Combined in Silico and in Vitro Approaches To Uncover the Oxidation and Schiff Base Reaction of Baicalein as an Inhibitor of Amyloid Protein Aggregation

The oxidized form of baicalein ( BA ) leads to covalent binding with human amyloid proteins. Such adducts hamper the aggregation and deposition of fibrils. A novel reaction of BA with pentylamine ( PA ) as a model for the lysine side chain is described. This is the first study addressing the atomistic details of a Schiff base reaction with the trihydroxylated moiety of BA . Nuclear magnetic resonance and mass spectrometry approaches clearly indicate the formation of dehydrobaicalein in solution as well as its condensation with PA under aerobic conditions, yielding regioselectively C6-substituted products. The combined results suggest initial ion pair formation between BA and PA , followed by a redox chain reaction: the initiation by oxygen/air; an o-quinone-based chain involving oxidation and reduction steps; and extra off-chain formation of a doubly oxidized product. These mechanistic details support the anti-amyloid activity of BA and endorse its trihydroxyphenyl moiety as a pharmacophore for drug-design studies.