Tetrahydroxanthene-1,3(2H)‑diones and Oxidized Hexadiene Derivatives from Uvaria leptopoda and Their Biological Activities

The first phytochemical investigation of the twig extract of Uvaria leptopoda resulted in the isolation and identification of three new tetrahydroxanthene-1,3­(2H)-diones, uvarialeptones A–C, two new oxidized hexadiene derivatives, uvarialeptols A and B, together with ten known compounds. Their structures were elucidated by spectroscopic techniques and mass spectrometry. Uvarialeptones A and B were unprecedented tetrahydroxanthene-1,3­(2H)-dione dimers which exhibited a cyclobutane ring via [2 + 2] cycloaddition from uvarialeptone C and 9a-O-methyloxymitrone, respectively. The structure of uvarialeptone A was confirmed by X-ray diffraction analysis using Mo Kα radiation. Compound 3 inhibited NO production at an IC50 value of 6.7 ± 0.1 μM.