| Abstract
| - Two pairs of ent-labdane diterpenoid lactone stereoisomers (1−4) including three new compounds (1−3) were isolated from the 85% EtOH extract of the aerial parts of Andrographis paniculata. The structures of these compounds were identified as 7R-hydroxy-14-deoxyandrographolide (1), 7S-hydroxy-14-deoxyandrographolide (2), 12S,13S-hydroxyandrographolide (3), and 12R,13R-hydroxyandrographolide (4) by spectroscopic data analyses and calculated 13C NMR data at the B3LYP/6-311++G(2d,p)//B3LYP/6-31G* level using the GIAO method. The 12S-configuration of 4 was revised to 12R based on the spectroscopic data. The antiproliferative activities of the two pairs of stereoisomers and 14 other ent-labdane diterpenoid derivatives were determined in human leukemia HL-60 cells. Andrographolide (7) and isoandrographolide (12) exhibited higher antiproliferative activities than other ent-labdane diterpenoids with GI50ʼs of 9.33 and 6.30 µM, respectively.
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