Agarwood has been used as an incense and in traditional medicines as aphrodisiac, sedative, cardiotonic, and carminative. In this study, five new 2-(2-phenylethyl)chromones (2, 13–16) and eleven known compounds (1, 3–12) were isolated from the agarwood. The structures of the new compounds were determined by 1H-, 13C-, and two-dimensional NMR together with electronic circular dichroism (ECD) spectroscopy. All isolated compounds were evaluated for the phosphodiesterase (PDE) 3A and 5A1 inhibitory activity by the fluorescence polarization method. Dimeric 2-(2-phenylehyl)chromones (13, 14, 16) had potent inhibitory activity to PDE 5A1 with IC50 values of micro molar range (13: 4.2 μM, 14: 7.9 μM, 16: 4.3 μM), whereas they had weak activity to PDE 3A. In contrast, compound (15), which has a phenylpropionic acid moiety instead of the 2-(2-phenylethyl)chromone moiety in the dimers, showed moderate inhibition of both PDE 3A (IC50: 42.6 μM) and PDE 5A1 (IC50: 15.1 μM).
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