Identification of Aminotadalafil and its Stereoisomers Contained in Health Foods Using Chiral Liquid Chromatography-Mass Spectrometry

Abstract

Using chiral liquid chromatography-mass spectrometry (LC/MS), a simple and rapid identification test was developed for aminotadalafil [(6R,12aR)-2-amino-6-(1,3-benzodioxol-5-yl)-2,3,6,7,12,12a-hexahydropyrazino[1 ,2 : 1,6]pyrido [3,4-b]indole-1,4-dione; RR-ATDF] and its stereoisomers contained in health foods, e.g. herbal products. A sample solution was prepared using methanol extraction. Analysis was performed on a chiral column with the mixture of 0.1% formic acid/acetonitrile (7 : 3) as mobile phase at 30• C. Each resolution value of four stereoisomers of ATDF was greater than 1.3. A mass spectrometer was used as a detector to enhance specificity by excluding the effects of general components derived from the sample. The four individual stereoisomers of ATDF in the health foods were identified based on their respective retention times. Results showed that structural conversions of RR-ATDF into (6R,12aS)-2-amino-6-(1,3-benzodioxol-5-yl)-2,3,6,7,12,12a-hexahydropyrazino[1 ,2 : 1,6]pyrido [3,4-b]indole-1,4-dione (RS-ATDF) and (6S ,12aS)-2-amino-6-(1,3-benzodioxol-5-yl)-2,3,6,7,12,12a-hexahydropyrazino[1 ,2 : 1,6]pyrido [3,4-b]indole-1,4-dione (SS-ATDF) into (6S ,12aR)-2-amino-6-(1,3-benzodioxol-5-yl)-2, 3,6,7,12,12a-hexahydropyrazino[1 ,2 : 1,6]pyrido [3,4-b]indole-1,4-dione (SR-ATDF) occurred under strongly basic conditions, which indicates that such conditions must be avoided during sample preparation. Using this method, RR-ATDF and SR-ATDF were detected in a health food; this is the first report describing that ATDF diastereomers are present in health foods.

Towards a decade of detecting new analogues of sildenafil, tadalafil and vardenafil in food supplements: A history, analytical aspects and health risks

“…The first analogue of tadalafil identified was amino-tadalafil [17,18,62,63]. Instead of using methylamine to cyclise chloropretadalafil the more reactive and toxic hydrazine was used [34].…”

“…Three of such analogues have now been reported as an adulterant in food supplements [64][65][66]. The use of other optical isomers of tadalafil has no apparent logic as these are weak PDE-5i's [63,67]. Its presence is probably best explained by the use of substandard reagents and lack of GMP.…”

Synthesis and Structure Revision of Dimeric Tadalafil Analogue Adulterants in Dietary Supplements

“…Most of the tadalafil analogues detected in illegal dietary supplements were generated by removal of an N-methyl group or its replacement by another group such as amino, ethyl, butyl, octyl or cyclopentyl. [5][6][7][8][9][10][11][12][13][14] Epimeric tadalafil analogues 5,15) and precursor-related analogues of tadalafil (1) have also been identified. [16][17][18] These analogues were presumably designed for use in adulteration to avoid identification by authorities.…”

Identification of N‐octylnortadalafil and its Stereoisomers in Dietary Supplements with Chiral Liquid Chromatography–Circular Dichroism

“…An analytical method to separate RR ‐TDF and its stereoisomers has been described using a Chiralpak AD column with n‐hexane/isopropyl alcohol (1:1, v/v) . Kurita et al successfully used the Chiralcel OD‐RH column with 0.1% formic acid/acetonitrile (7:3, v/v) to separate RR ‐ATDF and its stereoisomers . Yu et al also employed the Ultron ES‐OVM chiral column with an acetonitrile/water gradient to separate chloropretadalafil and its stereoisomers .…”

“…12 Kurita et al successfully used the Chiralcel OD-RH column with 0.1% formic acid/acetonitrile (7:3, v/v) to separate RR-ATDF and its stereoisomers. 13 Yu et al also employed the Ultron ES-OVM chiral column with an acetonitrile/water gradient to separate chloropretadalafil and its stereoisomers. 14 However, no other methods have been developed to separate RR-OTDF and its stereoisomers ( Fig.…”