Sulfonamide carbazole receptors for anion recognition

Carbazole-based receptors functionalized with two sulfonamide groups have been synthesized and their properties as anion receptors have been evaluated. The receptor with bis(trifluoromethyl)aniline groups has shown a very high affinity for halide ions, especially remarkable as only two hydrogen bonds are formed in the complexes. (1)H NMR and fluorescence titrations have been carried out and binding constants up to 7.9 × 10(6) M(-1) have been reached. X-ray structures have been obtained and a modelling study has shown the possible reasons for the large affinity of these compounds for halide anions.     

The importance of the N-H bond in Ru/TsDPEN complexes for asymmetric transfer hydrogenation of ketones and imines

Ru(II) complexes of TsDPEN containing two alkyl groups on the non-tosylated nitrogen atom are poor catalysts for asymmetric transfer hydrogenation of ketones and imines; this observation provides direct evidence for the importance of the N-H interaction in the transition state for ketone reduction.     

An organocatalytic approach to enantiomerically enriched α-arylcyclohexenones and cyclohexanones

The presence of a p-nitrophenyl group converts acetone into an excellent and versatile nucleophile in organocatalytic processes, able to react with α,β-unsaturated aldehydes affording β-substituted α-arylcyclohexenones via a Michael reaction/aldol reaction/dehydration sequence, which occurs in good yields, ee up to 96% and complete diastereoselectivity. The resulting compounds are excellent synthons for the diastereoselective preparation of a variety of synthetically useful polysubstituted cyclohexanones and derivatives.     

Synthesis of novel chromene scaffolds for adenosine receptors

A one-pot procedure was developed for the synthesis of novel 3-[amino(methoxy)methylene]-2-oxo-3,4-dihydro-2H-chromen-4-yl)-3-cyanoacetamides and chromeno[3,4-c]pyridine-1-carbonitriles from the reaction of 2-oxo-2H-chromene-3-carbonitriles and cyanoacetamides. These chromene derivatives were identified as new scaffolds for adenosine receptors and the hits 3a, 3c, 5a, and 5b were found.     

Potent "clicked" MMP2 inhibitors: synthesis, molecular modeling and biological exploration

A new series of MMP2 inhibitors is described, following a fragment-based drug design approach. One fragment containing an azide group and a well known hydroxamate Zinc Binding Group in a α-sulfone, α-tetrahydropyrane scaffold, has been synthesized. Water-LOGSY, STD and competition-STD experiments indicate that this fragment binds to the active site of the enzyme. A click chemistry reaction was used to connect the azide to lipophilic alkynes selected to interact selectively with the S1' subunit of MMP2, as shown by docking and molecular dynamic experiments of the designed compounds. The most potent compounds 18 and 19 displayed an IC(50) of 1.4 and 0.3 nM against MMP2 respectively, and showed negligible activity towards MMP1 and MMP7, two metalloproteinases which have a shallow S1' subsite. Compound 18 also showed a promising selectivity profile against some antitarget metalloproteinases, such as MMP8, and considerably less activity against MMP14 (IC(50) = 65 nM), and MMP9 (IC(50) = 98 nM), other MMPs characterized by having a deep S1' pocket and, therefore, more similar to MMP2.     

Reactivity of coordinatively unsaturated iron complexes towards carbon monoxide: to bind or not to bind?

An overview of the reactivity of coordinatively unsaturated iron complexes (in most cases Fe(II)) towards carbon monoxide is presented. Unsaturated iron complexes are known with coordination numbers (CN) of two to five adopting linear or slightly bent (CN = 2), trigonal (CN = 3), tetrahedral, square planar or trigonal pyramidal (CN = 4), and square-pyramidal or trigonal-bipyramidal geometries (CN = 5), respectively. The binding of CO depends strongly on the number and the nature of co-ligands (overall ligand field strength), the charge of the complex, the complex geometry, and the spin state of the unsaturated metal center. In many cases, CO addition to high-spin iron complexes takes place with concomitant spin state changes forming compounds in the lowest possible spin state, i.e., with S = 0. In several other cases, however, the addition of CO is reversible or is even totally rejected altogether for either thermodynamic or kinetic reasons. In the case of the latter such reactions are termed "spin-blocked" or "spin forbidden".     

Chemistry of 11-vertex rhodathiaboranes: reactions with monodentate phosphines

The reaction of [8,8-(PPh(3))(2)-nido-8,7-RhSB(9)H(10)] (1) with PR(3) in a 1:2 ratio affords mixtures that contain the mono-substituted bis-PR(3)-ligated rhodathiaboranes [8,8-(PPh(3))(L)-nido-8,7-RhSB(9)H(10)] [L = PMe(2)Ph (5), PMe(3) (6)] and the corresponding tris-PR(3)-ligated compounds [8,8,8-(L)(3)-nido-8,7-RhSB(9)H(10)] [L = PMe(2)Ph (7), PMe(3) (8)]. These latter species are more conveniently prepared from the reaction of 1 with three equivalents of the monodentate phosphines, PMe(2)Ph and PMe(3). Reaction between 1 and PMePh(2) in a 1:2 ratio yields the disubstituted rhodathiaborane [8,8-(PMePh(2))(2)-nido-8,7-RhSB(9)H(10)] (4), whereas the use of three equivalents of phosphine leads to the formation of B-ligated eleven-vertex [8,8,8-(PMePh(2))(2)(H)-nido-8,7-RhSB(9)H(9)-9-(PMePh(2))] (9). Compounds 4-9 have been characterized by NMR spectroscopy, and the structures of 8 and 9 confirmed by X-ray diffraction analyses. The characterization of the cluster compounds has been aided by the use of DFT calculations on some of the species. Variable-temperature NMR studies have demonstrated a lability of the PMePh(2) ligands in compounds 4 and 9, providing mechanistic insights about the ligand substitutional chemistry in these eleven-vertex rhodathiaboranes.     

Synthesis of glycerol carbonate from glycerol and urea with gold-based catalysts

The reaction of glycerol with urea to form glycerol carbonate is mostly reported in the patent literature and to date there have been very few fundamental studies of the reaction mechanism. Furthermore, most previous studies have involved homogeneous catalysts whereas the identification of heterogeneous catalysts for this reaction would be highly beneficial. This is a very attractive reaction that utilises two inexpensive and readily available raw materials in a chemical cycle that overall, results in the chemical fixation of CO(2). This reaction also provides a route to up-grade waste glycerol produced in large quantities during the production of biodiesel. Previous reports are largely based on the utilisation of high concentrations of metal sulfates or oxides, which suffer from low intrinsic activity and selectivity. We have identified heterogeneous catalysts based on gallium, zinc, and gold supported on a range of oxides and the zeolite ZSM-5, which facilitate this reaction. The addition of each component to ZSM-5 leads to an increase in the reaction yield towards glycerol carbonate, but supported gold catalysts display the highest activity. For gold-based catalysts, MgO is the support of choice. Catalysts have been characterised by XRD, TEM, STEM and XPS, and the reaction has been studied with time-on-line analysis of products via a combination of FT-IR spectroscopy, HPLC, (13)C NMR and GC-MS analysis to evaluate the reaction pathway. Our proposed mechanism suggests that glycerol carbonate forms via the cyclization of a 2,3-dihydroxypropyl carbamate and that a subsequent reaction of glycerol carbonate with urea yields the carbamate of glycerol carbonate. Stability and reactivity studies indicate that consecutive reactions of glycerol carbonate can limit the selectivity achieved and reaction conditions can be selected to avoid this. The effect of the catalyst in the proposed mechanism is discussed.     

Dinuclear silver(I) complexes for the design of metal-ligand networks based on triazolopyrimidines

Silver(I) coordination complexes with the versatile and biomimetic ligands 1,2,4-triazolo[1,5-a]pyrimidine (tp), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) and 7-amine-1,2,4-triazolo[1,5-a]pyrimidine (7atp) all feature dinuclear [Ag(2)(μ-tp)(2)](2+) building units (where tp is a triazolopyrimidine derivative), which are the preferred motif, independently of the counter-anion used. According to AIM (atoms in molecules) and ELF (electron localization function) analyses, this fact is due to the great stability of these dinuclear species. The complexes structures range from the dinuclear entities [Ag(2)(μ-tp)(2)(CH(3)CN)(4)](BF(4))(2) (1), [Ag(2)(μ-tp)(2)(CH(3)CN)(4)](ClO(4))(2) (2), [Ag(2)(μ-7atp)(2)](ClO(4))(2) (3) and [Ag(2)(μ-dmtp)(2)(CH(3)CN)](PF(6))(ClO(4)) (4) over the 1D polymer chain [Ag(2)(μ-CF(3)SO(3))(2)(μ-dmtp)(2)](n) (5) to the 3D net {[Ag(2)(μ(3)-tp)(2)](PF(6))(2)·～6H(2)O}(n) (6) with NbO topology.     

A new azorellane diterpenoid from Azorella madreporica

A new azorellane diterpenoid has been isolated and identified from the aerial parts of Azorella madreporica Clos. The structure of 1 was established by one- and two-dimensional NMR techniques.