The kynurenine pathway is a significant metabolic route involved in the catabolism of tryptophan, producing various bioactive metabolites with crucial roles as antioxidants in immune regulation and neurobiology. This study investigates the acid-base properties of picolinic acid, kynurenic acid, kynurenine, and 3-hydroxykynurenine, utilizing computational simulations and experimental techniques, including potentiometric and nuclear magnetic resonance titrations. The results reveal distinct pK_a values, with kynurenic acid exhibiting a single dissociation step around 2.4, while kynurenine displays three dissociation steps governed by interactions between its functional groups. Additionally, 3-hydroxykynurenine shows overlapping dissociations in two separate pH regions, suggesting nuanced behavior influenced by its molecular structure. The analysis of intramolecular hydrogen bonding in protonation microspecies across varying pH highlights the relevance of the charge state and hydrogen transfer potential of these metabolites in the context of their radical scavenging ability. At physiological pH, most kynurenine and 3-hydroxykynurenine entities exist in zwitterionic form, with hydrogen bonding stabilizing the aromatic amino group, which may significantly influence their interactions with proteins and reactive oxygen species. This study provides critical insights into the acid-base equilibria of kynurenine pathway metabolites.

Opiate analgetics are widely used therapeutic agents, but their side-effects can cause serious harm to users, and they are often abused for their euphoric effects. Their abuse is a serious healthcare problem worldwide, and in addition, pharmacological treatments of this disorder possess serious problems such as adverse effects, medication adherence complications, and relapse to addiction after the therapy. One possible way to combat the latter issue would be vaccination with macromolecule-opiate conjugates. Therefore, novel compounds are necessary not just as potential therapeutic agents, but also as new hapten-like molecules. In this work, we present the synthesis of novel N-cyanoalkyl- and N-aminoalkyl-noropiate derivatives, which could be used either as new therapeutic agents or haptens. An important aim of this work was to quantify biorelevant physicochemical properties (basicity, lipophilicity) of the newly synthesized compounds. The determination of the protonation macroconstants characterizing the acid-base properties was performed by pH-potentiometry. To determine the partition coefficients, we used the shake-flask method with different octanol/water phase ratios. The complex formation of the pharmacologically active N-cyanoalkyl derivatives with β-cyclodextrin was also investigated. The stoichiometry of the β-cyclodextrin complexes was determined by the Job's plot method, their structure by NMR spectroscopy, and their stability by NMR and circular dichroism spectroscopy. The study of this complex opens up the possibility of a more in-depth formulation investigation. The species-specific basicity of the new potential aminoalkyl haptens was also characterized, which can help further structure-activity relationship studies.

Background/Objectives: Stereochemistry can substantially influence the biological activity and pharmaceutical properties of small molecules. This study investigated the stereochemistry-dependent biological activity and chiral recognition of novel naphthylethyl thiourea enantiomers using an integrated biological, chromatographic, and computational approach. Methods: Ten pairs of naphthylethyl thiourea enantiomers were synthesized from enantiomerically pure precursors and characterized. Antiproliferative and antibacterial activity, chiral HPLC behavior on polysaccharide- and protein-based stationary phases, molecular docking, and multivariate relationships were evaluated. Results: Target-dependent enantioselectivity and substituent-dependent activity patterns were observed. All enantiomeric pairs were chromatographically distinguished under at least one condition, and selected compounds showed selector- and mobile-phase-dependent changes in elution order. AGP-based chromatography showed stereoselective recognition for a subset of compounds, while computational analyses provided complementary support for the experimental trends. Conclusions: Stereochemistry and substitution jointly influence biological and chromatographic behavior in this thiourea series. Integrated biological, chromatographic, and computational profiling provides a useful framework for early enantiomer-resolved developability assessment.