Search PubMed⌕ Search

Biomedical subjects

Sean Parkin

Publications and source records attributed to Sean Parkin.

49 records · Page 3Linked to original sources
PubMed2003

Two isomers of 2,4-dibenzyl-8-azabicyclo[3.2.1]octan-3-ol.

The crystal structures of the title compounds, 2 alpha,4 alpha-dibenzyl-3 alpha-tropanol (2 alpha,4 alpha-dibenzyl-8-methyl-8-azabicyclo[3.2.1]octan-3 alpha-ol), C(22)H(27)NO, (I), and 2 alpha,4 alpha-dibenzyl-3 beta-tropanol (2 alpha,4 alpha-dibenzyl-8-methyl-8-azabicyclo[3.2.1]octan-3 beta-ol), C(22)H(27)NO, (II), show that both compounds have a piperidine ring in a chair conformation and a pyrrolidine ring in an envelope conformation. Isomer (I) is asymmetric, the benzyl groups having different orientations, whereas isomer (II) is mirror symmetric, and the N and O atoms, the C atom attached to the hydroxy group, and the methyl C atom attached to the N atom lie on the mirror plane. In the crystal structures of both (I) and (II), the molecules are linked together by intermolecular O-H...N hydrogen bonds to form chains that run parallel to the a direction in (I) and parallel to b in (II).

Aza Compounds↗
PubMed2003

Low-temperature water reconstruction in concanavalin A, with implications for controlled protein crystal annealing.

Flash-cooled crystals of the I222 form of concanavalin A undergo a sharp non-destructive non-reversible phase transition upon warming to between 160 and 165 K, characterized by an anomalous increase in unit-cell volume. The expansion is anisotropic and primarily affects the b and c axes. Three sets of 1.7 A X-ray diffraction data were collected from one crystal: immediately after flash-cooling (130 K), after slow warming to 170 K and after re-cooling to 130 K. Measurable changes in reflection width after the transition were apparent. Each data set was collected under very similar conditions (aside from temperature). Structures refined against each data set using a powerful phase-bias reduction algorithm indicate negligible rearrangement of the protein molecule and its first hydration shell. Further away from the protein surface, on the edge of the fully disordered solvent regions, a small number of more dramatic changes were apparent. Little is known about the behaviour of water confined within dimensionally restricted spaces, but solvent cavities and channels in protein crystals provide a rich source of reproducible nanoscale water assemblies. This paper presents information on the behaviour of water confined within protein cavities in relation to the physics of protein crystal annealing.

Anisotropy↗
PubMed2003

(Z)-2-(3-hydroxy-4-methoxybenzylidene)-1-azabicyclo[2.2.2]octan-3-one.

Crystals of the title compound, C(15)H(17)NO(3), were obtained from a condensation reaction of 3-hydroxy-4-methoxybenzaldehyde with 1-azabicyclo[2.2.2]octan-3-one and subsequent crystallization of the product from methanol. The title compound, containing a double bond that connects the azabicyclic ring system to the 3-hydroxy-4-methoxybenzylidene group, was obtained with Z geometry.

Crystallography, X-Ray↗
PubMed2003

Supramolecular aggregation in 4,4'-bipyridin-1,1'-ium dichloride, 4,4'-bipyridin-1,1'-ium dinitrate and 4,4'-bipyridin-1-ium bromide.

4,4'-Bipyridin-1,1'-ium dichloride [C(10)H(10)Cl(2)N(2) (I)] and 4,4'-bipyridin-1,1'-ium dinitrate [C(10)H(10)N(4)O(6) (II)] have been prepared and the crystal structures determined at 90.0 (2) K. Molecules of (I) are linked by two chlorine-bridged, three-centered N-H...Cl hydrogen bonds into chains along the b axis. The chains are coupled by weak C-H...Cl interactions into a molecular ladder along the c direction. In (II) each nitrate is coordinated to four bipyridinium ions through the interplay of the N-H...O and C-H...O contacts, resulting in a three-dimensional zigzag sheet on the ab plane. The sheets stack along the c axis. In 4,4'-bipyridin-1-ium bromide monohydrate [C(10)H(9)N(2)(+).Br(-).H(2)O (III)] the bipyridinium ions are linked by three-center N-H.N' hydrogen bonds in a head-to-tail fashion to form chains along the b axis. The chains are linked by C-H...Br and C-H...OH2 into a three-dimensional framework.

Journal Article↗
PubMed2003

C,O-dialkylation of Meldrum's acid: synthesis and reactivity of 1,3,7,7-tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one.

Reaction of Meldrum's acid with 3,4-bis(chloromethyl)-2,5-dimethylthiophene (1) or 3,4-bis(bromomethyl)-2,5-dimethylthiophene (2) produces the kinetically favored C,O-dialkylation product, 1,3,7,7-tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one (4). Recrystallization of 4 from refluxing methanol results in the methanolysis product 5-(4-methoxymethyl-2,5-dimethylthiophen-3-ylmethyl)-2,2-dimethyl[1,3]dioxane-4,6-dione (5). Attempts to isomerize 4 to the thermodynamically favored C,C-dialkylation product, 1,3-dimethyl-5,6-dihydro-4H-cyclopenta[c]thiophene(2-spiro-5)2,2-dimethyl-4,6-dione (8), result in the formation of 1,3-dimethyl-7,8-dihydro-4H-thieno[3,4-c]oxepin-6-one (6). The transformation occurs via a retro-Diels-Alder elimination of acetone followed by hydrolysis and decarboxylation of the resulting ketene. The ketene is trapped by tert-butyl alcohol, furnishing 1,3-dimethyl-6-oxo-7,8-dihydro-4H,6H-thieno[3,4-c]oxepine-7-carboxylic acid tert-butyl ester (7). All compounds are characterized spectroscopically as well as by X-ray crystallography of products 4-7.

Journal Article↗
PubMed2002

The bicyclic n,n'-diacylaminal: a new motif for molecular self-assembly.

A cage-shaped N,N'-diacylaminal crystallizes from some aromatic solvents as "supramolecular chair cyclohexanes", squat cylindrical hexamers with approximate D3d symmetry containing two arene molecules, and from other aromatic and nonaromatic solvents as infinite tapes. A homologous diacylaminal crystallizes only as an infinite tape. The hexamers represent the first examples of cyclic hexamers held together by %@mt;sys@%%@bold@%R%@rsf@%%@sx@%2%@be@%2%@sxx@%%@fn;(;vis;full;auto@%8%@fnx;);vis;full@%-type%@mx@% hydrogen bonds in which the hydrogen-bonded atoms are not coplanar. The diacylaminal represents a new supramolecular synthon, one perhaps more suited to the design of three-dimensional architectures.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2002

Salen-type compounds of calcium and strontium.

Salen complexes of the heavy alkaline-earth metals, calcium and strontium, were prepared by the reaction of various salen(t-Bu)H(2) ligands with the metals in ethanol. Six new calcium and strontium compounds, [Ca(salen(t-Bu))(HOEt)(2)(thf)] (1), [Ca(salen(t-Bu))(HOEt)(2)] (2), [Ca(salpen(t-Bu))(HOEt)(3)] (3), [Ca(salophen(t-Bu))(HOEt)(thf)] (4), [Sr(salen(t-Bu))(HOEt)(3)] (5), and [Sr(salophen(t-Bu))(HOEt)(thf)(2)] (6), were formed in this way with the quatridentate Schiff-base ligands N,N'-bis(3,5-di-tert-butylsalicylidene)ethylenediamine (salen(t-Bu)H(2)), N,N'-bis(3,5-di-tert-butylsalicylidene)-1,3-propanediamine (salpen(t-Bu)H(2)), and N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine (salophen(t-Bu)H(2)). Initially, ammonia solutions of the metals were combined with the salen(t-Bu)H(2) ligands, and in the reaction of strontium with salen(t-Bu)H(2), the unusual tetrametallic cluster [(OC(6)H(2)(t-Bu)(2)CHN(CH(2))(2)NH(2))Sr(mu(3)-salean(t-Bu)H(2))Sr(mu(3)-OH)](2) (7) was produced (salean(t-Bu)H(4) = N,N'-bis(3,5-di-tert-butyl-2-hydroxybenzyl)ethylenediamine). In this compound, the imine bonds of the salen(t-Bu)H(2) ligand were reduced to form the known ligands salean(t-Bu)H(4) and (HO)C(6)H(2)(t-Bu)(2)CHN(CH(2))(2)NH(2). Compounds 1, 5, 6, and 7 were structurally characterized by single-crystal X-ray diffraction. Crystal data for 1 (C(44)H(74)CaN(2)O(6)): triclinic space group P(-)1, a = 8.3730(10) A, b = 14.8010(10) A, c = 18.756(2) A, alpha = 72.551(10) degrees, beta = 81.795(10) degrees, gamma = 78.031(10) degrees, Z = 2. Crystal data for 5 (C(38)H(64)SrN(2)O(5)): monoclinic space group P2(1)/c, a = 23.634(3) A, b = 8.4660(10) A, c = 24.451(3) A, beta = 101.138(10) degrees, Z = 4. Crystal data for 6 (C(46)H(67)N(2)O(5)Sr): orthorhombic space group P2(1)2(1)2(1), a = 10.5590(2) A, b = 16.2070(3) A, c = 26.7620(6) A, Z = 4. Crystal data for 7 (C(98)H(156)N(8)O(8)Sr(4)): triclinic space group P(-)1, a = 14.667(1) A, b = 15.670(1) A, c = 18.594(2) A, alpha = 92.26(1) degrees, beta = 111.84(1) degrees, gamma = 117.12(1) degrees, Z = 4.

Journal Article↗
PubMed2002

Mechanistic insight into fragmentation reactions of titanapinacolate complexes.

Reactions between terminal alkynes or aromatic ketones and titanapinacolate complexes (DMSC)Ti(OCAr(2)CAr(2)O) (2, Ar = Ph, and 3, Ar = p-MeC(6)H(4); DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) occur via rupture of the C-C bond of the titanacycle. Thus, reactions of 2 and 3 with terminal alkynes produce 2-oxatitanacyclopent-4-ene or 2-oxatitanacycloheptadiene complexes along with free Ar(2)CO. These compounds have been characterized spectroscopically and by X-ray crystallography. Because metallapinacolate intermediates have been implicated in important C-C bond-forming reactions, such as pinacol coupling and McMurry chemistry, the mechanism of the fragmentation reactions was studied. Analysis of the kinetics of the reaction of (DMSC)Ti[OC(p-MeC(6)H(4))(2)C(p-MeC(6)H(4))(2)O] (3) with Bu(t)Ctbd1;CH revealed that the fragmentation reactions proceed via a preequilibrium mechanism, involving reversible dissociation of titanapinacolate complexes into (DMSC)Ti(eta(2)-OCAr(2)) species with release of a ketone molecule, followed by rate-limiting reaction of (DMSC)Ti(eta(2)-OCAr(2)) species with an alkyne or ketone molecule.

Journal Article↗
PubMed2002

Crystallization and X-ray diffraction data for a new form of concanavalin A.

A new crystal form of concanavalin A, a well studied lectin from the jack bean (Canavalia ensiformis) is reported. These crystals, with the symmetry of orthorhombic space group C222(1), grow as large roughly equi-dimensional blocks. Unit-cell parameters at 120 K are a = 118.67 (12), b = 101.36 (13), c = 111.94 (9) A. On density considerations for two molecules per asymmetric unit, the water content is approximately 60%. Data to a nominal resolution of 1.5 A were collected.

Concanavalin A↗
PubMed2002

Catalytic dealkylation of phosphates with binuclear boron compounds.

The Salen(tBu) ligand and its derivatives were used to prepare binuclear boron complexes. These compounds have the formula, L(BBr2)2 (L = Salpen(tBu) and Salben(tBu)). These are formed from the reaction of the corresponding L[B(OMe)2]2 with BBr3. They represent a new type of binuclear boron compound. These compounds are active towards the dealkylation of many phosphates. They are also catalytically active with a stoichiometric amount of BBr3 to trimethylphosphate.

Alkylation↗
PubMed2002

A copper(II)-pyrazole complex cation with (macro)3 imposed symmetry.

The reaction of Cu(ClO(4))(2) x 6H(2)O, NaAsF(6) and excess pyrazole yields hexakis(pyrazole-kappa N(2))copper(II) bis(hexafluoroarsenate), [Cu(C(3)H(4)N(2))(6)](AsF(6))(2) or [Cu(pzH)(6)](AsF(6))(2) (pzH is pyrazole), (I). The analogous hexakis(pyrazole-kappa N(2))copper(II) hexafluorophosphate perchlorate complex, [Cu(C(3)H(4)N(2))(6)](PF(6))(1.29)(ClO(4))(0.71) or [Cu(pzH)(6)](PF(6))(1.29)(ClO(4))(0.71), (II), is obtained in a similar fashion, using KPF(6) in place of NaAsF(6). Both compounds contain the hitherto unknown [Cu(pzH)(6)](2+) complex cation, in which the copper(II) ion lies at the center of a regular octahedron of coordinated N atoms. The cation has crystallographically imposed -3 symmetry. The X-ray data indicate that the lack of the expected distortion can be accounted for by the presence of either static Jahn-Teller disorder or dynamic Jahn-Teller distortion.

Journal Article↗
PubMed2001

Z' = 4 structure without obvious pseudosymmetry: implications for the formation of solid-state compounds.

Crystals of 4-chloro-2'-biphenylol grown at 263 K and studied at both 293 and 142 K are loosely packed and contain OH.O bonded tetramers composed of four crystallographically independent molecules (Z' = 4). Approximate symmetry relationships between independent molecules are apparent in many, perhaps even most, structures with Z' > 1, but are not obvious in this structure. The inefficient crystal packing, the surprisingly large value of Z' and the absence of pseudosymmetry reflect the difficulty of finding a dense molecular arrangement that also allows for hydrogen-bond formation. Impediments to good packing are the steric congestion around the ortho hydroxyl groups and the difficulty in filling space with significantly twisted biphenyl fragments. The packing arrangement adopted is strongly reminiscent of the structure type found for eight simple 4,4'-biphenyl derivatives, but one of the four independent 4-chloro-2'-biphenylol molecules has an orientation that is significantly different from the orientations of the other three and that does not fit the 4,4'-XPhPhY pattern. It is suggested that molecules that crystallize with Z' > 1 are good candidates for solid-state compound formation.

Biphenyl Compounds↗