Novel 1,4-Diazepane derivatives as amyloid-beta (Aβ) aggregation inhibitors

Alzheimer's disease (AD) is characterized by the aggregation of amyloid-beta (Aβ) peptides, particularly Aβ42 and Aβ40, which contribute to neurotoxicity and disease progression. The development of novel small molecule inhibitors capable of preventing Aβ aggregation represents a promising therapeutic strategy. We report the design, synthesis and evaluation of a novel class of 1,4-diazepanes as anti-amyloid agents.

A novel series of (1,4-diazepan-1-yl) (phenyl)methanone derivatives (4a-n) incorporating a flexible seven-membered 1,4-diazepane scaffold was synthesized and screened for inhibition of Aβ42 and Aβ40 aggregation using a fluorescence-based thioflavin-T (ThT) kinetic assay. The effects of lead compounds on Aβ fibril morphology were subsequently examined by transmission electron microscopy (TEM). Neuroprotective potential was assessed by determining the ability of selected compounds to attenuate Aβ42-induced cytotoxicity in mouse hippocampal HT22 cells. Antioxidant activity was investigated using both the 2,2'-diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging assay and hydrogen peroxide-induced oxidative stress models in HT22 cells. Blood-brain barrier permeability was evaluated using the parallel artificial membrane permeability assay (PAMPA-BBB). In addition, molecular docking studies were performed using Discovery Studio Structure-Based Design software using Aβ aggregates to characterize ligand-Aβ interactions and provide mechanistic insights into the observed anti-aggregation activity.

Among the synthesized derivatives, compound 4m emerged as the lead Aβ42 aggregation inhibitor, demonstrating 42.0% inhibition at 25 µM. Notably, compounds 4k and 4l demonstrated dual inhibitory activity toward both Aβ42 and Aβ40 aggregation, with inhibition values of 40.4% and 57.3% for 4k, and 36.1% and 59.2% for 4l, respectively, at 25 µM. Compounds 4k-m significantly reduced Aβ42-induced cytotoxicity in mouse hippocampal HT22 cells. In addition, compound 4l exhibited antioxidant activity and attenuated hydrogen peroxide-induced cytotoxicity. Computational analyses suggested that these 1,4-diazepane derivatives interact with both the N- and C-termini regions of Aβ42 and Aβ40, stabilizing peptide assemblies and hindering further aggregation.

These findings identify the 1,4-diazepane ring as a novel structural scaffold for the development of anti-amyloid agents. The dual inhibition of Aβ42 and Aβ40 aggregation, combined with neuroprotective and antioxidant effects, highlights compounds 4k-m as attractive lead candidates for further optimization toward therapeutic intervention in Alzheimer's disease.