Use of liquid chromatography–mass spectrometry and a chemical cleavage reaction for the structure elucidation of a new sildenafil analogue detected as an adulterant in an herbal dietary supplement

Abstract

An herbal dietary supplement, marketed as a natural product for the enhancement of sexual function, was analyzed by HPLC with photodiode array and mass spectral detection and found to contain a compound related to the synthetic phosphodiesterase-5 (PDE-5) inhibitors. Based on UV spectra, mass spectra and direct infusion MS(n), the structure of the compound was tentatively identified as a sildenafil analogue in which the sulfonyl group had been replaced with an acetyl group. This new analogue is similar to acetildenafil, a previously reported sildenafil analogue, but differs in that it contains an N-methyl group where acetildenafil contains an N-ethyl group. The structure of the unknown was unequivocally established by chemical cleavage of the phenacylamine group of the molecule to generate N-methylpiperazine; other cleavage products matched those generated from acetildenafil. Since the new compound has one less CH(2) group than acetildenafil, it was named nor-acetildenafil.

Structure elucidation of thioketone analogues of sildenafil detected as adulterants in herbal aphrodisiacs

“…Acid hydrolysis proved to be a useful tool in the structure elucidation of sildenafil and vardenafil analogues [9,14,15]. Acidcatalyzed hydrolysis of the sulfonamide bond was followed by LC-PDA-MS analysis to characterize the resulting sulfonic acid products and GC-MS analysis to characterize the resulting amine product.…”

“…Today, there are three such drugs approved by the U.S. Food and Drug Administration: sildenafil citrate (Viagra ® , manufactured by Pfizer), vardenafil hydrochloride (Levitra ® , manufactured by Bayer), and tadalafil (Cialis ® , manufactured by Lilly). In the last few years, these ED drugs and structurally modified synthetic analogues have been found in "natural" herbal health supplements marketed as aphrodisiacs [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Most sildenafil analogues found as adulterants have been modified in the piperazine portion of the molecule, but recently, herbal dietary supplements were found to contain thiosildenafil [17] and thiohomosildenafil [16,17], two novel sildenafil analogues modified by replacing a carbonyl group in sildenafil with a thiocarbonyl group.…”

Isolation and Structural Elucidation of Cyclopentynafil and N-Octylnortadalafil Found in a Dietary Supplement

“…Thus far, a large number of analogues of sildenafil, tadarafil and vardenafil have been reported, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] while a new type of phosphodiesterase-5 (PDE-5) inhibitor, (R)-xanthoanthrafil, an anthranilic acid derivative, has been found in a dietary supplement advertising sexual enhancement for men. 24) (R)-Xanthoanthrafil was first synthesized as a candidate compound for the treatment of ED by Fujisawa Pharmaceutical Co., Ltd. (currently Astellas Pharma Inc., Tokyo, Japan), 25) and was reported as a PDE-5 inhibitor, FR226807, after the manufacturer discontinued the process of developing the drug for approval.…”

A review of analytical methods for the determination of four new phosphodiesterase type 5 inhibitors in biological samples and pharmaceutical preparations

“…There are several studies in the literature reporting the determination of sildenafil citrate in pharmaceuticals, plasma samples, herbal drugs or dietary supplements using liquid chromatography (LC) methods (Eerkes et al, 2002;Sheu et al, 2003;Wang et al, 2005;Reepmeyer, Woodruff, 2007;Ortiz et al, 2010;Bartošová et al, 2011;Hasegawa et al, 2012), gas chromatography (GC) (Berzas et al, 2002;Kim et al, 2003a;Man et al, 2009;Strano-Rossi et al, 2010) and capillary electrophoresis (CE) (Qin, Li, 2002;Flores et al, 2004).…”