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Biomedical subjects

Alan R Kennedy

Publications and source records attributed to Alan R Kennedy.

At least 37 records · Page 2Linked to original sources
PubMed2004

Crystallographic characterisation of binary alkali metal alkoxide-magnesium bis(alkyl) mixtures: differential binding of Na+ and K+ to a common dinuclear diorganomagnesiate.

Relevant to mixtures studied in solution and utilised in styrene polymerisation but hitherto not characterised in the solid, two crystal structures of alkali metal alkoxide-magnesium bis(alkyl) co-complexes have been determined, revealing that in binding to the C2O tripodal face of a common organomagnesiate anion, Na+ prefers O-coordination, whereas K+ prefers C-coordination.

Journal Article↗
PubMed2004

A homologous series of regioselectively tetradeprotonated group 8 metallocenes: new inverse crown ring compounds synthesized via a mixed sodium-magnesium tris(diisopropylamide) synergic base.

Subjecting ferrocene, ruthenocene, or osmocene to the synergic amide base sodium-magnesium tris(diisopropylamido) affords a unique homologous series of metallocene derivatives of general formula [(M(C(5)H(3))(2))Na(4)Mg(4)(i-Pr(2)N)(8)] (where M = Fe (1), Ru (2), or Os (3)). X-ray crystallographic studies of 1-3 reveal a common molecular "inverse crown" structure comprising a 16-membered [(NaNMgN)(4)](4+) "host" ring and a metallocenetetraide [M(C(5)H(3))(2)](4-) "guest" core, the cleaved protons of which are lost selectively from the 1, 1', 3, and 3'-positions. Variable-temperature NMR spectroscopic studies indicate that 1, 2, and 3 each exist as two distinct interconverting conformers in arene solution, the rates of exchange of which have been calculated using coalescence and EXSY NMR measurements.

Journal Article↗
PubMed2004

Supramolecular motifs in s-block metal-bound sulfonated monoazo dyes, part 1: structural class controlled by cation type and modulated by sulfonate aryl ring position.

The solid-state structures of 43 Li, Na, K, Rb, Mg, Ca and Ba salts of para- and meta-sulfonated azo dyes have been examined and can be categorised into three structural classes. All form alternating organic and inorganic layers, however, the nature of the coordination network that forms these layers differs from class to class. The class of structure formed was found to be primarily governed by metal type, but can also be influenced by the nature and position of the organic substituents. Thus, for the para-sulfonated azo dyes, Mg compounds form solvent-separated ion-pair solids; Ca, Ba and Li compounds form simple coordination networks based on metal-sulfonate bonding; and Na, K and Rb compounds form more complex, higher dimensional coordination networks. Compounds of meta-sulfonated azo dyes follow a similar pattern, but here, Ca species may also form solvent-separated ion-pair solids. Significantly, this first attempt to classify such dyestuffs using the principles of supramolecular chemistry succeeds not only for the simple dyes used here as model compounds, but also for more complex molecules, similar to modern colourants.

Arylsulfonates↗
PubMed2004

N,N'-Bis(2-methoxybenzylidene) adducts of ethane-1,2-diamine, propane-1,3-diamine and butane-1,4-diamine.

We have isolated and crystallographically characterized the three homologous compounds N,N'-bis(2-methoxybenzylidene)ethane-1,2-diamine (MeSalen), C18H20N2O2, N,N'-bis(2-methoxybenzylidene)propane-1,3-diamine (MeSalpr), C19H22N2O2, and N,N'-bis(2-methoxybenzylidene)butane-1,4-diamine (MeSalbu), C20H24N2O2. In contrast with MeSalpr, the molecules of MeSalen and MeSalbu, which have an even number of methylene units, have crystallographic -1 symmetry. Comparing these methoxy-substituted species with their hydroxy equivalents shows that the aryl rings rotate upon removal of the O-H.N hydrogen bonds. The packing of MeSalen and MeSalpr is controlled by C-H.pi interactions, whereas that of MeSalbu has only van der Waals contacts.

Journal Article↗
PubMed2004

Pushing the frontiers of hard and soft scorpionate chemistry.

The preparation and structure of the first scorpionate complex of a group 16 element, [Te(kappa(2)-Tm(Me))(2)], is reported. It displays square planar geometry at the Te atom and two distinct ligand conformations. In addition, the first pyrazolylborate complex of a group 15 element, [Bi(Tp)(2)(pzH)Cl], has been synthesized and characterized.

Journal Article↗
PubMed2004

Cyclobutanes from Combretum albopunctatum.

A dichloromethane extract of the aerial parts of Combretum albopunctatum Suesseng afforded five phenolic compounds-three known flavonoids and two novel cyclobutane chalcone dimers. The chemical structures were determined by standard spectroscopic techniques and the structure and relative stereochemistry of one chalcone dimer, rel-(1 alpha,2 beta)-di-(2,6-dimethoxy-4-hydroxy)-benzoyl-rel-(3 alpha,4 beta)-diphenylcyclobutane, were confirmed by single crystal X-ray diffraction.

Chalcone↗
PubMed2003

Bifurcated, modular syntheses of chiral annulet triazacyclononanes.

Three chiral 2,6-disubstituted tri-N-methyl azamacrocycles have been prepared by modular methods. These macrocycles were accessed from three chiral 1,4,7-triazaheptanes intermediates that were prepared by two independent routes. The first of these routes involved the benzylamine opening of chiral tosyl aziridines followed by debenzylation but was problematic on solubility grounds. A second, more effective, route was developed which avoided debenzylation by using ammonia in the nucleophilic opening of chiral tosyl aziridines.

Aza Compounds↗
PubMed2003

Fragmentation of carbohydrate anomeric alkoxy radicals: a new synthesis of chiral 1-halo-1-iodo alditols.

Treatment of 1,2-fluorohydrins, 1,2-chlorohydrins, 1,2-bromohydrins, and 1,2-iodohydrins of the D-gluco, D-galacto, D-lacto, L-rhamno, D-allo, L-arabino, 3-deoxy-D-gluco, and 3,4-dideoxy-D-gluco families of carbohydrates with the (diacetoxyiodo)benzene/iodine system afforded 1-fluoro-1-iodo, 1-chloro-1-iodo, 1-bromo-1-iodo, and 1,1-diiodo alditols, respectively, in excellent yields. The reaction was achieved by radical fragmentation of the C1bond;C2 bond, triggered by the initially formed anomeric alkoxy radical, and subsequent trapping of the C2-radical by iodine atoms. This methodology is compatible with the stability of the protective groups most frequently used in carbohydrate chemistry. The potential utility of these 1-halo-1-iodo alditols as chiral synthons was evaluated by their transformation into alk-1-enyl iodides and in the Takai E-olefination reaction.

Journal Article↗
PubMed2003

A magnesium-bis(diaryldiketiminate) complex.

The 1:1 of reaction of dibutylmagnesium with the ligand 2-[(2-isopropylphenyl)amino]-4-[(2-isopropylphenyl)imino]pent-2-ene gives only the 1:2 metal-ligand compound bis[N,N'-bis(2-isopropylphenyl)pentane-2,4-diiminato]magnesium(II), [Mg(C(23)H(29)N(2))(2)], as an isolated solid. The coordination geometry about the Mg atom is distorted tetrahedral [N-Mg-N angles range from 90.73 (5) to 136.40 (6) degrees ], with the metal lying out of the ligand plane. The ligands themselves have non-crystallographic C(s) geometry. The structure is isotypic with the Zn analogue, and the small differences between these two structures provide evidence for a significant covalent contribution to bonds that are generally described as largely ionic.

Journal Article↗
PubMed2003

Cephalexin: a channel hydrate.

The antibiotic cephalexin [systematic name: D-7-(2-amino-2-phenylacetamido)-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid] forms a range of isomorphic solvates, with the maximum hydration state of two water molecules formed only at high relative humidities. The water content of the structure reported here (C(16)H(17)N(3)O(4)S.1.9H(2)O) falls just short of this configuration, having three independent cephalexin molecules, one of which is disordered, and 5.72 observed water molecules in the asymmetric unit. The facile nature of the cephalexin solvation/desolvation process is found to be facilitated by a complex channel structure, which allows free movement of solvent in the crystallographic a and b directions.

Anti-Bacterial Agents↗
PubMed2003

4,4'-(azinodimethylene)dipyridinium chloranilate dichloromethane disolvate.

The dichloromethane disolvate of 4,4'-(azinodimethylene)dipyridinium chloranilate, C(12)H(12)N(4)(2+).C(6)Cl(2)O(4)(2-).2CH(2)Cl(2), consists of one-dimensional hydrogen-bonded molecular tapes that propagate along the [1-20] direction. Both cations and anions lie across centres of inversion. The molecular tapes are planar but do not stack in the expected segregated manner, instead having chloranilate anions sandwiched between azine groups.

Journal Article↗
PubMed2003

Fragmentation of carbohydrate anomeric alkoxyl radicals. A new synthesis of chiral beta-iodo azides, vinyl azides, and 2H-azirines.

[reaction: see text] The reaction of 3-azido-2,3-dideoxy-hexopyranose compounds from the d-gluco, d-galacto, d-lacto, and l-arabino carbohydrate series, with (diacetoxyiodo)benzene and iodine, generated 2-azido-1,2-dideoxy-1-iodo-alditols with one carbon less than the starting carbohydrate. These beta-iodo azides could be transformed by dehydroiodination into vinyl azides, which in turn afforded 3-monosubstituted 2H-azirines under thermal conditions. These beta-iodo azides and 2H-azirines may be interesting chiral synthons for the preparation of more complex heterocyclic systems.

Alcohols↗
PubMed2003

A new Na/Mg inverse crown ether.

A 'missing' member of the inverse crown ether family, namely mu(4)-oxo-tetrakis(mu-2,2,6,6-tetramethylpiperidinido)dimagnesium(II)disodium(I), [Na(2)Mg(2)O(C(9)H(18)N)(4)], has been synthesized by blocking the alternative aromatic metallation route via the use of sterically hindered 1,3,5-mesitylene as a solvent. [Na(2)Mg(2)O(NR(2))(4)] (NR(2) is 2,2,6,6-tetramethylpiperidinide) is shown to form a cationic planar eight-membered ring with alternating metal and N atoms, which captures at its core an oxide guest that lies on an inversion centre [principal dimensions: Na-O = 2.2405 (11) A, Na-N = 2.445 (3) and 2.572 (3) A, Mg-O = 1.8673 (9) A, and Mg-N = 2.032 (2) and 2.063 (2) A].

Journal Article↗
PubMed2003

The synthesis of an isopropyl substituted 1,4,7-triazacyclononane via an in situ sequential macrocyclisation method.

Using L-valine methyl ester hydrochloride as starting material, the synthesis of (2S)-2-isopropyl-1,4,7-trimethyl-1,4,7-triazacyclononane is described. Various standard Richman-Atkins cyclisation methods gave only poor yields in the key macrocyclisation step. Efficient macrocyclisation yields were, however, realised when an in situ sequential cyclisation method was developed.

Chemistry, Organic↗