Organic electrosynthesis using a fluoride ion mediator

Recent studies on fluoride ion-mediated anodic methoxylation of fluoroalkyl sulfides and sulfur-containing five-membered heterocyclic compounds together with its synthetic applications are summarized in this review. The first example of anodic methoxylation of 2-acyloxy-3,3,3-trifluoropropyl sulfides accompanying with [1,2]-rearrangement of acyloxy group is described. Fluoride ion-mediated anodic intramolecular cyclization of 3,3,3-trifluoropropyl sulfides bearing OH and t-BuCOO groups provides CF₃-containing 1,3-oxathiolane and ethylene carbonate derivatives, respectively. Fluoride ion mediator can be also applied to anodic intramolecular carbon–carbon coupling to form oxindole and 3-oxotetrahydroisoquinoline derivatives.     

Component Crystallization and Physical Collapse during Freeze-Drying of L-Arginine-Citric Acid Mixtures

Component crystallization and physical collapse during freeze-drying of aqueous solutions containing protein-stabilizing L-arginine and citric acid mixtures were studied. Freeze-drying microscopy (FDM) and thermal analysis of the solute-mixture frozen solutions showed collapse onset at temperatures (T(c)) approximately 10°C higher than their T(g)'s (glass transition temperatures of the maximally freeze-concentrated solute phase). Experimental freeze-drying of these solutions at a low chamber pressure showed the occurrence of physical collapse at shelf temperatures close to or slightly higher than the T(c). Slower ice sublimation at higher chamber pressures induced the physical collapse from lower shelf temperatures. The large effect of chamber pressures on the collapse-inducing shelf temperatures confirmed significance of the sublimation-related heat loss on the sublimation interface temperature during the primary drying. Drying of the single-solute L-arginine solution resulted in cake-structure solids composed of its anhydrous crystal. Thermal and powder X-ray diffraction (PXRD) analysis suggested slow crystal nucleation of L-arginine dihydrate in the frozen solutions. Characterization of the frozen solutions and freeze-dried solids should enable rational formulation design and process control of amino acid-containing lyophilized pharmaceuticals.     

Chemical mapping of hydration and dehydration process of theophylline in tablets using terahertz pulsed imaging

The purpose of this research is to investigate the topographical pattern of hydration and dehydration (also known as pseudo-polymorphic change) of drug substance in drug product using terahertz (THz) pulsed imaging. Emphasis is placed on (1) applicability of THz pulsed imaging and (2) kinetic analysis in the pseudo-polymorphic change. Either anhydrous or monohydrated form of theophylline was used as the drug substance, leading to initially anhydrous or monohydrated tablets. These tablets were stored at 25°C to keep the relative humidity constant at 84% (anhydrous tablets) or 45% (monohydrated tablets), respectively. The THz pulsed imaging was confirmed to enable visualization that the hydration of the anhydrous form or the dehydration of the monohydrated form began on the surface of the tablets and gradually progressed to the core side in the tablets with storage. Kinetic studies indicated that these pseudo-polymorphic changes followed the phase boundary mechanism. Since the other imaging techniques has been scarcely achieved to show the topographical pattern of pseudo-polymorphic change of drug substances in drug products directly and visually, it is considered that THz pulsed imaging has a potential ability to solve complicated issues in pharmaceutical development.     

Synthesis of soluble electron‐donating polymers containing vinylogous TTF by oxidative dimerization of 1,4‐bisdithiafulvenyl‐2,5‐dialkoxybenzene

A new electron‐donating polymer composed of a vinylogous tetrathiafulvalene (TTF) unit was prepared by the oxidative dimerization of 1,4‐bisdithiafulvenyl‐2,5‐didodecyloxybenzene using iodine. The polymer was soluble in common organic solvents such as CHCl₃ and toluene. The number‐average molecular weight of the polymer with dodecyloxy group was 24,900 determined from GPC. The UV–vis spectrum of the polymer showed the absorption maxima at 587, 712, and 803 nm, which are due to a cation radical of the vinylogous TTF unit in the polymer. The reduction of the polymer to its neutral state was performed using sodium hydrogen sulfite. The structure of the polymer was confirmed by ¹H NMR and UV–vis spectra compared with that of a dimer model compound prepared by oxidation of 1‐dithiafulvenyl‐2,5‐didodecyloxybenzene using iodine. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4600–4608, 2005     

Diffusivity of amorphous drug in solid dispersion

Filmy solid dispersion of terfenadine (TFD), fenofibrate (FFB), and carbamazepine (CBZ) and methacrylic acid methyl methacrylate copolymer (Eudragit^®) was prepared by evaporating their solution. Raman and IR measurements for the filmy samples were performed. Concentration profile of TFD, FFB, and CBZ in solid dispersions was evaluated by their characteristic peaks, and then their diffusion rate constants were calculated. The start point of the crystallization peak under isothermal condition was determined by XRD–DSC. Viscoelastic character of Eudragit^® was evaluated by dynamic mechanical analysis (DMA). The distribution map of drugs in their solid dispersions showed the diffusion state of drugs during storage. The concentration profile of TFD, FFB, and CBZ in the solid dispersion was calculated from obtained mapping data. The diffusion rate constant of both drug in Eudragit^® EPO was higher than that in Eudragit^® RLPO. The induction period of crystallization from amorphous CBZ was gradually delayed with increasing amounts of Eudragit^®. The IR peak due to C=O was shifted to higher wave number; it suggested that there were some molecular interactions between CBZ and Eudragit^®. From the results of the change in the interaction of drug-Eudragit^®, it may be concluded that the diffusivity of drug molecule in polymer closely related to the delay of the induction period of crystallization of amorphous. DMA measurement clarified the difference in the viscosity of Eudragit^® having different functional groups and molecular mass. These results suggested that the retardation of crystallization by Eudragit^® could be related to the sample viscosity.     

Construction of Stable Redox Systems Composed of the Crowded Triarylphosphines

Extremely crowded triarylphosphines were synthesized by the reaction of arylcopper(I) reagents with chlorophosphines, and the relationship between molecular structure and redox properties was studied by X-ray crystallography and cyclic voltammetry. As the substituent on phosphorus became bulkier, bond lengths and angles around phosphorus atom became longer and larger, and oxidation potential was significantly lowered. Especially, tris(2,4,6-triisopropylphenyl)phosphine had an extremely crowded structure and was oxidized to a stable radical cation at an extraordinarily low oxidation potential. Novel redox systems possessing the crowded triarylphosphine structure as one of the redox sites were designed and synthesized.     

Intramolecular cyclizations leading to bridgehead bicyclics 2. 5,5-dialkylhydantoin derivatives

The effect of substituenls in the 5-position on the course of hydantoin intramolecular alkylation reactions was studied. Dialkyl and diaryl substituted intermediates resulted in the same type product, 2,3-dihydro-6,6-disubstituted imidazo[2,1-b]oxazole-5(6H)ones, indicating alkylation on oxygen rather than nitrogen. The mass spectral and nmr characteristics of these bicyclic compounds are discussed.