Design and synthesis of novel carbohydrate-amino acid hybrids and their antioxidant and anti-β-amyloid aggregation activity.

Herein we report the synthesis of new furanoid sugar amino acids and thioureas, prepared by coupling aromatic amino acids and dipeptides with isothiocyanato- functionalized ribofuranose ring. Since carbohydrate-derived structures possess many biological activities, synthesized compounds were evaluated as anti-amyloid and antioxidant agents. The anti-amyloid activity of the studied compounds was evaluated based on their potential to destroy amyloid fibrils of intrinsically disordered Aβ peptide and globular hen egg-white (HEW) lysozyme. The destructive efficiency of the compounds differed between the studied peptides. While the destruction activity of the compounds on the HEW lysozyme amyloid fibrils was negligible, the effect on Aβ amyloid fibrils was significantly higher. Furanoid sugar α-amino acid 1 and its dipeptide derivatives 8 (Trp-Trp) and 11 (Trp-Tyr) were the most potent anti-Aβ fibrils compounds. The antioxidant properties of synthesized compounds were estimated by three complementary in vitro assays (DPPH, ABTS, and FRAP). The ABTS assay was the most sensitive for assessing the radical scavenging activity of all tested compounds compared to the DPPH test. Significant antioxidant activity was detected for compounds in the group of aromatic amino acids depending on the present amino acid, with the highest activity in the case of dipeptides 11 and 12 containing the Tyr and Trp moiety. Regarding the FRAP assay, the best reducing antioxidant potential revealed Trp-containing compounds 5, 10, and 12.