Identification of phototransformation products of sildenafil (Viagra) and its N-demethylated human metabolite under simulated sunlight

Recent publications on pharmaceutical monitoring are increasingly covering the field of illicit drugs and lately the forensic evaluation of designing illegal analogs of lifestyle drugs like the phosphodiesterase type 5 (PDE-5) inhibitors Viagra (sildenafil), Levitra (vardenafil) and Cialis (tadalafil). Recently, the presence of all three erectile dysfunction treatment drugs has been reported in wastewaters at very low concentrations. In the environment, contaminants undergo various physical or chemical processes classified into abiotic (photolysis, hydrolysis) and biotic (biodegradation) reactions. Thus, changes in the chemical structure lead to the formation of new transformation products, which may persist in the environment or be further degraded. This study describes the photolysis of sildenafil (SDF) and its human metabolite N-demethylsildenafil (DM-SDF) under simulated solar radiation (Xenon lamp). Following chromatographic separation of the irradiated samples, eight photoproducts in the SDF samples and six photoproducts for DM-SDF were detected and characterized. The combination of ultra performance liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry (UPLC-ESI-QToF-MS), liquid chromatography-atmospheric pressure chemical ionization-triple quadrupole mass spectrometry (LC-APCI-QqQ-MS) and hydrogen/deuterium-exchange experiments allowed to propose plausible chemical structures for the photoproducts, taking into account the characteristic fragmentation patterns and the accurate mass measurements. These mass spectral data provided sound evidence for the susceptibility of the piperazine ring toward photodegradation. A gradual breakdown of this heterocyclic structure gave rise to a series of products, which in part were identical for SDF and DM-SDF. The sulfonic acid, as the formal product of sulfonamide hydrolysis, was identified as key intermediate in the photolysis pathway. In both drug/metabolite molecules, phototransformation processes taking place beyond the sulfonamide group were deemed to be of minor relevance.     

Evolution of yttrium trifluoroacetate during thermal decomposition

A detailed analysis of the thermal decomposition of yttrium trifluoroacetate under different atmospheres is presented. Thermogravimetry, differential thermal analysis, and evolved gas analysis have been used for this in situ analysis. Solid residues at different stages have been characterized by means of X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The first decomposition stage (310 °C) is exothermic and involves the complete removal of carbon (organic part) and the formation of yttrium fluoride. This process is characterized by a fast mass loss rate. Afterwards, yttria (Y₂O₃) is formed at 1200 °C through a slow process controlled by the out diffusion of fluorine that involves the formation of yttrium oxyfluoride as an intermediate. The evolution of the mass during the decomposition and the structure of the yttria particles is not affected by the presence of oxygen or water. However, when the oxygen (water) partial pressure is as low as 0.02% (<0.002%), the kinetics and final particle structure are strongly affected.     

Synthesis of the HCV protease inhibitor Vaniprevir (MK-7009) using ring-closing metathesis strategy

A highly efficient synthesis of Vaniprevir (MK-7009) has been accomplished in nine linear steps and 55% overall yield. The key features of this synthesis include a cost-effective synthesis of the isoindoline subunit and efficient construction of the 20-membered macrocyclic core of Vaniprevir (MK-7009) utilizing ring-closing metathesis technology. A high-performing ring-closing metathesis protocol has been achieved by simultaneous slow addition of the ruthenium catalyst (0.2 mol %) and the diene substrate at a concentration of 0.13 M.     

The multiple-partners assignment game with heterogeneous sales and multi-unit demands: competitive equilibria

A multiple-partners assignment game with heterogeneous sales and multi-unit demands consists of a set of sellers that own a given number of indivisible units of potentially many different goods and a set of buyers who value those units and want to buy at most an exogenously fixed number of units. We define a competitive equilibrium for this generalized assignment game and prove its existence by using only linear programming. In particular, we show how to compute equilibrium price vectors from the solutions of the dual linear program associated to the primal linear program defined to find optimal assignments. Using only linear programming tools, we also show (i) that the set of competitive equilibria (pairs of price vectors and assignments) has a Cartesian product structure: each equilibrium price vector is part of a competitive equilibrium with all optimal assignments, and vice versa; (ii) that the set of (restricted) equilibrium price vectors has a natural lattice structure; and (iii) how this structure is translated into the set of agents?? utilities that are attainable at equilibrium.     

Effects of CO<Subscript>2</Subscript> Compressibility on CO<Subscript>2</Subscript> Storage in Deep Saline Aquifers

The injection of supercritical CO₂ in deep saline aquifers leads to the formation of a CO₂ plume that tends to float above the formation brine. As pressure builds up, CO₂ properties, i.e. density and viscosity, can vary significantly. Current analytical solutions do not account for CO₂ compressibility. In this article, we investigate numerically and analytically the effect of this variability on the position of the interface between the CO₂-rich phase and the formation brine. We introduce a correction to account for CO₂ compressibility (density variations) and viscosity variations in current analytical solutions. We find that the error in the interface position caused by neglecting CO₂ compressibility is relatively small when viscous forces dominate. However, it can become significant when gravity forces dominate, which is likely to occur at late times of injection.     

A Phenyl α-Nitronyl Nitroxide with a Forced Chiral Conformation

Summary.  A new phenyl α-nitronyl nitroxide bearing a hydroxyl group at position 2 of the aromatic ring and a chiral methyl lactate substituent at position 5 has been synthesized with the aim of combining the magnetic properties of this kind of radical with the optical properties endowed by the chiral group. The optically active compound forms intramolecular hydrogen bonds between the OH group and one of the NO groups and shows a large torsion angle between the two rings when compared with similar radicals with no substituent in this position. Therefore, the optical properties are distinct. The optical and magnetic properties of the new radical in both solution and solid state are presented. Received June 23, 2000. Accepted (revised) September 18, 2000     

Advantages of the Ns group in the reactions of N-SO2R inosines with benzylamine and with NH3

The reactivity of N¹-alkylsulfonyl- and N¹-arylsulfonyl-2′,3′,5′-tri-O-acetylinosine with benzylamine and with ¹⁵NH₃, regarding the attack on C2, has been shown to be in the order CF₃SO₂ (Tf) > 2,4-(NO₂)₂C₆H₃SO₂ (DNs) ? 4-NO₂C₆H₄SO₂ (pNs) ≈ C₆F₅SO₂ (PFBs) > 2-NO₂C₆H₄SO₂ (Ns) ? CH₃SO₂ (Ms) > 4-CH₃C₆H₄SO₂ (Ts) > 2,4,6-(CH₃)₃C₆H₂SO₂ (Mts). In spite of its intermediate reactivity, the Ns group is the most appropriate, since in this case the formation of by-products is minimised during the ring-opening and ring-closing steps of the process. Another advantage of the Ns group is thus disclosed.