Highly efficient C-8 oxidation of substituted xanthines with substitution at the 1-, 3-, and 7- positions using biocatalysts

A bacterial consortium consisting of strains belongings to the genus Klebsiella and Rhodococcus quantitatively converts 1-, 3- and 7-substituted xanthines to their respective 8-oxo compounds.

Prop-2-ynyl as a protective group for carboxylic acids: A mild method for the highly selective deprotection of prop-2-ynyl esters using tetrathiomolybdate

It is shown that prop-2-ynyl esters are useful protecting groups for carboxylic acids and that they are selectively deprotected in the presence of other esters on treatment with tetrathiomolybdate under mild conditions.

Synthesis, structure and spectroscopic studies on hydroxo-bridged heterotrinuclear complexes of cobalt(m) with ethane-l,2-diamine and ammonia as terminal ligands

Hydroxo-bridged homo- and hetero-trinuclear cobalt(III) complexes of the type [MII(H2O)2{(OH)2CoIII(N4)}2]X2·nH2O [MII= a divalent metal ion such as CoII, NiII or ZnII; N4=(en)2(en = ethane-1,2-diamine) or (NH3)4; X = SO4 or (ClO4)2; n= 3 or 5] have been prepared and spectroscopically characterized. The structure of [Cu{(OH)2Co(en)2}2][SO4]2·2H2O 1 has been determined. The geometry around copper atom is a pseudo-square-based pyramid, with the basal sites occupied by four bridging hydroxide oxygens and the apical site is occupied by a weakly co-ordinated sulfate anion [Cu–O 2.516(4)Å]. The hydroxo groups bridge pairs of cobalt(III) ions which are in near-octahedral environments. The ethylenediamine chelate rings have the twist conformation. In the crystal structure of [Cu{(OH)2Co(en)2}2][ClO4]4·2H2O 2 the perchlorate ion is not co-ordinated and the en ligands have envelope conformations. The sulfate ion in [Cu{(OH)2Co(NH3)4}2][SO4]2·4H2O 3 is not co-ordinated to the central copper ion. Electronic, infrared and variable-temperature EPR spectral data are discussed.

Homogeneous precipitation from solution by urea hydrolysis: a novel chemical route to the a-hydroxides of nickel and cobalt

Homogeneous precipitation from solution by hydrolysis of urea at elevated temperatures (T=120 degrees C) yields novel ammonia-intercalated alpha-type hydroxide phases of the formula M(OH)(x)(NH3)(0.4)(H2O)(y)(NO3)(2-x) where x=2, y=0.68 for M=Ni and x=1.85, y=0 for M=Co. These triple-layered hexagonal phases (a=3.08+/-0.01 Angstrom, c=21.7+/-0.05 Angstrom) are more crystalline than similar phases obtained by chemical precipitation or electrosynthesis. This method can be adapted as a convenient chemical route to the bulk synthesis of alpha-hydroxides.

The first observation of a Na2TiS2 related structure in a 2-D anionic manganese trimesate intercalated by cationic imidazole

A hydrothermal reaction of Mn(OAc)2·4H2O, trimesic acid, imidazole, KOH and water at 75 °C for 24 h gave rise to a 2-D compound, [HImd][Mn(BTC)(H2O)] (Imd = imidazole; BTC = trimesate), with protonated imidazole molecules occupying the inter-lamellar space, and the structure resembles the classic inorganic compound, the sodium intercalated TiS2 (Na2TiS2).

Synthesis and characterisation of heterometallic molecular triangles using ambidentate linker: self-selection of a single linkage isomer

The coordination driven self-assembly of discrete molecular triangles from a non-symmetric ambidentate linker 5-pyrimidinecarboxylate (5-pmc) and Pd(II)/Pt(II) based 90◦ acceptors is presented. Despite the possibility of formation of a mixture of isomeric macrocycles (linkage isomers) due to different connectivity of the ambidentate linker, formation of a single and symmetrical linkage somer in both the cases is an interesting observation. Moreover, the reported macrocycles represent the first example of discrete metallamacrocycles of bridging 5-pmc. While solution composition in both the cases was characterised by multinuclear NMR study and electrospray ionization mass spectrometry (ESI-MS), the identity of the assemblies in the solid state was established by X-ray single crystals structure analysis. Variable temperature NMR study clearly ruled out the formation of any other macrocycles by [4 + 4] or [2 + 2] self-assembly of the reacting components.

Acid-catalysed cyclisations: structures of novel products isolated in the reaction of 2-[3-(2,6-dimethoxyphenyl)but-2-enyl]-2-methylcyclopentane-1,3-dione with MeOH-HCl

Reaction of the title compound (1a) with anhydrous MeOH-HCl gave 2-endo-(2,6-dimethoxyphenyl)-2-exo-methyl-5-methylbicyclo[3.2.1]octane-6,8-dione (3a), 1,5,14-timethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),9(11)-tetraen-17-one (4), 1,5-dimethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),8,14-pentaen-17-one (5), and 3,4,5,6-tetrahydro-2,7-dimethoxy-3,6-dimethyl-3,2,6-(13-oxopropan[1]yI[3]ylidene)-2H-1-benzoxocin (6). Structures assigned to compounds (3a), (4), and (6) are based on spectral data. The exo-tricyclic acetal structure (6) was further confirmed by the analysis of the 1H n.m.r. spectra of the isomeric alcohols (11) and (12), obtained by sodium borohydride reduction of (6).

Crystalline A-DNA: The X-Ray Analysis of the Fragment d(G-G-T-A-T-A-C-C)

An A-DNA type double helical conformation was observed in the single crystal X-ray structure of the octamer d(G-G-T-A-T-A-C-C), 1, and its 5-bromouracil-containing analogue, 2. The structure of the isomorphous crystals (space group P61) was solved by a search technique based on packing criteria and R-factor calculations, with use of only low order data. At the present stage of refinement the R factors are 31 % for 1 and 28 % for 2 at a resolution of 2.25 A (0.225 nm). The molecules interact through their minor grooves by hydrogen bonding and base to sugar van der Waals contacts. The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found.

Studies of phosphazenes. Part 15. Chloro(phenoxy)cyclotetraphosphazenes, N4P4Cl8-n(OPh)n

The reaction of N4P4Cl8(1) with sodium phenoxide (or phenol in the presence of triethylamine) has been studied under a variety of experimental conditions. The chloro(phenoxy)-derivatives, N4P4Cl8-n(OPh)n[n= 1 or 2 (mixture of four non-geminal isomers), 3(mixture of non-geminal isomers), 4(mixture of isomers), 5(mixture of isomers), 6(mixture of four non-geminal isomers), or 8], have been isolated by column chromatography over silica gel. Attempts to separate geometric isomers were unsuccessful. Structural elucidation of the products is based on the 31P n.m.r. data for the chloro-precursors and 1H and 31P n.m.r. spectra of the dimethylamino- and/or methoxy-derivatives. The chlorine-replacement pattern is discussed.

Synthesis and characterization of a new sulphate derivative of hydrazine, N2H5HSO4

Hydrazinium(1 +) hydrogensulphate, N2H5HSO4, has been prepared for the first time by the reaction of solid ammonium hydrogensulphate with hydrazine monohydrate. The compound has been characterized by chemical analysis, infrared spectra, and X-ray powder diffraction. Thermal properties of N2H5HSO4 have been investigated using differential thermal analysis and thermogravimetric analysis and compared with those of N2H6SO4 and (N2H5)2SO4.

Zeeman effect of chlorine nuclear quadrupole resonance and hydrogen bonding in 2,6-, 2,5- and 3,5-dichlorophenols

The Zeeman effect of chlorine nuclear quadrupole resonance in polycrystalline samples of 2,6-, 2,5 and 3,5-dichlorophenol has been investigated at room temperature in order to study the effect of hydrogen bonding on the electric field gradient asymmetry parameter n. While the two n.q.r. lines in 3,5-dichlorophenol gave an asymmetry parameter of 10%, those in 2,6- and 2,5-dichlorophenol gave different values of n for the two chlorines. The chlorine atom which is ortho to the OH group and involved in hydrogen bonding (i.e., corresponding to the low frequency line) gave an asymmetry parameter of 0.21 in 2,6-dichlorophenol and 0.17 in 2,5-dichlorophenol while the other chlorine (i.e., corresponding to the high frequency line) gave a lower value of 0.12 in 2,6-dichlorophenol and 0.11 in 2,5-dichlorophenol. These values of n are discussed in terms of hydrogen bonding and bond parameters.

The crystal structure of the amino-terminal pentapeptide of suzukacillin. Occurrence of a four-fold peptide helix

The monohydrate of the protected amino-terminal pentapeptide of suzukacillin, t-butoxycarbonyl--aminoisobutyryl-L-prolyl-L-valyl--aminoisobutyryl-L-valine methyl ester, C29H51N5O8, crystallizes in the orthorhombic space group P212121 with a= 10.192, b= 10.440, c= 32.959 Å, and Z= 4. The structure has been solved by direct methods and refined to an R value of 0.101 for 1 827 observed reflections. The molecule exists as a four-fold helix with a pitch of 5.58 Å. The helix is stabilised by N–H O hydrogen bonds, two of the 51 type (corresponding to the -helix) and the third of the 41 type (310 helix). The carbonyl oxygen of the amino-protecting group accepts two hydrogen bonds, one each from the amide NH groups of the third (41) and fourth (51) residues. The remaining 51 hydrogen bond is between the two terminal residues. The lone water molecule in the structure is hydrogen bonded to carbonyl oxygens of the prolyl residue in one molecule and the non-terminal valyl residue in a symmetry-related molecule.

The dipole moments and molecular structure of substituted acetamides

Thioacetamide has a dipole moment substantially higher than the vector sum of the normal characteristic moments of its constituent bonds. However, the effect can reasonably be accounted for on the scheme of alterations in charge distribution and hence of bond moments proposed by Smith, Ree, Magee and Eyring. The same is probably true for chloroacetamide even though the problem of rotation about the C-C single bond renders the conclusion less certain. For cyanoacetamide, the observed moment cannot be accounted for satisfactorily on this basis.

X-ray and ultraviolet photoelectron spectroscopy studies of the interaction of carbon monoxide with oxygen adsorbed on silver covered with potassium, caesium or barium

X-ray and He(II) ultraviolet photoelectron spectroscopy studies of the interaction of CO with oxygen on potassium-, caesium- and barium-covered Ag surfaces have shown the formation of carbonate at 300 K. While on a caesium-covered surface only carbonate formation takes place, on the potassium- and barium-covered surfaces molecularly chemisorbed CO is also formed. The variation of the surface concentrations of carbon and oxygen with temperature has been examined and a reaction sequence for the interaction of CO with adsorbed oxygen on potassium-, caesium- and barium-covered Ag surfaces is suggested.

Catalysis and mechanism of malonyl transferase activity in type II fatty acid biosynthesis acyl carrier proteins

One of the unexplored, yet important aspects of the biology of acyl carrier proteins (ACPs) is the self-acylation and malonyl transferase activities dedicated to ACPs in polyketide synthesis. Our studies demonstrate the existence of malonyl transferase activity in ACPs involved in type II fatty acid biosynthesis from Plasmodium falciparum and Escherichia coli. We also show that the catalytic malonyl transferase activity is intrinsic to an individual ACP. Mutational analysis implicates an arginine/lysine in loop II and an arginine/glutamine in helix III as the catalytic residues for transferase function. The hydrogen bonding properties of these residues appears to be indispensable for the transferase reaction. Complementation of fabD(Ts) E. coli highlights the putative physiological role of this process. Our studies thus shed light on a key aspect of ACP biology and provide insights into the mechanism involved therein.