Corymbulosins D-H, 2-Hydroxy- and 2-Oxo-clerodane Diterpenes from the Bark of Laetia corymbulosa.

A bioactive CH3OH-CH2Cl2 (1:1) extract of the bark of Laetia corymbulosa provided five new clerodane diterpenes with an isozuelanin skeleton, designated as corymbulosins D-H (1-5), as well as the known corymbulosins B (6) and C (7), for which the relative configurations were not previously determined. The structures of 1-5 were characterized on the basis of 1D and 2D NMR spectroscopic and HRMS analysis. The absolute configurations of all isolated compounds 1-7 were verified through chemical methods, including modified Mosher esterifications or oxidation of the hydroxy group at C-2, ECD experiments, and spectroscopic data comparison. The isolated compounds were evaluated for antiproliferative activity against a small panel of human cancer cell lines.