Isolation and characterisation of a novel sildenafil analogue adulterant, desmethylpiperazinyl propoxysildenafil, in a dietary supplement

Analytical methods for the detection and characterization of unapproved phosphodiesterase type 5 inhibitors (PDE-5i) used in adulteration of dietary supplements- a review

This article is an up-to-date review of 112 unapproved phosphodiesterase type 5 inhibitors (PDE-5i) found as adulterants in sexual enhancement dietary supplements and other products from 2003 to July 2023. Seventy-five of these unapproved PDE-5i are analogues of sildenafil (67%), followed by 26 analogues of tadalafil (23%), 9 analogues of vardenafil (8%) and 2 other type of compounds (2%). The products have been formulated in various packaging, primarily in capsule, tablet, and powder forms. Common screening techniques allowing detection of such analogues include high performance or ultra-high performance liquid chromatography in tandem with ultra-violet detector (HPLC-UV or UPLC-UV) (50%) and thin-layer chromatography in tandem with ultra-violet detection (TLC-UV) (7%). Screening by mass spectrometry (MS) is relatively less common with the use of single-, triple-quadrupole or time-of-flight (TOF) mass spectrometers (9%). Meanwhile, the combined detection by UV-MS has been recorded at 10% usage. Screening by proton nuclear magnetic resonance spectroscopy (NMR) (11%) has also been applied. For compound characterization, i.e. structural elucidation, NMR spectroscopy has been preferred (100 out of 112 compounds), followed by high-resolution mass spectrometry (HRMS) (74 out of 112 compounds) and Fourier-transform infrared spectroscopy (FTIR) (44 out of 112 compounds). Over the past two decades, analytical technology has been evolving with enhanced sensitivity and resolution. Despite this, structural elucidation of the new emerging analogues in adulterated dietary supplements remains a challenge, especially when the analogues involve complex structural modification. Therefore, the above-mentioned techniques may not be adequate to characterize the analogues. Additional work involving chiroptical methods, two-dimensional (2D) NMR experiments and X-ray crystallography are likely to be required in the future.

A novel vardenafil analog in a healthcare product: Preparation, characterization, and quantification

OBJECTIVE

This study is aimed to develop a qualitative and quantitative method to detect a novel vardenafil analogue from a healthcare product, which is claimed to enhance sexual function. Method: The unknown compound was detected by non-targeted screening using ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS). MS2 spectra showed that the characteristic fragment ions of this unknown compound were highly similar to those of vardenafil. This compound was subsequently isolated by silica gel column chromatography and characterized by 1D (dimension) and 2D nuclear magnet resonance (NMR) specta, ultra-violet (UV) spectra, and fourier transform infrared (IR) spectra. A quantitative method for analyzing this identified compound in various healthcare product was developed based on high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).

RESULTS

The unknown compound was identified as 2-(5-((4-ethylpiperazin-1-yl)sulfonyl)-2-propoxyphenyl)-5-methyl-7-propylimidazo.[5,1-f] [1,2,4]triazin-4(3H)-one based on the spectroscopic data. Quantitative results revealed that the matrix calibration curves of this compound had a good linear ranges of 2～50 ng/mL in pressed candy (R2 = 0.998), energy coffee (R2 = 0.999), and health wine (R2 = 0.997), respectively. The matrix effects, recoveries, and limit of quantitation (LOQ) of this compound all met the requirements of quantitative validation. Finally, the content of this compound in 5 batches of positive samples ranged from 1.24 to 7.20 g/kg. Conclusion: This study identified a novel vardenafil analog from a healthcare product and named it O-propyl vardenafil, and this compound was distinguished from vardenafil by the replacement of the ethyl group with a propyl group at the aryl alkyl ether moiety. Our developed quantitative method could meet practical needs. The high positive rate (16.67%) in 30 samples suggested that the related regulators should be alert to O-propyl vardenafil in routine test since it has not been detected ever before.

A multi-analyte screening method for the rapid detection of illicit adulterants in dietary supplements using a portable SERS analyzer

The popularity and number of dietary supplements on the health market have experienced an unprecedented boost in recent years. Simultaneously, their increased use has been accompanied by an increase in acute intoxication cases linked to the adulteration of these products with illicit and undeclared substances. In this study, a SERS-based screening methodology was developed to rapidly detect illegally added pharmaceutically active substances to dietary supplements. A portable analyzer and silver printed-SERS substrates were used to enhance the signal, requiring less than 20 min of sample preparation prior to the analysis. The method was successful in the qualitative identification of eleven out of twenty-three illicit adulterants in the dietary supplements; it could detect the target compounds at realistic adulteration levels (0.1-5.0% w/w), demonstrating the potential of SERS-based methodologies for forensic rapid screening applications. The developed method is quick, easy to use, requires no skilled technicians and little sample preparation, and allows in-situ analyses. For these reasons, it is suitable for quick screening to be performed by inspectors at customs. Moreover, the low specificity of spectroscopic methods, to which SERS belongs, would benefit the detection of newly synthesized analogues of the target adulterants, which would otherwise be more difficult using common mass spectrometry methods in absence of reference standards.

Detection of 94 PDE-5is and Their Analogs Including N-Desmethylthiosildenafil in Various Formulations of Dietary Supplements and Food Samples Using HPLC and LC-Q-TOF/MS

Consumption of foods and dietary supplements (DS) adulterated with unprescribed or non-permitted phosphodiesterase-5 inhibitors (PDE-5i) and their analogs can cause serious risk to human health. This study aims to analyze 93 PDE-5i and their analogs present in adulterated foods and DS using an established and validated method involving high-performance liquid chromatography (HPLC). The method was validated in solid and liquid samples, resulting in a limit of detection and quantitation of 0.03-0.5 and 0.08-1.6 μg/mL, respectively. Using the validated method, a total of 404 samples were screened. It was found that 32% of 404 samples were illegally adulterated with PDE-5i and their analogs; moreover, 16.9% of the adulterated samples were found to contain more than three compounds. HPLC-quadrupole-time-of-flight (TOF)/mass spectrometry (MS) analysis was conducted on all the samples to confirm the detected compounds accurately based on fragmentation ion patterns. In addition, sildenafil and tadalafil were detected from the capsule shells of DS unusually. Subsequently, the detected compounds were identified and quantified using HPLC at concentrations ranging from 0.007 to 370.0 mg/g. NMR analysis was carried out to confirm the accurate chemical structure of a compound found during the TOF/MS analysis, which did not match with the 93 reference standards.; it was identified to be N-desmethylthiosildenafil. In this study, various PDE-5i compounds and their analogs were detected from low to high concentrations in a sample. Therefore, the study sheds light on the misuse of PDE-5i and their analogs in consumable products, which pose a severe threat to public health.

Using a quantum dot bead-based lateral flow immunoassay to broadly detect the adulteration of PDE-5 inhibitors in functional foods

In this study, a designed hapten possessing the classic structure of PDE-5 inhibitors was synthesized. A monoclonal antibody (mAb) with broad recognition for six PDE-5 inhibitors was further produced. For the determination of lodenafil, methisosildenafil, mirodenafil, udenafil and tadalafil, the limit of detection (LOD) and IC50 ranged from 1.01 to 26.91 ng mL-1 and 12.75 to 278 ng mL-1, respectively. Thereafter, a quantum dot bead-based lateral flow immunoassay (QB-LFIA) was developed, which improved the LOD and IC50 to 0.32-6.52 ng mL-1 and 7.45-133.8 ng mL-1, respectively. Method validation was conducted using honey and capsule samples spiked with PDE-5 inhibitors, and the recoveries of the intra- and inter-assays ranged from 81.01% to 108.16%, with coefficients of variation below 12.71%. In addition, the validity and the consistency have been confirmed with a comparison between QB-LFIA and HPLC-MS/MS (R2 = 0.9957). Furthermore, the developed QB-LFIA was employed for the inspection of real products, and several samples were found to be adulterated with lodenafil and methisosildenafil.

Drug adulteration of sexual enhancement supplements: a worldwide insidious public health threat

Worldwide, the consumption of dietary supplements for the enhancement of sexual performance is common. Consumers are generally fond of these products because they often want to avoid drugs, preferring "natural" than "chemical" solutions. This is challenging, as many of these supplements labelled "herbal" or "natural" are actually adulterated with drugs, mainly phosphodiesterase-5 inhibitors. This phenomenon is facilitated by fewer demanding regulations for marketing supplements. Thus, consumers may be widely exposed to serious adverse events, such as acute liver injury, kidney failure, pulmonary embolism, stroke or even death. We aim to warn physicians about this issue. This multidisciplinary review simultaneously deals with clinical consequences of this phenomenon, analytical toxicology and regulation. Indeed, after outlining this worldwide issue and highlighting that a drug-adulterated dietary supplement is actually a falsified drug, we discuss its main contributing factors. Then, we describe some examples of adverse events of which a case of sildenafil-tadalafil-induced ischaemic stroke that benefited medical care in our hospital. Furthermore, we present some means to avoid adulteration and discuss their limitations that may be explained by the heterogeneity of the regulation of dietary supplements between countries. Doing so, we point out the requirement of a global harmonization of this regulation for an efficient eradication of this public health threat. Meanwhile, dietary supplements should be considered adulterated until proven otherwise. Thus, we encourage physicians to investigate these products in the drug histories of their patients, especially when clinical conditions cannot be explained by classical aetiologies.

Structure elucidation of a PDE5 inhibitor detected as an illegal adulteration in a libido-boosting dietary supplement

A compound with potent inhibitory activity for phosphodiesterase type 5 (PDE5) was identified as an illegal adulteration in a libido-boosting dietary supplement being sold at a store in Tokyo. This compound was identified as 5,6-diethyl-2-{5-[(4-methylpiperazin-1-yl)sulphonyl]-2-propoxyphenyl}pyrimidin-4(3H)-one using liquid chromatography-diode array detector (LC-DAD), liquid chromatography-tandem mass spectrometer (LC-MS), LC-HRMS, nuclear magnetic resonance (NMR), and X-ray crystallography. The IC₅₀ value of the inhibitory activity for PDE5A1 (one of the PDE5 isoforms) was 2.0 nM (sildenafil IC₅₀ value was 4.5 nM). This compound was previously synthesised as a PDE5 inhibitor by Shanghai Institute of Materia Medica. The dietary supplement contained 85 mg of this compound in a capsule, which was about 26% of the capsule content (320 mg).

[LC/Tribrid Orbitrap Analysis of Phosphodiesterase-5 Inhibitors and Their Analogs as Adulterants in Dietary Supplements]

LC/Tribrid Orbitrap was developed to determine phosphodiesterase-5 (PDE-5) inhibitors and their analogs as adulterants in dietary supplements. High-resolution MS/MS and MS³ spectra of PDE-5 inhibitors and their analogs were obtained by LC/Tribrid Orbitrap using both higher-energy collisional dissociation and collision-induced dissociation. We investigated dietary supplements that claim to enhance men's sexual performance, and detected PDE-5 inhibitors and their analogs. We also estimated the structures of the PDE-5 inhibitor analogs and the impurities of PDE-5 inhibitors and their analogs in the dietary supplements.