A zinc–porphyrin–peptide conjugate via “click-chemistry”: synthesis and amyloid-β interaction

The discovery of systems capable of recognizing amyloid-β protein (Aβ) oligomeric species with high sensitivity and specificity, also producing detectable signals, could represent an attractive approach for the early diagnosis of Alzheimer's disease (AD). In this regard, peptide-based inhibitors of Aβ aggregation have been extensively studied with particular attention to those derived from original amyloid sequences, such as the hydrophobic Aβ16–20 core (KLVFF). In this study we combined the antifibrillogenic action of the KLVFF peptide motif with the spectroscopic features of the porphyrin macrocycle. Specifically, we describe the synthesis of a new water-soluble zinc metallated porphyrin–peptide conjugate, in which the porphyrin macrocycle is linked via 1,2,3-triazole linkage to the hydrophobic Aβ16–20 sequence. The zinc–porphyrin–peptide conjugate was obtained by copper-catalyzed azide–alkyne cycloaddition (CuAAC) in the presence of Cu(I) as a catalyst. The “click” reaction was carried out between the azido-KLVFF peptide and the alkyne-porphyrin. The ability of the porphyrin–peptide conjugate to interact with Aβ was investigated. The zinc-metallated porphyrin–peptide conjugate was studied by biophysical techniques, including UV-vis, circular dichroism (CD), and Bis-Ans fluorescence. Finally, cell viability studies were performed on differentiated neuroblastoma cells.