# Design and Evaluation of Quinoline-derived Fluorophores for Labeling Amyloid Beta 1–42 in Alzheimer’s Disease

## TL;DR

This paper introduces new quinoline-based fluorescent compounds that effectively label amyloid beta in Alzheimer's disease, aiding early diagnosis.

## Contribution

The study introduces novel quinoline-derived fluorophores with aggregation-induced emission properties for amyloid beta detection.

## Key findings

- 3QnCN showed the strongest binding to Aβ1–42 with a binding energy of –11.9 kcal/mol.
- 3QnCN demonstrated effective fluorescence labeling of Aβ1–42 in PC12 cells confirmed by confocal microscopy.
- The fluorophores exhibited enhanced fluorescence in aggregated states due to restricted intramolecular motion.

## Abstract

Amyloid beta (Aβ)
is a key biomarker in Alzheimer’s
disease, driving the formation of senile plaques that contribute to
neuronal death within a complex etiology. Typically, most treatments
begin at advanced stages, when irreversible brain atrophy has already
occurred; therefore, early diagnosis is essential for effective intervention.
Several probes based on the conventional donor−π–acceptor
(D−π–A) structural motif have been developed as
diagnostic tools, yet few have reached clinical trials. Alternatively,
quinoline-based fluorescent compounds with push–pull structures
and aggregation-induced emission properties show enhanced fluorescence
in the aggregated state due to restricted intramolecular motion (RIM).
Accordingly, four quinoline derivatives2QnCN, 3QnCN, 3QnB,
and 4QnBBwere synthesized using standard methods, including
benzoxazole segments and a cyano (−CN) group. They were chemically
and optically characterized, and their photophysical properties were
calculated. Theoretical analyses include band gap estimation and visualization
of intramolecular charge transfer. Molecular docking was also performed
to assess binding with the Aβ1–42 pentamer
(PDB: 2BEG),
identifying 3QnCN as the most promising candidate with a binding energy
of–11.9 kcal/mol. Cytotoxicity was tested using the MTT assay
to determine the optimal working concentration. The fluorescence intensity
of 3QnCN in PC12 cells was quantified, and confocal microscopy confirmed
its effectiveness in labeling Aβ1–42.