Flavonoids from Pyrus communis L. ‘Kashi’: Isolation, Structural Identification, NO Inhibitory Activity, and Molecular Docking

Pyrus communis L. ‘Kashi’, a Xinjiang pear cultivar, is traditionally consumed after baking to alleviate inflammation-related ailments, although its active constituents remain unclear. Flavonoids were isolated chromatographically and identified by nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). Cytotoxicity and nitric oxide (NO) inhibition were evaluated in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Griess assays, respectively. Docking was performed with inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Eleven flavonoids were isolated and identified; four were isolated and NMR-characterized from Pyrus for the first time. Cell viability remained above 60% at 100 μM. Apigenin, kaempferol, and isorhamnetin-3-O-galactoside showed the strongest NO-inhibitory effects, with half-maximal inhibitory concentration (IC50) values of 22.75 ± 3.23, 37.54 ± 4.40, and 58.19 ± 10.41 μM, respectively. Preliminary structure–activity relationship (SAR) analysis suggested that reduced hydroxylation in compounds 1–3 and shorter sugar chains among the glycosides examined tended to be associated with lower normalized NO levels; Isorhamnetin-3-O-galactoside was more active than the corresponding glucoside. Docking revealed differences in predicted ligand orientation and residue interactions, providing complementary qualitative structural information. These findings expand the flavonoid profile of P. communis L. ‘Kashi’ and highlight preliminary NO-inhibitory SAR trends.