Crystals of maleates of three amino acids with hydrophobic side chains [L‐leucenium hydrogen maleate, C6H14NO2+·C4H3O4−, (I), L‐isoleucenium hydrogen maleate hemihydrate, C6H14NO2+·C4H3O4−·0.5H2O, (II), and L‐norvalinium hydrogen maleate–L‐norvaline (1/1), C5H11NO2+·C4H3O4−·C5H12NO2, (III)], were obtained. The new structures contain C22(12) chains, or variants thereof, that are a common feature in the crystal structures of amino acid maleates. The L‐leucenium salt is remarkable due to a large number of symmetrically non‐equivalent units (Z′ = 3). The L‐isoleucenium salt is a hydrate despite the fact that L‐isoleucine is a nonpolar hydrophobic amino acid (previously known amino acid maleates formed hydrates only with lysine and histidine, which are polar and hydrophilic). The L‐norvalinium salt provides the first example where the dimeric cation L‐Nva...L‐NvaH+ was observed. All three compounds have layered noncentrosymmetric structures. Preliminary tests have shown the presence of the second harmonic generation (SGH) effect for all three compounds. 相似文献
Reaction between cysteamine (systematic name: 2‐aminoethanethiol, C2H7NS) and L‐(+)‐tartaric acid [systematic name: (2R,3R)‐2,3‐dihydroxybutanedioic acid, C4H6O6] results in a mixture of cysteamine tartrate(1−) monohydrate, C2H8NS+·C4H5O6−·H2O, (I), and cystamine bis[tartrate(1−)] dihydrate, C4H14N2S22+·2C4H5O6−·2H2O, (III). Cystamine [systematic name: 2,2′‐dithiobis(ethylamine), C4H12N2S2], reacts with L‐(+)‐tartaric acid to produce a mixture of cystamine tartrate(2−), C4H14N2S22+·C4H4O62−, (II), and (III). In each crystal structure, the anions are linked by O—H...O hydrogen bonds that run parallel to the a axis. In addition, hydrogen bonding involving protonated amino groups in all three salts, and water molecules in (I) and (III), leads to extensive three‐dimensional hydrogen‐bonding networks. All three salts crystallize in the orthorhombic space group P212121. 相似文献
A novel route with L ‐ascorbic acid as a single common starting material to asymmetric synthesis of all eight diastereomers of L ‐hexoses is described. Assessment of this new approach is demonstrated by the expedient synthesis of L ‐galactopyranose and L ‐talopyranose derivatives. Key steps involve stereoselective preparation of chiral (E)‐ and (Z)‐γ‐hydroxy‐α,β‐unsaturated esters and their stereo‐controlled dihydroxylation by OsO4. 相似文献
The scarcity and expense of access to L ‐sugars and other rare sugars have prevented the exploitation of their biological potential; for example D ‐psicose, only recently available, has been recognized as an important new food. Here we give the definitive and cheap synthesis of 99.4% pure L ‐glucose from D ‐glucose which requires purification of neither intermediates nor final product other than extraction into and removal of solvents; a simple crystallization will raise the purity to >99.8%. 相似文献
New opportunities, provided by the 2,2'-[1,1'-binaphthyl-2,2'-diylbis(nitrylomethilidyne)]diphenol (SB(OH)2)/Al(OiPr)3/racemic lactide (rac-LA) polymerization system, employing a combination of stereoelection with (S) and (R) ligand-exchange mechanism at Al-alkoxide active centers were explored. The stereoelectivity was comparable to that determined for the process with an additional synthetic step of isolation and purification of the SBO2Al-OiPr alkoxide. The resultant poly(rac-LA) had a gradient stereocopolymer structure and exhibited enhanced thermal stability due to a stereocomplex formation (Tm = 210 degrees C). This is the highest melting temperature reported until now for poly(lactide) (PLA) prepared directly from rac-LA. 相似文献
A simple, sensitive, and rapid method for determination of L‐trantinterol in rat plasma was developed for the first time by using LC coupled to MS/MS based on chiral stationary phase. A baseline separation of the enantiomers of trantinterol was achieved on a Chirobiotic V column, using a mixture of acetonitrile–methanol–ammonia–acetic acid (80:20:0.01:0.02, v/v/v/v) as the mobile phase. The detection was performed on a triple‐quadrupole tandem mass spectrometer by multiple reaction monitoring mode via ESI. The calibration curve was linear in concentration range from 0.270 to 108 ng/mL in plasma with the lower limit of quantification of 0.270 ng/mL. The intra‐ and interday precision (relative standard deviation) values were within 10.9% and the accuracy (relative error) was from 2.6 to 9.2% at all quality control levels. The method has been successfully applied to a study of L‐trantinterol pharmacokinetics in rats. 相似文献
An enantiopure phosphonothioic acid showed a unique and superior chiral recognition ability, arising from its P-stereogenicity, for racemic 1-phenylethylamine derivatives through diastereomeric crystallization. Spherical molecular clusters, associated by hydrogen bonds and CH/pi interactions, aggregated with high symmetry in the less-soluble diastereomeric salts. 相似文献
The syntheses of a range of enantiopure organosulfur donors with hydrogen bonding groups are described including TTF related materials with two, four, six and eight hydroxyl groups and multiple stereogenic centres and a pair of chiral N-substituted BEDT-TTF acetamides. Three charge transfer salts of enantiopure poly-hydroxy-substituted donors are reported, including a 4:1 salt with the meso stereoisomer of the dinuclear [Fe2(oxalate)5]4− anion in which both cation and anion have chiral components linked together by hydrogen bonding, and a semiconducting salt with triiodide. 相似文献
Moisture or water has the advantages of being green, inexpensive, and moderate. However, it is challenging to endow water‐induced shape memory property and self‐healing capability to one single polymer because of the conflicting structural requirement of the two types of materials. In this study, this problem is solved through introducing two kinds of supramolecular interactions into semi‐interpenetrating polymer networks (semi‐IPNs). The hydrogen bonds function as water‐sensitive switches, making the materials show moisture‐induced shape memory effect. The host–guest interactions (β‐cyclodextrin‐adamantane) serve as both permanent phases and self‐healing motifs, enabling further increased chain mobility at the cracks and self‐healing function. In addition, these polyvinylpyrrolidone/poly(hydroxyethyl methacrylate‐co‐butyl acrylate) semi‐IPNs also show thermosensitive triple‐shape memory effect.
Under hydrothermal (solvothermal) reaction conditions chiral compounds 1, 2, and 3 and one acentric compound 4 were obtained by the reaction of Zn(2+) or Cd(2+) with racemic 3-(3-pyridyl)-3-aminopropionic acid (rac-HPAPA). Compounds 1 and 2 crystallized in chiral space group P2(1)2(1)2(1). At 105 degrees C, racemic 3-pyridyl-3-aminopropionic acid (rac-HPAPA) reacted with Zn(ClO4)(2).6 H2O and dehydrogenated in situ to form the first chiral coordination polymer [Zn[(E)-3-C(5)H4N-C(NH2)=CH-COO]]ClO4 (1) with a beta-dehydroamino acid. Beyond 120 degrees C, the reaction of rac-HPAPA with Zn(ClO4)(2).6 H2O deaminates in situ to form chiral coordination polymer [Zn[(E)-3-C5H4N-CH=CH-COO](OH)] (2). At relatively low temperatures (70 degrees C), the solvothermal reaction of Zn(NO3)(2).6 H2O with rac-HPAPA in methanol does not lead to any change in the ligand and results in the formation of a chiral (P2(1)2(1)2(1)) coordination polymer [Zn(papa)(NO3)] (3). The same reaction of Cd(ClO4)(2).6 H2O with HPAPA also does not lead to any change in ligand and results in the formation of noncentric (Cc) coordination polymer [Cd(papa)(Hpapa)]ClO4.H2O (4). The network topology of both 1 and 3 is 10,3a, while 2 has a diamondoid-like (KDP-like, KDP=potassium dideuterophosphate) network. Particularly interesting from a topological perspective is that 4 has an unprecedented three-dimensional network. Compounds 1, 2, 3, and 4 are all second harmonic generation (SHG) active with 1 exhibiting the strongest response, while only 4 also displays good ferroelectric properties. 相似文献
Palladium-catalyzed cross-coupling reactions of racemic alpha-bromo sulfoxides with boronic acids are carried out in either aqueous or nonaqueous medium with formation of a new C sp(3)-C sp(2) bond. The arylation of chiral alpha-bromo sulfoxides occurs without racemization. The cross-coupling reaction is general and gives high yields with arylboronic acids substituted with either donor or acceptor groups but gives poor results with heteroarylboronic acids. The best yields are obtained using degassed solvents and CsF instead of aqueous base. The use of aqueous base and the presence of oxygen favor the homocoupling side reaction. 相似文献
The crystal structures of the low‐melting 1,2‐ and 1,3‐dichlorobenzene isomers have been determined by X‐ray analysis and in situ crystallisation techniques. Attempts to predict these structures in advance by force‐field calculations were not successful, although the known crystal structures of two of the three polymorphs of the 1,4‐isomer were successfully `a posteriori' predicted. Calculated lattice energies were supplemented with estimated lattice‐vibrational entropies obtained in the rigid‐body approximation. Energy calculations for actual and virtual crystal structures indicate that the higher melting point of the 1,4‐isomer can be largely attributed to more efficient crystal packing. 相似文献