Isolation and Identification of a Sildenafil Analogue Illegally Added in Dietary Supplements

A new sildenafil analogue was found to be added illegally to a dietary supplement marketed for erectile dysfunction. The structure was determined as 5-{2-ethoxy-5-[2-(4-ethylpiperazine-1-yl)-acetyl]phenyl}-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one. The sample was extracted with methanol and purified with a liquid-liquid partition method. The structure was identified with a series of 1-D and 2-D NMR techniques, infrared spectrum, high-resolution mass and LC/MS/MS. Having compared the structure with sildenafil, the results showed the methylpiperazine was switched with an ethylpiperazine and the sulfonyl group with an acetyl group. This new sildenafil analogue was isolated and identified for the first time in Taiwan. Since the structure was similar to that of sildenafil, side effects of sildenafil might associate with this new analogue. Therefore, it has been included in the inspection list of illegal health-related substances in Taiwan.