Proteophenes – Amino Acid Functionalized Thiophene‐based Fluorescent Ligands for Visualization of Protein Deposits in Tissue Sections with Alzheimer's Disease Pathology

Protein deposits composed of specific proteins or peptides are associated with several neurodegenerative diseases and fluorescent ligands able to detect these pathological hallmarks are vital. Here, we report the synthesis of a class of thiophene‐based ligands, denoted proteophenes, with different amino acid side‐chain functionalities along the conjugated backbone, which display selectivity towards specific disease‐associated protein aggregates in tissue sections with Alzheimer's disease (AD) pathology. The selectivity of the ligands towards AD associated pathological hallmarks, such as aggregates of the amyloid‐β (Aβ) peptide or tau filamentous inclusions, was highly dependent on the chemical nature of the amino acid functionality, as well as on the location of the functionality along the pentameric thiophene backbone. Finally, the concept of synthesizing donor‐acceptor‐donor proteophenes with distinct photophysical properties was shown. Our findings provide the structural and functional basis for the development of new thiophene‐based ligands that can be utilized for optical assignment of different aggregated proteinaceous species in tissue sections.