Impact of Indole\nInclusion in the Design of Multi-Tactical\nMetal-Binding Tetra-Aza Macrocycles that Target the Molecular Features\nof Neurodegeneration

Numerous small molecules have been studied for their\nability to\ncounteract oxidative stress, a key contributor to neurodegenerative\ndiseases such as Alzheimer’s. Despite these efforts, the pharmacological\nproperties and structure–activity relationships of these compounds\nremain insufficiently understood, yet they are critical in evaluating\na drug molecule’s therapeutic potential. A modified tetra-aza\nmacrocycle has demonstrated strong antioxidant activity through various\nmechanisms; however, its limited permeability presents challenges\nfor advanced formulation studies. To enhance permeability while preserving\nthe beneficial reactivity of the parent molecule, two synthetic modifications\ninvolving indole functionality were explored and compared to modifications\nusing methyl groups alone. New synthetic strategies were developed\nto produce the indole-containing molecules, which were characterized\nby 1D/2D NMR techniques. Isoelectric points, metal binding, and radical\nscavenging activity were determined to validate that the reactivity\nof the parent molecules was retained. The permeability of all molecules\nexplored was improved. Protection against oxidative stress through\nactivation of the Nrf2 pathway was demonstrated for molecules containing\nindoles in cellular models by measuring ROS levels upon treatment\nand mRNA levels of HO-1 and Nrf2. In contrast, no protection or Nrf2\nactivation was observed with the methylation of the O- or N atom.\nThese results suggest that while alkylation improves permeability\noverall, concomitant antioxidant protection and positive permeability\nare achieved with the indole congeners alone.