. In in vivo assessment, all synthesized derivatives showed notable anti-inflammatory activity in the carrageenan-induced rat paw edema model. Moreover, compounds 3c, 3f, and 3k produced significant spatial memory improvement in the diseased mice, along with marked enhancement of AD hallmarks and associated histopathological alterations. To gain mechanistic insights, the derivatives were investigated in silico, where molecular docking elucidated favorable binding modes within AChE, BACE-1, and MAO-B active sites. Among them, compound 3f displayed the most consistent performance across biological assays and computational studies and was further subjected to molecular dynamics simulation, which confirmed its stable accommodation within all three enzyme binding pockets. In conclusion, the molecular elongation strategy successfully generated a new series of MTDL candidates with multi-enzyme inhibitory activity against AChE, BChE, BACE-1, and MAO-B, highlighting their potential as promising anti-AD therapeutics.