Decalactone Derivatives from Corynespora cassiicola, an Endophytic Fungus of the Mangrove Plant Laguncularia racemosa

Chemical investigation of the ethyl acetate extract of Corynespora cassiicola, isolated from leaf tissues of the Chinese mangrove medicinal plant Laguncularia racemosa, yielded four new secondary metabolites, including three decalactones, xestodecalactones DF (13) as well as corynesidone C (4), in addition to four known compounds. The structures of the new compounds were determined on the basis of one- and two-dimensional NMR spectroscopy as well as by high-resolution mass spectrometry. Absolute configurations of the optically active compounds 13 were determined by TDDFT ECD calculations of their solution conformers, proving that they belong to the (11S) series of xestodecalactones, opposite to the (11R) configuration of the known xestodecalactones AC. All compounds were tested against a panel of human protein kinases. Among the isolated compounds, two inhibited several kinases such as IGF1-R and VEGF-R2 with IC50 values mostly in the low micromolar range.