Aromatase inhibitors isolated from a flowering tea, snow Chrysanthemum (the capitula of Coreopsis tinctoria Nutt.).

Methanol extract from the capitula of Coreopsis tinctoria Nutt. (Asteraceae), which is also known as a flowering tea or blooming tea "Snow Chrysanthemum," was found to inhibit the enzymatic activity of aromatase. A total of 24 known isolates (1-24) were identified from the extract, including three chalcones (1-3), an aurone (4), five flavanones (5-9), four flavanols (10-13), a flavonol (14), and two biflavanones (15, 16). Among them, okanin (1, Ki = 1.6 μM), (2S)-naringenin (5, 0.90 μM), isookanin (6, 0.81 μM), (2S)-7,3',5'-trihydroxyflavaone (7, 0.13 μM), and (2S)-5,7,3',5'-tetrahydroxyflavanone (8, 0.32 μM) exhibited relatively potent competitive inhibition. Specifically, the isolates 7 and 8, having a common 3',5'-resorcinol moiety at the B ring in their flavanone skeleton, exhibited potent inhibitory activities compared to those of a clinically applied aminoglutethimide (0.84 μM) and naturally occurring flavone, chrysin (0.23 μM), which is a common non-steroidal aromatase inhibitor. Importantly, the active flavonoid constituents (1 and 5-8) did not inhibit the activity of 5α-reductase enzyme, which normally reacts with the same substrate "testosterone," thus, these compounds were suggested to be specific to aromatase.