Alzheimer’s disease (AD) is a chronic neurodegenerative disorder in which the aggregation of amyloid β (Aβ) and tau protein plays a key role. Despite advances in immunochemical and imaging methods, early, accessible, and cost-effective AD diagnostics remain challenging. One promising option is small fluorescent molecular probes that could detect AD biomarkers in body fluids by fluorescence measurements. This thesis focused on designing, synthesizing, and evaluating small organic D–π–A fluorophores for the detection of AD-associated aggregates.
We prepared four generations of rod-like fluorophores, differing in donor (D), acceptor (A), and the length and structure of the π-conjugated system (π). The first generation comprises ketones, β-diketones, β-enaminones, and malononitriles with benzene, naphthalene,
naphthyl–phenyl, and stilbene π-skeletons. The second generation is based on variously substituted 2H-pyran-2-ones, the third on 3-acetyl and BF$_2$-β-diketonate 2H-pyran-2-ones, and the fourth on conjugated alkenes with a nitro group. The fluorophores were synthesized using organic synthetic methods, including the Suzuki–Miyaura and Heck reactions,
the Horner–Wadsworth–Emmons reaction, the Bucherer reaction, Buchwald–Hartwig amination, mixed Claisen condensation, Knoevenagel condensation, cyclization to the
2H-pyran-2-one ring, and the Henry reaction. This enabled the preparation of structurally diverse compound generations, allowing systematic investigation of the influence of the
D, π and A on their optical and binding properties.
The optical properties of the prepared fluorophores were studied in solvents of different polarity, namely hexane, dichloromethane, acetonitrile, methanol, and HEPES buffer. We showed that absorption and emission maxima, Stokes shifts, and quantum yields are significantly influenced by the nature of the acceptor A and the length and structure of the
π-conjugated system. Extension of the π-system and stronger acceptor motifs generally led to a bathochromic shift of absorption and emission, in some cases even into the near-infrared region.
An important part of the thesis also involved in vitro evaluation of the optical and binding properties of the prepared fluorophores in the presence of Aβ$_{1-42}$ fibrils. The results showed that these properties are not determined solely by the length of the π-conjugated system, but also by the nature of the aromatic skeleton and by the acceptor and donor groups. Across several generations of compounds, an appropriate combination of these structural elements provided a favorable balance between affinity for Aβ$_{1-42}$ fibrils and the position and intensity of the emission maxima upon binding.
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