An in vitro screening of New Caledonian plants allowed the selection of several species with a significant dengue virus NS5 RNA-dependent RNA polymerase (RdRp) inhibiting activity. The chemical investigation of Cryptocarya chartacea led to the isolation of a series of new mono- and dialkylated flavanones named chartaceones A–F (1–6), along with pinocembrin. They were isolated as racemic mixtures and characterized using extensive one- and two-dimensional NMR spectroscopy. Four diastereomers of chartaceone A (1) were separated using chiral HPLC, and their absolute configurations were established by comparison of their experimental and calculated ECD spectra. The dialkylated flavanones, chartaceones C–F (3–6), exhibited the most significant NS5 RdRp inhibiting activity, with IC₅₀ ranging from 1.8 to 4.2 μM. Chartaceones represent a new class of non-nucleosidic inhibitors of the DENV NS5 RdRp.