Impact of Indole Inclusion in the Design of Multi-Tactical Metal-Binding Tetra-Aza Macrocycles that Target the Molecular Features of Neurodegeneration

Numerous small molecules have been studied for their ability to counteract oxidative stress, a key contributor to neurodegenerative diseases such as Alzheimer's. Despite these efforts, the pharmacological properties and structure-activity relationships of these compounds remain insufficiently understood, yet they are critical in evaluating a drug molecule's therapeutic potential. A modified tetra-aza macrocycle has demonstrated strong antioxidant activity through various mechanisms; however, its limited permeability presents challenges for advanced formulation studies. To enhance permeability while preserving the beneficial reactivity of the parent molecule, two synthetic modifications involving indole functionality were explored and compared to modifications using methyl groups alone. New synthetic strategies were developed to produce the indole-containing molecules, which were characterized by 1D/2D NMR techniques. Isoelectric points, metal binding, and radical scavenging activity were determined to validate that the reactivity of the parent molecules was retained. The permeability of all molecules explored was improved. Protection against oxidative stress through activation of the Nrf2 pathway was demonstrated for molecules containing indoles in cellular models by measuring ROS levels upon treatment and mRNA levels of HO-1 and Nrf2. In contrast, no protection or Nrf2 activation was observed with the methylation of the O- or N atom. These results suggest that while alkylation improves permeability overall, concomitant antioxidant protection and positive permeability are achieved with the indole congeners alone.