We have previously shown that ethanol or chloroform extracts of the leaves ofImpatiens balsamina (LIB) have anti-tumor activity against the human hepatocellularcarcinoma cell line HepG2. The ethanol extracts were separated into five fractionsaccording to polarity. An MTT assay indicated that two of the fractions had anti-tumoractivity and that the petroleum ether fraction (PEF) was the most active. But the availablequantities of both the PEF and chloroform fractions (CHF) were limited, precluding furtherstudy. The chloroform extract (CHE) shared almost all the same spots with the PEF andCHF and was plentiful enough to carry out further separations. Thus, the CHE was furtherseparated into six sub-fractions (CHE1~6) by column chromatography. A MTT assayshowed that only the CHE2 fraction had a strong tumor inhibition ratio (IC50
= 6.47±0.05mg/L), which was superior to that of curcumin (IC50
= 13.95±0.11 mg/L). However, TLCrevealed that CHE2 was not pure and still contained two more components. After furtherseparation and purification, followed by TLC and MTT assay confirmation, the final activecomponent was isolated and identified as 2-methoxy-1,4-naphthoquinone by m.p., UV, MSand 13
C- and 1
H-NMR data. This is the first report demonstrating that2-methoxy-1,4-naphthoquinone has intensive in vitro anti-tumor activity against HepG2cells.