Zhang_2020_Bioorg.Chem_100_103903

Twenty-four new limonoids (1-24), named hainanxylogranins A-X, were isolated from leaves and barks of the Hainan mangrove, Xylocarpus granatum, together with a known compound, tabulvelutin B (25). The structures of these compounds were established by high resolution electrospray ionization mass spectroscopy (HRESIMS), extensive NMR spectroscopic investigations, single-crystal X-ray diffraction analyses, and the comparison of experimental electronic circular dichroism (ECD) spectra. Most notably, the absolute configurations of seven compounds, viz., 1, 2, 6, 16, 17, 22, and 25, were unambiguously determined by single-crystal X-ray diffraction analyses, conducted with Cu Kalpha radiation. Compounds 1-4 belong to a unique group of mexicanolides containing a C3-O-C8 bridge and a C-17 substituted gamma(21)-hydroxybutenolide moiety, whereas 5-9 are mexicanolides comprising a C1-O-C8 bridge. Compounds 10-16 are typical mexicanolides, among which 14 and 15 contain a C-17 substituted gamma(23)-hydroxybutenolide moiety. Compounds 17 and 18 are phragmalin 8,9,30-orthoesters, whereas 19 and 20 are phragmalin 1,8,9-orthoesters. Compound 21 consists of a C1-O-C29 bridge, while 22-24 are derivatives of azadirone. The inhibitory activities of 1, 5-8, 11, 17, 19, 21-23, and 25 against human carboxylesterase 2 (CES2) were assayed. All the tested compounds exhibited inhibition rates of 30-64% at the concentration of 100.0 microM.