Unsymmetrically substituted furoxans. Part 16 . Reaction of benzenesulfonyl substituted furoxans with ethanol and ethanethiol in basic medium

The use of benzenesulfonyl substituted furoxans as flexible intermediates for the synthesis of new functionalized furoxans interesting for their potential biological properties is discussed. Reaction of benzenesul-fonylphenylsulfonylfuroxan isomers 7a and 7b with ethanol and ethanethiol in basic medium affords the expected ethers and sulphides respectively. Reaction of bis(benzenesulfonyl)furoxan ( 1 ) with ethanol in basic medium gives 3-benzenesulfonyl-4-ethoxyfuroxan ( 2 ) or diethoxyfuroxan (3), according to the experimental procedure. In contrast the reaction of 1 with ethanethiol gives a mixture of substitution compounds and the 4-benzenesulfonyl-3-ethylthiofurazan ( 11 ). The structure of the compounds has been assigned by nmr spectroscopy and, in the case of 3-benzenesulfonyl-4-ethylthiofuroxan ( 9b ), confirmed by X-ray analysis.     

Analytical assays based on detecting conformational changes of single molecules.

One common strategy for the detection of biomolecules is labeling either the target itself or an antibody that binds to it. Herein, a different approach, based on detecting the conformational change of a probe molecule induced by binding of the target is discussed. That is, what is being detected is not the presence of the target or the probe, but the conformational change of the probe. Recently, a single-molecule sensor has been developed that exploits this mechanism to detect hybridization of a single DNA oligomer to a DNA probe, as well as specific binding of a single protein to a DNA probe. Biomolecular recognition often involves large conformational changes of the molecules involved, and therefore this strategy may be applicable to other assays.     

Fast exopolysaccharide secretion of Pseudomonas aeruginosa on polar polymer surfaces

The influence of the surface chemical structure and related physicochemical properties on the adhesion of P. aeruginosa has been studied for moderately hydrophobic polymers and for hydrophilic surfaces obtained by O2-plasma treatments and 50 keV Ar+ beam irradiation of poly(hydroxymethylsiloxane) and poly(ethyleneterephthalate). The surface chemical structure has been obtained by X-ray photoelectron spectroscopy, the roughness was measured by atomic force microscopy, and the surface free energy was evaluated from contact angle measurements for all the polymer substrates before and after the irradiation treatments. It is shown that a massive and unusually fast secretion of exopolysaccharides onto highly polar surfaces, corresponding to the formation of complex three-dimensional multilayers (i.e., biofilm-like structures), occurs already after 2 h of incubation. It is suggested that such highly polar surfaces can operate either by promoting, by means of a still unknown biomolecular mechanism, an early gene expression process or by mimicking the P. aeruginosa cellular walls.     

Preparation of the Enantiomerically Enriched Isomers of the Odorous Cyclic Ethers Clarycet ®, Florol ®, and Rhubafuran ® by Enzymatic Catalysis

All the enantiomerically enriched stereoisomers of Clarycet ^® ( 1 ), Florol ^® ( 2 ), and Rhubafuran ^® ( 3 ) were prepared by biocatalysis routes. Their absolute configurations were established, and their olfactory properties were fully evaluated.     

A computational study of [2.2]cyclophanes

A computational study of isomeric [2.2]cyclophanes, namely [2.2]paracyclophane 1, [2.2]metacyclophane 2, and [2.2]metaparacyclophane 3, has been carried out. For 1, geometry optimizations performed by various methods at different basis sets showed that MP2/6-31+G(d,p) and B3PW91/6-31+G(d,p) provide the best results in comparison to the X-ray data. Compound 1 has D(2) symmetry with distorted bridges. A conformational search was performed for [2.2]cyclophanes 2 and 3. Each cyclophane exists in two conformations which have different energies in the case of 3 but are degenerate in the case of 2. Relative energies and strain energies at the bridges follow the same order, indicating that the relief of bridge tension and repulsion between pi clouds are determining factors for the stability of [2.2]cyclophanes. Through a decomposition of strain energy, it can be concluded that both the rings or the bridges can absorb strain, but it depends on the conformer of butane that is considered in the calculation of SE(br). Changes in aromaticity of these compounds were evaluated by NICS and HOMA and were compared with benzene and xylenes dimers as models. Despite distortions from planarity and shortening and lengthening of the C-C bonds relative to the mean, the phenyl rings are aromatic. NICS suggests a concentration of electronic density between the rings as a result of bridging process. Computed MK, NPA, and GAPT charges were compared for the isomeric cyclophanes. The GIAO chemical shifts were calculated and indicate that 1 has a larger diamagnetic anisotropy than the other isomers.     

Gas-phase chemistry of the negative ions of fully-protected peptides by high-resolution electrospray ionization tandem mass spectrometry

Fully-protected C-terminal free peptides can be conveniently analyzed by high-resolution electrospray tandem mass spectrometry (ESI-MS/MS) in a quadrupole quadrupole time-of-flight tandem hybrid mass spectrometer, operated in the negative (-) ionizaionization mode. The unusual choice of negative ions in mass spectrometry applications to peptide analysis was needed to obtain exhaustive sequence and structural data. The low-energy collision-induced dissociation (CID) experiments provided, in fact, tandem mass spectra displaying highly diagnostic fragments with a good signal-to-noise ratio. The method is applied to segments of porcine calcitonin (Cal), Cal (1016, 1), Cal (1724, 2) and Cal (2528, 3) whose [M H]- deprotonated molecular ions provided low-energy CID mass spectra which allow the evaluation either of the primary structure of the peptide and of the location of the side-chain protective groups. ESI (+) MS can be conveniently used, in the high resolution mode, to achieve precise information on the elemental composition of the examined peptides.     

Crystal and molecular structure of a 1:1 complex of a chiral α-d-glucosido-benzo-18-crown-6 and potassium thiocyanate

C₂₈H₃₆O₁₀. KSCN is monoclinic, space groupP2₁ withZ=2,a=10.390(3),b=8.959(7),c=16.377(7) Å, =92.49(5)°. FinalR=0.053 for 1437 reflections measured at room temperature. The K^– ion lies on the least-squares plane formed by the six oxygen atoms in the macrocyclic ring. The SCN^– ion was found on the same face of the macrocycle as the chiral glucopyranoside moiety.Methyl-4,6-O-benzylidene-2,3-O-(1,2-bis(ethoxyethoxy)benzenediyl)--d-glucopyranoside.     

The osmylation of flexible 3-substituted cyclopentenes

The osmylation of several 3-substituted cyclopentenes has been studied. A preference for OsO₄ addition syn to an allylic CHR₂ substituent is observed. By contrast, bulkier substituents of type CMeR₂ give rise to a striking reversal of selectivity. These results are interpreted in terms of the stereodivergent nature of the two differently reactive envelope conformations.     

Synthesis of new pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines and related heterocycles

The reaction between 5-amino-4-imino-1(2)-substituted-1(2)H-4,5-dihydropyrazolo[3,4-d]pyrimidines and several commercially available reactants afforded new heterocycles with a conserved pyrazolo[3,4-d]pyrimidine nucleus. The key intermediates employed proved to be suitable compounds by virtue of their two vicinal amino and imino groups that were used to obtain five, six and seven-membered rings.