Sildenafil Analogues Research Articles

A Brief Review on the Synthesis of the N-CF3 Motif in Heterocycles

The trifluoromethyl group is widely recognized for its significant role in the fields of medicinal chemistry and material science due to its unique electronic and steric properties that can alter various physiochemical properties of the parent molecule, such as lipophilicity, acidity, and hydrogen bonding capabilities. Compared to the well-established C-trifluoromethylation, N-trifluoromethylation has received lesser attention. Considering the extensive contribution of nitrogen to drug molecules, it is predicted that constructing N-trifluoromethyl (N-CF3) motifs will be of great significance in pharmaceutical and agrochemical industries. This review is mainly concerned with the synthesis of heterocycles containing this motif. In three-membered heterocycles containing the N-CF3 motif, the existing literature mostly demonstrated the synthetic strategy, as it does for four- and larger-membered heterocycles. Certain structures, such as oxaziridines, could serve as an oxidant or building blocks in organic synthesis. In five-membered heterocycles, it has been reported that N-CF3 azoles showed a higher lipophilicity and a latent increased metabolic stability and Caco-2-permeability compared with their N-CH3 counterparts, illustrating the potential of the N-CF3 motif. Various N-CF3 analogues of drugs or bioactive molecules, such as sildenafil analogue, have been obtained. In general, the N-CF3 motif is developing and has great potential in bioactive molecules or materials. Give the recent development in this motif, it is foreseeable that its synthesis methods and applications will become more and more extensive. In this paper, we present an overview of the synthesis of N-CF3 heterocycles, categorized on the basis of the number of rings (three-, four-, five-, six- and larger-membered heterocycles), and focus on the five-membered heterocycles containing the N-CF3 group.

The POWER saga from 2007 to 2022: An example of a sexual enhancement dietary supplement tainted by different adulterants and still on the market

Ten POWER dietary supplements, chronologically called tabs, pills then caps, and advertised as 100% natural aphrodisiacs, were analyzed by 1H NMR from 2007 to 2022. They were all tainted by PDE-5 inhibitors. Eight different adulterants were identified (sildenafil (1), sildenafil analogues (6), and vardenafil analogue (1)). Their amounts ranged from 15 to 145 mg/capsule. Four supplements contained at least 100 mg/capsule of PDE-5 inhibitor or analogue, the maximal recommended dose of sildenafil. The nature of the adulterant has changed over time, probably to evade its detection by regulatory agencies routine screening tests. Despite several warnings and/or seizures from several European food and/or health authorities, the dietary supplement POWER is still on sale on the Internet, thus demonstrating the impossibility of controlling this market. Faced with this situation, the consumer should be better informed by establishing at the European level a public database of tainted dietary supplements on the model of that of the US Food and Drug Administration. It should indicate the product name, its photo, the adulterant name, and be easily accessible to everyone.

Survey on Sildenafil, Tadalafil, and Vardenafil Concentrations in Food Supplements for Erectile Dysfunction

The aim of the study was to analyze the presence of undeclared sildenafil, tadalafil, and vardenafil in food supplements (FSs) for erectile dysfunction. The presence of sildenafil, tadalafil, and vardenafil was determined using the generated ultraviolet (UV)-spectra and mass-spectrometry (MS)-spectra as well as chromatograms produced by the photodiode array (PDA)-detector and ion trap MS-detector. The results were processed by Xcalibur ver. 2.0.7. Fourteen of the 20 analyzed FSs contained undeclared ingredients. Sildenafil was present in 12 of them. Many violations and discrepancies between the label information and the real composition of the FS were identified. 70% of the samples contained undeclared ingredients of an erectile dysfunction medicinal product. The quantities varied within broad limits from 2 mg per tablet to 116.55 mg per tablet. Sildenafil was present in amounts exceeding 16.55 mg that is the maximum recommended dose, thus creating risk of overdose. Besides that, food supplements adulterated with sildenafil analogues are a health risk for consumer's health as there is no evidence of modified sildenafil toxicity. All analyzed FSs were claimed to be 100% natural, not provoking side effects. No information for any FS contained indications of age limits or risk for interaction with other FSs or medical products.

Development of a detector tube for rapid detection of tadalafil in adulterated dietary supplements

ABSTRACT Introduction Products marketed as dietary supplements for improving sexual performance at times include phosphodiesterase type 5 (PDE5) inhibitors, such as sildenafil and analogues. The ingestion of these dietary supplements is extremely dangerous as these are not evaluated for their efficacy and safety as pharmaceuticals, and their manufacture is not controlled. For this reason, regulatory authorities conduct inspections on these products to prevent the occurrence and spread of health hazards. Tadalafil is one of the PDE5 inhibitors, and its analogues are found as the most major adulterants in sexual products after analogues of sildenafil. Tadalafil has two chiral carbons that are both R configuration, which is important for PDE5 inhibitory activity. To confirm the molecular configuration of the tested compound, it is subject to instrumental analysis such as circular dichroism detection or X-ray crystal structure analysis. Therefore, it takes longer for testing tadalafil than for other compounds that do not require these processes. Meanwhile, in 2020, the product containing 120 times more tadalafil than the normal dosage was detected in Tokyo, making it an urgent issue to remove these dangerous products from the market. This study proposes a simple and rapid method to detect tadalafil with a newly devised detector tube. Objective Development of a detector tube for the rapid screening of tadalafil with simple functioning. Methods Approximately 80 mg of silica gel powder impregnated with sulfuric acid was filled in a glass tube, having a 3-mm inner diameter, to prepare a detector tube. The measuring method of this detector tube is quite simple; first, both tips of the detector tube are cut, then the sample solution is aspirated, and a decision is made by the colour of the detector tube after 5 minutes. It was defined as a positive result when the detector tube turned violet and negative when it showed other colours. First, the reaction of tadalafil and analogues were confirmed using the prepared detector tube. Then, specificity was tested for active pharmaceutical ingredients and common additives. The tube was also tested for the applicability to some commercially available dietary supplements. Results All tested tadalafil and analogues showed positive results in the test. The limit of detection was 5 μg/mL for tadalafil. Except for levomepromazine, results for additives and any pharmaceutical ingredients tested were negative. This tube was able to detect all real samples containing tadalafil and analogues. None of the real samples that did not contain tadalafil and analogues gave false positives. Conclusions The developed detector tube could rapidly detect tadalafil and analogues with high sensitivity in a simple procedure. It was suggested that false-positive results could occur only if levomepromazine was included in the sample. Other than that, no significant interference that leads to false results was observed in tested common adulterants and additives of supplements. Furthermore, the tube was able to detect tadalafil and analogues in all tested real samples. Accordingly, the proposed test method has the potential for the use of preliminary screening of tadalafil.

Identification of phosphodiesterase type-5 (PDE-5) inhibitors in herbal supplements using a tiered approach and associated consumer risk

The use of herbal supplements for improved sexual performance is a common practice amongst the youth and some senior citizens in Ghana. These products are considered ‘natural’ and greatly preferred over synthetic alternatives due to the assurance of little to no adverse effects by producers. However, the high rate of adulteration often compromises their safety. Forty herbal supplements, of which 25 were previously shown to result in medium to high intake of phosphodiesterase type-5 (PDE-5) inhibitors using a PDE-Glo bioassay, were further investigated using liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis to examine the reliability of the bioassay and whether the observed higher responses could be ascribed to inherent plant constituents or adulterants. Results showed significant amounts of vardenafil, tadalafil and especially sildenafil, in 2, 1 and 10 samples, respectively, with total concentration levels resulting in estimated daily intakes (EDIs) above 25 mg sildenafil equivalents with six supplements even having EDIs above 100 mg sildenafil equivalents. Only one sample contained a natural ingredient (icariin), but its concentration (0.013 mg g−1) was too low to explain the observed potency in the bioassay. The estimated concentrations of PDE-5 inhibitors in 35 supplements, according to the bioassay, were in line with those of the LC–MS/MS analysis. However, discrepancies were observed for five supplements. Further examination of one of the latter supplements using the PDE-Glo bioassay to select the positive fraction and further examination with LC–MS/MS and 1H-NMR revealed the presence of hydroxythiohomosildenafil, a sildenafil analogue not yet included in the liquid chromatography–mass spectrometry reference library. This study demonstrates the significance of applying a tiered approach, where the use of a bioassay is followed by chemical analysis of bioactive samples in order to identify unknown bioactive compounds.

Olefin Metathesis in Continuous Flow Reactor Employing Polar Ruthenium Catalyst and Soluble Metal Scavenger for Instant Purification of Products of Pharmaceutical Interest.

In recent years, the development of continuous-flow reactors has attracted growing attention from the synthetic community. Moreover, findings in the precise control of the reaction parameters and improved mass/heat transfer have made the flow setup an attractive alternative to batch reactors, both in academia and industry, enabling safe and easy scaling-up of synthetic processes. Even though a majority of the pharmaceutical industry currently rely on batch reactors or semibatch reactors, many are integrating flow technology because of easier maintenance and lower risks. Herein, we demonstrate an operationally simple flow setup for homogeneous ring-closing metathesis, which is applicable to the synthesis of active pharmaceutical ingredients precursors or analogues with high efficiency, low residence time, and in a green solvent. Furthermore, through the addition of a soluble metal scavenger in the subsequent step within the flow system, the level of ruthenium contamination in the final product can be greatly reduced (to less than 5 ppm). To ensure that this method is applicable for industrial usage, an upscale process including a 24 h continuous-flow reaction for more than 60 g of a Sildenafil analogue was achieved in a continuous-flow fashion by adjusting the tubing size and flow rate accordingly.

Sildenafil 4.0-Integrated Synthetic Chemistry, Formulation and Analytical Strategies Effecting Immense Therapeutic and Societal Impact in the Fourth Industrial Era.

Sildenafil is a potent selective, reversible inhibitor of phosphodiesterase type 5 (PDE5) approved for the treatment of erectile dysfunction and pulmonary arterial hypertension. Whilst twenty years have passed since its original approval by the US Food and Drug Administration (USFDA), sildenafil enters the fourth industrial era catalyzing the treatment advances against erectile dysfunction and pulmonary hypertension. The plethora of detailed clinical data accumulated and the two sildenafil analogues marketed, namely tadalafil and vardenafil, signify the relevant therapeutic and commercial achievements. The pharmacokinetic and pharmacodynamic behavior of the drug appears complex, interdependent and of critical importance whereas the treatment of special population cohorts is considered. The diversity of the available formulation strategies and their compatible administration routes, extend from tablets to bolus suspensions and from per os to intravenous, respectively, inheriting the associated strengths and weaknesses. In this comprehensive review, we attempt to elucidate the multi-disciplinary elements spanning the knowledge fields of chemical synthesis, physicochemical properties, pharmacology, clinical applications, biopharmaceutical profile, formulation approaches for different routes of administration and analytical strategies, currently employed to guide the development of sildenafil-based compositions.

Structural Determination, Biological Function, and Molecular Modelling Studies of Sulfoaildenafil Adulterated in Herbal Dietary Supplement.

Unapproved ingredients included in herbal medicines and dietary supplements have been detected as adulterated synthetic drugs used for erectile dysfunction. Extraction from a dietary supplement was performed to isolate the compounds by HPLC analysis. The structural characterization was confirmed using mass spectrometry (ESI-TOF/MS and LC-MS/MS), 1H NMR, and 13C NMR spectroscopy techniques. Results identified the thus-obtained compound to be sulfoaildenafil, a thioketone analogue of sildenafil. The biological activities of this active compound have been focused for the first time by the experimental point of view performance in vitro. The results revealed that sulfoaildenafil can affect the therapeutic level of nitric oxide through the upregulation of nitric oxide synthase and phosphodiesterase type 5 (PDE5) gene expressions. This bulk material, which displays structural similarity to sildenafil, was analyzed for the presence of a PDE5 inhibitor using a theoretical calculation. These unique features of the potential activity of PDE5 protein and its inhibitors, sildenafil and sulfoaildenafil, may play a key consideration for understanding the mode of actions and predicting the biological activities of PDE5 inhibitors.

Isolation and identification of an isomeric sildenafil analogue as an adulterant in an instant coffee premix

The proliferation of adulterated health foods and beverages in the market demands a comprehensive analytical strategy to identify the adulterants, particularly those of isomeric phosphodiesterase 5 (PDE5) inhibitors. An instant coffee premix (ICP) purchased from an online retailer was flagged for suspected adulteration through PDE5 inhibition assay. The ICP was then analysed using suspected-target and non-targeted screenings of a liquid chromatography-quadrupole time-of-flight mass spectrometry. Based on these findings, a PDE5 inhibitor initially assigned as compound X was isolated from the ICP by employing a liquid chromatography-diode array detection before its structural elucidation with liquid chromatography-ultraviolet (LC-UV) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The suspected-target screening matched the protonated molecule ([M + H]+) precursor ion of compound X at m/z 499.2310 with two suspected analytes that are structural isomers of one another. The fragmentation patterns of compound X were comparable to those analogues in the dithiocarbodenafil group through the non-targeted screening. These findings, complemented by the LC-UV and NMR spectroscopy data, together with the chromatographic separation of related structural isomers, conclude the identity of compound X. To our best knowledge, this is the first study to report the presence of 3,5-dimethylpiperazinyl-dithiodesmethylcarbodenafil in an ICP sample. Key points The herbal-based male sexual performance products’ lucrative market has instigated their rampant adulteration, particularly with PDE5 inhibitors. The adulterated products may also contain analogues of the approved PDE5 inhibitors, which usually passed into the market undetected as they are not included in the routine targeted screening procedure. The present study detected, isolated, and identified an isomeric sildenafil analogue from an instant coffee premix sample using rapid qualitative assay and comprehensive analytical analysis. This paper highlighted the applicability of the established strategies for routine casework, particularly in a forensic drug testing laboratory.

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.

Isolation and identification of a novel sildenafil analogue adulterated in dietary supplements

A suspected sildenafil analogue (1) was firstly detected from dietary supplements, which claimed for energy enforcement, by TLC and UV method. The UV spectrum of this suspected compound showed close similar pattern to that of acetildenafil (2, sildenafil analogue). In order to identify this compound, separation and purification were carried out as well as structure determination was conducted by various NMR techniques, mass spectrum and IR. This new compound 1 had an acetyl group instead of sulfonyl-N-methylpiperazine moiety in sildenafil (3), and its structure was determined as 5-[2-ethoxy-5-acetyl-phenyl]-1-methyl-3-n-propyl-1, 6-dihydro-7H-pyrazolo [4, 3-d] pyrimidin-7-one (molecular formula C19H22N4O3, molecular weight 354). So far no related report and literature to describe its pharmacological action and to provide related safety evaluation of this compound was published. The above results revealed that this compound was illegally adulterated into the dietary supplements, and has thus been included in our routine analysis list for public health.

Identification of a sildenafil analogue adulterated in two herbal food supplements

Consumption of herbal supplements becomes more and more popular in the world. For the sake of public health, enhanced supervision on those products is needed. A novel sildenafil analogue is detected from two herbal dietary supplements in our laboratory. Its structure has been identified by various NMR techniques, mass spectrum, IR and X-ray diffraction. This compound is slightly different from sildenafil (Viagra) in the piperazine moiety, where N-methyl group in sildenafil is replaced by N-hydroxy-ethyl group. Thereby this compound is named as hydroxyhomosildenafil. Noticeably, this compound has not been approved as medication. Therefore, it is necessary to monitor diverse analogues besides the commercial chemical compounds.

Isolation and identification of a new sildenafil analogue, hydroxycarbodenafil, found as an adulterant in a health supplement

During routine screening of illegal adulterants in health supplements, a novel sildenafil analogue was discovered, and subsequently isolated by recrystallization. Its structure was elucidated by extensive analyses of high resolution mass spectrometry (HRMS), one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) data. The analogue was finally determined as hydroxycarbodenafil, featuring a hydroxyethyl group instead of an ethyl group on piperazine ring in comparison with carbodenafil.

Use of near infrared spectroscopy and spectral databases to assess the quality of pharmaceutical products and aid characterization of unknown components

This research was initiated as part of the fight against public health problems of rising counterfeit, substandard and poor quality medicines and herbal products. An effective screening strategy using a two-step combination approach of an incremental near infrared spectral database (step 1) followed by principal component analysis (step 2) was developed to overcome the limitations of current procedures for the identification of medicines by near infrared spectroscopy which rely on the direct comparison of the unknown spectra to spectra of reference samples or products. The near infrared spectral database consisted of almost 4000 spectra from different types of medicines acquired and stored in the database throughout the study. The spectra of the test samples (pharmaceutical and herbal formulations) were initially compared to the reference spectra of common medicines from the database using a correlation algorithm. Complementary similarity assessment of the spectra was conducted based on the observation of the principal component analysis score plot. The validation of the approach was achieved by the analysis of known counterfeit Viagra samples, as the spectra did not fully match with the spectra of samples from reliable sources and did not cluster together in the principal component analysis score plot. Pre-screening analysis of an herbal formulation (Pronoton) showed similarity with a product containing sildenafil citrate in the database. This finding supported by principal component analysis has indicated that the product was adulterated. The identification of a sildenafil analogue, hydroxythiohomosildenafil, was achieved by mass spectrometry and Nuclear Magnetic Resonance (NMR) analyses. This approach proved to be a suitable technique for quick, simple and cost-effective pre-screening of products for guiding the analysis of pharmaceutical and herbal formulations in the quest for the identification of potential adulterants.

Inhibition of PDE5 attenuates streptozotocin-induced neuroinflammation and tau hyperphosphorylation in a streptozotocin-treated rat model

Intracerebroventricular (icv) streptozotocin (STZ) injection decreases cerebral insulin signal pathway function and produces multiple effects that resemble the molecular, pathological, and behavioural features of Sporadic Alzheimer’s disease (SAD). We previously reported that yonkenafil (yonk), the analogue of sildenafil and a novel PDE5 inhibitor exerts an anti-amyloidogenesis effect by regulating the Aβ level and inhibiting the expression of β-amyloid precursor protein in the APP/PS1 transgenic mice model. In this study, the effects of yonk on cognitive behaviors as well as the pathological features in streptozotocin-induced SAD rat model were investigated. The results demonstrated that administration of yonk at doses of 3 and 10 mg/kg for three weeks significantly improved cognitive deficits, attenuated STZ-induced neuronal death, inhibited the over-activation of microglia and astrocytes and the levels of pro-inflammatory markers, as well as decreased PDE5 protein expression in the hippocampus. Furthermore, yonk (3 mg/kg) notably prevented changes in tau hyperphosphorylation, decreased IRS-1and JNK phosphorylation and increased the GSK3β (ser9) phosphorylation induced by STZ. In summary, these data suggested that yonk significantly reversed STZ-induced memory deficits by inhibiting the over-activation of microglia and astrocytes, as well as ameliorated the levels of pro-inflammatory makers and tau hyperphosphorylation through regulating GSK3β signalling pathway.

Characterization of a new illicit phosphodiesterase-type-5 inhibitor identified in the softgel shell of a dietary supplement

A new sildenafil analog has been identified in the softgel shell of a dietary supplement. The compound was investigated by UV spectroscopy and high-resolution MS analysis, leading to the proposed structure 1-methyl-5-{5-[2-(4-methylpiperazin-1-yl)acetyl]-2-propoxyphenyl}-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one. A synthetic reference compound with the proposed structure was prepared, and the two sets of analytical data were compared, confirming the structure of the new compound. The compound was named propoxyphenyl noracetildenafil from its structure and similarity with the known compound.

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

A new sildenafil analogue was detected during routine screening of dietary supplements suspected to be adulterated with an erectile dysfunction drug(s) using HPLC-DAD. The UV spectrum of this compound was highly similar to that of sildenafil and almost identical to that of desmethylpiperazinyl sildenafil. The analogue was purified by using semi-preparative HPLC and structurally elucidated by performing mass spectrometric and NMR spectroscopic experiments. The spectral data revealed that this sildenafil analogue bears an n-propoxy group instead of an ethoxy group and possesses no methylpiperazinyl moiety. The isolated compound, structure of which was further confirmed by spectral comparison with synthetic one, was thus named as desmethylpiperazinyl propoxysildenafil.

New metabolites of hongdenafil, homosildenafil and hydroxyhomosildenafil

Recently, illegal sildenafil analogues have emerged, causing serious social issues. In spite of the importance of sildenafil analogues, their metabolic profiles or clinical effects have not been reported yet. In this study, new metabolites of illegal sildenafil analogues such as hongdenafil, homosildenafil, and hydroxyhomosildenafil were determined using liquid chromatography quadrupole-time of flight mass spectrometry (LC-Q-TOF-MS) and tandem mass spectrometry (LC-Q-TOF-MS/MS). To prepare metabolic samples, in vitro and in vivo studies were performed. For in vivo metabolites analysis, urine and feces samples of rats treated with sildenafil analogues were analyzed. For in vitro metabolites analysis, human liver microsomes incubated with sildenafil analogues were extracted and analyzed. All metabolites were characterized by LC-Q-TOF-MS and LC-Q-TOF-MS/MS. As a result, five, six, and seven metabolites were determined in hongdenafil, homosildenafil, and hydroxyhomosildenafil treated samples, respectively. These results could be applied to forensic science and other analytical fields. Moreover, these newly identified metabolites could be used as fundamental data to determine the side effect and toxicity of illegal sildenafil analogues.

Identification and structural elucidation of a new sildenafil analogue, dithiopropylcarbodenafil, from a premixed powder intended as a dietary supplement.

A new sildenafil analogue was detected during the monitoring of a premixed powder intended as a dietary supplement. The ultraviolet (UV) spectrum of the unknown compound was similar to that of dithiodesmethylcarbodenafil and dithiodesethylcarbodenafil, although their corresponding HPLC peaks were observed at different retention times. The chemical structure of the unknown compound was characterized by liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-TOF/MS), followed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The comparison of its structure with that of dithiodesmethylcarbodenafil, revealed that the N-methyl group on the piperazine ring is replaced by a propyl group. This new sildenafil analogue was identified as 5-(2-ethoxy-5-(4-propylpiperazine-1-carbonothioyl)phenyl)-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidine-7-thione and designated as a dithiopropylcarbodenafil. To the best of our knowledge, this is the first study reporting the identification and characterization of dithiopropylcarbodenafil.

Palladium-Catalyzed 2,2,2-Trifluoroethoxylation of Aromatic and Heteroaromatic Chlorides Utilizing Borate Salt and the Synthesis of a Trifluoro Analogue of Sildenafil.

A simple and convenient method was developed for the introduction of a 2,2,2-trifluoroethoxy group to various aromatic and heteroaromatic systems. The novel process utilizes aromatic chlorides as substrates, and tetrakis(2,2,2-trifluoroethoxy) borate salt as an inexpensive and readily available fluoroalkoxy source in a palladium-catalyzed cross-coupling reaction. The power of the developed methodology was demonstrated in the synthesis of a fluorous derivative of Sildenafil.