Strophanthidin D- and L-arabinosides

Conclusions Strophanthidin 3--D-arabinopyranoside and strophanthidin 3--L-arabinopyranoside have been synthesized from strophanthidin and D - and L-arabinoses. The L -arabinoside possesses a cardiotonic activity 1.4 times greater than that of the D-arabinoside.     

Magnetic Chirality Transitions of D- and L-Alanine

A chiral spin state of (N⁺H) in D- and L-alanine was established by monitoring the temperature dependence of dc-magnetic susceptibility (dc: direct current) under the external magnetic field of 1 T. An intrinsic spin chirality of electrons in the atomic magnetic dipole moment of (N⁺H) was also supported by polarized Raman spectroscopy. Magnetic chirality was associated with a strongly correlated electron system that was related to spin rigidity. Raman vibrational spectra were unrelated to structural chirality but could reflect spin chirality due to the reversal of motion breaking. The spin transition of (N⁺H) occured at 270 K without bond breaking but was assisted by an intermediate hydrogen bond elongation, splitting and reformation with NH₃⁺ torsion. The energy difference of spin chirality transitions between D- and L-alanine was around 10⁻⁴-10⁻⁵ eV·molecule⁻¹.     

D-和L-丙氨酸的磁手性相变

利用变温直流磁化率测定, 在外加磁场强度为1 T, 磁场平行晶体c轴, 发现在温度270 K, D-和L-丙氨酸发生磁手性相变. 结合中子衍射确定磁手性相变机制为, D-和L-丙氨酸中的(N+H)有类金属氢原子特性, 在相变点270 K, 由(N+H)释放的电子自旋有磁手性. 用变温偏振拉曼光谱进一步证明, D-丙氨酸中的(N+H)的电子自旋(↑), 而L-丙氨酸中的电子自旋(↓), 处于高低不同的能态.磁手性相变(宇称和时间反演都破缺)能差为10^-4-10^-5 eV·molecule^-1.     

Synthesis and stereoselective glycosylation of D- and L-glycero-beta-D-manno-heptopyranoses

[reaction: see text] A method for the direct stereocontrolled synthesis of D- and L-glycero-beta-D-manno-heptopyranosides such as those found in the repeating unit of the O-specific polysaccharide from the CNCTC 113/92 LPS (serotype 54) is described. The method relies on the presence of a 4,6-O-benzylidene acetal to effect stereocontrol at the anomeric center; the configuration at C6 (L- or D-glycero) is of minimal importance.     

De novo asymmetric synthesis of D- and L-swainsonine

[reaction: see text] The enantioselective syntheses of both enantiomers of the indolizidine natural product swainsonine have been achieved in 13 steps from furan. The indolizidine ring system is installed by a one-pot hydrogenolysis of both an azide and an O-Bn group along with an intramolecular reductive amination reaction. The asymmetry of swainsonine was introduced by Noyori reduction of an acylfuran. This route relies upon an Achmatowicz rearrangement, a diastereoselective palladium-catalyzed glycosylation, Luche reduction, and a dihydroxylation reaction.     

Chiral assembly of achiral pseudoisocyanine with D- and L-phenylalanine

Supramolecular chirality and molecular self-assembly are important and interesting phenomena in living and non-living systems.In this work,supramolecular chirality of achiral pseudoisocyanine(PIC) J-aggregates was successfully induced by D-,L-phenylalanine(Phe) and other amino acids in NaCl solution.The chiral J-aggregates showed a characteristic,induced circular dichroism(ICD) in the visible region of J-band chromophore which depends on the absolute configuration,concentration and side groups of α-amino ac...     

A comparison of gradient capacity anion chromatography using macrocycles D-2.2.2 and D-2.2.1 in constant or variable temperature mode

The ability of macrocyclic ligands to complex alkali metal cations has been exploited to perform chromatographic separations of anions. Macrocycles adsorbed to reversed phase columns can complex eluent cations, thus generating anion exchange sites. Gradient separations of anions can be performed by changing the column capacity during the course of the separation, either by changing the eluent cation or by changing the column temperature. Gradient anion separations are performed by changing the eluent from sodium hydroxide to lithium hydroxide with the cryptand D-2.2.2, while similar anion separations are achieved with D-2.2.1 by a KOH-LiOH gradient. Since the complexation of cations by macrocycles is exothermic, increasing the column temperature decreases the anion column capacity, allowing temperature gradient separations. The experimentally measured DeltaH values for D-2.2.1 are higher than for D-2.2.2, leading to steeper gradients and thus better separations with D-2.2.1.     

D-，L-苯丙氨酸诱导非手性菁染料的手性组装

超分子手性与分子自组装是生命体中非常重要和有趣的现象．报道了D,L-苯丙氨酸等氨基酸在氯化钠溶液中通过非共价键相互作用诱导非手性菁染料（Pseudoisocyanine,PIC）J-聚集体超分子手性的形成．实验结果表明,诱导的手性菁染料PIC聚集体发色团在π-π^＊跃迁区域产生了特征的镜像圆二色性,其圆二色信号和强度强烈地依赖于氨基酸的绝对构型、浓度、侧链基团和溶液温度．原子力显微镜照片清楚地表明,^聚集体由相互交联的纳米纤维组成,诱导的圆二色性可能来源于纤维状聚集体的宏观螺旋排列．     

Enzymic Acylation of Methyl D- and L-Glucopyranosides and 6-Deoxy-glucopyranosides

Abstract

Methyl 6-O-butyryl-α-D- and L-glucopyranosides and methyl 6-deoxy-α-D- and L-glucopyranosides have been submitted to lipase catalyzed butyrylation, using porcine pancreatic, Candida cylindracea, and Pseudomonas cepacia lipases in organic solvents. The influence of the orientation of the secondary hydroxyl groups on the regioselectivity of the butyrylation is discussed.     

Directed evolution of D-2-keto-3-deoxy-6-phosphogluconate aldolase to new variants for the efficient synthesis of D- and L-sugars

BACKGROUND: Exploitation and improvement of enzymes as catalysts for organic synthesis is of current interest in biocatalysis. A representative enzyme for investigation is the Escherichia coli D-2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase, which catalyzes the highly specific reversible aldol reaction using the D-configurated KDPG as substrate. RESULTS: Using in vitro evolution, the aldolase has been converted into aldolases with improved catalytic efficiency, altered substrate specificity and stereoselectivity. In particular, some evolved aldolases capable of accepting both D- and L- glyceraldehyde in the non-phosphorylated form as substrates for reversible aldol reaction have been obtained, providing a new direction to the enzymatic synthesis of both D- and L-sugars. CONCLUSIONS: This research has demonstrated the effectiveness of using in vitro evolution to rapidly alter the properties of an aldolase to improve its utility in asymmetric synthesis. The evolved aldolases, differing from the native enzyme which is highly phosphate- and D-sugar-dependent, catalyze the efficient synthesis of both D- and L-sugars from non-phosphorylated aldehydes and pyruvate. The principles and strategies described in this study should be applicable to other aldolases to further expand the scope of their synthetic utility.     

Attempts for the chromatographic separation of D- and L-penicillamine enantiomers

Summary The chromatographic characteristics of the thiazolidine carboxylic acids formed by the reaction of D- and L-penicillamine with various substituted benzaldehydes and heterocyclic aldehydes have been studied on Chiralplate layers. It has been found that the nature and position of substituents strongly affect the R_F values and resolution factors (R_S) of the isomers. An unambiguous relationship has been established between the R_S values of the L- and D-enantiomers and the dipole moment of the aldehydes. The transformation to thiazolidine carboxylic acids with benzaldehyde and substituted benzaldehydes, however, is not complete, thus the reaction with formaldehyde is still more suitable for quantitative determination of penicillamine isomers.     

Photochemically catalyzed reaction of ochratoxin A with D- and L-cysteine

The photolysis (>300 nm) of ochratoxin A (OTA, N-[[(3R)-5-chloro-8-hydroxy-3-methyl-1-oxo-7-isochromanyl]carbonyl]-3-phenyl-L-alanine, 1) in the presence of excess (2 and 12 molar equiv) cysteine (CySH) has been investigated and found to yield sulfur adducts 5 and 6 that are characterized by liquid chromatography-mass spectrometry and 1H-NMR spectroscopy. The adduct 5 was ascribed to the Michael addition conjugate resulting from covalent attachment of CySH to the ochratoxin quinone (4) generated by photooxidation of OTA. This species was also formed by photolysis of a synthetic sample of the hydroquinone of OTA (ochratoxin hydroquinone, 3) in the presence of 12 equiv L-CySH. The conjugate 5 derived from photolysis of 3 with L-CySH was used for 1H-NMR analysis. The sulfur adduct 6 was the major species detected from covalent attachment of CySH to photoactivated OTA, and it resulted from direct displacement of the OTA Cl atom by CySH. The implications of the cysteinyl adducts to the in vivo toxicity of OTA are discussed, with particular emphasis given to conjugate 5, as products from the photooxidative pathway may be of relevance to the nephrotoxic properties of OTA.     

Synthesis of D- and L-selenomethionine double-labeled with deuterium and selenium-82

The synthesis of D- and L-selenomethionine labeled with ?2Se and three deuteriums at Se-methyl group (D- and L-[2H?, ?2Se]selenomethionine) was described. D- And L-[2H?, ?2Se]selenomethionine were prepared by condensation of (R)- and (S)-2-amino-4-bromobutylic acid with lithium [2H?, ?2Se]methaneselenolate, which was prepared from metal (82)Se and [2H?]methyl iodide. The optical purities of D- and L-[2H?, ?2Se]selenomethionine were determined by HPLC with a chiral stationary phase column and were found more than 99% ee. The chemical ionization mass spectra showed that the molecular related ion for N-isobutyloxycarbonyl ethyl ester derivatives of [2H?, ?2Se]selenomethionine did not overlap with the m/z values known from that of non-labeled selenomethionine.     

Design and Synthesis of a Potential Dopamine D-1 Antagonist

The diastereoselective synthesis of (±)-trans-transoid-7-bromo-8-hydroxy-1-methyl-1,2,3,4,4a,5,10,10a-octahydro-10-phenylbenzo[g]quinoline ( 8 ) is described, using an intramolecular Diels-Alder reaction and a reductive cyclisation for piperidine ring-formation as key steps. Compound 8 was prepared as a putative D-1 receptor antagonist which contains (2,2-diphenylethyl)amine as a partial structure.     

Blue two-photon excited fluorescence of several D-π-D, A-π-A, and D-π-A compounds featuring dimesitylboryl acceptor

Several donor-π-donor (D-π-D), acceptor-π-acceptor (A-π-A), and donor-π-acceptor (D-π-A) types of organic compounds with fluorene as π bridge and dimesitylboryl group as electron acceptor, which show strong two-photon excited blue fluorescence, have been synthesized and structurally investigated. The symmetric A-π-A type of compound exhibits the shortest wavelength of two-photon excited fluorescence (TPEF) at λ_em=405 nm under the excitation of λ_ex=730 nm; the unsymmetric D-π-A type of compound with diphenylamino as donor exhibits the most intense TPEF at blue region (λ_em=484 nm) with a two-photon absorption cross-section of 425 GM under λ_ex=800 nm.