Synthesis of pyrroles from 1-dialkylamino-3-phosphoryl(or phosphanyl)allenes through 1,5-cyclization of conjugated azomethine ylide intermediates

1-Dialkylamino-1,3-diaryl-3-diphenylphosphanylallenes 3a-e are thermally converted into a-annulated 3,5-diarylpyrroles 6a-f and [a]-annulated benzo[c]azepines 7a,b,d. These transformations are likely to include conjugated azomethine ylide intermediates that can undergo either a 1,5- or a 1,7-electrocyclization. The periselectivity is markedly shifted toward 1,5-cyclization when the diphenylphosphanyl substituent is replaced by the diphenylphosphoryl group. Thus, 1-dialkylamino-3-(diphenylphosphoryl)allenes 4a-f yield pyrroles 6 exclusively and with improved yields, unless the 3-aryl substituent in the allene is too electron-rich (e.g., benzodioxol-5-yl, 4f --> 7f). The preparation and thermal transformation of aminoallenes 4 over three or four steps can be conducted as a one-pot procedure, thus providing a convenient synthesis of [a]-annulated 3,5-diarylpyrroles from enaminoketones.     

Template synthesis of a tetraazamacrocyclic ligand with two pendant pyridinyl groups: properties of the isomers of the metal-free ligand and of their first-row transition metal compounds

The one-step reaction of [Cu(en)(2)](2+) (en = 1,2-diaminoethane) with formaldehyde, ethyl 2-pyridyl acetate, and base produces a mixture of [Cu(s-pypymac)](2+) and [Cu(a-pypymac)](2+) (s-pypymac = syn-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane, a-pypymac = anti-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane; syn-to-anti ratio approximately 1:9) in low yield (6%). Ion exchange chromatography is used for isomer separation, and the two isomers of the metal-free ligand are obtained by reduction of the copper(II) complexes and subsequent ion exchange chromatography. Crystal structure analyses of the metal-free a-pypymac ligand, of two isomeric copper(II) compounds of a-pypymac and one of s-pypymac, and of the cobalt(III) complexes of a- and s-pypymac and nickel(II), as well as zinc(II) complexes of a-pypymac, are reported and discussed on the basis of the expectations from force field calculations and from published experimental data of the transition metal compounds of the bis-pendant amine derivative diammac.     

Unusual peak defocusing in capillary GC on hexakis(2,6-diO-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase

An unusual peak defocusing effect influencing chromatographic performance over a limited range of elution temperatures is described for hexakis(2,6-di-O-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase. Since this phenomenon is likely to be dependent on minor details of the cyclodextrin molecule, full assignment of the ¹H- and ¹³C-NMR-spectra are given.     

Host-guest antenna materials

The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.     

Stereoisomeric flavor compounds,part LVIII: The use of heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as a chiral stationary phase in flavor analysis

The characteristics of the new chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin are outlined and compared with permethyl- and perethyl-β-cyclodextrins.     

Different thermal reactivity of a 1,2-thiaphospholo[a]phosphirane in free and metal carbonyl complexed form

The W(CO)5 and Fe(CO)4 complexes of the bicyclic phosphirane 3,5,6,6-tetraphenyl-1-phospha-2-thiabicyclo[3.1.0]hex-3-ene undergo a thermal 2-phenylphosphirane --> dihydrophosphaisoindole ring expansion, while the free phosphirane suffers both a [2 + 1] cycloreversion and a fragmentation yielding a butadienyl sulfide.     

Pixel-by-pixel analysis of DCE MRI curve patterns and an illustration of its application to the imaging of the musculoskeletal system

Dynamic contrast enhanced (DCE) MRI is a widespread method that has found broad application in the imaging of the musculoskeletal (MSK) system. A common way of analyzing DCE MRI images is to look at the shape of the time-intensity curve (TIC) in pixels selected after drawing an ROI in a highly enhanced area. Although often applied to a number of MSK affections, shape analysis has so far not led to a unanimous correlation between these TIC patterns and pathology. We hypothesize that this might be a result of the subjective ROI approach. To overcome the shortcomings of the ROI approach (sampling error and interuser variability, among others), we created a method for a fast and simple classification of DCE MRI where time-curve enhancement shapes are classified pixel by pixel according to their shape. The result of the analysis is rendered in multislice, 2D color-coded images. With this approach, we show not only that differences on a short distance range of the TIC patterns are significant and cannot be appreciated with a conventional ROI analysis but also that the information that shape maps and conventional standard DCE MRI parameter maps convey are substantially different.     

ChemStable: a web server for rule-embedded naïve Bayesian learning approach to predict compound stability

Predicting compound chemical stability is important because unstable compounds can lead to either false positive or to false negative conclusions in bioassays. Experimental data (COMDECOM) measured from DMSO/H₂O solutions stored at 50 °C for 105 days were used to predicted stability by applying rule-embedded naïve Bayesian learning, based upon atom center fragment (ACF) features. To build the naïve Bayesian classifier, we derived ACF features from 9,746 compounds in the COMDECOM dataset. By recursively applying naïve Bayesian learning from the data set, each ACF is assigned with an expected stable probability (p _s ) and an unstable probability (p _uns ). 13,340 ACFs, together with their p _s and p _uns data, were stored in a knowledge base for use by the Bayesian classifier. For a given compound, its ACFs were derived from its structure connection table with the same protocol used to drive ACFs from the training data. Then, the Bayesian classifier assigned p _s and p _uns values to the compound ACFs by a structural pattern recognition algorithm, which was implemented in-house. Compound instability is calculated, with Bayes’ theorem, based upon the p _s and p _uns values of the compound ACFs. We were able to achieve performance with an AUC value of 84 % and a tenfold cross validation accuracy of 76.5 %. To reduce false negatives, a rule-based approach has been embedded in the classifier. The rule-based module allows the program to improve its predictivity by expanding its compound instability knowledge base, thus further reducing the possibility of false negatives. To our knowledge, this is the first in silico prediction service for the prediction of the stabilities of organic compounds.