Eurycomanoic Acids A–C: Three New Quassinoid Carboxylic Acids from <i>Eurycoma longifolia</i> (Simaroubaceae)

quassinoids, eurycomanoic acids A-C (1-3), were isolated from a 70% MeOH extract of the roots of Eurycoma longifolia Jack (Simaroubaceae), collected in Malaysia. Their structures were elucidated based on extensive spectroscopic analyses, including one-dimensional (1D) and 2D-NMR, IR, and UV spectroscopy, and high-resolution electrospray ionization mass spectrometry. Compounds 1-3 have a tetrahydrofuran ring in the D-ring moiety, bearing a carboxy group and a hydroxy group at C-15. The stereochemistry at C-15 of 1-3 was determined to be S by comparing the total energies of the most stable conformers of both C-15 epimers, obtained from density functional theory calculations. Eurycomanoic acid A (1) may be biosynthesized from 15β-hydroxyklaineanone (4) via 15-oxoklaineanone.