Tetrahydroxanthene-1,3(2)-diones and Oxidized Hexadiene Derivatives from and Their Biological Activities.

The first phytochemical investigation of the twig extract of resulted in the isolation and identification of three new tetrahydroxanthene-1,3(2)-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(2)-dione dimers which exhibited a cyclobutane ring via [2 + 2] cycloaddition from uvarialeptone C and 9a--methyloxymitrone, respectively.