Development of an integrated microfluidic platform for dynamic oxygen sensing and delivery in a flowing medium

This paper describes a platform for real-time sensing of dissolved oxygen in a flowing microfluidic environment using an oxygen-sensitive luminescent dye (platinum octaethylporphyrin ketone) integrated into a micro-oxygenator device. Using a phase-based detection method, the luminescent decay lifetime of the dye was consistent with the linear Stern-Volmer relationship using both gaseous and aqueous samples. Maximum sensor resolution varied between 120-780 ppb across a range of dissolved oxygen (DO) concentrations ranging from 0-42.5 ppm. The sensor was subsequently used to determine the convective mass-transfer characteristics of a multi-layer polydimethylsiloxane (PDMS) microfluidic oxygenator. The membrane-based oxygenator showed excellent agreement with an analytical convection model, and the integrated oxygen sensor was accurate across a wide range of tested flow rates (0.05-5 mL min(-1)). The device is unique for its ease of fabrication and highly flexible configuration, as well as the novel incorporation of oxygen delivery and detection in a single micro-device. Potential applications include tissue engineering, cell culturing, and miniaturized bio-assays that require the delivery and/or detection of precise quantities of oxygen within a microfluidic construct.     

A convenient synthesis of 7-halo-1-indanones and 8-halo-1-tetralones

A regioselective oxidation of N-indan-4-yl-acetamide or N-(5,6,7,8-tetrahydronaphthalen-1-yl)acetamide with potassium permanganate followed by acidic hydrolysis gave 7-aminoindan-1-one or 8-aminotetral-1-one in good yield. The amino ketones were converted to the corresponding 7-haloindanone or the 8-halotetralone. Another method to prepare 7-haloindan-1-ones was completed by a cyclization of 3-chloro-1-(2-halophenyl)propan-1-one under Friedel-Crafts conditions to produce the product in gram quantity.     

Determination of mercury by continuous flow cold vapor atomic fluorescence spectrometry using micromolar concentration of sodium tetrahydroborate as reductant solution

Systematic experiments were conducted to evaluate and compare the analytical figures of merit of two reducing agents (SnCl2 and NaBH4) in a continuous flow cold vapor atomic fluorescence mercury analyzer. It was found that sodium tetrahydroborate can efficiently reduce Hg2+ in various environmental samples at a concentration as low as 10 microM (ca. 3.8 x 10(-5)% w/v). Most commonly encountered transition metals (Fe2+, Fe3+, Zn2+, Cu2+, Ni2+, Pb2+ and Cr3+) did not interfere with total Hg determination. No interference from hydride-forming elements (Se4+, Sb3+ and As3+) was observed. Interference caused by Mn2+ and Ag+ could be readily removed by dilution and by using appropriate modification of the reaction matrix. A higher concentration of NaBH4 (0.1 M) is stable for I month when stored in the NaOH matrix (0.2 M) and at low temperature (4 degrees C). A working solution of NaBH4 can be freshly prepared by dilution. With NaBH4, the whole continuous flow system is kept clean much more easily as no precipitate is formed, which in turn considerably reduces memory effects, simplifies analytical operation and reduces the chemical cost six-fold.     

A quadruply hydrogen bonded heterocomplex displaying high-fidelity recognition

An exceptionally strong quadruply hydrogen-bonded complex is formed between 2,7-diamido-1,8-naphthyridine 3 (DAN) and the butylurea of guanosine 6 (UG) in chloroform. The UG unit can be prepared in four steps from guanosine on a 10 g scale in excellent yields without chromatographic purification. The association constant (Kassoc approximately 5 x 10(7) M(-1)) for the UG.DAN complex determined by fluorescence energy transfer from the naphthyridine unit of 3 to coumarin 343 covalently linked UG (18) is among the highest reported for a neutral DNA base-pair analogue. The weak self-association of DAN (Kdimer < 10 M(-1)) and UG (Kdimer ca. 200-300 M(-1)) means that the UG.DAN complex forms with unparalleled fidelity.     

Optimisation of microdialysis sampling recovery by varying inner cannula geometry

In vitro microdialysis recoveries of glucose were evaluated and optimised by varying the inner cannula dimensions for a concentric type microdialysis probe. The recovery was shown to be significantly dependent on the outer radius of the inner cannula (r alpha). Increasing r alpha by 50% while holding all other microdialysis variables constant caused a 26% increase in recovery under the conditions tested. Mass transport modeling of microdialysis sampling showed that the magnitude of the recovery change in response to changes in r alpha may depend on other experimental variables such as effective dialysis length, membrane dimensions, membrane type and medium composition. These data indicate that microdialysis recovery may be substantially improved by optimising the outer diameter of the inner cannula. These data also suggest that in order to fully characterise and compare data from microdialysis experiments, r alpha should become one of the reported variables.     

Efficient synthesis of NK(1) receptor antagonist aprepitant using a crystallization-induced diastereoselective transformation

An efficient stereoselective synthesis of the orally active NK(1) receptor antagonist Aprepitant is described. A direct condensation of N-benzyl ethanolamine with glyoxylic acid yielded a 2-hydroxy-1,4-oxazin-3-one which was activated as the corresponding trifluoroacetate. A Lewis acid mediated coupling with enantiopure (R)-1-(3,5-bis(trifluoromethyl)phenyl)ethan-1-ol afforded a 1:1 mixture of acetal diastereomers which was converted into a single isomer via a novel crystallization-induced asymmetric transformation. The resulting 1,4-oxazin-3-one was converted via a unique and highly stereoselective one-pot process to the desired alpha-(fluorophenyl)morpholine derivative. Interesting and unexpected [1,2]-Wittig and [1,3]-sigmatropic rearrangements were identified during the optimization of these key steps. In the final step, a triazolinone side chain was appended to the morpholine core. The targeted clinical candidate was thus obtained in 55% overall yield over the longest linear sequence.     

Chelation-controlled diastereoselective reduction of alpha-fluoroketones

The effect of Ti-based Lewis acids on the reduction of alpha-fluoropropiophenone was examined to determine whether chelation control could be used to direct the diastereoselectivity of conversion to an alpha-fluoro alcohol. Pretreatment of alpha-fluoropropiophenone with TiCl4 followed by reduction with LiBH4 in diethyl ether or methylene chloride provided the syn diastereomer predominantly, while use of Ti(OiPr)4 under identical conditions provided the anti diastereomer as the major product. The products are consistent with a chelation-controlled mechanistic pathway in the former reduction and a nonchelation pathway in the latter case. Detailed 1H, 13C, and 19F NMR studies were consistent with chelation between TiCl4 and alpha-fluoropropiophenone under the reaction conditions utilized in this study. Reduction of other alpha-fluoroketones in the presence of TiCl4 also provided a high degree of diastereoselectivity in the conversion to alpha-fluoro alcohols, showing the generality of this approach.     

Conformational analysis of furanose rings with PSEUROT: parametrization for rings possessing the arabino,lyxo, ribo,and xylo stereochemistry and application to arabinofuranosides

The solution conformation of a furanose ring can be assessed through PSEUROT analysis of three-bond (1)H-(1)H coupling constants ((3)J(HH)) of the ring hydrogens. For each coupling constant, PSEUROT requires two parameters, A and B, which are used to translate the H[bond]C[bond]C[bond]H dihedral angle predicted from the (3)J(HH) into an endocyclic torsion angle from which the identity of the conformers can be determined. In this paper, we have used density functional theory methods to generate a family of envelope conformers for methyl furanosides 1-8. From these structures, A and B were calculated for each H[bond]C[bond]C[bond]H fragment. In turn, the values of these parameters for the arabinofuranose ring were used in PSEUROT calculations to determine the conformers populated by monosaccharides 1 and 2 as well as the furanose rings in oligosaccharides 9-15. The results of these analyses are consistent with the low-energy conformers identified from previous computational and X-ray crystallographic studies of 1 and 2.     

Ferromagnetic interaction in mu1,3-cyanamido-derived copper(II) cryptates

The reaction of dinuclear copper(II) cryptates with calcium cyanamide, CaNCN, and sodium dicyanamide, Na[N(CN)(2)] results in dinuclear compounds of formulae [Cu(2)(HNCN)(R3Bm)](ClO(4))(3) (1), [Cu(2)(dca)(R3Bm)](ClO(4))(3)4H(2)O (2), and [Cu(2)(NCNCONH(2))(R3Bm)](CF(3)SO(3))(3) (3), in which R3Bm=N[(CH(2))(2)NHCH(2)(C(6)H(4)-m)CH(2)NH(CH(2))(2)](3)N and dca=dicyanamido ligand (NCNCN(-)). The X-ray diffraction analysis reveals for both 1 and 3 a dinuclear entity in which the copper atoms are bridged by means of the -NCN- unit. The molar magnetic susceptibility measurements of 1-3 in the 2-300 K range indicate ferromagnetic coupling. The calculated J values, by using theoretical methods based on density functional theory (DFT) are in excellent agreement with the experimental data. Catalytic hydration of a nitrile to an amide functional group is assumed responsible for the formation of 3 from a mu(1,3)-dicyanamido ligand.     

Total synthesis of buergerinin F and buergerinin G

Syntheses of buergerinin F (1) and buergerinin G (2) were carried out to establish the absolute stereochemistry of these natural products. A linear sequence was used to synthesize 1 in 15 steps and 9% overall yield from thymidine. Subsequent oxidation of 1 with ruthenium tetroxide afforded 2 in 77% yield.