Reactions of the homoleptic acetonitrile complexes of palladium and platinum with diethylamine

The homoleptic [M(MeCN)₄]²⁺ cations (M = Pd, Pt) as the tetrafluoroborato derivatives were reacted with NHEt₂. The platinum species affords the amidino derivative {Pt[(E)-HNC(NEt₂)Me]₄}[BF₄]₂, 1, as the only detected product of the addition of the amine to the coordinated nitrile. On the contrary, for [Pd(MeCN)₄][BF₄]₂ competition between the substitution of the nitrile and addition of the amine to the nitrile group is operative: by carrying out the reaction in acetonitrile as solvent, complete conversion was obtained to the crystallographically defined {Pd[(E)-HNC(NEt₂)Me]₄}[BF₄]₂. Consistent with these findings, PdCl₂(MeCN)₂ reacts with NHEt₂ in acetonitrile yielding the substitution complex PdCl₂(NHEt₂)₂, whereas the amidino complex cis-PtCl₂[(E)-HNC(NEt₂)Me]₂, 3 was obtained from PtCl₂(MeCN)₂. Complex 3 was characterized by X-ray diffractometry.     

Neighboring group participation. Part 15. Stereoselective synthesis of some steroidal tetrahydrooxazin-2-ones, as novel presumed inhibitors of human 5alpha-reductase

During the alkaline methanolysis of 3beta-acetoxy-21-chloromethyl-pregn-5-ene-20beta-N-phenylurethane, and its p-substituted phenyl derivatives, cyclization occurs, in the course of which 17beta-[3-(N-phenyl)tetrahydrooxazin-2-on-6-yl]androst-5-en-3beta-ol and its p-substituted phenyl derivatives are formed. The cyclization takes place with (N(-)-6) neighboring group participation. Oppenauer oxidation of the 3beta-hydroxy-exo-heterocyclic steroids yielded the corresponding delta4-3-ketosteroids. The structures of the new compounds were proved by IR, 1H and 13C NMR spectroscopy, using up-to-date measuring techniques such as 2D-COSY, HMQC, and HMBC. The inhibitory effects (CI50) of the delta4-3-ketosteroids on 5alpha-reductase were studied.     

Reactions of the HCN-tetramer with aldehydes

The HCN-tetramer, a 'classic' of the prebiotic chemistry of HCN, is shown to undergo a remarkable reaction with acetaldehyde in slightly basic or neutral aqueous solution at room temperature. The reaction consists in an aldolization-type C,C-bond formation, accompanied by a (presumably aldehyde-catalyzed) hydration of one of the two nitrile groups and the formation of two cyclic aminal-type groupings, each of the latter incorporating an additional molecule of the aldehyde. Should this so far unexplored type of chemistry of the HCN-tetramer prove to have some generality, the finding might add a new dimension to the potential etiological relevance of this HCN-oligomer.     

Unexpected formation of complex bridged tetrazoles via intramolecular 1,3-dipolar cycloaddition of 1,2-O-cyanoalkylidene derivatives of 3-azido-3-deoxy-D-allose

An unexpected and interesting intramolecular side reaction occurred during the attempted synthesis of glycosyl cyanides upon treatment of 1-O-acetyl-3-azido-3-deoxyallose derivatives with TMSCN and different Lewis acids. Exo-1,2-O-cyanoalkylidene derivatives formed by neighboring group participation and attack of cyanide underwent, after Lewis-acid mediated isomerization to the endo-isomer, intramolecular azide-cyanide cycloaddition leading to the formation of tetrazoles embedded in bridged tetracyclic ring systems. The efficiency of cycloaddition is dependent on the ring structure of the sugar (pyranose or furanose). Of the studied molecules, 3-azido-1,2-O-cyanoethylidene-3-deoxy-allopyranose provides the most suitable scaffold for intramolecular [2+3] cycloaddition under exceptionally mild conditions. Our results highlight the capability of carbohydrates to act as scaffolds for the precise positioning of functional groups productive for a specific chemical reaction.     

Reactions of nitrones with transition metal nitrile complexes: cycloaddition, ligand substitution, or hydrolysis

The reaction of nitrones with transition metal nitrile complexes of the type [MCl₂(PhCN)₂] and [MCl₄(MeCN)₂] leads to different products, depending on the metal. Reaction of [PdCl₂(PhCN)₂] with RCHN(Me)O (R=Ph, p-C₆H₄Me) afford Δ⁴-1,2,4-oxadiazoline complexes as products of [2 + 3] cycloaddition of the nitrone across the C≡N bond of the nitrile. The oxophilic transition metal compounds [TiCl₄(MeCN)₂] and [ZrCl₄(MeCN)₂] undergo rapid ligand exchange to form nitrone complexes from which the nitrone can be released without decomposition. The closely related compounds [MoCl₄(MeCN)₂] and [WCl₄(MeCN)₂] mediate the hydrolysis of nitrones to the corresponding aldehydes.     

Chemo- and enantioselective hydrolysis of nitriles and acid amides, respectively, with resting cells of Rhodococcus sp. C3II and Rhodococcus erythropolis MP50

The two new bacterial strains, Rhodococcus sp. C3II and Rhodococcus erythropolis MP50, which have been especially selected for the enantioselective hydrolysis of pharmaceutically interesting 2-arylpropionitriles like naproxen nitrile, have been applied for the hydrolysis of various aliphatic and aromatic nitriles and acid amides. From the enantioselective hydrolysis of racemic ibuprofen amide 4, 2-phenylbutyronitrile 5a as well as the profen-related atrolactamide 8 we deduce the decisive role of both an alkyl and aryl substituent in the -position to the nitrile or amide function for high enantioselectivity of the hydrolysis. Strain C3II and MP50 differ in the activity of their nitrile hydratase–amidase enzyme systems. This is of interest for the regioselective hydrolysis of the dinitriles 10a–13a to diacids 10f–13f. While strain C3II is suitable to preferentially produce mononitrile monoamide derivatives, strain MP50 can be used especially to form mononitrile monoacid and monoamide monoacid derivatives.     

Fatty acids,part 38: Neighbouring group participation in the oxymercuration-demercuration reaction. Another route to 1,4- and 1,5-epoxides

Oxymercuration-demercuration of hydroxy alkenes follows an intramolecular pathway to furnish 1,4-epoxides (tetrahydrofurans) when the hydroxyl group is β (trans only) or γ to a double bond and 1,5-epoxides (tetrahydropyrans) when the hydroxyl group is δ to the double bond. The cis and trans isomers of methyl ricinoleate and methyl 9-hydroxyoctadec-12-enoate, and a series of cis and trans octadecenols (Δ2–Δ6) are used to establish these relationships.1,4- and 1,5-Epoxides are also formed during the oxymercuration of methyl densipolate and methyl 12,13-dihydroxyoleate and during the hydroxymercuration of methyl octadeca-9,12 and 8,12-dienoates.     

Synthesis and spectral luminescent characteristics of the porphyrin complexes with the platinum group metals

The syntheses of complexes of natural and synthetic porphyrins with Pt, Pd, Rh, and Ru are reported. Their electronic absorption spectra, phosphorescence spectra, and lifetimes at room temperature both in the presence and in the absence of oxygen were studied. Variations in the nature of the central metal atom and in the substituents in pyrrol and phenyl rings allow the obtaining of metalloporphyrins phosphorescing at room temperature with various phosphorescence excitation and emission spectra.     

Neighboring group participation. Part 16. Stereoselective synthesis and receptor-binding examination of the four stereoisomers of 16-bromomethyl-3,17-estradiols

The four possible isomers of 3-benzyloxy-16-hydroxymethylestra-1,3,5(10)-trien-17-ol (1a-4a) with proven configurations were converted into the corresponding 3-benzyloxy-16-bromomethylestra-1,3,5(10)-triene-3,17-diols (5e-8e). Depending on the reaction conditions the cis isomers of 3-benzyloxy-16-hydroxymethylestra-1,3,5(10)-trien-17-ol (1a and 2a) were transformed into 3-benzyloxy-16-bromomethylestra-1,3,5(10)-trien-17-yl acetate (5b and 6b) or 16-bromomethyl-3-hydroxyestra-1,3,5(10)-trien-17-yl acetate (5c and 6c) on treatment with HBr and acetic acid. The mechanism of the process can be interpreted as involving front-side neighboring group participation. Under similar experimental conditions, the trans isomers (3a and 4a) yielded only 3-benzyloxy-16-acetoxymethylestra-1,3,5(10)-trien-17-yl acetates (3b and 4b) or 16-acetoxymethylestra-1,3,5(10)-triene-3,17-diyl diacetates (3d and 4d). Both the cis (1a and 2a) and the trans (3a, and 4a) isomers were transformed into 16-bromomethylestra-1,3,5(10)-trien-17-ol (5a-8a) by the Appel reaction on treatment with CBr4/Ph3P. Debenzylation of 5a-8a was carried out with HBr and acetic acid to yield 5e-8e. The debenzylation process in the presence of acetic anhydride produces the diacetates 5d-8d. The structures of the compounds were determined by means of MS, 1H NMR and 13C NMR spectroscopic methods. Compounds 5c-8c and 5e-8e were tested in a radioligand-binding assay. Except for the affinity of 7e for the estrogen receptor (Ki=2.55 nM), the affinities of the eight compounds (5c-8c and 5e-8e) for the estrogen, androgen and progesterone receptors are low (Ki > 0.55, 0.52 and 0.21 microM, respectively).     

Incorporation of thiolate donation using 2,2'-dithiodibenzaldehyde: complexes of a pentadentate N2S3 ligand with relevance to the active site of Co nitrile hydratase

The use of 2,2'-dithiodibenzaldehyde (DTDB) as a reactant for incorporating thiolate donors into the coordination sphere of a transition metal complex without the need for protecting groups is expanded to include the synthesis of complexes with pentadentate ligands. The ligand N,N'-bis(thiosalicylideneimine)-2,2'-thiobis(ethylamine) (tsaltp) is synthesized at a cobalt center by the reaction of DTDB with a Co complex of thiobis(ethylamine). The resulting Co complexes are thus coordinated by the N(2)S(3) pentadentate ligand through two imine N atoms, two thiolate S atoms, and one thioether S atom. A dimeric, bis-thiolate-bridged complex (1) is isolated and converted to a monomeric CN adduct (2) by treatment with KCN. The N(2)S(3) coordination environment provided by the tsaltp ligand is similar to that provided by the protein donors at the active site of the nitrile hydratase enzymes, with 2 being the first octahedral Co complex reported with such a coordination sphere.     

On the causal relationship between participation in national commemorations and feelings of national belonging

It is often theoretically argued that participation in national commemorations increases feelings of national belonging. Previous studies have also empirically demonstrated that participation in national commemorations and feelings of national belonging are positively related. We are uncertain, however, about the direction of this relationship. Does participating in national commemorations increase feelings of national belonging (increase hypothesis) or do people who attend such ceremonies feel a greater sense of national belonging compared to people who not attend (selection hypothesis)? Using an innovative research design, this study sheds more light on the direction of the relationship between participation in national commemorations and feelings of national belonging. We collected data from respondents before (n?=?469), during (n?=?50) and after (n?=?226) the national ceremony on Remembrance Day in 2015 in the Netherlands. In this study, we found support for the selection hypothesis, but not for the increase hypothesis.     

Polar group conformation of 1,2-di-O-alkylglycerophosphocholines in the absence and presence of ions

The conformation of the glycerophosphocholine (GPC) group of various 1,2-di-O-alkyl and 1,2-diacylglycerophosphocholines forming small micelles or single-bilayer vesicles in H₂O has been studed by NMR in the absence and presence of lanthanide ions. In the absence of lanthanides the motionally averaged polar group conformation of 1,2-di-O-alkylglycerophosphocholine (dialkyl-GPC) is similar to that of the diacyl compound. The replacement of the ester linkages in diacyl phosphatidylcholine by ether bonds has therefore no significant effect on the conformation and segmental motion of the glycerophosphocholine group. This conformation is found to be independent of the state of aggregation, i.e., the main features are the same below and above the critical micellar concentration (CMC). The determining factor must therefore be the intramolecular energetics. Within the experimental accuracy the conformation of dialkyl-GPC in the presence of lanthanide ions is also the same as that of the corresponding diacyl compound. Furthermore, in the presence of lanthanides the polar group conformation of dialkyl-GPC is the same within experimental accuracy in small micelles and single bilayer vesicles. The conformational change induced by lanthanides leads to a reorientation of the OPN dipole. In the presence of lanthanides the OPN dipole increases its angle of tilt with respect to the bilayer plane from about 0° (coplanar orientation) to an average inclinication of about 45°. This gives rise to a more extended disposition of the polar group with respect to the bilayer normal.     

Isolation and characterization of glycosphingolipids with J blood group activity from bovine spleen1,2

Two glycosphingolipids with J blood group activity were found in J-positive bovine spleen. They were tentatively identified as ceramide deca- and dodecahexosides containing galactose, glucose, N -acetylgalactosamine and N -acetylglucosamine in a molar ratio of 5:3:1:1 and 6:3:2:1, respectively. Fucose was not present. Ceramide decahexosides without J activity were also found in J-negative bovine spleen. The principal component fatty acids of the J-active glycosphingolipids were saturated even-numbered long-chain acids with 16 to 24 C atoms. Their principal long-chain bases were sphingosine and dihydrosphingosine with smaller amounts of phy-tosphingosine.
Both J-active glycosphingolipids were readily water-soluble and showed strong activity in the bovine J and in the porcine A blood group system. They exhibited no cross-reactivity in the human A system. However, a J-negatiye glycosphingolipid fraction - also from J-negative spleen - with shorter carbohydrate chain-length showed strong activity in the human A system.     

Antimicrobial activity of ZnII, CdII, and HgII complexes of 1,2-bis-[2-(5-R)-1H-benzimidazolyl]-1,2-ethanediols and 1,4-bis-[2-(5-R)-1H-benzimidazolyl]-1,2,3,4-butanetetraols

1,2-Bis-[2-(5-H/Me/Cl/NO2)-1H-benzimidazolyl]-1,2-ethanediols (L1-L4), 1,4-bis-[2-(5-H/Me/Cl)-1H-benzimidazolyl]-1,2,3,4-butanetetraols (L5-L7) and their complexes with ZnCl2, CdCl2 and HgCl2 were synthesized and antibacterial activity of the compounds was tested toward Staphylococcus aureus, S. epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri, Proteus mirabilis and antifungal activity against Candida albicans. HgII complexes have a considerably higher antimicrobial activity against all microorganisms. Some HgII complexes show higher antifungal activity than clotrimazole toward C. albicans. Zn2(L3)Cl4, Zn2(L4)Cl4, and Cd(L3)Cl2 were moderately effective against S. aureus and S. epidermidis; Cd(L4)Cl2 exhibited a weak activity only against S. epidermidis.     

Iron(III), nickel(II) and cadmium(II) complexes of triazamacrocyclic ligand with pendant nitrile groups 1,4,7-tris(cyanomethyl)-1,4,7-triazacyclononane: Synthesis, structural characteristics and artificial nuclease activity

Three novel transition metal complexes with 1,4,7-tris(cyanomethyl)-1,4,7-triazacyclononane (L) were synthesized and structurally characterized. In complex [FeLCl₃]·2H₂O (1), three N-donors from the macrocyclic backbone and three chloride anions complete the coordination polyhedron around Fe(III) and lead to a neutral [FeLCl₃] unit. The neutral Fe(III) units of the same chirality are linked through weak interactions into 3D supramolecular network with hexagonal channels. Guest water molecules trapped inside the channel are associated into an unprecedented 1D linear chain. The crystal structures of complexes [NiL(CH₃CN)₃](ClO₄)₂·0.5H₂O (2) and [CdL(CH₃CN)₃](ClO₄)₂·0.5H₂O (3) reveal that the metal center lies in a distorted octahedral N6 environment with three acetonitrile occupying the remaining coordination sites opposite to the macrocyclic ring. The artificial nuclease activity of redox-active complex 1 towards pMD-AMT plasmid DNA was assessed by gel electrophoresis. As a result, complex 1 can effectively cleave supercoiled DNA under near physiological conditions with/without H₂O₂ in a time- and complex concentration-dependent manner.     

Complexes of the imine/thioether mixed-donor ligand 8-methylthioquinoline with d-configurated transition metal centers: synthesis, structures and comparison with complexes of 1-methyl-2-(methylthiomethyl)-1H-benzimidazole

Coordination compounds of chelating 8-methylthioquinoline (MTQ) with the complex fragments Re^I(CO)₃Cl, [Ru^II(bpy)₂]²⁺, [Rh^III(C₅Me₅)Cl]⁺, [Ir^III(C₅Me₅)Cl]⁺, and Pt^IVMe₄ were synthesized and structurally characterized. Whereas the ruthenium(II) complex displays the strongest preference of bonding to N versus S, the compound (MTQ)PtMe₄ shows the most balanced metal-donor bonding within the chelate ring due to a relatively short bond to S (2.319 Å) versus N (2.150 Å). The complex fac-(MTQ)Re(CO)₃Cl exhibits a particularly long metal-sulfur bond at 2.472 Å. Cyclic voltammetry of [(MTQ)Ru(bpy)₂](PF₆)₂ reveals one reversible oxidation to Ru^III and three closely spaced reduction waves for the coordinated ligands. In comparison with the imine/thioether chelate ligand 1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) the MTQ ligand with its more rigid chelate setting N(sp²)-C(sp²)-C(sp²)-S forms generally shorter M-S bonds and displays stronger π acceptor behaviour.     

Benzene-1,2-, 1,3-, and 1,4-di-N-substituted carbamates as conformationally constrained inhibitors of acetylcholinesterase

Benzene-1,2-, 1,3-, and 1,4-di-N-substituted carbamates (1-15) are synthesized as the conformationally constrained inhibitors of acetylcholinesterase and mimic gauche, eclipsed, and anti-conformations of acetylcholine, respectively. All carbamates 1-15 are characterized as the pseudo substrate inhibitors of acetylcholinesterase. For a series of geometric isomers, the inhibitory potencies are as follows: benzene-1,4-di-N-substituted carbamate (para compound) > benzene-1,3-di-N-substituted carbamate (meta compound) > benzene-1,2-di-N-substituted carbamate (ortho compound). Therefore, benzene-1,4-di-N-substituted carbamates (para compounds), with the angle of 180 degrees between two C(benzene)-O bonds, mimic the preferable anti C-O/C-N conformers of acetylcholine for the choline ethylene backbone in the acetylcholinesterase catalysis.     

Antimicrobial activity of 1,2-bis-[2-(5-R)-1H-benzimidazolyl]-1,2-ethanediols, 1,4-bis-[2-(5-R)-1H-benzimidazolyl]-1,2,3,4-butanetetraols and their FeIII, CuII, and AgI complexes

1,2-Bis-[2-(5-H/Me/Cl/NO2)-1H-benzimidazolyl]-1,2-ethanediols (L1-L4), 1,4-Bis-[2-(5-H/Me/Cl)-1H-benzimidazolyl]-1,2,3,4-butanetetraols (L5-L7) and their complexes with FeCl3, CuCl2, and AgNO3 were synthesized; antibacterial activity of the compounds was determined toward Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri, Proteus mirabilis, and antifungal activity against Candida albicans. The AgI complexes have considerable activity toward the microorganisms. Some AgI complexes show higher activity toward S. epidermidis than AgNO3 and cefuroxime. Cu(L3)Cl2 and Fe(L3)Cl3 show an antifungal effect on C. albicans but L3 itself has no activity.     

Synthesis, electrochemistry and spectroscopic properties of ruthenium phthalocyanine and naphthalocyanine complexes with triphenylarsine ligands

The synthesis, electrochemistry and spectroscopic properties of [PcRu(AsPh₃)₂] (1) and [{(tBu)₄Nc}Ru(AsPh₃)₂] (2), where Pc = phthalocyanine and Nc = naphthalocyanine are reported. These complexes are the first examples of metal phthalocyanine and naphthalocyanine complexes with axially-coordinated arsine ligands. The AsPh₃ ligands readily dissociate in non-coordinating solvents with 2 showing more rapid dissociation. In cyclic voltammetry experiments, 1 displayed three macrocycle-centred redox processes; one reduction and two oxidation processes. One reduction and three oxidation processes were observed for 2. The reduction and first oxidation are assigned to macrocycle-centred processes. The UV-Vis spectra of both complexes recorded over time showed macrocycle-centred oxidation. The oxidation was hindered by removing dioxygen from the solvent or adding excess AsPh₃.     

Asymmetric hydrolyses of 1,2- and 1,3-diacetoxycyclohexanes with the cultured suspension cells of Marchantia polymorpha

Very high enantioselectivities were observed in the hydrolysis of racemic 1,2- and 1,3-diacetoxycyclohexanes and their derivatives by cultured cells of Marchantia polymorpha in suspension. Asymmetry was also induced in the hydrolyses of meso-1,2- and 1,3-diacetates to the corresponding monoacetates. These findings indicate that these cultured cells hydrolyze the acetoxyl groups enantioselectively at the stereogenic center of R-configuration. Chirality 9:250–253, 1997. © 1997 Wiley-Liss, Inc.