A new thermal study of the reaction of 6‐azidopyridones with different amines and hydrazines

Reacting of 6‐azidopyridone derivatives 1 with o‐phenylenediamine ( 2a ) in chloroform at room temperature afforded the new azidopyridones 3 . However, its fusion with 2a,b at 100–110°C gave the interesting pyrido[2,3‐b][1,5]diazepines 4a,b . Alternatively, compound 4a could also be obtained by heating azidopyridones 3 at 100–110°C. When compound 1 was allowed to react with hydrazines 7a‐d at room temperature it gave the corresponding azido compounds 8a‐d . Fusion of 1 with phenylhydrazine ( 7d ) at 140–160°C afforded the new aminopyridones 10 . The 6‐azidopyridones 1 could also be converted to the corresponding 6‐alkylaminopyridones 15a‐d by reaction with an excess of alkylamines at room temperature.     

Fused polyaza‐heterocycles and 1,3,4‐thiadiazoles via a tricyano synthon

Treatment of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with some heterocyclic diazonium salts afforded the corresponding heterocyclic hydrazones. Some of the latter hydrazones were converted into fused polyaza‐heterocycles upon boiling in pyridine. Reaction of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with phenylisothiocyanate gave a tricyano‐thiole derivative which on treatment with hydrazonoyl chlorides and 1‐(benzothiazol‐2‐yl)‐2‐bromoethanone furnished 1,3,4‐thiadiazole and thiazole derivatives, respectively.     

Regioselectivity of the reactions of 4,5‐diphenylimidazole‐2‐thione with 1‐chloro‐2,3‐epoxy‐propane and 1‐bromo‐propene,efficient precursors for imidazo[2,1‐b]thiazine and thiazole. Effect of microwave and solid support

A solid support under microwave (MW) irradiation without solvent allowed the synthesis of the 2,3‐epoxy‐propyl‐thioimidazole 4 , regioselectively, and prohibited its cyclization to give the imidazo[2,1‐b]thiazine 3 from the reaction of 4,5‐diphenylimidazole‐2‐thione ( 1 ) with 1‐chloro‐2,3‐epoxy‐propane ( 2 ). The formation of the latter required basic conditions whereby it became the sole product; the change of the basic catalyst changed the ratio of the two products under both conventional and microwave (MW) conditions. A regioselective allylation of 1 with allyl bromide in presence of triethylamine gave the S‐allyl 8 , while in presence of potassium carbonate led to the S,N‐bis(allylated) derivative 9 . The intramolecular ring closure of 8 in presence of sulfuric acid afforded the imidazothiazole 16 . Protection of the sulfur in 1 and subsequent reaction with allyl bromide gave the N‐allylated derivative and with 2 gave N‐3‐chloro‐prop‐1‐yl derivative that shed light on the preferred route for the formation of 3 and 4 . The reactivity encountered during the alkylation of 1 with 2 has been theoretically investigated by using the AM1 method.     

Synthesis of 3‐arylazo‐6‐oxopyridazin‐5‐carbonitriles: A versatile precursor for condensed arylazopyridazin‐6‐ones

1‐[2‐Phenyl‐1‐diazenyl]‐1‐[2‐phenylhydrazono]acetone or 1‐[‐2‐(4‐methylphenyl)‐1‐diazenyl]‐1‐[‐2‐(4‐methylphenyl)hydrazono]‐butan‐2‐one were produced via coupling the (E) 2‐oxopropanal‐1‐phenyl‐hydrazone or (E) 2‐oxobutanal‐1‐(4‐methylphenyl)hydrazone with aromatic diazonium salts. These formazanes condensed readily with ethyl cyanoacetate to yield 5‐methyl‐3‐oxo‐2‐phenyl‐6‐phenylazo‐2,3‐dihydropyridazine‐4‐carbonitrile compound ( 9a ), 5‐ethyl‐3‐oxo‐2‐p‐tolyl‐6‐p‐tolylazo‐2,3‐dihydro‐pyridazine‐4‐carbonitrile and/or 5‐ethyl‐3‐oxo‐2,6‐di‐p‐tolyl‐2,3‐dihydropyridazine‐4‐carbonitrile that reacted with sulphur in presence of piperidine to yield the aminothienopyridazinones. The latter reacted with electron poor olefins and acetylenes to yield aminophthalazines. Compound ( 9a ) reacted also with benzylidenemalononitrile to yield the arylazophthalazinone.     

The role of intermolecular interactions in the assemblies of Fe and Co tetrakis-isothiocyanatometalates with tris(1,10-phenanthroline)-Ru: Crystal structures of two dual-metal assemblies featuring octahedral cationic and tetrahedral anionic modules

Two new dual-metal assemblies: 2[Ru(phen)₃]²⁺·[Fe(SCN)₄]²⁻·2SCN⁻·4H₂O 1 and [Ru(phen)₃]²⁺·[Co(SCN)₄]²⁻2, (phen:1,10-phenanthroline), have been prepared and their structures were characterized by X-ray diffraction. In 1, the cationic octahedral enantiomers are arranged with a ΛΔΛΔΛ sequence supported by π-π stacking and the anionic inorganic tetrahedral units are oriented between these stacks by interacting with the nearby water molecules through strong O-H?O and O-H?S hydrogen bonds. In 2, homochiral double helices in the b-direction are revealed, with tetrakis-isothiocyanate Co^II anions arranged in the crystal to furnish one-dimensional (1D)-helical chains with S?S intermolecular interactions at 3.512(2) and 3.966(2) Å supporting [Ru(phen)₃]²⁺Λ- and Δ-helices with Ru?Ru shortest distance of 8.676(7) Å. In both 1 and 2, the supramolecular assembly is maintained by C-H?S hydrogen bonds extending between the phenanthroline aromatic carbons in the cationic nodes and the sulphur atoms of the isothiocyanates anions. Analysis of S?S interactions in isothiocyanate containing compounds using Cambridge structural database (CSD) showed an angle dependence categorizing these interactions into “type-I” and “type-II”.     

A pyrazole-based orthogonal ferromagnetically coupled [2 × 2] homoleptic square Cu4 grid: Magnetostructural correlations

The synthesis and structure of a pyrazole-based orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid complex [Cu₄(PzOAPyz)₄(ClO₄)₂](ClO₄)₂ · 6H₂O (1), formed by the reaction between the ditopic ligand PzOAPyz and Cu(ClO₄)₂ · 6H₂O, are described. The ligand contains terminal pyrazole and pyrazine residues bound to a central flexible diazine subunit (N–N) as well as one potentially bridging alkoxo group. The two adjacent metal centers are linked by an alkoxo oxygen forming essentially a square Cu₄(μ-O₄) cluster. In the Cu₄(μ-O₄) core, out of the four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by one of the oxygen atoms of a coordinated perchlorate ion. Complex 1 has been characterized structurally and magnetically. Although the large Cu–O–Cu bridge angles (137–138°) and short Cu–Cu distances (3.964–3.970 Å) are suitable for the transmission of the expected antiferromagnetic coupling, the square-based Cu₄(μ-O₄) cluster exhibits an intramolecular ferromagnetic exchange (J = 7.47 cm⁻¹) between the metal centers with an S = 2 magnetic ground state associated with the quasi orthogonal arrangement of the magnetic orbitals (d_x2-y2${\text{d}}_{x^2-y^2}$). The exchange pathway parameters have been evaluated from density functional calculations.     

A Silver(I)–Gold(II) Hexanuclear Guanidinate–Benzoate Cluster with Short Au–Au Bonds

Abstract  Attempts to remove the halide atoms from [Au₂(hpp)₂Cl₂], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, with Ag(I) benzoate lead to the formation of the Au(I)–Ag(I) product, [(PhCOO)₂Au₄(hpp)₄Ag₂(PhCOO)₄], 2. This material is stable to air and light at room temperature and shows a UV–vis spectrum in THF with absorbances at 575, 440, 345, and 273 nm. The mixed metal product crystallizes as green crystals in the monoclinic space group P2₁/n. The Au–Au distances of 2.4473(19) ? are the shortest gold–gold distances reported to date. The gold···silver distance is 3.344(3) ? and the silver···silver distance is 2.771(6) ?. This latter distance is short compared with the Ag···Ag distance of 2.902(3) ? in the eight-membered silver benzoate dimer starting material. The Au(II) hpp and Ag(I) benzoate components are linked by carboxylate groups and two gold-silver interactions. This result stands in structural contrast to terminal carboxylate products observed with Au(II) ylides and amidinates wherein the carboxylate is not bridging to another metal atom. Index Abstract  Three equivalents of silver benzoate react with [Au₂(hpp)₂Cl₂], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, to form the gold(II)-silver(I) product, 2, [(PhCOO)₂Au₄(hpp)₄Ag₂(PhCOO)₄]. The gold–gold distance of 2.4473(19) ? is the shortest gold–gold distance reported to date. The gold–silver distance is 3.344(3) ? and the silver–silver distance is 2.771(6) ?. Dedicated to the memory of F. Albert Cotton (1930–2007).     

Understanding microscopic binding of human microsomal prostaglandin E synthase-1 with substrates and inhibitors by molecular modeling and dynamics simulation

Microsomal prostaglandin E synthase-1 (mPGES-1) is a promising target for development of next-generation anti-inflammatory drugs. It is crucial for rational design of the next-generation anti-inflammatory drugs to know the three-dimensional (3D) structure of mPGES-1 trimer and to understand how mPGES-1 binds with substrates and inhibitors. In the current work, a 3D structural model of human mPGES-1 trimer has been developed, for the first time, by performing combined homology modeling, molecular docking, and molecular dynamics simulation. The 3D structural model enables us to understand how mPGES-1 binds with its substrates/inhibitors, and the key amino acid residues for the mPGES-1 binding with ligands have been identified. The detailed 3D structures and calculated binding free energies for mPGES-1's binding with substrates and inhibitors are all consistent with available experimental data, suggesting that the 3D model of the mPGES-1 trimer and the enzyme-ligand binding modes are reasonable. The new structural insights obtained from this study should be valuable for rational design of next-generation anti-inflammatory drugs.     

The prize collecting Steiner tree problem: models and Lagrangian dual optimization approaches

We propose a generalized version of the Prize Collecting Steiner Tree Problem (PCSTP), which offers a fundamental unifying model for several well-known -hard tree optimization problems. The PCSTP also arises naturally in a variety of network design applications including cable television and local access networks. We reformulate the PCSTP as a minimum spanning tree problem with additional packing and knapsack constraints and we explore various nondifferentiable optimization algorithms for solving its Lagrangian dual. We report computational results for nine variants of deflected subgradient strategies, the volume algorithm (VA), and the variable target value method used in conjunction with the VA and with a generalized Polyak–Kelley cutting plane technique. The performance of these approaches is also compared with an exact stabilized constraint generation procedure.     

Positive Elements and Automatic Continuity of Algebra Morphisms

We use positive elements of Hermitian algebras to give results on automatic continuity of algebra morphisms. Consequences and applications are also given.