Copper(II) hypophosphite: the α‐ and β‐forms at 270 and 100 K,and the γ‐form at 270 K

Copper(II) hypophosphite has been shown to exist as several polymorphs. The crystal structures of monoclinic α‐, ortho­rhombic β‐ and ortho­rhombic γ‐Cu(H₂PO₂)₂ have been determined at different temperatures. The geometry of the hypophosphite anion in all three polymorphs is very close to the idealized one, with point symmetry mm2. Despite having different space groups, the structures of the α‐ and β‐polymorphs are very similar. The polymeric layers formed by the Cu atoms and the hypophosphite ions, which are identical in the α‐ and β‐polymorphs, stack in the third dimension in different ways. Each hypophosphite anion is coordinated to three Cu atoms. On cooling, a minimum amount of contraction was observed in the direction normal to the layers. The structure of the polymeric layers in the γ‐­polymorph is quite different. There are two symmetry‐independent hypophosphite anions; the first is coordinated to two Cu atoms, while the second is coordinated to four Cu atoms. In all three polymorphs, the Cu atoms are coordinated by six O atoms of six hypophosphite anions, forming tetragonal bipyramids; in the α‐ and β‐polymorphs, there are four short and two long Cu—O distances, while in the γ‐polymorph, there are four long and two short Cu—O distances.     

An intermediate in a new synthesis approach to β‐substituted β‐hydroxy­aspartame

The crystal and molecular structure of 1‐tert‐butyl 4‐ethyl (2′R,3′R,5′R,2S,3S)‐3‐bromo­methyl‐3‐hydroxy‐2‐[(2′‐hydroxy‐2′,6′,6′‐tri­methyl­bi­cyclo­[3.1.1]­hept‐3′‐yl­idene)­amino]­succinate, C₂₁H₃₄BrNO₆, is presented. This compound is an intermediate in the new synthetic route to β‐substituted β‐hydroxy­aspartates, which are blockers of glutamate transport.     

Thermodynamic Phase Transition Through Crystal‐to‐Crystal Process of Photochromic 1,2‐Bis(5‐phenyl‐2‐propyl‐3‐thienyl)perfluorocyclopentene

A photochromic diarylethene, 1,2‐bis(5‐phenyl‐2‐propyl‐3‐thienyl)perfluorocyclopentene ( 1a ), was found to have two polymorphic crystal forms, α‐ and β‐crystals. From X‐ray crystallographic analysis, the space groups of α‐ and β‐crystals were determined to be P2₁/c and C2/c, respectively. The difference between two crystal forms is ascribed to the orientation of two of four molecules in the unit cell. The thermodynamic phase transition from α‐ to β‐forms occurred via a crystal‐to‐crystal process, as confirmed by differential scanning calorimetry measurements, optical microscopic observations in the reflection mode and under crossed Nicols, and powder X‐ray diffraction measurements. The movement of the molecules in the crystal was evaluated by analyzing the change of face indices before and after the phase transition.     

1‐(β‐d‐Erythrofuranos­yl)cytidine (β‐erythrocytidine)

1‐(β‐d ‐Erythrofuranosyl)cytidine, C₈H₁₁N₃O₄, (I), a derivative of β‐cytidine, (II), lacks an exocyclic hydroxy­methyl (–CH₂OH) substituent at C4′ and crystallizes in a global conformation different from that observed for (II). In (I), the β‐d ‐erythrofuranosyl ring assumes an E₃ conformation (C3′‐exo; S, i.e. south), and the N‐glycoside bond conformation is syn. In contrast, (II) contains a β‐d ‐ribofuranosyl ring in a ³T₂ conformation (N, i.e. north) and an anti‐N‐glycoside linkage. These crystallographic properties mimic those found in aqueous solution by NMR with respect to furan­ose conformation. Removal of the –CH₂OH group thus affects the global conformation of the aldofuranosyl ring. These results provide further support for S/syn–anti and N/anti correlations in pyrimidine nucleosides. The crystal structure of (I) was determined at 200 K.     

Stereoselective Synthesis of α‐ and β‐Glycofuranosyl Amides by Traceless Ligation of Glycofuranosyl Azides

A highly stereoselective synthesis of α‐ or β‐glycofuranosyl amides based on the traceless Staudinger ligation of glycofuranosyl azides of the galacto, ribo, and arabino series with 2‐diphenylphosphanyl‐phenyl esters has been developed. Both α‐ and β‐isomers can be obtained with excellent selectivity from a common, easily available precursor. The process does not depend on the anomeric configuration of the starting azide but appears to be controlled by the C2 configuration and by the protection/deprotection state of the substrates. A mechanistic interpretation of the results, supported by ³¹P NMR experiments, is offered and merged with our previous mechanistic analysis of pyranosyl azide ligation reactions.     

Effect of cosolvent on solid phase transitions of α‐ to β‐form crystal of syndiotactic polystyrene occurred in supercritical Co2 containing solvent

The solid phase transition mechanism of α‐ to β‐form crystal upon specific treating with supercritical CO₂ + cosolvent on original pure α and mixed (α+β) form syndiotactic polystyrene (sPS) was investigated, using wide angle X‐ray diffraction and differential scanning calorimetry measurements as a function of temperature, pressure, and cosolvent content. As in the supercritical CO₂, sPS in supercritical CO₂ + cosolvent underwent solid phase transitions from α‐ to β‐form, and higher temperature or higher pressure favored this transformation. Due to the higher dipole moment of acetone, small amounts of acetone used as cosolvent with CO₂ made the transition of α‐ to β‐form occur at lower temperature and pressure than in supercritical CO₂, and made the α‐form crystal completely transform to β‐form in the original mixed (α+β) form, whereas ethanol did not. The original β‐form crystal in the original mixed (α+β) form sample acted as the nucleus of new β‐form crystal in the presence of cosolvent as it did in supercritical CO₂, when compared with the original pure α‐form sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1625–1636, 2007     

d‐Secoestrone derivatives. VI. 17β‐Benzyl‐17α‐hydroxy‐3‐methoxyestra‐1,3,5(10)‐trien‐16‐one

The title mol­ecule, C₂₆H₃₀O₃, shows a novel chemical rearrangement of the substituents at position 17, i.e. an α‐­orientation of the hydroxy group and a β‐orientation of the bulky benzyl moiety. The packing arrangement consists of coils formed by O2?O3 hydrogen bonds along the c axis. The compound shows complete loss of oestrogenic activity, and neither does it exhibit an antagonistic effect.     

3,4‐Di­hydro‐6‐methyl‐3‐β‐d‐ribo­furan­osyl‐4,5′‐cyclo‐9H‐imidazo[1,2‐a]­purin‐9‐one hydrate

In the title compound, C₁₃H₁₃N₅O₄·H₂O (4,5′‐cyclo­wyosine·H₂O), the cyclization forces a syn arrangement of the aglycon with respect to the sugar moiety. The ribo­furan­ose part of the mol­ecule displays a β‐d configuration with an envelope C1′‐endo pucker. The mol­ecules are arranged in columns along the short a axis and are linked to water mol­ecules through O—H?O and O—H?N hydrogen bonds.     

7,7‐Dimethyl‐5H‐di­benzo[e,i][1,4,8]triaza­cyclo­undecine‐6,9,15(7H,8H,14H)‐trione pyridine solvate

The X‐ray crystal structure and hydrogen‐bonding patterns of the title compound, C₁₈H₁₇N₃O₃·C₅H₅N, a non‐N‐alkyl­ated cyclotripeptide containing one α‐ and two β‐amino acids, are reported. The amides in the 11‐membered ring have an unprecedented all‐transoid configuration. The torsion angles and Dunitz parameters describing non‐planarity of the amides contained in the cyclotripeptide are discussed.     

Separation of α‐ from β‐arylalanines by nickel nitrilotriacetate chromatography

A method is described to separate α‐ from β‐arylalanines by ligand exchange chromatography on a nickel nitrilotriacetate agarose column with UV monitoring of the effluent. Separate mixtures containing an α‐ and β‐arylalanine pair (1 mg of each) were individually loaded onto the nickel resin pre‐equilibrated with the mobile phase at room temperature, and the amino acids were eluted from the column with a gradient from pH 12.0–8.0. The β‐arylalanines eluted first, followed by the α‐isomers. The four α/β‐amino acid pairs tested were well separated with baseline resolution. An aliquot of each fraction was chemically treated to derivatize the amino acids to their N‐acyl methyl ester analogs, and their identities were confirmed by GC/MS analysis. The sample recovery was quantitative (>98%), and the column matrix was very resilient, as demonstrated by consistent separation of the solutes after ～100 preparative cycles.     

A new γ‐polymorph of chlorpropamide: 4‐chloro‐N‐(propylaminocarbonyl)benzenesulfonamide

The structure of a new polymorph of the title compound, C₁₀H₁₃ClN₂O₃S, known as the antidiabetic drug chlorpropamide, is monoclinic, in contrast with the two previously described orthorhombic α‐ and β‐forms. The molecules in the γ‐polymorph are linked into bands by hydrogen bonds similar to those in the α‐polymorph. The conformation of the molecules in the γ‐form is close to that in the β‐polymorph.     

γ‐Alumina: a single‐crystal X‐ray diffraction study

The structure of γ‐alumina (Al_21+1/3□_2+2/3O₃₂) crystals obtained as a product of a corrosion reaction between β‐sialon and steel was refined in the space group Fdm. The oxygen sublattice is fully occupied. The refined occupancy parameters are 0.83 (3), 0.818 (13), 0.066 (14) and 0.044 (18) for Al ions in 8a, 16d, 16c and 48f positions, respectively. The Al ions are distributed over octa­hedral and tetra­hedral sites in a 63:37 ratio, with 6% of all Al ions occupying non‐spinel positions.     

Methyl 4‐O‐β‐l‐galactopyranosyl‐β‐d‐glucopyranoside (methyl β‐l‐lactoside)

Methyl β‐l ‐lactoside, C₁₃H₂₄O₁₁, (II), is described by glycosidic torsion angles ϕ (O5_Gal—C1_Gal—O4_Glc—C4_Glc) and ψ (C1_Gal—O1_Gal—C4_Glc—C5_Glc) of 93.89 (13) and −127.43 (13)°, respectively, where the ring atom numbering conforms to the convention in which C1 is the anomeric C atom and C6 is the exocyclic hydroxy­methyl (CH₂OH) C atom in both residues (Gal is galactose and Glc is glucose). Substitution of l ‐Gal for d ‐Gal in the biologically relevant disaccharide, methyl β‐lactoside [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (I), significantly alters the glycosidic linkage inter­face. In the crystal structure of (I), one inter‐residue (intra­molecular) hydrogen bond is observed between atoms H3O_Glc and O5_Gal. In contrast, in the crystal structure of (II), inter‐residue hydrogen bonds are observed between atoms H6O_Glc and O5_Gal, H6O_Glc and O6_Gal, and H3O_Glc and O2_Gal, with H6O_Glc serving as a donor with two intra­molecular acceptors.     

手性噁唑硼烷催化α-和β-氨基酮不对称还原反应立体选择性的AM1过渡态模型研究

AM1 transition state (TS) models were developed for the enanfioselecfivifies in the reductions of α-and β-aminoketones catalyzed by (S)-4-benzyl-5,5-diphenyl-1,3,2-oxazaborolidine. The result showed that β-aminoketone gave better enanfioselectivity than its α-analog. Different chiralifies of the final products were obtained, R for the former and S for the latter. These semiempirical TS models are consistent with the experimental data.     

Form II of monoclinic methyl β‐carboline‐3‐carboxyl­ate

The crystal structure of the second monoclinic P2₁/c form of the β‐carboline‐3‐carboxyl­ate, C₁₃H₁₀N₂O₂, has been determined. Very small changes in the packing scheme lead to a different unit cell; the role of weak C—H?O hydrogen bonds seems to be crucial.     

The β‐polymorph of phenazine

In β‐phenazine, C₁₂H₉N₂, the mol­ecules show a sandwich herring‐bone type of packing. The experimental crystal structure shows very good agreement with that predicted earlier from systematic searches of potential packing arrangements for the known unit cell [Hammond, Roberts, Smith & Docherty (1999). J. Phys. Chem. B, 103 , 7762–7770].     

X‐ray investigations of bicyclic α‐methyl­ene‐δ‐valerolactones. III. trans‐(4aR,8aR)‐4a‐Methoxy‐3‐methyleneperhydro­chromen‐2‐one

The title compound, C₁₁H₁₆O₃, adopts a conformation in which the δ‐valerolactone and cyclo­hexane rings are almost coplanar with one another. The β‐methoxy substituent occupies an axial position with respect to the cyclo­hexane ring. The δ‐valerolactone moiety adopts a half‐chair arrangement, while the cyclo­hexane ring exists in a chair conformation.     

X‐ray investigations of bicyclic α‐methyl­ene‐δ‐valerolactones. II. (4aS,8aS)‐4a‐Methyl‐3‐methyl­eneper­hydro­chromen‐2‐one

The title compound, C₁₁H₁₆O₂, adopts a semifolded conformation with the δ‐lactone and cyclo­hexane rings almost perpendicular to one another. The β‐methyl substituent occupies an axial position with respect to the cyclo­hexane ring. The δ‐lactone moiety adopts a slightly distorted half‐chair arrangement, while the cyclo­hexane ring exists in an almost ideal chair conformation.     

From α‐carbamoyl‐α‐cyano­oxiranes to 3‐halogenopyruv­amides

The crystal structures of the first stable α‐diol from the α‐halogenopyruv­amide series, 3‐chloro‐2,2‐di­hydroxy‐3‐phenyl­propan­amide, C₉H₁₀­ClNO₃, and three products [3‐(4‐chloro­phenyl)‐2‐cyano‐2,3‐epoxy­propan­amide, C₁₀H₇­ClN₂O₂, 3‐bromo‐2‐cyano‐2‐hydroxy‐3‐p‐tolyl­propan­amide, C₁₁H₁₁Br­N₂O₂, 3‐bromo‐2‐oxo‐3‐p‐tolyl­propan­amide, C₁₀H₁₀­BrNO₂] obtained during the systematic synthesis of α‐halogenopyruv­amides are reported. The crystal structures are dominated by hydrogen bonds involving an amide group. The stability of the geminal diol could be ascribed to hydrogen bonds which involve both hydroxyl groups.     

α‐ and β‐Lipomycin: Total Syntheses by Sequential Stille Couplings and Assignment of the Absolute Configuration of All Stereogenic Centers

40 years ago spectroscopy, derivatization, and degradation revealed the structures of α‐lipomycin and its aglycon β‐lipomycin except for the configurations of their side‐chain stereocenters. We synthesized all relevant β‐lipomycin candidates: the (12R,13S) isomer has the same specific rotational value as the natural product. By the same criterion the (12R,13S)‐configured D ‐digitoxide is identical to α‐lipomycin. We double‐checked our assignments by degrading α‐ and β‐lipomycin to the diesters 33 and 34 and proving their 3D structures synthetically.