Anti-Helicobacter pylori Compounds from Carpinus tschonoskii Leaves

In our ongoing research for anti-Helicobacter pylori compounds from natural resources, the methanol extract of Carpinus tschonoskii Maxim. (Betulaceae), Asian hornbeam, distributed in eastern Asia showed significant anti-Helicobacter pylori activity. Five fractions of n-hexane, CH₂Cl₂, EtOAc, n-BuOH, and aqueous fractions were obtained from the MeOH extract of C. tschonoskii leaves, and tested against H. pylori strains 51 and 26695. The EtOAc fraction, demonstrating superior inhibitory activity, was subjected to further chromatography, leading to the isolation of four flavonols, namely isoquercetin (1), quercitrin (2), afzelin (3), and kaempferol (4), and a hydroquinone (5). The chemical structures of these compounds were elucidated using UV, ¹H-NMR, ¹³C-NMR, and mass spectrometry. Among these isolates, compounds 4 and 5 displayed significant growth inhibition on H. pylori at a final concentration of 100 μM. While compound 4 showed anti-H. pylori activity against both the tested strains 51 and 26695 with MIC₅₀ values of 63.6 μM and 55.1 μM, respectively, the values of compound 5 were more than 100 μM for the two strains. Structurally, compound 3, with a rhamnose moiety at the oxygen atom of the C-3 position of compound 4, failed to exhibit a significant inhibitory capability. Molecular docking studies predicted that compound 4 interactions occur at αTyr32, αVal33, βPhe441, and βLys445 of H. pylori urease 1E9Y. The five isolated compounds, except compound 3, are novel reports of isolation from this plant. Moreover, compound 1 is isolated first from the genus Carpinus. These findings suggest that the EtOAc fraction of C. tschonoskii leaves or kaempferol may be useful candidates for eradicating H. pylori infection. Further studies are required to elucidate the exact mechanism of action and their efficacy on the human body with safety issues.