Kaempferia parviflora Wall. ex Baker has been popularly used as male sexual performance enhancer in Thailand. However, its
mechanisms were still unknown. One of the possible mechanism for this remedy is phosphodiesterase 5 (PDE5) inhibition.
Among 41 plant extracts, the rhizomes of K. parviflora ethanolic extract could inhibit PDE5 at 50 μg/ml. Therefore, eight 7-
methoxyflavones which are the major the chemical constituents isolated from rhizomes of K. parviflora were further
investigated on inhibitory activity against PDE5. Moreover, the selectivity of these compounds on PDE5 over PDE6 was
evaluated. The results showed that 7-methoxyflavones from this plant showed inhibition effect toward both enzymes. The most
potent PDE5 inhibitor was 5,7-dimethoxyflavone (IC50=10.64±2.09 μM, selectivity on PDE5 over PDE6 = 3.71). Structure
activity relationship showed that the methoxyl group at C-5 position of 7-methoxyflavones was necessary for PDE5 inhibition.
K. parviflora rhizome extract and its 7-methoxyflavone constituents had moderate inhibitory activity against PDE5. This
finding provides an explanation for enhancing sexual performance in the traditional use of K. parviflora. Moreover, 5,7-
dimethoxyflavones could be a useful lead compound for clinically efficacious PDE5 inhibitors.