Synthesis of the enantiomers of 6-deoxy-myo-inositol 1,3,4,5-tetrakisphosphate, structural analogues of myo-inositol 1,3,4,5-tetrakisphosphate

D-myo-Inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] is produced rapidly from the established second messenger D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P4] in stimulated cells. Despite extensive investigations, in particular concerning its potential role in mediating cellular Ca2+ influx, no exact cellular function has been described for this inositol phosphate; however, binding sites have been identified in a number of tissues and it has been shown to act synergistically with Ins(1,4,5)P3. To assist in the elucidation of the mechanism of action and structural requirements within the Ins(1,3,4,5)P4 moiety that are necessary for recognition and activation of the receptor, structural analogues of this tetrakisphosphate are required. Routes for the synthesis of racemic 6-deoxy-myo-inositol 1,3,4,5-tetrakisphosphate [6-deoxy-DL-Ins(1,3,4,5)P4] and the chiral antipodes D- and L-6-deoxy-myo-inositol 1,3,4,5-tetrakisphosphate are described here. The racemic tetrakisphosphate was synthesised from DL-1,2-O-isopropylidene-myo-inositol in eight steps. Deoxygenation at C-6 was achieved following the Barton-McCombie procedure. Both chiral tetrakisphosphates were synthesised through resolution of racemic cis-diol 6-deoxy-1,4,5-tri-O-p-methoxybenzyl-myo-inositol with the chiral auxiliary (S)-(+)-O-acetylmandelic acid. Absolute configuration was confirmed by synthesis of the known D-6-deoxy-myo-inositol. Both D-6-deoxy-Ins(1,3,4,5)P4 and its enantiomer will be useful tools to unravel the enigmatic role of Ins(1,3,4,5)P4 in the polyphosphoinositide pathway of signal transduction.     

Synthesis of D- and L-myo-Inositol 1,4,6-Trisphosphate, Regioisomers of a Ubiquitous Second Messenger

A regioisomer of the second messenger D-myo-inositol 1,4,5-trisphosphate [D-Ins(1,4,5)P(3), 1], DL-myo-inositol 1,4,6-trisphosphate [DL-Ins(1,4,6)P(3), 4ab], together with the chiral antipodes D-Ins(1,4,6)P(3)(4a) and L-Ins(1,4,6)P(3)(4b), was synthesized from myo-inositol. The racemic diol 6, after removal of the trans-ketal of fully protected 5 was p-methoxybenzylated to give the 6-O-alkylated derivative 9, as the major product in 52% yield. Gentle acidic hydrolysis of 9, followed by benzylation of the resulting triol, gave the fully protected compound 11ab. Isomerization of the two allyl groups followed by acidic hydrolysis of the resulting cis-prop-1-enyl moieties and the p-methoxybenzyl group gave the triol 13ab. Phosphorylation of 13ab followed by deprotection of the resulting compound, 14ab, with sodium in liquid ammonia and purification by ion exchange chromatography provided 4ab in 60% yield. The intermediate 9 was converted into the cis-diol 16ab in two steps. Selective acylation at the equatorial hydroxyl group using (S)-(+)-O-acetylmandelic acid in the presence of DCC and DMAP provided two diastereoisomers, 18 and 19, which were separated by flash chromatography. Further transformations provided the corresponding D- and L-1,4,6 triols, 13a and 13b, respectively, and phosphorylation, followed by deprotection of the fully blocked products as for the racemic 4ab, gave 4a and 4b, respectively. The absolute configuration of fully protected 11a was determined by transformation to the known compound L-1,2,4,5-tetra-O-benzyl-myo-inositol (22). Compound 4a was a full agonist at the platelet Ins(1,4,5)P(3) receptor for Ca(2+) release, but 4b was devoid of activity.     

A definitive synthesis of D-myo-inositol 1,4,5,6-tetrakisphosphate and its enantiomer D-myo-inositol 3,4,5,6-tetrakisphosphate from a novel butane-2,3-diacetal-protected inositol

New and rapid syntheses of the enantiomeric intracellular signalling molecules d-myo-inositol 1,4,5,6-tetrakisphosphate (1 a) and D-myo-inositol 3,4,5,6-tetrakisphosphate (1 b) are described. The synthetic strategy employs the novel butane-2,3-diacetal-protected (BDA-protected) myo-inositol (+/-)-3 ab, directly accessible from myo-inositol on a large scale, and an optical resolution with diastereoisomeric (R)-(-)-acetylmandelate esters. The X-ray crystal structure of (+/-)-4, an unusual side product of acid-catalysed reaction of myo-inositol with butanedione is also presented, and the absolute configurations of 1 a and 1 b are definitively assigned by conversion of key precursors into (+)-bornesitol and L-iditol hexaacetate, respectively. Biological activity of synthetic 1 b was confirmed in comparison with the natural polyphosphate.     

Chiral HPLC and physical characterisation of orthoconic antiferroelectric liquid crystals

New orthoconic antiferroelectric liquid crystalline materials were synthesised and characterised in their racemic forms and as (S) enantiomers. The materials possess oligo-methylene spacers of different lengths in semi-fluorinated achiral chains and lateral substitution by fluorine at two different positions of the molecular core. For comparison purposes, analogical materials without fluorine lateral substitutions were also prepared. Polysaccharide chiral stationary phases based on two different chiral selectors were used for the separation of the enantiomers of the individual racemic mixtures by high-performance liquid chromatography. A baseline separation of (S) and (R) enantiomers was obtained for four of the six studied liquid crystalline materials. Two of the materials were partially separated under the optimised separation conditions. The elution order of the individual enantiomers in the racemic mixtures was successfully assigned, as pure (S) enantiomers of all the studied materials were available. Both the position of the fluorine atom within the molecular core and the size of the achiral moiety had significant effects on the separation of the individual enantiomers of the studied compounds. Moreover, it was also found that the structure of the chiral stationary phase selector significantly influenced the enantiomeric resolution.     

D-、L-和DL-青霉胺的太赫兹时域光谱

利用太赫兹时域光谱技术(THz-TDS)对D-、L-和DL-青霉胺的研究发现, 三种样品在0.2 THz到1.8 THz波段的吸收光谱存在显著差异, 实验结果表明, THz吸收光谱能够鉴别青霉胺对映异构体, 这一特点将可以用于青霉胺药物的检测. 本文利用纯D-、L-青霉胺的THz吸收光谱, 对D-、L-青霉胺混合样品的THz吸收光谱进行拟合, 证明可以用THz光谱定量分析混合样品中D-、L-青霉胺的相对含量. 这项研究为手性药物分子检测和分析提供了新的实验方法, 也对深入了解手性药物与生物靶分子之间相互作用提供了启示.     

Green aspects during synthesis,application and chromatographic analysis of chiral pesticides

The agro-industry uses large quantities of chiral pesticides to mitigate the detrimental effects of pests on crops. Pesticides play a very important role of insuring food security in the world but this benefit may be eroded if principles of green chemistry are not embraced during their synthesis, application and analysis. Commercial chiral pesticide formulations are, usually, synthesised and sold as racemates. The enantiomers of the chiral pesticides in these racemic mixtures usually have enantioselective bioactivities on target organisms. One enantiomer, usually, will be active on the target organism while others are inactive and are discharged into the environment, posing serious pollution problems. This is a serious environmental problem and can be rectified through embracing general principles of green chemistry. This paper reviews the aspects that can enhance greenness during synthesis and the subsequent application of chiral pesticides during pest management in the agro-industry. Particular emphasis is placed on stereo-selective synthesis of chiral pesticides and the application of their enantiopure formulations. The green aspects during chromatographic separation of enantiomers of chiral pesticides are also discussed. These include the use of green mobile and chiral stationary phases during chromatographic analysis of chiral pesticides.     

Diastereoselective synthesis of D- and L-myo-inositol 3,4,5,6-tetrakisphosphates from D-glucose via dihydroxylation of (+)-conduritol B derivatives

Syntheses of D- and L-myo-inositol 3,4,5,6-tetrakisphosphates were achieved via diastereoselective 1,2-addition of vinylcopper reagent with the chiral aldehyde prepared from 1,2,5,6-diisopropylidene-D-glucose, ring-closing metathesis of 1,7-diene with Grubbs catalyst followed by catalytic OsO(4) dihydroxylation of (+)-conduritol B derivatives.     

A new thiatriazine isomer: synthesis, tautomerism, and molecular structure of 3,6-diphenyl-4H-1,2,4,5-thiatriazine as a precursor to the 1,2,4,5-thiatriazinyl radical

The diphenyl derivative of 4H-1,2,4,5-thiatriazine (5) was prepared by oxidative cyclization of 9. The molecular structure of 5, obtained by X-ray diffraction [orthorhombic, Pna2(1), a = 9.7746(13) A, b = 21.692(2) A, c = 5.6580(8) A], compares favorably with that predicted with ab initio calculations. The thiatriazine 5 was used as a precursor to the 3,6-diphenyl-1,2,4,5-thiatriazinyl radical (4) through either oxidation with PbO(2), or conversion to and reduction of sulfiminyl chloride 6 with Ph(3)Sb. The weak ESR quintet (a(N) = 1.03 mT, g = 2.0103) observed in the latter case correlates well with the molecular structure of 4, but the results of DFT calculations are ambiguous. Ab initio calculations show that 4H-1,2, 4,5-thiatriazine (I-4H) is the most stable tautomer and is the second most stable isomer among the six possible thiatriazines. All isomeric thiatriazinyl radicals exhibit similar spin distribution patterns. 1,2,4,5-Thiatriazinyl radical (I-R) is calculated to be 23. 1 kcal/mol less stable than the most stable 1,2,4,6 isomer II-R.     

Synthesis and chromatographic properties of a novel chiral stationary phase derived from heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-beta-cyclodextrin immobilized onto amino-functionalized silica gel via multiple urea linkages

A novel chiral stationary phase (PPHCDN7) was prepared by immobilization of heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-β-cyclodextrin (PPHCD) onto the surface of amino-functionalized silica gel via multiple urea linkages derived from an extended application of the Staudinger reaction. A wide range of structurally divergent racemic drugs and other compounds were successfully separated into their enantiomers under both normal and reversed-phase conditions. β-Adrenergic blockers and racemic tertiary, secondary and primary amines were readily separated using a mixture of methanol and aqueous triethylammonium acetate buffer. The optimal pH value for the separation falls in the range of 4.65 to 6.30. With atropine and isoproterenol, good enantioseparations with separation factors of >5 were easily attainable.     

Synthesis and characterization of pyridine-based polyamido-polyester optically active macrocycles and enantiomeric recognition for D- and L-amino acid methyl ester hydrochloride

Five new chiral macrocycles, 3a-e, have been prepared by the acylation cyclization of chiral diamine dihydrobromide intermediates 2a-c with 2,6-pyridinedicarbonyl dichloride in highly diluted solution at room temperature. The chiral diesters 1a-c needed for the preparation of the macrocycles were obtained from condensation of corresponding N-(Z)-L-amino acids and 2,6-bishydroxymethyl pyridine in the presence of DCC and DMAP. The enantiomeric recognition of chiral macrocycles 3a-e for D- and L-amino acid methyl ester hydrochlorides has been characterized by fluorescence spectra, which indicate that some of them exhibited significant chiral recognition for the enantiomers of D- and L-amino acid methyl ester hydrochlorides. The stoichiometry and binding constants of 3a-L-Am(2) and 3c-L-Am(2) complexes have been determined. An X-ray analysis of the chiral macrocycle 3b show that the chiral ligand is rather rigid and strained.     

Synthesis and chromatographic properties of a novel chiral stationary phase derived from heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-β-cyclodextrin immobilized onto amino-functionalized silica gel via multiple urea linkages

A novel chiral stationary phase (PPHCDN7) was prepared by immobilization of heptakis(6-azido-6-deoxy-2,3-di-O-phenylcarbamoylated)-β-cyclodextrin (PPHCD) onto the surface of amino-functionalized silica gel via multiple urea linkages derived from an extended application of the Staudinger reaction. A wide range of structurally divergent racemic drugs and other compounds were successfully separated into their enantiomers under both normal and reversed-phase conditions. β-Adrenergic blockers and racemic tertiary, secondary and primary amines were readily separated using a mixture of methanol and aqueous triethylammonium acetate buffer. The optimal pH value for the separation falls in the range of 4.65 to 6.30. With atropine and isoproterenol, good enantioseparations with separation factors of α>5 were easily attainable.     

Enantiomer separations by capillary electrochromatography using chiral stationary phases

The applicability of capillary electrochromatography (CEC) using packed capillary column to enantiomer separations was investigated. As chiral stationary phases, OD type packing materials of 5 and 3 microm particle diameters, originally designed for conventional high-performance liquid chromatography (HPLC) were employed. The chiral packing materials were packed by a pressurized method into a 100 microm I.D. fused-silica capillary. Several racemic enantiomers, such as acidic, neutral and basic drug components, were successfully resolved, typically by using acidic or basic solutions containing acetonitrile as mobile phases. The separation efficiencies for some enantiomers in the chiral CEC system using the 5 microm OD type packing were superior to those obtained in HPLC using chiral packings. The plate heights obtained for several enantiomers were 8-13 microm or the reduced plate height of 1.6-2.6, which indicates the high efficiency of this chiral CEC system.     

New derivatives of cyclodextrins as chiral selectors for the capillary electrophoretic separation of dichlorprop enantiomers

-, β- and γ-cyclodextrins (CDs), as well as some of their chemical derivatives, have been tested as chiral resolving agents for the capillary zone electrophoretic resolution of the racemic herbicide dichlorprop, (±)-2-(2,4-dichlorophenoxy)propionic acid, of which only the (+)-isomer is herbicidally active. The complexation constants of the herbicide enantiomers with the cyclodextrin host molecules have been calculated from the electrophoretic migration time data at variable cyclodextrin concentration. The experimental results showed that several of the investigated CDs allowed dichlorprop enantiomer resolution. In particular, a newly synthesised ethylcarbonate derivative of β-CD showed the best enantiomer resolution properties among the tested compounds, while the remaining ones showed inferior or no performances at all. The calculated inclusion constants allowed identification of the best conditions for enantioresolution, and an explanation of the different complexation properties of the investigated compounds has been proposed on the basis of molecular modeling.     

酒石酸和氰基二苯基二氢吡唑的高效液相色谱手性分离

以不同配比的甲醇和水作洗脱液,对手性物质酒石酸和5-氰基-1,3-二苯基-4,5-二氢吡唑进行了手性色谱柱高效液相色谱分离。对于亲水性的酒石酸,以纯水作为洗脱液,手性异构体不能得到分离;洗脱液中甲醇的含量增加到50%,D-和L-异构体得到分离,但是内消旋异构体和D-异构体仍然混在一个峰中;以100%甲醇作洗脱液,酒石酸的内消旋及D-和L-三个异构体的色谱峰全部分开。对于憎水性的5-氰基-1,3-二苯基-4,5-二氢吡唑,以100%甲醇作为洗脱液;当洗脱液中水的含量增加到30%时,R-和S-手性异构体的色谱峰开始分离,但是两个峰大小不相等,分离效果不理想;当洗脱液中水的含量增加到35%时,R-和S-手性异构体的色谱峰分离为两个大致相等的色谱峰,但是两个色谱峰仍有部分交叠。保留时间加长,有利于对映异构体的分离,保留时间长的色谱峰变宽。     

Chiral capillary electrophoresis as predictor for separation of drug enantiomers in continuous flow zone electrophoresis

Separation of the enantiomers of chlorpheniramine and methadone in acidic buffers containing carboxymethyl-betacyclodextrin (CMCD) as chiral selector was investigated by capillary zone electrophoresis. For a range of pH and CMCD concentrations, the mobility difference and resolution of the enantiomers were determined. Then, conditions known to provide well resolved enantiomers and optimized chiral separation were applied to chiral continuous flow electrophoresis. In that approach, a thin film of fluid flowing between two parallel plates is employed as carrier for electrophoresis. The electrolytes and the sample are continuously admitted at one end of the electrophoresis chamber and are fractionated by an array of outlet tubes at the other. The number of pure enantiomeric fractions obtained by chiral continuous flow electrophoresis was found to be directly dependent on the enantiomeric mobility difference. For racemic chlorpheniramine separated in a betaine-acetic acid buffer at a total throughput of 5 mg/h, complete enantiomeric separation is shown to require a mobility difference of about 3 x 10(-9) m2/V s. Furthermore, compared to the previous investigations with hydroxypropyl-beta-cyclodextrin, CMCD was found to permit improved fractionation of methadone enantiomers. With a total racemic drug throughput of about 15 mg/h, continuous flow zone electrophoresis processing with CMCD as chiral selector is shown to have the potential of providing pure enantiomers on a mg/h scale. The results indicate that chiral capillary zone electrophoresis data can be employed as predictor for preparative scale chiral separations based upon continuous flow zone electrophoresis.     

Evaluation of chiral recognition ability of a novel uranyl-salophen-based receptor: an easy and rapid testing protocol

A novel member of a new class of chiral uranyl-salophen complexes has been synthesised. The chiral recognition ability of this receptor toward the enantiomers of two primary amines, a sulfoxide, and a quaternary ammonium chloride has been evaluated for the first time. The enantioselectivities obtained are encouraging. The NMR method developed for this purpose allows a fast, quantitative determination of the enantioselectivity of the host directly from its racemic mixture and could find application as a preliminary screening tool in the search for new receptors using combinatorial methods. The experiments carried out in this context demonstrated also that the activation barrier for the racemisation of such chiral uranyl-salophen receptors is much higher than the lower limit of 21 kcal mol(-1) previously reported.     

CE coupling with end-column electrochemiluminescence detection for chiral separation of disopyramide

CE with electrochemiluminescence (ECL) detection technique was successfully applied for the chiral separation of a kind of class IA antiarrhythmic racemic drug. To the best of our knowledge, this is the first report of ECL detection used in chiral CE. To get better detection sensitivity and good enantioresolution at the same time, the conditions of capillary inlet and outlet buffer were systematically optimized. Unlike the traditional chiral separation method, the buffers we used in the capillary inlet and outlet differed from each other in terms of buffer pH, ionic strength, type of BGE as well as buffer composition. Under the optimum conditions, baseline enantioseparation and highly sensitive detection of the enantiomers were achieved. Wide linear relationship of each enantiomer was achieved in the range of 5 x 10(-7) to 2 x 10(-5) mol/L with relative coefficients of 0.996 and 0.997, respectively. The detection limits were estimated to be 8 x 10(-8) and 1.0 x 10(-7) mol/L (S/N = 3) for the enantiomers, respectively. In addition, a successful application of this new method to the chiral separation of the racemic drug in spiked plasma samples confirmed the validity and applicability of the chiral CE-ECL method.     

Enantiomeric separation of D- and L-carnitine by integrating on-line derivatization with capillary zone electrophoresis.

A new capillary zone electrophoretic method has been developed for the enantiomeric separation and quantification of enantiomers of carnitine, D- and L-carnitine were derivatized with 9-fluorenylmethyl chloroformate in a flow system, working on-line with the capillary electrophoretic equipment. The separation was performed using a selective chiral buffer containing 2,6-dimethyl-beta-cyclodextrin (heptakis). Triethanolamine was used as electroosmotic modifier and the separation was carried out in a uncoated capillary. Under the optimal conditions the resolution between D- and L-carnitine was 1.2 and the limits of detection for both isomers were about 5.0 microM. The proposed method was applied to the determination of D-carnitine in excess of L-carnitine in synthetic samples, and the results demonstrated that the maximal D-:L-carnitine ratio determined was approximately 1:100.     

Synthesis of new chiral calix[4]azacrowns for enantiomeric recognition of carboxylic acids

Two novel chiral calix[4]azacrown ethers 4 and 5 bearing a furfuryl group on the nitrogen atom were developed by the reaction of dibromo- or ditosyl derivatives of p-tert-butylcalix[4]arenes 2 and 3 with a chiral diol, 1. The enantioselective recognition of these receptors towards the enantiomers of racemic carboxylic acids has been studied by ¹H NMR spectroscopy. The molar ratio and the association constants of the chiral compounds 4 and 5 with each of the enantiomers of guest molecules were determined by using Job plots and a nonlinear least-squares fitting method, respectively. The Job plots indicate that both of the hosts form 1:1 instantaneous complexes with (R)- or (S)-mandelic acid and (l)- or (d)-dibenzoyltartaric acid. The receptors exhibited different chiral recognition abilities towards the enantiomers of racemic guests.     

Large optical activity of gold nanocluster enantiomers induced by a pair of optically active penicillamines

We have succeeded for the first time in preparing a pair of gold nanocluster enantiomers protected by optically active thiols: D- and L-penicillamine (D-Pen and L-Pen). Circular dichroism (CD) spectroscopy confirmed the mirror image relationship between the D-Pen-capped and the L-Pen-capped gold nanoclusters, suggesting that the surface modifier acts as a chiral selector, and that the nanoclusters have well-defined stereostructures as common chiral molecules do. No CD signals could be obtained when the gold nanoclusters were synthesized by using a racemic mixture (rac-Pen). These chiroptical properties were investigated for the three separated fractions of each of the gold nanoclusters (D-Pen-capped, L-Pen-capped, or rac-Pen-capped clusters) by polyacrylamide gel electrophoresis (PAGE). Each fractioned component has the mean diameter of 0.57, 1.18, or 1.75 nm that was determined by a solution-phase small-angle X-ray scattering. With a decrease in the mean cluster diameter, optical activity or anisotropy factors gradually increased. On the basis of the kinetic and the structural considerations, the origins of large optical activity of the gold nanocluster enantiomers are discussed.