Development of Coumarin-Sulfonamide Derivatives as Versatile Polyphenol Oxidase Inhibitors With Favorable...

Enzymatic browning mediated by polyphenol oxidase (PPO) remains a persistent challenge in food preservation. We report the rational design, synthesis, and evaluation of nine coumarin-sulfonamide hybrid inhibitors (DS1-9) featuring 6,7-dihydroxy-2-oxo-2H-chromen-4-yl cores linked to N-substituted benzenesulfonamide scaffolds, confirmed by FT-IR and ¹H-NMR. Enzyme kinetics against Agaricus bisporus tyrosinase revealed competitive inhibition across the series, with K_i values spanning 46-775 uM. DFT calculations (B3LYP/def2-TZVP) characterized the electronic landscape, HOMO-LUMO energies (-5.716 to -6.455 eV; -1.716 to -2.278 eV), electrophilicity indices (3.5-4.2 eV), and dipole moments (4.98-11.24 Debye), while C-PCM solvation modeling, MEP mapping, and RDG analysis established that intramolecular hydrogen bonding (sign λ₂ρ ≈ -0.025 to -0.035 a.u.) preorganizes binding-competent conformations. Molecular docking against PPO3 (PDB: 2Y9X) yielded binding affinities of -7.66 to -8.99 kcal/mol, substantially exceeding tropolone (-4.65 kcal/mol). DS-7 (N-3,4-dimethylisoxazol-5-yl) emerged as the lead compound (IC₅₀ = 103 ± 5.64 µM; K_i = 46 uM), its potency driven by hydrogen bonding with Glu322, His85, and Asn260 alongside π-sigma/π-anion contacts. DS-1 (N-thiazol-2-yl; IC₅₀ = 99.7 ± 0.91 µM; K_i = 57 uM) achieved comparable inhibition through a distinctive π-sulfur interaction with His85 and copper coordination. DS-6 (N-ethyl-N-phenyl; IC₅₀ = 90.3 ± 4.86 µM; K_i = 129 uM) outperformed docking predictions via apparent induced-fit binding involving dual copper π-alkyl coordination. SAR analysis identified the 6,7-dihydroxycoumarin core, Val283 π-sigma anchoring, and lipophilic N-substitution as non-negotiable pharmacophoric elements, positioning DS-7, DS-1, and DS-6 for food preservation and biocatalytic applications.