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ABSTRACT: Cob(i)alamin reacts with phenylacetylene to produce two diastereomers in which the organic ligand is coordinated to the upper (β) and lower (α) face of the corrin ring, respectively. The isomers were separated chromatographically and characterised by ESI-MS and, in the case of the β isomer, by (1)H and (13)C NMR. Only the β isomer crystallised and its molecular structure, determined by X-ray diffraction, shows that the organic ligand coordinates Co(iii) through the β carbon of the phenylvinyl ligand. The Co-C bond length is 2.004(8) Å while the Co-N bond length to the trans 5,6-dimethylbenzimidazole (dmbzm) base is 2.217(8) Å, one of the longest Co-Ndmbzm bond lengths known in an organocobalamin. Unlike benzylcobalamin (BzCbl), phenylvinylcobalamin (PhVnCbl) is stable towards homolysis. DFT calculations (BP86/TZVP) on model compounds of BzCbl and PhVnCbl show that the Co-C bond dissociation energy for homolysis to Co(ii) and an organic radical in the former is 8 kcal mol(-1) lower than in the latter. An analysis of the electron density at the Co-C bond critical point using Bader's QTAIM approach shows that the Co-C bond in PhVnCbl is shorter, stronger and somewhat more covalent than that in BzCbl, and has some multiple bond character. Together with calculations that show that the benzyl radical is more stable than the phenylvinyl radical, this rationalises the stability of PhVnCbl compared to BzCbl. The phenylvinyl ligand has a large trans influence. The pKa for deprotonation of dmbzm and its coordination by the metal in β-PhVnCbl is 4.60 ± 0.01, one of the highest values reported to date in cobalamin chemistry. The displacement of dmbzm ligand by CN(-) in β-PhVnCbl occurs with log K = 0.7 ± 0.1; the trans influence order of C-donor ligands is therefore CN(-) < CCH < CHCH2 = PhVn < Me < Et.
Dalton Transactions 03/2013; · 3.84 Impact Factor
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ABSTRACT: Tungsten-183 NMR data are reported for the complexes cis-[W(CO)(4) (PPh(3) )(4-RC(5) H(4) N)] (R = H, Me, Ph, COMe, COPh, OMe, NMe(2) , Cl, NO(2) ). The (183) W chemical shift (obtained by indirect detection using (31) P) is found to correlate with the Hammett σ function for the group R, with (183) W shielding increasing approximately linearly with the donor strength of the pyridine over a range of 93 ppm. The X-ray structures of cis-[W(CO)(4) (PPh(3) )(4-MeOC(5) H(4) N)] and cis-[W(CO)(4) (PPh(3) )(4-PhCOC(5) H(4) N)] are also reported. Copyright © 2013 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry 02/2013; · 1.44 Impact Factor
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ABSTRACT: The title macrocyclic amino alcohol compound, C14H30N4O, is investigated as a solid-state synthon for the design of a self-assembled tubular structure. It crystallizes in a helical column constructed by stereospecific O—H- - - -N and N—H- - - -N interactions. The hydrogen-bonding interactions, dependent upon macrocyclic ring helicity and molecular conformation, link R,R and S,S enantiomers in a head-to-tail fashion, forming a continuous hydrophilic inner core.
Acta Crystallographica Section C. 10/2012; C(68):o383-o386.
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ABSTRACT: In the crystal structure of the 1:1 title salt, C(4)H(12)NO(2) (+)·C(6)H(4)BrO(-), hydrogen-bonding inter-actions originate from the ammonium cation, which adopts a syn conformation. A gauche relationship between the C-O and C-N bonds of the 2-hy-droxy-ethyl fragments also facilitates O-H⋯O inter-actions of bis-(2-hy-droxy-eth-yl)ammonium cation chains to phenolate O atoms. The resulting double-ion chains along [100] are further linked by N-H⋯O inter-actions, forming chains parallel to [110].
Acta Crystallographica Section E Structure Reports Online 09/2012; 68(Pt 9):o2610. · 0.35 Impact Factor
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ABSTRACT: The synthesis of two closely related pyranonaphthoquinones, dehydroherbarin and anhydrofusarubin, is described. The construction of the naphthalene nuclei was achieved using the Stobbe condensation reaction using 2,4-dimethoxybenzaldehyde and 2,4,5-trimethoxybenzaldehyde as their respective starting materials. Two key steps en route include a PIFA-mediated addition of a methoxy substituent onto the naphthalene skeleton and a Wacker oxidation reaction to construct the benzo[g]isochromene nucleus. Two interesting oxidation reactions of the intermediate isochromene enol ether of 7,9-dimethoxy-3-methyl-1H-benzo[g]isochromene-5-ol were observed. Treatment of the substrate with salcomine resulted in the formation of (3-formyl-4-hydroxy-6,8-dimethoxynaphthalene-2-yl)methyl acetate, while treatment of the same substrate with CAN resulted in the formation of racemic (3R,4R)-3-hydroxy-7,9-dimethoxy-3-methyl-5,10-dioxo-3,4,5,10-tetrahydro-1H-benzo[g]isochromen-4-yl nitrate.
Organic & Biomolecular Chemistry 08/2012; 10(38):7809-19. · 3.70 Impact Factor
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ABSTRACT: In the crystal structure of the title compound, C(21)H(14)ClN(3)OS, mol-ecules assemble into inversion dimers via pairs of N-H⋯N hydrogen bonds involving the N-H hydrogen of the thia-zine ring and the N atom of the pyridine ring. There is a close intra-molecular contact [2.570 (2) Å] between the carbonyl O atom of the benzamide and the S atom of the puckered thia-zine ring. The title compound can exist in two tautomeric forms, viz. amino or imino. The observed structure is compatible with the imino form on the basis of observed residual electron density and the two C-N bond lengths of 1.308 (2) and 1.353 (2) Å.
Acta Crystallographica Section E Structure Reports Online 08/2012; 68(Pt 8):o2346. · 0.35 Impact Factor
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ABSTRACT: The title salt, C(4)H(10)Br(2)N(+)·Br(-), crystallizes with four cations and four anions in the asymmetric unit. In the crystal, the bis-(2-bromo-eth-yl)ammonium cations and bromide anions are linked into chains by N-H⋯Br hydrogen bonds describing a binary C(2) (1)(4) motif along [010]. Each of these chains is formed by a unique cation and anion pair. The ammonium cations occur in the less preferred anti conformation, characterized by different NCCBr torsion angles. Adjacent chains are linked by weak C-H⋯Br inter-actions, forming a three-dimensional network. The crystal studied was a pseudo-merohedral twin with twin ratio 0.640 (2):0.360 (2).
Acta Crystallographica Section E Structure Reports Online 08/2012; 68(Pt 8):o2570-1. · 0.35 Impact Factor
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ABSTRACT: Six ammonium carboxylate salts, namely cyclopentylammonium cinnamate, C(5)H(12)N(+)·C(9)H(7)O(2)(-), (I), cyclohexylammonium cinnamate, C(6)H(14)N(+)·C(9)H(7)O(2)(-), (II), cycloheptylammonium cinnamate form I, C(7)H(16)N(+)·C(9)H(7)O(2)(-), (IIIa), and form II, (IIIb), cyclooctylammonium cinnamate, C(8)H(18)N(+)·C(9)H(7)O(2)(-), (IV), and cyclododecylammonium cinnamate, C(12)H(26)N(+)·C(9)H(7)O(2)(-), (V), are reported. Salts (II)-(V) all have a 1:1 ratio of cation to anion and feature three N(+)-H···O(-) hydrogen bonds forming one-dimensional hydrogen-bonded columns consisting of repeating R(4)(3)(10) rings, while salt (I) has a two-dimensional network made up of alternating R(4)(4)(12) and R(6)(8)(20) rings. Salt (III) consists of two polymorphic forms, viz. form I having Z' = 1 and form II with Z' = 2. The latter polymorph has disorder of the cycloheptane rings in the two cations, as well as whole-molecule disorder of one of the cinnamate anions. A similar, but ordered, Z' = 2 structure is seen in salt (IV).
Acta crystallographica. Section C, Crystal structure communications 05/2012; 68(Pt 5):o188-94. · 0.78 Impact Factor
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ABSTRACT: The crystal strucure of the title compound, C(7)H(9)NO, displays N-H⋯O hydrogen bonds which link mol-ecules related by translation along the b axis, and O-H⋯N and further N-H⋯O hydrogen bonds which link mol-ecules related by the 2(1) screw axis along the c axis. The resulting combination is a hydrogen-bonded layer of mol-ecules parallel to (011).
Acta Crystallographica Section E Structure Reports Online 01/2012; 68(Pt 1):o174. · 0.35 Impact Factor
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ABSTRACT: In the title compound, C(4)H(10)NO(+)·Br(-), which was synthesized by dehydration of diethano-lamine with HBr, morpholinium and bromide ions are linked into chains by N-H⋯Br hydrogen bonds describing a C(2) (1)(4) graph-set motif. Weaker bifurcated N-H⋯Br inter-actions join centrosymmetrically related chains through alternating binary graph-set R(4) (2)(8) and R(2) (2)(4) motifs, to form ladders along [100]. In addition, C-H⋯O inter-actions between centrosymmetric morpholinium cations link ladders, via[Formula: see text](8) motifs, to yield sheets parallel to (101), which in turn are crosslinked by weak C-H⋯O inter-actions, related across a glide plane, to form a three-dimensional network.
Acta Crystallographica Section E Structure Reports Online 10/2011; 67(Pt 10):o2594. · 0.35 Impact Factor
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ABSTRACT: A stable yellow derivative of cobyrinic acid heptamethyl ester, (5R,6R)-Coα,Coβ-dicyano-5,6-dihydro-5-hydroxy-heptamethylcob(III)yrinate-c,6-lactone (DCSYCbs), was prepared from dicyanocobyrinic acid heptamethyl ester (DCCbs). The C5 carbon is oxidized and the c side chain cyclized to form a lactone at C6; the 13 atom, 14 π-e(-) delocalized system of corrins is interrupted, giving a triazamethine system with four conjugated double bonds between N22 and N24 and an isolated double bond between N21 and C4. Stable yellow aquacyanocobyrinic acid heptamethyl ester (ACSYCbs) was prepared by driving off HCN with N(2) in a methanol/acetic acid solution. The electronic spectra of DCCbs and DCSYCbs appear similar except that the bands in DCSYCbs are shifted to shorter wavelengths and the γ-band is much less intense. The experimental spectra were adequately modeled using TD-DFT at the PBE1PBE/6-311G(d,p) level of theory. DCSYCbs crystallizes in the space group P2(1)2(1)2(1) (R(1) = 6.08%) with Z = 4, including one methanol solvent molecule and one water molecule per cobester. The addition of a hydroxyl group at C5 causes loss of the double bond between C5 and C6 and elongation of the C5-C6 bond. From a combination of two-dimensional (1)H TOCSY and ROESY NMR spectra and (1)H/(13)C HSQC and HMBC data, the complete (1)H and (13)C NMR assignments of DCSYCbs were possible, except for two of the ester methyl groups and the (13)C resonances of the two axial cyanide ligands. The latter were assigned using relative chemical shifts calculated by GIAO-DFT methods. The (59)Co resonance of DCCbs was observed at 4074 ppm while that of DCSYCbs is shifted downfield to 4298 ppm. Comparison with available (59)Co data of analogous systems suggests that the more π-conjugated corrin of DCCbs interacts more strongly with the metal than the less extensively conjugated macrocycle of DCSYCbs. As the strength of the interaction between Co(III) and an equatorial macrocycle increases, ν(CN) of axially coordinated CN(-) shifts to lower frequency; in DCSYCbs and DCCbs ν(CN) occurs at 2138 and 2123 cm(-1), respectively. Hence the corrin ligand in DCCbs interacts more strongly with the metal than the stable yellow corrin ligand, with its diminished conjugation. The UV-vis spectral data and DFT-calculated MOs are consistent with greater overlap between the corrin and the metal orbitals in DCCbs relative to DCSYCbs, which gives the metal in the former a softer, more covalent character.
Inorganic Chemistry 08/2011; 50(18):8700-18. · 4.60 Impact Factor
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Igor V Magedov,
Liliya Frolova,
Madhuri Manpadi,
Uma devi Bhoga,
Hong Tang,
Nikolai M Evdokimov,
Olivia George,
Kathy Hadje Georgiou,
Steffen Renner,
Matthäus Getlik,
Tiffany L Kinnibrugh, Manuel A Fernandes,
Severine Van slambrouck,
Wim F A Steelant,
Charles B Shuster,
Snezna Rogelj,
Willem A L van Otterlo,
Alexander Kornienko
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ABSTRACT: Structural simplification of an antimitotic natural product podophyllotoxin with mimetic heterocyclic scaffolds constructed using multicomponent reactions led to the identification of compounds exhibiting low nanomolar antiproliferative and apoptosis-inducing properties. The most potent compounds were found in the dihydropyridopyrazole, dihydropyridonaphthalene, dihydropyridoindole, and dihydropyridopyrimidine scaffold series. Biochemical mechanistic studies performed with dihydropyridopyrazole compounds showed that these heterocycles inhibit in vitro tubulin polymerization and disrupt the formation of mitotic spindles in dividing cells at low nanomolar concentrations, in a manner similar to podophyllotoxin itself. Separation of a racemic dihydropyridonaphthalene into individual enantiomers demonstrated that only the optical antipode matching the absolute configuration of podophyllotoxin possessed potent anticancer activity. Computer modeling, performed using the podophyllotoxin binding site on β-tubulin, provided a theoretical understanding of these successful experimental findings.
Journal of Medicinal Chemistry 06/2011; 54(12):4234-46. · 4.80 Impact Factor
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ABSTRACT: Two polymorphs of N-[2-(hydroxymethyl)phenyl]benzamide have been identified and their structures elucidated. Both crystallize in P21/n but with different unit cell parameters and crystal packing. The less stable polymorph II undergoes a first order phase transition to polymorph I at 85 °C, as determined using variable temperature powder diffraction studies. The arrangement of molecules in both structures is characterized by intramolecular ring-forming N−H···O(H) and chain-forming intermolecular O−H···O═C hydrogen bonds. It is, however, the nature of the dispersive interactions due to π overlap that differentiates the two structures. In polymorph I, these exist in a molecule···molecule interaction that also accommodates the O−H···O═C hydrogen bond. Calculations using atom−atom potential methods, and corroborated using DFT methods, indicate that the interaction energy of this pair of molecules accounts for at least half of the total lattice energy of the structure. Carrying out the equivalent calculations on polymorph II shows that the dispersive interactions due to π overlap and the O−H···O═C hydrogen bond are separated into two different molecule···molecule interactions. This suggests that determining the distinctive interactions between pairs of molecules may provide some insight into how to inhibit them and, hence, favor the growth of other crystal forms.
04/2011;
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ABSTRACT: The achiral meso form of the title compound, C(18)H(38)N(2)O(4)(2+)·2Cl(-), crystallizes to form undulating layers consisting of chains linked via weak hydroxyalkyl C-H...Cl contacts. The chains are characterized by centrosymmetric hydrogen-bonded dimers generated via N-H...Cl and hydroxycycloalkyl O-H...Cl interactions. trans-N-Alkyl bridges subdivide the chains into hydrophilic segments flanked by hydrophobic cycloalkyl stacks along [001].
Acta crystallographica. Section C, Crystal structure communications 11/2010; 66(Pt 11):o553-6. · 0.78 Impact Factor
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ABSTRACT: Reaction of (2,4,5-trimethoxyphenyl)(2-hydroxyphenyl)methanone with ceric ammonium nitrate furnished the xanthone, 2,3-dimethoxy-9H-xanthen-9-one. Under the same conditions the related (1,4-dimethoxynaphthalen-2-yl)(2-hydroxyphenyl)methanone resulted in the formation of 12a-methoxy-5H-benzo[c]xanthenes 5,7(12aH)-dione. Other examples of this novel transformation are also outlined.
The Journal of Organic Chemistry 11/2010; 75(24):8701-4. · 4.45 Impact Factor
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ABSTRACT: The synthesis and solid state structure of the amino-alcohol ligand, (1R,2R,1'S,2'S)-N,N'-bis(2-hydroxycyclopentyl)ethane-1,2-diamine (Cyp(2)en) obtained by the reaction of cyclopentene oxide with ethylenediamine, as well as its bromide, chloride, perchlorate, and nitrate salts, is reported. In all five structures, the Cyp(2)en ligand sits on a center of inversion with the two amino groups and two hydroxyl groups of the cyclopentyl moieties trans to each other across that inversion center. Comparing this conformation to that of a density functional theory (DFT)-calculated structure of cis-[Ni(Cyp(2)en)(H(2)O)(2)](2+) suggests that the ligand is not well pre-organized for coordinating a metal ion. The likely solution structure of this ligand, and that of the related ligands bis(2-hydroxy)ethane-1,2-diamine (Bheen) and bis(2-hydroxycyclohexyl)ethane-1,2-diamine (Cy(2)en), was explored using molecular mechanics modeling with the generalized AMBER force field. A Boltzmann distribution of the lowest energy conformations found shows that 36 conformations of Bheen each contribute more than 1% to the population at 300 K; this decreases to 27 conformations for Cyp(2)en and to 12 for Cy(2)en, and Cy(2)en is the most rigid of the three ligands. The population-weighted root-mean-square deviation (rmsd) between these lowest energy conformations and the conformation required for coordinating a metal ion increased in the order Cy(2)en < Cyp(2)en < Bheen, while stability constants for coordinating Ni(II) decrease in the order Cy(2)en > Bheen > Cyp(2)en. The high pre-organization of Cy(2)en is due to an intramolecular N-H....O hydrogen bond, apparently missing in the other two ligands. Pre-organization is likely to be an important, but not the only factor, that controls the value of the stability constants of these ligands with metal ions.
Inorganic Chemistry 09/2010; 49(17):8003-11. · 4.60 Impact Factor
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ABSTRACT: The crystal structure of the title compound, C(8)H(17)NO(2), consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen-bonded dimers, generated via N-H...O and O-H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction.
Acta crystallographica. Section C, Crystal structure communications 04/2010; 66(Pt 4):o229-32. · 0.78 Impact Factor
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ABSTRACT: The crystal structure of the nitrate salt of N,N'-bis(2-hydroxyethyl)-ethane-1,2-diamine (BHEEN), and its complex with Zn(II) and Cd(II) are reported. (H(2)BHEEN)(NO(3))(2) packs in a layered structure with a herringbone pattern within each layer arising from H-bonding between amino and alcohol protons and NO(3)(-) counterions. In [Zn(BHEEN)(2)]Cl(2), each ligand coordinates to Zn(II) through its two N-donors producing a distorted tetrahedral geometry at the metal centre. The two hydroxyethyl arms of each ligand are trans to each other and the crystals obtained contained a racemic mixture of the bis-trans-R,R and the bis-trans-S,S isomers. All four hydroxyl groups are H-bonded to chloride counter ions, creating a layered structure. Whilst distant from the metal ion (average 3.00 A), the four O atoms of the pendent hydroxylamino groups appear positioned to interact with the metal. The orientation of the arms is preserved in a B3LYP gas phase calculation of the structure. An analysis using Bader's Atoms in Molecules indicates that the Zn-N bonds are predominantly ionic with some covalent character and that there is a weak interaction between the metal and the hydroxyl groups. Several other weak interactions including four O...HN, five O...HC and a H-H dihydrogen bond were identified. The Cd(II) complex of BHEEN crystallised as a dimer [(mu-Cl)(2)(Cd(BHEEN)Cl)(2))] with two asymmetrically-bound bridging Cl(-) ligands and a terminally-coordinated Cl(-) on each metal ion. One hydroxyl group of each ligand is coordinated to the metal and the uncoordinated hydroxyl group is H-bonded to the H atom of the coordinated hydroxyl group of the second ligand in the complex. The ESI-MS spectrum shows the presence of di-cadmium complexes, but the most intense peaks are due to mono-cadmium complexes. The gas phase B3LYP structure of the dimer energy-minimises into two monomers and the longer bond between Cd(II) and bridging Cl(-) breaks. Hence, dimerisation may be a consequence of the crystallisation process and the dimer may not be the predominant species in solution.
Dalton Transactions 12/2009; · 3.84 Impact Factor
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ABSTRACT: The title compound, C(7)H(13)NO, forms R(2)(2)(8) N-H...O hydrogen-bonded dimers and C4 N-H...O-linked chains, which are further stabilized by a C-H...O interaction. The combination of these interactions results in a hydrogen-bonded network parallel to (100), with a motif that can be described by the secondary graph set R(4)(6)(16). The existence of the same hydrogen-bonding motif in 1-phenylcyclopentanecarboxamide and 1-(2-bromophenyl)cyclohexanecarboxamide [Lemmerer & Michael (2008). CrystEngComm, 10, 95-102 indicates that replacing the H atom on position 1 with a more bulky group does not necessarily disrupt the observed hydrogen-bonding pattern. The presence of a C-H...O interaction to stabilize the R(4)(6)(16) network does, however, seem to be required. In addition, the title compound is isomorphous with a previously published structure of cyclopentanecarboxamide [Winter et al. (1981). Acta Cryst. B37, 2183-2185].
Acta crystallographica. Section C, Crystal structure communications 11/2009; 65(Pt 11):o553-4. · 0.78 Impact Factor
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ABSTRACT: The structures of two distinct polymorphic forms of N-(2,6-difluorophenyl)formamide, C(7)H(5)F(2)NO, have been studied using single crystals obtained under different crystallizing conditions. The two forms crystallize in different space groups, viz. form (Ia) in the orthorhombic Pbca and form (Ib) in the monoclinic P2(1) space group. Each polymorph crystallizes with one complete molecule in the asymmetric unit and they have a similar molecular geometry, showing a trans conformation with the formamide group being out of the plane of the aromatic ring. The packing arrangements of the two polymorphs are quite different, with form (Ia) having molecules that are stacked in an alternating arrangement, linked into chains of N-H...O hydrogen bonds along the crystallographic a direction, while form (Ib) has its N-H...O hydrogen-bonded molecules stacked in a linear fashion. A theoretical study of the two structures allows information to be gained regarding other contributing interactions, such as pi-pi and weak C-H...F, in their crystal structures.
Acta crystallographica. Section C, Crystal structure communications 10/2009; 65(Pt 9):o470-4. · 0.78 Impact Factor
