An Integrated Experimental-Computational Platform for Evaluating Blood-Brain Barrier Permeability of Novel Kynurenic Acid Derivatives.

Kynurenic acid (KYNA) is an endogenous neuroactive metabolite with considerable therapeutic potential, but its clinical translation is limited by poor blood-brain barrier (BBB) permeability. Although numerous KYNA derivatives have been developed to improve brain delivery, the molecular determinants governing BBB permeability remain insufficiently understood. Here, we established an integrated experimental-computational platform for the rational evaluation and optimisation of BBB permeability in novel KYNA derivatives. The platform combines a validated UHPLC-MS/MS assay, experimental determination of lipophilicity using a modified shake-flask method, and computational prediction of protonation states, tautomeric equilibria, solvent-accessible surface areas, and BBB-related molecular descriptors. Targeted structural modifications markedly improved lipophilicity and BBB permeability compared with KYNA. Apparent permeability coefficients (Papp) ranged from 3.4 × 10⁻⁶ to 1.1 × 10⁻⁵ cm s⁻¹, with Compound 4a exhibiting the highest permeability (3.23-fold higher than KYNA), followed by Compounds 4b (2.57-fold) and 4d (2.11-fold). Experimental BBB permeability showed significant correlations with experimentally determined logD, predicted logBB, and solvent-accessible surface area descriptors. The superior permeability of Compound 4a was associated with a substantially higher population of the zwitterionic enol tautomer, suggesting a possible contribution of tautomeric equilibria to the observed permeability differences. Overall, this work establishes an integrated platform linking molecular structure, physicochemical properties, and BBB permeability to support the rational evaluation and prioritisation of compounds within the investigated KYNA derivative series. Among the investigated derivatives, Compound 4a showed the most favourable in vitro BBB permeability profile and therefore warrants further pharmacokinetic and in vivo evaluation.