Pyrazolopyrimidines in 'all-natural' products for erectile dysfunction treatment: the unreliable quality of dietary supplements.

A herbal food supplement advertised as a potency pill was screened for the presence of PDE5 inhibitors. The resulting signals were characterised by UV, LC-MS in ESI-negative mode, and NMR spectroscopy using 1D and 2D experiments. Several substances were identified, bearing the basic chemical structure of sildenafil, but were not supposed to exhibit PDE5 inhibition. These compounds may be process-related impurities or by-products of different reaction steps in the synthesis of PDE5 analogues. As they were found to be present in different capsules at different concentrations, this is an example of the unreliable quality of dietary supplements.