6-Substituted-5H-pyrrolo[2,3-b]pyrazines via palladium-catalyzed heteroannulation from N-(3-chloropyrazin-2-yl)-methanesulfonamide and alkynes

We herein report the efficient and convenient synthesis of 6-substituted-5H-pyrrolo[2,3-b]pyrazines. The reaction is a palladium-catalyzed heteroannulation process followed by deprotection to yield the desired pyrrolo[2,3-b]pyrazine substrates. The reaction starts with readily accessible N-(3-chloropyrazin-2-yl)-methanesulfonamide and commercially available terminal alkynes and works with aryl- and alkylalkynes.     

Redox processes of ruthenium (II) polypyridine complexes induced by fast-atom bombardment mass spectrometry

Fast-atom bombardment (FAB) mass spectrometry in the negative ionization mode enables the sputtering into the gas phase of the ruthenium complexes [Ru(2,2′-bipyridine[bpy])₂(2,5-bis) (pyrydil)pyrazine[dpp])](PF₆)₂; [Ru(bpy)₂,(2,3dpp)](PF₆)₂;[Ru(bpy)₂,(2,3-dpp-Me)]( PF₆)₃; and [Ru(bpy)₂(?-2,3-dpp)]₂ RuCl₂(PF₆)₄ as intact radical anions. These data, combined with those avaiiable from the positive FAB spectra allow a full characterization of the analytes.     

Rationalisation of weak ferromagnetism in manganese(III) chains: the relation between structure and ordering phenomena

The synthesis, structure and magnetic properties of the one-dimensional chain compounds [Mn(cyclam)(SO4)]ClO4.H2O (1) and [Mn(cyclam)(HCOO)](CF3SO3)(ClO4) (2) are reported. Cyclam is the cyclic tetradentate ligand 1,4,7,11-tetraazacyclotetradecane. Both chain compounds exhibit antiferromagnetic interactions within the chains. A magnetic ordering phase transition at 5.5 K in (1) is investigated by magnetisation measurements along the three principal crystallographic axes of a single crystal and the results show unambiguously that the ferromagnetic ordering is only taking place along one crystallographic axis. The spin structure of the magnetic ordered phase and the magnitude of the ferromagnetic moment are correlated with the crystal structure and symmetry of the compound.     

Synthesis and polymerisation of lipophilic peptide nucleic acids derived from stearic acid and pentacosa-10,12-diynoic acid

The adenine, cytosine and thymine peptide nucleic acid (PNA) monomers and PNA T₁₀ oligomers bearing either a diacetylenic or stearoyl moiety at the N- or C-terminus have been successfully prepared. The resulting thymine monomeric and T₁₀-mer derivatives have been subsequently incorporated into polydiacetylene-containing liposomes.     

N,O-heterocyclics. 13. Isoxazolidinium salts as synthons to N,N, O-trisubstituted hydroxylamines

Substituted isoxazolidinium salts react with lithium aluminium hydride to yield open-ring products which have hydroxylamine structures. The bimolecular reaction-mechanism has been investigated by substituent effect and the structure of the products ascertained by spectroscopic methods with the aid of the MIKE technique. The overall process of the ring-opening substitution is controlled by the polarisation of the C? N bond with steric and conformational factors acting mainly at the C-5 position of the nucleus. The mechanism of isoxazolidinium ion reaction defines the use of these synthons towards the synthesis of N,N,O-trisubstituted hydroxylamines and substituted 1,3-amino-alcohols.     

Copper bronze catalyzed Heck reaction in ionic liquids

Heck reaction of aryl iodides and activated aryl bromides catalyzed by copper bronze in tetrabutylammonium bromide as solvent and tetrabutylammonium acetate as base was developed. The effective catalysts are Cu nanoparticles deriving from the reaction of iodobenzene with copper bronze. These nanoparticles are very stable in tetraalkylammonium salts, are easily recycled, and can be stored for months without a loss of catalytic efficiency. [reaction: see text]     

Separation of biomolecules by μ-high-performance anion-exchange chromatography using a tentacle-like stationary phase

A variety of biomolecules and their variants, which have previously been problematic to separate, have been analysed using a novel anion-exchange resin based on a non-porous polystyrene polymeric support with a hydrophilic coating and grafted tentacular quaternary ammonium functional groups. The hydrophilic coating results in minimal interaction between the support and the biomolecule, while the highly flexible tentacular-like anion-exchange groups increase the ionic interaction potential and act as an umbrella to hold the proteins away from the surface. Because of the removal of silanophilic interactions, minimisation of hydrophobic interactions, and the highly flexible nature of the tentacle-like ion exchangers, ionic interactions can therefore dominate the separation. As such this phase is highly suited to the separation of highly charged biomolecules and their variants. This polymeric strong anion-exchange (SAX) support was packed into a fused-silica capillary column and, using a salt concentration gradient, various recombinant proteins were analysed by -HPLC resulting in baseline resolution.Awarded a poster prize on the occasion of the Euranalysis XIII conference, Salamanca, Spain, 5–10 September 2004     

Thermal behavior of orthorhombic polymorphs I and II of spironolactone

Investigation into the thermal behavior of orthorhombic Forms I and II of spironolactone, by means of differential scanning calorimetry and high-resolution X-ray powder diffraction, showed that Form I melts then recrystallizes into Form II at 373–393 K, i.e. in the temperature range within which high resolution X-ray powder diffration showed that Form I transforms into Form II. Refinements of the lattice parameters of the two forms indicated that Form I is denser than Form II in the range from 298 K up to the temperature at which it melts.     

Fullerohelicates: a new class of fullerene-containing supermolecules

A multicomponent array made of a bis-copper(I) helicate core and two peripheral fullerene subunits has been prepared and electron transfer from the photoexcited Cu(I)-complexed unit to C60 occurs.     

Uncharged water-soluble Co(II)-porphyrin: a receptor for aromatic alpha-amino acids

Changes in the UV-vis spectra and induced circular dichroism (ICD) signals observed, in correspondence with the porphyrin Soret region, for aqueous solutions of achiral 5,10,15,20-tetrakis{p-[omega-methoxy poly(oxy-ethylene)]phenyl}porphyrin cobalt (II) (Co-P) and aromatic alpha-L-amino acids (Trp and Phe) give direct evidence for the coordination between the Co-P and amino acids. Considering that Co-P, besides the Co atom (one-fixation-point system), does not contain in the molecule active ligand groups and that no ICD signals have been observed in the case of Co-P/Ala, it has been concluded that hydrophobic interactions or stacking interactions between the aromatic rings of the porphyrin and those of Trp or Phe, acting as further amino acid (AA) fixation points, can strongly reduce the mobility of the chiral guest, thus permitting the generation of ICD signals. The effects of changes of both pH (in the range 2-9) and amino acid structure on the ICD phenomenon have also been investigated. In particular, the following have been observed: (i) strong ICD signals for all of the Co-P/N-acetyl amino acid aqueous solutions at pH 7, (ii) an unexpected ICD band with a bisignate form for the Co-P/Ala solution at pH 9 after long aging, and (iii) an opposite ICD signal when alpha-D-Phe and alpha-D-Trp enantiomers have been used. The data reported in this paper show how the binding mechanism between receptor and AAs changes by modulating properly the pH or the molecular structures and indicate that in these aqueous solutions the coordination Co-N is not the fundamental mechanism giving rise to the formation of the complexes and that the binding can be driven by hydrophobic interactions. These occurrences, through the analysis of the spectroscopic response (and, in particular, the form of the ICD band), can allow the recognition of AAs.