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. The oxidation of baicalein and subsequent Schiff base reaction with pentylamine (lysine side‐chain model) have been assessed by computational and experimental approaches. The reaction proceeds through initial ion pair formation followed by a redox chain reaction. The atomistic mechanistic findings (transient intermediates) can be used in drug design campaigns against amyloidogenesis.