No abstract

Sitafloxacin hydrate (STFX hydrate: (Ϫ)-7-[(7S)-1) Fluoroquinolones are important synthetic antimicrobial agents and they have been widely used as therapeutic agents for general bacterial infectious diseases. However, some fluoroquinolones are known to induce phototoxicity as a side effect.2) A large number of studies have been reported to elucidate the mechanism of phototoxicity of fluoroquinolones. We reported that carbon centered radical (· C), hydroxyl radical (· OH), and singlet oxygen ( 1 O 2 ) are generated during photodegradation of fluoroquinolones in neutral aqueous solutions.3) The fluoroquinolones substituted at the 8-position by fluorine generated a high degree of 1 O 2 and · OH against photoirradiation. Such reactive species were related to DNA damage. 4) Some fluoroquinolones are photo-labile compounds and the phototoxicity might arise from photodegradation products. This study was done based on such a background. This report describes the photochemical behavior of STFX in aqueous solution including the identification of major photodegradation products of STFX, the mechanistic consideration of photodegradation, and the effect of pH. Furthermore, the possibility improving the photostability of STFX was examined in the presence of chloride ion. ExperimentalMaterials STFX was synthesized at Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan.Structural Elucidation of Photodegradation Products Ninety-four milligrams of STFX hydrate was dissolved in 1 l of purified water and irradiated with fluorescent lamps (Biophotochamber LX-2100 (TAITEC Co., Tokyo)) at approximately 10000 lux for ca. 350000 lux · h. After irradiation, the solution was loaded onto a preparative HPLC system and fractionated.Preparative HPLC was carried out on a gradient system consisting of an LC 10AD pump (Shimadzu Co., Kyoto) equipped with a SPD-6A UV/vis detector (Shimadzu Co.). HPLC conditions were as follows: column, TSKgel ODS-80T M (21.5 mm i.d.ϫ300 mm, Tosoh Co., Tokyo); eluent, 0.05 M phosphate buffer (pH 2.4) : acetonitrileϭ82 : 18 (from 0 to 65 min) to 50 : 50 (from 65 to 100 min); flow rate, 5.0 ml/min (from 0 to 65 min) to 7.0 ml/min (from 65 to 100 min); injection, 2 ml; detection, 278 nm; column temperature, 40°C.The collected fractions were concentrated and lyophilized. Then the sample was redissolved in water and loaded onto a desalting preparative HPLC. HPLC conditions were as follows: column, TSKgel ODS-80T M (21.5 mm i.d.ϫ300 mm, Tosoh Co.); eluent, 0.1% acetic acid and acetonitrileϭ30 : 70; flow rate, 7.0 ml/min; injection, 2 ml; detection, 278 nm; column temperature, 40°C. Isolated photodegradation products were elucidated by using a 1 H-NMR (JNM-GSX500 FT-NMR spectrometer (500 MHz), JEOL Co., Tokyo) and electron impact (EI), chemical ionization (CI), fast atom bombardment (FAB)-MS (JMS-HX110 mass spectrometer, JEOL Co.) spectra.Kinetics of Photodegradation STFX was dissolved in Britton-Robinson buffer solutions of pH 2.0-11.0 and 0.1 mol/l sodium hydroxide (pH 13.0) (STFX, about 50 mg/ml). Each sample solution (2 ml...

Sitafloxacin (STFX) hydrate is a non-stoichiometric hydrate. The hydration state of STFX hydrate varies non-stoichiometrically depending on the relative humidity and temperature, though X-ray powder diffraction (XRPD) of STFX hydrate was not affected by storing at low and high relative humidities. The detailed properties of crystalline water of STFX hydrate were estimated in terms of hygroscopicity, thermal analysis combined with X-ray powder diffractometry, crystallography and density functional theory (DFT) calculation. STFX hydrate changed the water contents continuously and reversibly from an equivalent amount of dihydrate through that of sesquihydrate depending on the relative humidity at 25°C. Thermal analysis and X-ray powder diffraction (XRPD) simultaneous measurement also revealed that STFX hydrate dehydrated into a hydrated state equivalent to monohydrate by heating up to 100°C, whereas XRPD patterns were slightly affected. This indicated that the crystal structure of STFX hydrate was retained at the dehydration level of monohydrate. Single-crystal X-ray structural analysis showed that two STFX molecules and four water molecule sites were contained in an asymmetric unit. STFX molecules formed a channel structure where water molecules were included. At the partially dehydrated state, at least two of four water molecules were considered to be disordered in occupancy and/or coordinates. Insight into the crystal structure of STFX hydrate stored at low and high relative humidities and geometry of the hydrogen bond were helpful to estimate the origin of non-stoichiometric hydration of STFX hydrate.

Ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one ( Fig. 1) has been developed for use as an antioxidative agent. It is a lipophilic compound with varied antioxidant activities similar to those of glutathione (GSH) peroxidase.1-3) These activities are thought to prevent against disease states by scavenging reactive free radicals, but the mechanisms of these redox reactions have not yet been clarified.One of the most active oxygen species is the superoxide anion radical (O 2 · Ϫ ), which is produced by the one-electron reduction of molecular oxygen. This radical species is implicated in several harmful biological processes, such as lipid peroxidation and protein denaturation. The reactivity of O 2 · Ϫ in an aqueous media is quite different from that in aprotic media. In an aqueous system, O 2 · Ϫ spontaneously disproportionates into hydrogen peroxide and molecular oxygen, whereas in an aprotic media O 2 · Ϫ is stable and can have several reactivities, e.g. electrogenerated base, nucleophile, reductant or oxidant.To evaluate the antioxidative mechanism of certain lipophilic compounds, it is important to understand the reactivity of these antioxidants with O 2 · Ϫ in aprotic media in order to mimic the lipophilic domain of the lipid bilayer. In this report we describe the mechanism of redox reactions of ebselen with O 2 · Ϫ in aprotic media using both electrochemical and ESR techniques. Electrochemical measurements provide useful information on the mechanisms of electron transfer and free radical reactions for redox active compounds. The voltammetric behavior of ebselen, primarily of its anodic oxidation, 4) has already been studied. The primary oxidation step has been identified as the formation of selenoxide. However, no cathodic reduction behavior of ebselen has been reported. Therefore, in the present study we used cyclic voltammetry to determine the interaction between superoxide anion radical and ebselen in both cathodic and anodic currents. As ESR spin-trapping is useful in discriminating trapped radical species and in estimating various short-lived radicals, 5,6) we employed this technique to evaluate the antioxidative activity of ebselen. Further, rapid mix, continuous-flow ESR was used to examine a short-lived free radical species which is generated during the reaction of ebselen with superoxide. ExperimentalMaterials Ebselen was synthesized at Aventis Pharma AG (Frankfurt, Germany). 5,5-Dimethyl-1-pyrroline N-oxide (DMPO), potassium superoxide (KO 2 ) and 18-crown-6 ether were purchased from Sigma Co., Ltd., (St. Louis, MO, U.S.A). Tetraethylammonium perchlorate (TEAP) was purchased from Aldrich Chemical Co., Ltd., (Milwaukee, WI, U.S.A).ESR Spin-Trapping ESR measurements were recorded on a JEOL JES-FE2XG spectrometer (JEOL, Tokyo, Japan) with 100 kHz field modulation operating at 9.44 GHz and at room temperature. The following instrument parameters were employed: modulation amplitude, 0.063 mT; microwave power, 8.0 mW; scan time, 2 min.Five milliliters of a dry toluene-DMSO (3/2, v/v) solution containin...