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Poloxamer 188, a commonly used emulsifying and solubilizing agent, was found to be the cause of crystallization of an investigational drug, AMG 579, from its amorphous solid dispersion at accelerated storage conditions. Investigation of this physical stability issue included thorough characterization of poloxamer 188 at non-ambient conditions. At 40°C, poloxamer 188 becomes deliquescent above relative humidity of 75%. Upon returning to ambient conditions, the deliquescent poloxamer 188 loses water and re-solidifies. The reversible phase transformation of poloxamer 188 may cause physical and chemical stability issues and this risk should be assessed when selecting it as an excipient for formulation development., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In the past decade, surface plasmon resonance (SPR) biosensor-based technology has been exploited more and more to characterize the interaction between drug targets and small-molecule modulators. Here, we report the successful application of SPR methodology for the analysis of small-molecule binding to two therapeutically relevant cAMP phosphodiesterases (PDEs), Trypanosoma brucei PDEB1 which is implicated in African sleeping sickness and human PDE4D which is implicated in a plethora of disease conditions including inflammatory pulmonary disorders such as asthma, chronic obstructive pulmonary disease and central nervous system (CNS) disorders. A protocol combining the use of directed capture using His-tagged PDE_CDs with covalent attachment to the SPR surface was developed. This methodology allows the determination of the binding kinetics of small-molecule PDE inhibitors and also allows testing their specificity for the two PDEs. The SPR-based assay could serve as a technology platform for the development of highly specific and high-affinity PDE inhibitors, accelerating drug discovery processes., (Copyright © 2016 Elsevier Inc. All rights reserved.)

A valid, sensitive and rapid spectrofluorimetric method has been developed and validated for determination of both tadalafil (TAD) and vardenafil (VAR) either in their pure form, in their tablet dosage forms or spiked in human plasma. This method is based on measurement of the native fluorescence of both drugs in acetonitrile at λem 330 and 470 nm after excitation at 280 and 275 nm for tadalafil and vardenafil, respectively. Linear relationships were obtained over the concentration range 4-40 and 10-250 ng/mL with a minimum detection of 1 and 3 ng/mL for tadalafil and vardenafil, respectively. Various experimental parameters affecting the fluorescence intensity were carefully studied and optimized. The developed method was applied successfully for the determination of tadalafil and vardenafil in bulk drugs and tablet dosage forms. Moreover, the high sensitivity of the proposed method permitted their determination in spiked human plasma. The developed method was validated in terms of specificity, linearity, lower limit of quantification (LOQ), lower limit of detection (LOD), precision and accuracy. The mean recoveries of the analytes in pharmaceutical preparations were in agreement with those obtained from the comparison methods, as revealed by statistical analysis of the obtained results using Student's t-test and the variance ratio F-test., (Copyright © 2015 John Wiley & Sons, Ltd.)

Fragment-based drug design (FBDD) relies on direct elaboration of fragment hits and typically requires high resolution structural information to guide optimization. In fragment-assisted drug discovery (FADD), fragments provide information to guide selection and design but do not serve as starting points for elaboration. We describe FADD and high-throughput screening (HTS) campaign strategies conducted in parallel against PDE10A where fragment hit co-crystallography was not available. The fragment screen led to prioritized fragment hits (IC50's ∼500μM), which were used to generate a hypothetical core scaffold. Application of this scaffold as a filter to HTS output afforded a 4μM hit, which, after preparation of a small number of analogs, was elaborated into a 16nM lead. This approach highlights the strength of FADD, as fragment methods were applied despite the absence of co-crystallographical information to efficiently identify a lead compound for further optimization., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Extended release (ER) of water-soluble drugs from hydroxypropylmethylcellulose (HPMC) matrix mini-tablets (mini-matrices) is difficult to achieve due to the large surface area to volume ratio of the mini matrices. Therefore, the aims of this study were to control the release of a water-soluble drug (theophylline) from mini-matrices by applying ER ethylcellulose film coating (Surelease®), and to assess the effects of Surelease®:pore former (Opadry®) ratio and coating load on release rates. Mini-matrices containing 40%w/w HPMC K100M CR were coated with 100:0, 85:15, 80:20, 75:25 or 70:30 Surelease®:Opadry® to different coating weight gains (6-20%). Non-matrix mini-tablets were also produced and coated with 80:20 Surelease®:Opadry® to different coating weight gains. At low coating weight gains, nonmatrix mini-tablets released the entire drug within 0.5 h, while at high coating weight gains only a very small amount (<5%) of drug was released after 12 h. The gel formation of HPMC prevented disintegration of mini-matrices at low coating weight gains but contributed to rupture of the film even at high coating weight gains. As a result, drug release from mini-matrices was slower than that from nonmatrix mini-tablets at low coating weight gains, yet faster at high coating weight gains. An increase in the lag time of drug release from mini-matrices was observed as the concentration of Opadry® reduced or the coating weight gain increased. This study has demonstrated the possibility of extending the release of a water-soluble drug from HPMC mini-matrices by applying ER film coating with appropriate levels of pore former and coating weight gains to tailor the release rate.

Phosphodiesterase 4 (PDE4), is a hydrolytic enzyme, is proposed as a promising target in asthma and chronic obstructive pulmonary disease. PDE4B selective inhibitors are desirable to reduce the dose limiting adverse effect associated with non-selective PDE4B inhibitors. To achieve this goal, ligand based pharmacophore modeling and molecular docking approach is employed. Pharmacophore hypotheses for PDE4B and PDE4D are generated using HypoGen algorithm. The best PDE4B pharmacophore hypothesis (Hypo1&#95;PDE4B) consist of one hydrogen-bond acceptor and two ring aromatic features, whereas PDE4D pharmacophore hypothesis (Hypo1&#95;PDE4D) consist of one hydrogen-bond acceptor, one hydrophobic aliphatic, and two ring aromatic features. The validated pharmacophore hypotheses are used in virtual screening to identify selective PDE4B inhibitors. The hits were screened for their estimated activity, FitValue, and quantitative estimation of drug likeness. After molecular docking analysis, ten hits were purchased for in vitro analysis. Out of these, six hits have shown potent and selective inhibitory activity against PDE4B with IC50 values ranging from 2 to 378nM., (Copyright © 2015 Elsevier Inc. All rights reserved.)

CTP-499 is a novel oral multi-subtype selective inhibitor of PDEs that is currently in clinical testing, in combination with angiotensin modulators, as a potentially first-in-class treatment for diabetic kidney disease. The compound was discovered and developed by using Concert's proprietary DCE Platform(®) in which deuterium was incorporated at select positions of 1-((S)-5-hydroxyhexyl)-3,7-dimethylxanthine (HDX). CTP-499 metabolizes to five major metabolites: C-21256, D-M2, D-M3, D-M4 and M5, of which all contains deuterium except M5. During in vivo metabolism, however, H/D exchange takes place. As a result, each analyte, except M5, has multiple molecular masses. To accurately quantify the analytes, we developed an LC-MS/MS method focusing on the core structures of the molecules, termed "core-structure analyses". The core-structure analyses method was then validated under GLP guidance in dog, rat and rabbit plasma, with a sample volume of 50 μL. Results demonstrated that this approach accurately quantifies each of the six analytes despite partial exchange of deuterium with hydrogen atoms in the in vivo samples. The validation parameters included accuracy, precision, sensitivity, stability, dilution integrity, hemolysis, matrix effect, selectivity, and recovery. Acceptable intra-run and inter-run assay precision (%CV ≤ 5.5%) and accuracy (90.1-106.7%) were achieved over a linear range of 10-5,000 ng/mL of each analyte. Various stability tests, including bench-top, freeze/thaw, stock solution, and long-term storage, were also performed. All stability results met acceptance criteria. The robustness of the methods was demonstrated by the incurred sample reproducibility (ISR) tests. After validation, the method was successfully used in support of multiple toxicological studies of CTP-499., (Copyright © 2014 Elsevier B.V. All rights reserved.)

An analytical procedure for selective extraction of sildenafil and vardenafil in herbal dietary supplements (HDSs) has been set up by using the magnetic molecularly imprinted polymers (MMIPs) as the extraction and clean-up materials, followed by high performance liquid chromatography-ultraviolet (HPLC-UV). The MMIPs were prepared by a surface molecular imprinting technique, using Fe(3)O(4) magnetite as a magnetically susceptible component, sildenafil as template molecule, 2-(trifluoromethyl) acrylic acid (TFMAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as polymeric matrix components. The MMIPs were characterized by transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. The heterogeneity of the MMIPs was modeled with the Freundlich isotherm equation. The resulting MMIPs had high recognition ability and fast binding kinetics for sildenafil. The MMIPs were used as dispersive solid-phase extraction (DSPE) materials to selectively extract sildenafil and vardenafil from HDSs, the contents of sildenafil and vardenafil were found to be 8.05 and 3.86 μg g(-1), respectively, and the average recoveries in spiked HDSs were 70.91-91.75% with a relative standard deviation (R.S.D.) below 7%. The MMIPs were successfully used to selectively enrich and determine sildenafil and vardenafil from HDSs., (Copyright © 2011 Elsevier B.V. All rights reserved.)

During this study, Fourier transform infrared spectroscopy (FT-IR), near infrared spectroscopy (NIR) and Raman spectroscopy were applied to 55 samples of counterfeit and imitations of Viagra and 39 samples of counterfeit and imitations of Cialis. The aim of the study was to investigate which of these techniques and associations of them were the best for discriminating genuine from counterfeit and imitation samples. Only the regions between 1800-400 cm(-1) and 7000-4000 cm(-1) were used for FT-IR and NIR spectroscopy respectively. Partial least square analysis has been used to allow the detection of counterfeit and imitation tablets. It is shown that for the Viagra samples, the best results were provided by a combination of FT-IR and NIR spectroscopy. On the other hand, the best results for the Cialis samples were provided by the combination of NIR and Raman spectroscopy (1400-1190 cm(-1)). These techniques not only permitted a clear discrimination between genuine and counterfeit or imitation samples but also the distinction of clusters among illegal samples. This might be interesting for forensic investigations by authorities., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

Ayurvedic/herbal healthcare products are considered safe under the impression that they are derived from natural products. But recently, there have been several reports worldwide on the adulteration of synthetic PDE-5 inhibitors in aphrodisiac herbal formulations. Therefore, the objective of the present study was to explore the presence of synthetic PDE-5 inhibitors (sildenafil, tadalafil and/or vardenafil) in ayurvedic/herbal healthcare products sold in Indian market for aphrodisiac/related uses. In total, 85 herbal formulations (HFs) were included in the study. The formulations were extracted with methanol and subjected to centrifugation. The supernatant was analysed by HPLC and LC-MS/TOF. Early detection of the presence of sildenafil, tadalafil and vardenafil in the herbal samples was done by the study of extracted ion mass chromatograms at the m/z values of respective parent ions, and two prominent fragments of each. In case of sildenafil and tadalafil, adulteration was also detected by comparing the relative retention times (RR(T)) and UV spectra. Further substantiation was done through comparison of accurate mass spectra with those of the two available standards. Of the 85 HFs tested, only one was eventually found to be adulterated with sildenafil. The extent of adulterant in this sample was determined to the therapeutic dose in the formulation. The study thus indicates emergence of the problem of adulteration of Indian herbal products with PDE-5 inhibitors., (Copyright 2009 Elsevier B.V. All rights reserved.)

A simple and sensitive method was developed for determination of illegal adulterants (yohimbine, sildenafil, vardenafil and tadalafil) in dietary supplements by HPLC-MS/MS. The separation was achieved on a C(18) column with the mobile phase consisting of acetonitrile and 0.1% acetic acid aqueous solution with a gradient elution at a flow rate of 0.5 mL/min. The analytes were quantified and identified by two characteristic transitions using the multiple-reaction monitoring mode. The recoveries of the analytes ranged from 77.5 to 109.3% with the RSD less than 8.1% (n=6). The method has been successfully applied to screen illegal adulterations of natural dietary supplements.

Studies of the phosphodiesterase PDE7 family are impeded by there being only one commercially available PDE7 inhibitor, BRL50481. The authors have employed a high-throughput screen of commercial chemical libraries, using a fission yeast-based assay, to identify PDE7 inhibitors that include steroids, podocarpanes, and an unusual heterocyclic compound, BC30. In vitro enzyme assays measuring the potency of BC30 and 2 podocarpanes, in comparison with BRL50481, produce data consistent with those from yeast-based assays. In other enzyme assays, BC30 stimulates the PDE4D catalytic domain but not full-length PDE4D2, suggesting an allosteric site of action. BC30 significantly enhances the anti-inflammatory effect of the PDE4 inhibitor rolipram as measured by release of tumor necrosis factor alpha from activated monocytes. These studies introduce several new PDE7 inhibitors that may be excellent candidates for medicinal chemistry because of the requirements for drug-like characteristics placed on them by the nature of the yeast-based screen.

This work describes the development and applicability of two functional assays for the detection of yessotoxin (YTX), a polycyclic ether marine toxin produced by dinoflagellates. The assays are based on the interaction between this toxin and the phosphodiesterase (PDE) enzyme and the subsequent measurement of the enzyme activity by colorimetric and electrochemical methods. Firstly, several enzyme substrates were tested in order to select those able to be detected by colorimetry or electrochemistry after enzymatic hydrolysis. The substrates that provided the highest absorbance values and density currents were p-nitrophenyl phenylphosphonate and alpha-naphthyl phosphate, respectively. After optimisation of the experimental parameters, limits of detection of 0.8 and 0.6 microM were attained by colorimetry and electrochemistry, respectively. An inhibitory effect of YTX on the PDE activity was observed. The assays have been applied to the analysis of YTX production by Protoceratium reticulatum cultures, and results were compared with liquid chromatography-tandem mass spectrometry analysis.

Vardenafil is a phosphodiesterase-5 (PDE-5) inhibitor for the treatment of erectile dysfunction (ED). Undeclared vardenafil and related analogues adulterated in herbal products are a threat to public health. To screen vardenafil and its analogues in herbal matrix rapidly, an immunoassay based on a group specific monoclonal antibody (McAb) was developed. Glutaraldehyde was used to link vardenafil to immunogen and coating-antigen, respectively. Through the assessment of the structural specificity of eight anti-vardenafil McAbs, the McAb of 4B9 was characterized as being specific to the common structure of vardenafil and its analogues. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was established based on this McAb, the limit of detection of vardenafil was 5.0 ng mL(-1), the calibration curve was linear from 5.0 to 40 ng mL(-1) (R(2)=0.952) with an IC(50) value of 18.2 ng mL(-1). In the extracts of 20 Chinese traditional drugs, the detection capability (CCbeta) of vardenafil was 0.08 mg g(-1), the recoveries were 76-116% and the coefficients of variation (CV%) were 9.7%-16.2%. The ic-ELISA was in good agreement with LC-UV when detected herbal products containing vardenafil and its analogue. The method is a suitable tool for screening vardenafil and its analogues as illegal additives in herbal products., (Copyright 2009 Elsevier B.V. All rights reserved.)

Counterfeit drugs, medical devises and dietary supplements are inherently dangerous and a growing problem. In Europe the growth of the counterfeit medication market is attributable in part to registration of phosphodiesterase type 5 inhibitors (PDE-5) used for the erectile dysfunction. "Viagra, Levitra and Cialis belong to this group. It has been estimated that up to 2.5 million men in Europe are exposed to an illicit sildenafil, suggesting that there may be as many illegal as legal users of sildenafil. In Europe a strong trend is observed towards increasingly professional counterfeits and imitations of Viagra, Cialis and Levitra, with regard to the appearance of tablets, capsules and packaging. The professional presentation will deceive potential consumers into assuming these products are legal, efficacious and safe. Globally, increased obstacles for counterfeiters are necessary to combat pharmaceutical counterfeiting, including fines and penalties. The worldwide nature of the counterfeit problem requires proper coordination between countries to ensure an adequate enforcement. We described the usefulness of the time-of-flight mass spectrometry with the electrospray ionization (LC-ESI-MS-TOF) and the X-ray powder diffraction method (XRPD) for PDE-5 counterfeit screening from the Polish illegal market.

A simple high-performance liquid chromatography (HPLC) method with ultraviolet diode array (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) detection has been developed for the determination of vardenafil, sildenafil, tadalafil, testosterone, procaine, lidocaine, prilocaine, and benzocaine in cosmetic creams sold as promising remedies for male erectile dysfunction and female genitals stimulation. The presence of these substances in commercial cosmetic samples is prohibited. Aliquots (1 g) of the cosmetic creams under investigation were diluted 1:100 in methanol, subjected to ultrasonic treatment, added with benzoic acid as internal standard, and analyzed by HPLC-DAD and HPLC-ESI-MS after a further 1:1000 dilution. The compounds were separated by reversed phase chromatography with water (0.02% trifluoroacetic acid) and acetonitrile gradient elution and detected by UV-DAD at 228, 255 and 290 nm and by ESI-MS positive ionisation mode. Benzoic acid was used as internal standard. Linearity was studied with UV-DAD detection from 2.5-7.8 to 250 microg/g range, depending on the different compounds and with ESI-MS in the 3.3-8.9 to 250 ng/g range. Good determination coefficients (r(2) > or = 0.99) were found in both UV-DAD and ESI-MS. Limits of quantifications ranged between 2.5 and 7.8 microg/g for HPLC-UV-DAD assay and between 3.3 and 8.9 ng/g for HPLC-ESI-MS assay depending on different analyzed substances. At three concentrations spanning the linear dynamic ranges of both UV-DAD and ESI-MS assay, mean recoveries were always higher than 90% for the different analytes and intra-assay and inter-assay precision always better than 15% and 12%. This method was successfully applied to the analysis of substances under investigations present in cosmetic creams, freely sold on the Internet web-sites.

An unknown compound is detected and isolated from two herbal dietary supplements bought on the internet. The structure of the unknown compound is elucidated using ESI-MS/MS, NMR, UV and IR. The compound, named hydroxythiohomosildenafil, is identified as an analogue of sildenafil in which the oxygen atom is substituted with a sulfur atom in the pyrazolopyrimidine moiety, and a hydroxyethyl group instead of a methyl group is attached to the piperazinyl nitrogen. It is the first report of this compound being detected in herbal dietary supplements. The UV, IR and completely assigned NMR data of hydroxythiohomosildenafil is recorded.

A new sildenafil analogue, cyclopentynafil (1) and a new tadalafil analogue, N-octylnortadalafil (2) were isolated from a dietary supplement illegally marketed for erectile dysfunction. The structures of the sildenafil and tadalafil analogues were elucidated by using HPLC-photodiode array (PDA), LC-MS, high-resolution MS, NMR and circular dichroism (CD). These compounds were determined to be 5-[2-ethoxy-5-(4-cyclopentylpiperazin-1-ylsulfonyl)phenyl]-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one and (6R,12aR)-2-octyl-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, respectively. Recently, a large number of phosphodiesterase-5 (PDE-5) inhibitors, including their analogues, have been isolated from dietary supplements, while cyclopentynafil and N-octylnortadalafil are the first compounds reported to be new sildenafil and tadalafil analogues, respectively. Quantitative HPLC analysis showed that the contents of 1 and 2 in the product were about 130 mg/tablet (301 microg/mg) and about 27 mg/tablet (64.1 microg/mg), respectively.

Tyrosyl-DNA phosphodiesterase I (Tdp1) resolves topoisomerase I (Top1)-DNA adducts accumulated from natural DNA damage as well as from the action of certain anticancer drugs. Tdp1 catalyzes the hydrolysis of the phosphodiester bond between the catalytic tyrosine residue of topoisomerase I and the DNA 3'-phosphate. Only a limited number of weak inhibitors have been reported for Tdp1, and there is an unmet need to identify novel chemotypes through screening of chemical libraries. Herein, we present an easily configured, highly miniaturized, and robust Tdp1 assay using the AlphaScreen technology. Uninhibited enzyme reaction is associated with low signal, whereas inhibition leads to a gain of signal, making the present assay format especially attractive for automated large-collection high-throughput screening. We report the identification and initial characterization of four previously unreported inhibitors of Tdp1. Among them, suramin, NF449, and methyl-3,4-dephostatin are phosphotyrosine mimetics that may act as Tdp1 substrate decoys. We also report a novel biochemical assay using the SCAN1 Tdp1 mutant to study the mechanism of action of methyl-3,4-dephostatin.

A new type of phosphodiesterase-5 (PDE-5) inhibitor, thioquinapiperifil (1), was found in dietary supplements. LC-MS analysis indicated that the supplements contain two major compounds. One was identified as thiodenafil (synonym: thiosildenafil) by direct comparison with the authentic compound. The other showed a molecular weight of 448, and accurate mass measurement showed its elemental composition to be C(24)H(28)N(6)O(1)S(1). Together, the mass and NMR spectrometric data revealed that the compound is an imidazoquinazoline derivative: 3-ethyl-1,3-dihydro-8-[[[2-[4-(hydroxymethyl)-1-piperidinyl]phenyl]methyl]amino]-2H-imidazo[4,5-g]quinazoline-2-thione. This compound had been synthesized as a PDE-5 inhibitor, formerly reported as KF31327 by Kyowa Hakko Kogyo Co., Ltd. Considering this compound's general properties, it has been renamed thioquinapiperifil with the agreement of Kyowa Hakko Kogyo Co., Ltd. The detection of imidazoquinazoline-type compounds in dietary supplements has not been reported. Quantitative analysis showed that the contents of 1 and thiodenafil in the products were about 13-15 mg/tablet (43-48 microg/mg) and about 0.4 mg/tablet (1 microg/mg), respectively.

A tadalafil analogue was detected in a dietary supplement marketed for tonic effect, along with hydroxyhomosildenafil and aminotadalafil. The tadalafil analogue was isolated by preparative thin layer chromatography (TLC) and its structure was elucidated using high-performance liquid chromatography (HPLC), liquid chromatography electrospray ionization-mass spectrometry (LC-ESI-MS), Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) and nuclear magnetic resonance (NMR) spectroscopy. The compound was determined to be methyl-1-(1,3-benzodioxol-5-yl)-2-(chloroacetyl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylate.

A sample labeled to be a natural herbal supplement for the enhancement of sexual function, was sent to Health Sciences Authority (HSA) of Singapore for testing. An unknown compound was detected and isolated from the product. The structure of the unknown compound was identified using LC-UV, high-resolution MS, ESI-MS/MS, IR, and NMR. The compound was characterized as a phosphodiesterase-5 (PDE-5) inhibitor, benzamidenafil. This is the first report of benzamidenafil, representing a new class of PDE-5 inhibitors, as an adulterant of a dietary supplement.

Two unknown compounds are detected and isolated from health supplements for the enhancement of sexual function. The structures of the unknown compounds are elucidated using high-resolution MS, ESI-MS/MS, NMR, UV and IR. One compound is identified as an analogue of sildenafil in which the oxygen atom is substituted with a sulfur atom in the pyrazolopyrimidine moiety, and an ethyl group instead of a methyl group is attached to the piperazinyl nitrogen. Hence, this compound is named thiohomosildenafil. Another compound is also a sildenafil analogue in which the oxygen atom is substituted with a sulfur atom in the pyrazolopyrimidine moiety. This compound is named thiosildenafil. Both the two compounds are first detected in health supplements. The UV, IR and completely assigned NMR data of thiohomosildenafil and thiosildenafil are first reported.

Two analogs of sildenafil and vardenafil in food were detected by column liquid chromatography (LC) with a photodiode array detector. They were isolated by preparative LC; their structures were established by mass spectrometry and nuclear magnetic resonance spectrometry. One analog was found to be methisosildenafil (compound A), 5-(5-(3,5-dimethylpiperazin-1-ylsulfonyl)-2-ethoxy-phenyl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]-pyrimidin-7(6H)-one. It is a sildenafil analog with a dimethylpiperazine ring substituted for the methylpiperazine group. The second analog, hydroxyvardenafil (compound B) is reported for the first time in this study. Hydroxyvardenafil's International Union of Pure and Applied Chemistry name is 2-(2-ethoxy-5-(4-(2-hydroxyethyl)-piperazin-1-ylsulfonyl)phenyl)-5-methyl-7-propyl-imidazo[1,5-f][1,2,4]triazin-4(3H)-one. The novel vardenafil analog has a hydroxyl group added to the ethylpiperazine group.

A new herbal health product marketed for enhancing erectile function, namely Power58 Platinum, was purchased over-the-counter in Hong Kong. The product was tested for adulteration with sildenafil, tadalafil, and vardenafil as well as their structurally modified analogues. A new analogue of vardenafil, in which the N-ethylpiperazine ring and the sulphonyl group were removed from the vardenafil structure, was identified in the product.

We describe here the first case of the finding of xanthoanthrafil, a phosphodiesterase-5 inhibitor, in a dietary supplement. A methanol extract of the supplement product was first analyzed by TLC and HPLC. The results indicated that the extract contained an unknown compound. The molecular weight of the compound was 389 and the accurate mass showed its elemental composition to be C(19)H(23)N(3)O(6). Combined with this data, NMR analysis revealed the planar structure of the unknown compound to be N-(3,4-dimethoxybenzyl)-2-(1-hydroxypropan-2-ylamino)-5-nitrobenzamide. The R-configuration of this compound had been synthesized as a phosphodiesterase-5 inhibitor, formerly reported as FR226807 by Fujisawa Pharmaceutical Co., Ltd. The absolute configuration of the isolated compound was estimated to have R-configuration by its optical rotation. Considering its general properties, this compound is renamed as (R)-xanthoanthrafil with the agreement of Astellas Pharma Inc. which is the successor of Fujisawa Pharmaceutical Co., Ltd. Quantitative analysis revealed that the content of (R)-xanthoanthrafil in the product was about 31 mg/capsule.

The cDNA encoding PDE10A (phosphodiesterase 10A) was cloned and a stable recombinant HEK-293 (human embryonic kidney-293) cell line expressing high levels of PDE10A was generated. Transient transfection of pCRE-Luc plasmid, harbouring the luciferase reporter gene under the control of CRE (cAMP-response element)-binding sequence, into the stable recombinant cell line, followed by treatment with PDE10 inhibitor, resulted in a dose-dependent increase in luciferase activity. This method provides a simple and sensitive cell-based assay for screening of PDE10 inhibitors for development of novel therapeutics for the treatment of neurological disorders.

Sensitive and selective stability-indicating assay methods (SIAMs) are suggested for the determination of cilostazol (CIL) in the presence of its acid, alkaline and oxidative degradation products. Developing SIAMs is necessary to carry out any stability study. Stress testing of CIL was performed according to the International Conference on Harmonization (ICH) guidelines in order to validate the stability-indicating power of the analytical procedures. Stress testing showed that CIL underwent acid, alkaline and oxidative degradation; on the other hand, it showed stability towards photo- and thermal degradation. Two chromatographic SIAMs were developed, namely HPLC and HPTLC methods. The concentration range and the mean percentage recovery were 1.0-31.0 microg/ml and 99.96+/-0.46 and 0.6-14.0 microg/spot and 99.88+/-1.10 for HPLC and HPTLC methods, respectively. In addition, derivative spectrophotometric methods were developed in order to determine CIL in the presence of its acid degradation product; these were performed by using the third derivative spectra (3D) and the first derivative of the ratio spectra (1DD) methods. The linearity range and the mean percentage recovery were 2.0-34.0 microg/ml and 100.27+/-1.20 for the (3D) method, while they were 2.0-30.0 microg/ml and 99.94+/-1.18 for the (1DD) method. Also, two chemometric-assisted spectrophotometric methods, based on using partial least squares (PLS) and concentration residual augmented classical least squares method (CRACLS), for the determination of CIL were developed. Both methods were applied on zero order spectra of the mixtures of CIL and its acid degradation product, the mean percentage recovery was 100.03+/-1.09 and 99.91+/-1.27 for PLS and CRACLS, respectively. All methods were validated according to the International Conference on Harmonization (ICH) guidelines and applied on bulk powder and pharmaceutical formulations.

A high-performance liquid chromatographic method was developed for the chiral separation of a new selective phosphodiesterase 5 inhibitors, tadalafil and its three isomers. The chiral separation was performed on a Chiralpak AD column. The mobile phase was hexane-isopropyl alcohol (1:1, v/v). UV detection was at 220 nm. Baseline chiral separation for the four isomers was obtained within 30 min. Each of the resolutions of the two pairs enantiomers were more than 2.0. The limits of quantitation were 0.60, 0.90, 1.20, and 1.80 ng for (6R, 12aS), (6R, 12aR), (6S, 12aS), and (6S, 12aR) isomers, respectively. Relative standard deviation of the method was below 2% (n=5). The method is suitable in quality control.

Counterfeit and illegally manufactured drugs become a very important problem all over the world, hence, a search for new fast, easy, reliable and not expensive methods of drugs screening is essential. We describe the use of X-ray powder diffraction method for the fast screening of tablets for counterfeit medicines identification. The original Viagra tablets and some counterfeit and/or imitations of Viagra were used as example. We demonstrate the application of diffraction method for discrimination of tablets coatings and for identification of differences in drug composition. The X-ray diffraction method turns out to be very fast and reliable for detecting counterfeits and imitation, and it correctly predicts the presence or absence of active substance and/or particular excipients.

SK3530.2HCl, (2-(5-(4-(2-hydroxyethyl)piperazin-1-ylsulfonyl)-2-n-propoxyphenyl)-5-ethyl-7-n-propyl-3,5-dihydro-4H-pyrrolo[3,2-d]pyrimidin-4-one dihydrochloride), is a novel a new phosphodiesterase type V (PDE V) inhibiting agents. The pharmaceutical development of SK3530 necessitated the availability of an assay for the quantification and purity determination of SK3530 active pharmaceutical ingredient (API) and its pharmaceutical dosage form. A reversed-phase high performance liquid chromatographic (HPLC) method with ultraviolet (UV) detection was developed, consisting of separation on a C18 column with a CapcellPack MG (4.6 mm x 150 mm, 5 microm) column with ammonium acetate buffer (pH 4.0, 20 mM)-acetonitrile (60:40, v/v) as the isocratic mobile phase and UV detection at 250 nm. The method has been shown good chromatographic separation for SK3530 and the other related substances. The method was found to be linear 200-300 microg/ml, precise and accurate. Stress testing showed degradation products, which were well separated from the parent compound, confirming its stability-indication capacity. Moreover, the use of LC-MS and on-line diode array detection enabled us to propose structures for degradation products.

New analogues of vardenafil and sildenafil illegally added to dietary supplements were detected by high-performance liquid chromatography (HPLC) analysis with a photodiode array detector (PDA). These compounds were isolated and their structures elucidated by mass spectrometry (MS), infrared (IR) spectroscopy, one- and two-dimensional nuclear magnetic resonance (NMR). One of the new analogues given the trivial name pseudovardenafil (compound 1) was structurally elucidated and shown to be 1-[[3-(1,4-dihydro-5-methyl-4-oxo-7-propylimidazo[5,1-f][1,2,4]triazin-2-yl)-4-ethoxyphenyl]sulfonyl]-piperidine. It was a vardenafil analogue isolated from a dietary supplement capsule. Compared with vardenafil, the piperidine ring was substituted for the ethylpiperazine group. The second new analogue, trivially named hydroxyhongdenafil (compound 2), was separated from bulk powder used as a raw material for a dietary supplement. The piperazine and phenyl groups were connected through an acetyl group instead of a sulfonyl group, and hydroxyethylpiperazine was substituted for the methylpiperazine of sildenafil. It was structurally elucidated as 5-[2-ethoxy-5-[[4-(2-hydroxyethyl)-1-piperazinyl]acetyl]phenyl]-1,4-dihydro-1-methyl-3-propyl-7H-pyrazolo[4,3-d]pyrimidin-7-one.

Sildenafil, the active ingredient in Viagra (Pfizer), is a prescription medicine used for erectile dysfunction. Compounds with chemical structures similar to that of sildenafil were isolated and purified during the analysis of some herbal products marketed for treatment of erectile dysfunction. Structural elucidation using liquid chromatography-diode array detection, infrared spectroscopy, liquid chromatography-tandem mass spectrometry, and nuclear magnetic resonance spectroscopy confirmed that the compounds were homosildenafil, hydroxyhomosildenafil, and acetildenafil. The implications of adulteration by compounds structurally related to prescription drugs are discussed. Unlike established drugs, the efficacy and safety of such analogues are largely unknown. This poses a great challenge for safety and health administrators to detect these modified structures and to regulate them. Consumers who use such adulterated products are at risk of developing serious adverse reactions, potentially leading to death. Greater collaboration and exchange of information between various health authorities, health professionals, academics, researchers, and industry, as well as public education, are key steps in the efforts to stem the growing trend of adulteration of herbal products by analogues of prescription drugs.

An herbal dietary supplement, marketed as a natural product for the enhancement of sexual function, was purchased covertly over the internet. The product was analyzed by LC-MS and found to contain a compound related to synthetic phosphodiesterase 5 (PDE-5) inhibitors. Based on LC with photodiode array and mass spectral detection, along with collision-induced dissociation-mass spectral analysis, the structure of the compound was tentatively identified as a designer drug of vardenafil in which the N-ethylpiperazine ring had been replaced by a piperidine ring. This structure was unambiguously confirmed by acid hydrolysis of both the unknown ("piperidenafil") and vardenafil and comparison of their hydrolysis products by LC-MS and GC-MS. The hydrolytic technique proved to be a useful tool for the structure elucidation of piperidenafil and may be a useful technique for the structure elucidation of other erectile dysfunction designer drugs in the future. The dosage level of piperidenafil in the herbal product was 41 mg per capsule when calculated as the free base.

Purpose: To develop a method of using isolated rat retina as a biosensor in experiments on controlled drug release for measuring the resultant concentration of free model drug in living tissue and for testing the biocompatibility of the polymers and polymeric nanostructures used as drug carriers., Methods: The method is based on the monotonic dependence of the photoresponse kinetics of retinal rods on the concentration of the membrane-permeable phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Changes in the time to peak (tp) of linear-range rod photoresponses were followed by transretinal ERG mass potential recordings in the aspartate-treated, dark-adapted rat retina. The dependence of tp on [IBMX] was measured, and the calibration curve thus obtained was used to determine the amount of IBMX released from polymeric structures. The biocompatibility of the carrier was first assessed by the degree to which rods retained stable function in the presence of the polymer or monomers alone., Results: The dependence of tp on [IBMX] was well-described by a second-order polynomial. After each change of [IBMX], a new equilibrium state was reached within 6 to 9 minutes, depending on temperature. The amounts of IBMX released from biocompatible polymeric structures were measurable with good accuracy in the range 10 to 300 microM., Conclusions: This method enables accurate concentration determinations of the model drug IBMX in retinal tissue in drug-release experiments. The concentration dependence of the photoresponse kinetics has to be calibrated for each retina and temperature. The same preparation can be used for rapid testing of possible bioincompatibility of various molecules.

Adulteration of allegedly "natural herbal medicines" with undeclared synthetic drugs is a common and dangerous phenomenon of alternative medicine. The purpose of the study was to develop a procedure for detection of most common synthetic adulterants in herbal remedies, using high-pressure liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS-MS). Eighty drugs belonging to various pharmacological classes were included in the study. For most drugs two transitions were monitored, using protonated or deprotonated molecules as precursor ions. The drugs were isolated from herbal remedies using simple methanol extraction. Chromatographic separation was done in gradient of acetonitrile-10 mM ammonium formate buffer (pH 3.0). Drugs tested were grouped in suites, comprising analgesic drugs, antibiotics, antidiabetic drugs, antiepileptic drugs, aphrodisiacs, hormones and anabolic drugs, psychotropic drugs, and weight reducing compounds. These suites were used according to the declared benefits of examined preparations. Limits of detection ranged from 5 pg to 1 ng per injected sample. Drug-free herbal remedy spiked with eight various pharmaceuticals occurring in adulterated herbal preparations was used for internal proficiency testing. The recoveries of spiked drugs ranged from 63 to 100%. The procedure was applied in everyday casework. Several undeclared drugs were identified in "herbal" remedies, like e.g. sildenafil, tadalafil, testosterone, or glibenclamide. Pharmacological properties of detected drugs always corresponded with the claims of the "natural" remedies. The method presents a valuable extension of standard GC-MS screening used for this purpose.

We describe a near-infrared spectroscopy (NIRS) method for fast-screening Viagra tablets, counterfeit Viagra tablets, and imitations of Viagra. The method can (1) check the homogeneity of a batch; (2) distinguish counterfeits and imitations from authentic Viagra; (3) screen for the presence of sildenafil citrate, the pharmacologically active substance in Viagra, irrespectively of the excipients present; (4) and detect whether similar samples have been previously analysed. We applied the method to 103 samples with a diversity of appearance, chemical composition, and origin. Other analytical methods confirmed the positive screening results for sildenafil citrate and the presence of other pharmacological active substances. The NIRS screening indicated the absence of sildenafil citrate in the presence of another pharmacological substance for only 2 samples, where the reference methods showed the presence of sildenafil citrate in addition to that of clomifene citrate. Otherwise, the method gave no false positive or negative results. The NIRS screening method is very fast and reliable for detecting counterfeits and imitations, and it correctly predicts the presence or absence of sildenafil citrate in 98% of the samples.

In recent years, dietary supplements and herbal medicines are increasing in popularity all over the world. However, it is problematic that some manufacturers illegally included synthetic drugs in their products. Due to the extremely complex matrices of those products, most existing methods for screening illegal adulterations are time-consuming and liable to false positive. In this paper, a robust LC/MS/MS method for the high-throughput, sensitive and reliable determination of illegal adulterations from herbal medicines and dietary supplements was established. Minimal LC separation was employed and MRM was used to simultaneously monitor the three transitions under their respective optimal collision energy for each compound. Positive results were determined only if well-defined peaks appeared at all of the three transitions and the ratios among the peak areas were within given threshold. In this study, the method had been applied for the screening of nine most commonly adulterated therapeutic substances, such as sildenafil (Viagra) and famotidine, and the lower limits of detection of these compounds ranged from 0.05 to 1.5 ng/ml. Little sample preparation was needed for this method and the analysis time was less than 5 min/sample. The reliability has been demonstrated by the test with blank matrix. Over 200 products that were under suspicion by SDA of China had been assayed and till now no false negative or positive result was found. This method is rapid, simple, reliable and capable of screening multiple adulterants in one run.

A high-performance liquid chromatography-diode array detection (HPLC-DAD) method and a liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method were developed to screen for the presence of synthetic phosphodiesterase-5 (PDE-5) inhibitors and their analogues, namely sildenafil, vardenafil, tadalafil, homosildenafil, acetildenafil and hydroxyhomosildenafil. The methods were applied to pre-market samples submitted to the Health Sciences Authority of Singapore (HSA) for testing. One sample was in the form of capsules while six other samples were pre-mixed bulk powder samples for dietary supplements to be repackaged or formulated into the final dosage forms (usually capsules). Identification of PDE-5 inhibitors and their analogues was achieved by comparing individual peak retention times, UV spectra and mass spectra with those of reference standards. The seven samples were found to contain at least one of the following compounds: sildenafil, vardenafil, hydroxyhomosildenafil, homosildenafil and acetildenafil. The five compounds were simultaneously determined by LC-ESI-MS/MS in multiple reactions monitoring (MRM) scan mode. The method has been validated for accuracy, precision, linearity and sensitivity.

A high performance liquid chromatography-mass spectrometry (LC-MS) analytical method for illicit drugs, apomorphine, sildenafil and alprostadil, in medicines for erectile dysfunction has been developed. The samples were extracted with methanol using ultrasound-assisted extraction. The chromatographic separation was performed on a Zorbax Eclipse XDB-C18 column using acetonitrile-0.5% formic acid aqueous solution as mobile phase. The three compounds were identified by retention time and m/z and quantified by peak area. The results demonstrated that the linear ranges were 50.0 - 5 000.0 microg/L, 10.0 - 1 000.0 microg/L, 40.0 - 4 000.0 microg/L, with detection limits of 20.0, 4.0, 10.0 microg/L for apomorphine, sildenafil and alprostadil, respectively. The average recoveries and the relative standard deviations were 89% - 95% and 9.5% - 11%. The method is simple, rapid, accurate and suitable for the simultaneous determination of these drugs in medicines for erectile dysfunction.

A high-performance liquid chromatographic method coupled with ultraviolet detection and electrospray ionization mass spectrometry (HPLC-UV-ESI-MS) was developed for simultaneous determination of banned additives-sildenafil, vardenafil and tadalafil in dietary supplements for male sexual potency. The separation was achieved on a C18 column with acetonitrile and aqueous solution (20 mmol ammonium acetate, 0.2% formic acid) as mobile phase at a flow rate of I ml/min with a linear gradient program. UV detection was at 292 nm. Identification of drugs was accomplished using ESI-MS. Good linearity between response (peak area) and concentration was found over a concentration range of 0.8-80 microg/ml for sildenafil; 2.25-225 microg/ml for vardenafil; and 1.1-110 microg/ml for tadalafil, with regression coefficient is better than 0.999. The recovery of the method ranged from 93.3 to 106.1%, and the relative standard deviation varied from 2.0 to 5.6% (n = 6). The method has been successfully applied to the analysis of practical samples of natural dietary supplements.

Cyclic nucleotide phosphodiesterases (PDEs) comprise a large family of enzymes that regulate a variety of cellular processes. We describe a family of potent PDE4 inhibitors discovered using an efficient method for scaffold-based drug design. This method involves an iterative approach starting with low-affinity screening of compounds followed by high-throughput cocrystallography to reveal the molecular basis underlying the activity of the newly identified compounds. Through detailed structural analysis of the interaction of the initially discovered pyrazole carboxylic ester scaffold with PDE4D using X-ray crystallography, we identified three sites of chemical substitution and designed small selective libraries of scaffold derivatives with modifications at these sites. A 4,000-fold increase in the potency of this PDE4 inhibitor was achieved after only two rounds of chemical synthesis and the structural analysis of seven pyrazole derivatives bound to PDE4B or PDE4D, revealing the robustness of this approach for identifying new inhibitors that can be further developed into drug candidates.

A liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) method was developed to screen for the presence of synthetic phosphodiesterase type 5 (PDE-5) inhibitors including sildenafil, tadalafil and vardenafil. The method was applied to the analysis of dietary supplements and bulk herbal materials. Bulk powders or composites of tablets, capsules or liquids were prepared and an extraction of PDE-5 inhibitors was performed using a mixture of acetonitrile and water with sonication. Identification of sildenafil, vardenafil or tadalafil was accomplished using a single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface. Positive ion detection in the full scan mode was used while in-source collision induced dissociation (CID) provided several structurally significant fragment ions to aid in the mass spectral identification. Approximately half of the 40 botanical products analyzed were found to contain undeclared synthetic PDE-5 inhibitors. For products found to contain one of these three compounds by LC-MS, HPLC with UV detection was used for quantitation.

A new system for the determination of dipyridamole with flow injection chemiluminescence was described. It is based on the chemiluminescence reaction of dipyridamole-potassium permanganate with rhodamine B. Tween-80 was found to be an enhancer of the chemiluminescence reaction. A method based on the enhanced chemiluminescence for dipyridamole determination has been developed. The method has high sensitivity, selectivity and good repeatability with a linear concentration range of 5.0 x 10(-8) - 5.0 x 10(-5) g x mL(-1), a detection limit of 1.7 x 10(-8) g x mL(-1) and a RSD of 1.1% (n = 11, cs = 1.0 x 10(-6) g x mL(-1)).