New furanoid labdane diterpenes, potamogetonyde (3) and potamogetonol (4), together with two known compounds, potamogetonin (1) and 15,16-epoxy-12-oxo-8(17),13(16),14-labdatrien-20,19-olide (2), were isolated from the CH(2)Cl(2) extract of Potamogeton malaianus. The chemical structures of 1-4 were elucidated by the analyses of their spectral data, mainly by 1D and 2D NMR techniques. Potamogetonyde (3) and potamogetonol (4) exhibited potent antiviral (HSV-1) activity with respective IC(50) values of 8 and 3 microg/mL. Compounds 1-4 possessed cytotoxicity toward insect cells (fall armyworm and mosquito larvae, IC(50) of 11-72 microg/mL). Furanoid diterpenes 3 and 4 also exhibited cytotoxicity against the Vero cell line with respective IC(50)'s of 31 and 28 microg/mL, while 1 and 2 were inactive at 50 microg/mL. Compounds 1-4 were inactive (at 20 microg/mL) against KB and BC cell lines and showed only weak antimycobacterial activity against Mycobacterium tuberculosis H37Ra with minimum inhibitory concentrations of 50-100 microg/mL.

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