The synthesis of 4H-imidazo[5,1-c][1,4]benzothiazine derivatives

A facile synthesis of the 4H-imidazo[5,1-c][1,4]benzothiazine ring system is described. The synthesis utilized the annulation of an imidazole ring onto a 2H-1,4-benzothiazin-3(4H)-one via the addition of the anion of ethyl isocyanoacetate. Methods for the functionalization of the 1-, 3-, 4-, and 5-positions of the ring system are presented.     

Influence of frictional heating on temperature gradients in ultra-high-pressure liquid chromatography on 2.1mm I.D. columns

The effects of viscous heat dissipation on some important HPLC parameters, such as efficiency (N) and retention factors (k), using 2.1mm columns at pressures up to 1000 bar have been investigated from both a theoretical and experimental point of view. Two distinct experimental set-ups and their respective influences on non-homogenous temperature gradients within the column are described and discussed. In the first instance, a still-air column heater was used. This set-up leads to approximate 'adiabatic' conditions, and a longitudinal temperature gradient is predicted across the length of the column. The magnitude of this gradient is calculated, and its occurrence confirmed with experimental measurements also indicating that no appreciable loss in efficiency occurs. Secondly, when a water bath is used to thermostat the column, a radial temperature gradient is prevalent. The extent of this gradient is estimated, and the loss in efficiency associated with this gradient is predicted and demonstrated experimentally. It is also observed that approximate adiabatic conditions can lead to floating retention factors. The implications of temperature gradients for routine HPLC analysis at ultra-high pressure are discussed.     

Fusion of small unilamellar vesicles onto laterally mixed self-assembled monolayers of thiolipopeptides

Monolayers of the thiolipopeptide NH(2)-Cys-Ala-Ser-Ala-Ala-Ser-Ser-Ala-Pro-Ser-Ser-(Myr)Lys(Myr)-OH (III) were formed on gold surfaces by self-assembly, mixed with a lateral spacer of the same peptide composition, NH(2)-Cys-Ala-Ser-Ala-Ala-Ser-Ser-Ala-Pro-Ser-Ser-Lys-OH (I). Different mixing ratios were employed ranging from 0.1 to 1, corresponding to 10-100% thiolipopeptide. These self-assembled monolayers (SAMs) were then exposed to a suspension of liposomes with the aim of forming lipid bilayers as a function of the mixing ratio. A clear optimum with respect to homogeneity and electrical properties of the membranes was obtained in the middle region (0.5) of mixing ratio, as revealed by surface plasmon resonance spectroscopy, impedance spectroscopy, and fluorescence microscopy. The combination of these methods was shown to be a powerful tool, although a true lipid bilayer was not obtained. Instead, vesicle adsorption was shown to be the predominant process, and FRAP (fluorescence recovery after photobleaching) measurements showed that the films were not fluid on the micrometer length scale.     

Cyclic condensations of 2-amino-1,3,4-thiadiazole with 1,3-dicarbonyl compounds

The reactions of 2-amino-1,3,4-thiadiazole with 1,3-dicarbonyl compounds are described. 2,4-Pentanedione gave 2-thiocyanato-4,6-dimethylpyrimidine while diethylmalonate and ethyl acetoacetate yielded 5-hydroxy-7H-1,3,4-thiadiazolo[3,2-a]pyrimidin-7-one and 7-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one, respectively. The structure of the latter compound was confirmed by a synthesis of the alternative isomeric structure (5-methyl-7H-1,3,4-thiadiazolo[3,2-a]pyrirnidin-7-one) from 2-amino-1,3,4-thiadiazole and α-bromocrotonic acid.     

Synthesis of phellanphos,an efficient chiral 1,2-diphosphine for asymmetric catalysis

A chiral 1,2-diphosphine was prepared in two steps from ()-α-phellandrene. This phosphine phellanphos gives a cationic rhodium complex (phellanphos-cyclooctadienerhodium hexafluorophosphate) which catalyses asymmetric reductions. N-Acetylphenylalanine and N-acetylalanine have been prepared in 94–95% enantiomeric excess.     

Calculation of valence electron vertical ionization potentials using a limited Cl approach

A method is outlined for the calculation of valence electron vertical ionization potentials based on CNDO/2 and CNDO/S SCF molecular ground states improved by including a limited number of doubly excited configurations and ionic states obtained from a single Cl calculation considering a limited set of singly and doubly excited configurations based on the closed shell ground state MO's of the parent molecule. From numerical results on carbon dioxide, sulphur dioxide, ethylene, and trans-butadiene it is shown that the Cl procedure leads to the right sequence of ionic states and their reasonable relative location in contrast to respective Koopmans' ionic states predictions.     

Radio frequency versus susceptibility effects of small conductive implants--a systematic MRI study on aneurysm clips at 1.5 and 3 T

PURPOSE: Metallic implants cause enlarged artifacts in magnetic resonance (MR) images at higher magnetic fields, B0, due to their magnetic susceptibility. Interactions of conductive material with radio frequency (RF) pulses also change for higher field strengths, B0, due to the frequency dependence of resonance conditions. Systematic measurements on commercial aneurysm clips and simplified copper models were performed in order to investigate both phenomena at 1.5 and 3 T. MATERIALS AND METHODS: Six different commercial aneurysm clips made of titanium, straight copper wires and bent copper models were examined in Gd-DTPA-doped water. RF-related effects were measured by adapted 2D and 3D spin-echo sequences. For reliable differentiation from susceptibility-related effects, variable transmitter voltages were applied. In addition, RF-induced heating was controlled by an infrared (IR) camera. RESULTS: At 3 T, a significant RF-induced electric response could be demonstrated for the copper samples and more moderate for one of the commercial clips, dependent on the geometrical structure determining possible resonant RF coupling. Related RF effects could be distinguished from susceptibility artifacts: a signal enhancement at reduced transmitter voltages indicated locally amplified B1-field amplitudes. No significant heating effect could be measured by IR measurements. CONCLUSION: MR imaging was used to analyze possible RF-induced effects. At 3 T, resonant RF coupling even of small metallic implants has to be considered carefully. Despite a local enhancement of the RF amplitude, no significant RF-induced heating inside the surrounding fluid was found. A direct thermal endangering of patients seems to be unlikely, but extremely high B1-field amplitudes might occur adjacent to the metallic surface with potential nonthermal affection of tissue.     

2-(Aminomethyl)phthalimide. A new reagent for the synthesis of 2,4-benzodiazepines

2,4-Benzodiazepines can be prepared by condensation of an activated 2-benzoylbenzoic acid with 2-(aminomelhyl)phthalimide. A synthesis of this reagent is described.