Α-methoxyphenylacetic Acid Research Articles

Luminescence, CPL and magnetic properties of 1D enantiopure Ln3+ complexes with (S-) and (R-) α-methoxyphenylacetate ligand.

The reaction of Ln(NO3)2·6H2O (Ln = Eu, Tb, Dy and Sm) with (R)-(-)-α-methoxyphenylacetic acid (R-HMPA) and 1,10-phenanthroline (phen) in EtOH/H2O allows the isolation of 1D chiral compounds of formula [Ln(μ-R-MPA)(R-MPA)2(phen)]n in which Ln = Eu (R-Eu), Tb (R-Tb), Dy (R-Dy) and Sm (R-Sm). The same synthesis by using (S)-(+)-α-methoxyphenylacetic acid (S-HMPA) instead of (R)-(-)-α-methoxyphenylacetic acid allows the isolation of the enantiomeric compounds with formula [Ln(μ-S-MPA)(S-MPA)2(phen)]n where Ln = Eu (S-Eu), Tb (S-Tb), Dy (S-Dy) and Sm (S-Sm). Single crystal X-Ray diffraction measurements were performed for compounds R/S-Eu, R/S-Tb, S-Dy and S-Sm. The luminescence and the circular dichroism measured in the solid state are reported. All compounds show sensitized luminescence, notably the Eu3+ and Tb3+ ones, whose emission color can be perceived by the naked eye. For the Eu3+ and Tb3+ derivatives the quantum yield and the circular polarized luminescence have been measured. For the magnetic allowed transition 5D0 → 7F1 of the Eu3+ compound, the anisotropy factor glum is ±0.013 (+for S-Eu). Also, magnetic properties of all compounds were studied with the Dy3+ analogue showing slow relaxation of the magnetization under a direct current magnetic field of 1000 Oe.

Direct Synthesis of α-Methoxyphenylacetic Acid Via Tandem Catalysis from Styrene and Methanol with Co3O4/CuCo2O4 Heterostructures

Direct Synthesis of α-Methoxyphenylacetic Acid Via Tandem Catalysis from Styrene and Methanol with Co3O4/CuCo2O4 Heterostructures

Novel optically active 2D materials based on λ-zirconium phosphate and chiral monocarboxylic acids: Synthesis and characterization

Five novel chiral 2D materials with general formula λ-ZrPO4(OH)1-x(RCOO)x(dmso) have been prepared by covalent anchoring of five different chiral carboxylic acids to the sheets of λ-zirconium phosphate (λ-ZrP), namely (S)-(+)-Mandelic acid (MAN), (R)-(−)-α-Methoxyphenylacetic acid (MPA), (S)-(+)-Ibuprofen (IBU), (S)-(+)-6-Methoxy-α-methyl-2-naphthaleneacetic acid (MMN) and (−)-Menthyloxyacetic acid (MEN). The synthesized materials were characterized by X-ray diffractometry, FT-IR spectrophotometry, elemental and thermogravimetric analyses and polarimetry. The X-ray diffraction patterns revealed that the interlayer separations increase from 1.02 nm (pure λ-ZrP) to 1.31–2.31 nm as a result of the incorporation of the mentioned acids within the interlayer gallery. The polarimetry measurements showed that the synthesized materials have appreciable optical activities suggesting they could have protentional applications in the field of chiral separation techniques.

Chiral Coordination Polymers of Mandelate and its Derivatives: Tuning Crystal Packing by Modulation of Hydrogen Bonding

Chiral coordination polymers constructed from mandelic acid have shown promise in enantioselective recognition and sensing, whereas its methoxy-protected derivative, α-methoxyphenyl acetic acid, is rarely used as a ligand in coordination polymers. In this study, mandelic acid, 3,5-difluoromandelic acid, and α-methoxyphenyl acetic acid were combined with divalent transition metals and bridging dipyridyl co-ligands to obtain a series of six 1D coordination polymers. The coordination polymers of mandelate and 3,5-difluoromandelate possessed densely packed structures stabilised by hydrogen bonding. In contrast, the use of (R)-α-methoxyphenyl acetic acid gave rise to zig-zag chains with significant solvent-accessible void space.

Stability study of α-bromophenylacetic acid: Does it represent an appropriate model analyte for chiral separations?

The stability of α-bromophenylacetic acid (BPAA) in 50% aqueous methanol solution has been tested. CE in different running buffers was used to separate BPAA from the decomposition reaction products α-hydroxyphenylacetic (mandelic) acid and α-methoxyphenylacetic acid. Suitable CE separation of all three compounds and other product, bromide, was achieved in 60mmol/L formate buffer (pH 3.0) at -30kV in 50μm (i.d.) poly(vinyl alcohol)-coated fused silica capillary (30cm/24.5cm) with UV detection at 200nm. The CE method was applied to determine the reaction order of the decomposition of BPAA (0.47mmol/L) via nucleophilic substitution in 50% aqueous methanol. The first-order reaction kinetics was confirmed by linear and non-linear regression, giving the rate constants 1.52 × 10-4±2.76 × 10-5 s-1 and 7.89 × 10-5±5.02 × 10-6 s-1, respectively. Additionally, the degradation products were identified by CE coupled to mass spectrometric (MS) detection. The CE-MS experiments carried out in 60mmol/L formate buffer (pH 3.0) and in 60mmol/L acetate buffer (pH 5.0) confirmed the results obtained by CE-UV. Furthermore, the stability of BPAA in polar solvents was tested by 1H NMR experiments. Our results provide strong evidence of the instability and fast degradation of BPAA in 50% aqueous methanol indicating that BPAA is not suitable as the model analyte for chiral separations.

Influence of an additive on growth and solubility behavior of chiral 2-chloromandelic acid

In this study the growth behavior of chiral 2-chloromandelic acid (2-ClMA) was investigated aimed at deriving crystallization conditions for ‘Preferential Crystallization’ of its (S)-enantiomer. Therefore, the metastable conglomerate of 2-ClMA was generated by addition of (±)-α-methoxyphenylacetic acid (MPAA) as additive for stabilization. Solubility and kinetic single crystal growth experiments were performed under the influence of the used additive. As a result, MPAA could successfully applied for a robust recovery of the 2-ClMA conglomerate. Low MPAA contents (<1 wt%) showed an inhibiting effect on the crystal growth of (S)-2-ClMA and a weak influence on the solubility in the chiral system.

Three-State Switchable Chiral Stationary Phase Based on Helicity Control of an Optically Active Poly(phenylacetylene) Derivative by Using Metal Cations in the Solid State.

An unprecedented three-state switchable chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) was developed using a helical poly(phenylacetylene) bearing a chiral ( R)-α-methoxyphenylacetic acid residue as the pendant (poly-1). The left- and right-handed helical conformations were induced in poly-1-based CSP upon coordination with a catalytic amount of soluble sodium and cesium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts (MBArF), respectively, which are soluble in the HPLC conditions [hexane-2-propanol (95:5, v/v)]. The switch between the two different helical states of poly-1 can be easily achieved by rinsing the poly-1-based CSP with MeOH and the subsequent addition of the proper MBArF salt. Using this dynamic helical CSP, we demonstrate how changes on the orientation of the secondary structure of a chiral polymer (right-handed, left-handed, and racemic helices) can alter and even invert the elution order of the enantiomers. This study was done without adding chiral additives or changing the mobile phase, which could produce changes on the retention times and make it more difficult to determine the role of the secondary structure during the chiral recognition process.

Enantiomeric Variability of Distaminolyne A. Refinement of ECD and NMR Methods for Determining Optical Purity of 1-Amino-2-Alkanols.

Sample configurations of distaminolyne A (1a); isolated from the ascidians Pseudodistoma opacum and P. cereum, and collected at different sites in New Zealand, were investigated by two methods: Exciton coupled electronic circular dichroism (EC ECD) of the corresponding N,O-dibenzoyl derivative 1b; and chiral reagent derivatization of 1a with (S)- and (R)-α-methoxyphenylacetic acid (MPA), followed by 1H-NMR analysis. Configuration and optical purity of 1a (%ee) was found to vary depending on the geographic distribution of ascidian colonies. An improved method for preparing N,O-diarenoyl derivatives of 1a was optimized. The EC ECD method was found to be complementary to the MPA-NMR method at different ranges of %ee.

Comparison of chiral NMR solvating agents for the enantiodifferentiation of amines

Chiral, enantiomerically pure organic-soluble acids are often used as NMR chiral solvating agents (CSAs) for analyzing the enantiopurity of amines. However, the reports that describe CSAs for amines provide limited comparisons to other previously reported reagents. As such, it is difficult to know which among the many CSAs to pick when studying a new amine. We report a comparison of thirteen commercially available CSAs for the analysis of primary, secondary and tertiary amines in chloroform-d. (R)-α-methoxyphenylacetic acid, (R)-(-)-O-acetylmandelic acid, (R)-2-methoxy-2-(1-naphthyl)propionic acid and (R)-(-)-1,1′-binaphthyl-2,2′-diylhydrogenphosphate are identified as the best four to use as a starting point for the analysis of a new amine.

Solvation of a chiral carboxylic acid: effects of hydrogen bonding on the IR and VCD spectra of α-methoxyphenylacetic acid.

Strong hydrogen bonding to solvent molecules can significantly alter the IR and VCD spectra of a chiral solute. This can be particularly troublesome for the determination of absolute configurations, as all spatial configurations of solute-solvent clusters need to be considered explicitly in spectra calculations. With this contribution, we aim to derive general guidelines for the explicit solvation of carboxylic acids, and characterize the solute-solvent interactions of the model compound α-methoxyphenylacetic acid (MPAA) in organic solvents of different polarity. We show that, in the typical concentration range employed for VCD studies, MPAA prefers the formation of dimers in chloroform. In the other investigated solvents (acetonitrile, methanol, and dimethyl sulfoxide), hydrogen bonded solute-solvent clusters have to be considered explicitly for the spectral analysis. We discuss the origin of the solvent dependence of the VCD spectra of MPAA in detail, show which vibrational modes are most strongly affected, and that the spectral response correlates with the hydrogen bonding strength.

Structural, analytical and DSC references to resolution of 2-methoxy-2-phenylacetic acid with chiral 1-cyclohexylethylamines through gas-antisolvent precipitation

The system of intermolecular interactions is very similar in the solid state of the chiral and racemic α-methoxyphenylacetic acids (α-MPAA) indicated by both Differential Scanning Calorimetry (DSC) and FTIR-spectroscopy, and even proved by single crystal structure determination. It makes the resolution of such a racemate compound challenging even by supercritical fluid extraction. The chiral (S)-α-methoxyphenylacetic acid (1) crystallizes in orthorhombic crystal system (space group P212121, a=6.8795(3) Å, b=7.0124(3) Å, c=17.4578(8) Å, Z=4, R=0.0373), while its 1:1 salt formed with (S)-1-cyclohexylethyl amine (3) is found to be monoclinic (s.g. P21, a=9.5290(12) Å, b=6.5909(10) Å, c=13.869(2) Å, β=103.13(3)°, Z=2, R=0.0477). The packing arrangement in the (S)-(S) ammonium carboxylate type salt is columnar. The columns are hydrophylic inward and hydrophobic outward, that results in fibrous growth of the salt crystals melting at 163°C. The crystal habit of the higher melting diastereomeric (S)-(R) salt (mp. 187°C) is also fibrous, its structure is closely related to the (S)-(S)-salt by the similarities observed in their IR spectra. The DSC and powder XRD studies on the chiral and racemic acids, and on the pair of diastereomeric salts helped us to construct and calculate the binary and ternary phase diagrams of the system components, including their eutectic temperatures and compositions, as well.

ChemInform Abstract: Montecrinanes A—C: Triterpenes with an Unprecedented Rearranged Tetracyclic Skeleton from Celastrus vulcanicola. Insights into Triterpenoid Biosynthesis Based on DFT Calculations.

Three new triterpenoids with an unprecedented 6/6/6/6-fused tetracyclic carbon skeleton, montecrinanes A-C (1-3), were isolated from the root bark of Celastrus vulcanicola, along with known D:B-friedobaccharanes (4-6), and lupane-type triterpenes (7-12). The stereostructures of the new metabolites were elucidated based on spectroscopic (1D and 2D NMR) and spectrometric (HR-EIMS and HR-ESIMS) techniques. Their absolute configurations were determined by both NMR spectroscopy, with (R)-(-)-α-methoxyphenylacetic acid as a chiral derivatizing agent, and biogenetic considerations. Biogenetic pathways for montecrinane and D:B-friedobaccharane skeletons were proposed and studied by DFT methods. The theoretical results support the energetic feasibility of the putative biogenetic pathways, in which the 1,2-methyl shift from the secondary baccharenyl cation represents a novel and key reaction step for a new montecrinane skeleton.

New chiral oxo-bridged calix[2]arene[2]triazine for the enantiomeric recognition of α-racemic carboxylic acids

The enantiomeric excess is a key parameter for chemical and pharmaceutical industries for its ability to determine the activity and therapeutic action of chiral compounds. The determination of the enantiomeric excess using nuclear magnetic resonance is generally based on the formation of diastereomeric complexes. Herein we report novel chiral oxo-bridged calix[2]arene[2]triazine derivatives, which were synthesized from (1S,2R)-(−)-1-amino-2-indanol or (1S,2R)-(+)-2-amino-1,2-diphenylethanol. The structures of these compounds were established by various spectroscopic methods. Their enantiomeric recognition abilities towards the enantiomers of α-racemic carboxylic acids were examined by using 1H NMR spectroscopy. The ΔΔδ values of α-H signals were appropriate to give a good baseline resolution for most of the tested analytes, which ranged from 0.005 to 0.053ppm. The α-hydroxy acids, especially those containing aromatic group such as mandelic acid, α-methoxyphenylacetic acid, showed a bigger ΔΔδ value in comparison to the other carboxylic acids.

Montecrinanes A-C: Triterpenes with an Unprecedented Rearranged Tetracyclic Skeleton from Celastrus vulcanicola. Insights into Triterpenoid Biosynthesis Based on DFT Calculations.

Three new triterpenoids with an unprecedented 6/6/6/6-fused tetracyclic carbon skeleton, montecrinanes A-C (1-3), were isolated from the root bark of Celastrus vulcanicola, along with known D:B-friedobaccharanes (4-6), and lupane-type triterpenes (7-12). The stereostructures of the new metabolites were elucidated based on spectroscopic (1D and 2D NMR) and spectrometric (HR-EIMS and HR-ESIMS) techniques. Their absolute configurations were determined by both NMR spectroscopy, with (R)-(-)-α-methoxyphenylacetic acid as a chiral derivatizing agent, and biogenetic considerations. Biogenetic pathways for montecrinane and D:B-friedobaccharane skeletons were proposed and studied by DFT methods. The theoretical results support the energetic feasibility of the putative biogenetic pathways, in which the 1,2-methyl shift from the secondary baccharenyl cation represents a novel and key reaction step for a new montecrinane skeleton.

Absolute Stereochemistry of 1,2-Diols from Lipids of Thermomicrobia.

1,2-Diol based phospholipids are a well-known feature of bacteria from the class Thermomicrobia. Since these bacteria contain only lipids with an alkyldiol-1-phosphate backbone instead of sn-glycero-3-phosphate, it is important to elucidate the stereochemistry of the 1,2-diols. We have studied the absolute stereochemistry of long-chain 1,2-diols isolated from Thermorudis pharmacophila (formerly known as Thermomicrobia sp. WKT50.2) by nuclear magnetic resonance (NMR) using α-methoxyphenylacetic acid (MPA). Low-temperature (-60°C) NMR of bis-(R)-MPA ester showed (R) stereochemistry of the 1,2-diols. This is the first report concerning the stereochemistry of natural 1,2-diols, which replace the glyceride moiety in phospholipids. The (R) stereochemistry of the diols is expected as it is the same configuration as for the common bacterial lipid backbone-sn-glycero-3-phosphate. This is the first application of low-temperature NMR of a single MPA derivative for assignment of stereochemistry of natural 1,2-diols. The results were confirmed by the comparison of NMR data with bis-(R)-MPA ester of (R) and rac-1,2-octanediol.

An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

Critical assessment of performance of alternative molecular modeling methods depending on a specific object and goal of the investigation is a question of continuous interest. This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry optimization of generated conformers, with the aim of selecting a set for further optimization. What was performed herein was a comparison of LLMs: MM3, MM+, UFF, Dreiding, AM1, PM3, and PM6 on the optimization of conformers’ geometry of α-methoxyphenylacetic acid (MPA) 2-butyl esters as a set of typical diastereomeric esters of a chiral derivatizing agent. This set of esters calculated represents only compounds of this certain type in the current work. The LLM conformer energies were correlated with benchmark energies found by using higher level reference method B3LYP/6-311++G** on the geometries gained previously by optimization with LLMs. In an alternative treatment, the energy range to be covered and corresponding number of LLM optimized conformers obligatory for submitting to further optimization using a high level optimization cascade were considered on the basis of determination of the cut-off conformer (COFC).

An efficient synthesis of (R)- and (S)-8-ethoxy-2-(4-fluorophenyl)-3-nitro-2H-chromene

Racemic 8-ethoxy-2-(4-fluorophenyl)-3-nitro-2H-chromene (S14161) was recently identified as a potent inhibitor of phosphoinositide 3-kinase (PI3K). In order to investigate the effects of its two enantiomers on tumor cell lines, we designed a novel synthesis for (R)-S14161 and (S)-S14161 using a chemical resolution and derivation strategy. The readily available 3-(tert-butyldimethylsilyloxy)-salicylaldehyde underwent a tandem oxa-Michael–Henry reaction with trans-4-fluoro-β-nitrostyrene in the presence of a catalytic amount of l-proline and triethylamine to give the 3-nitro-2H-chromene. Upon removal of the TBS protecting group, the resolution of the resulting racemic 2-(4-fluorophenyl)-8-hydroxy-3-nitro-2H-chromene was achieved via diastereomeric ester formation using (S)-(+)-α-methoxyphenylacetic acid as the derivatizing agent, followed by aminolysis. Finally, the ethyl ether formation of each enantiomer furnished (R)-S14161 and (S)-S14161 in enantiomerically pure forms. The absolute configurations of these chiral molecules were determined by a circular dichroism method. The two enantiomers showed no marked differences in inhibition of growth of human myeloma LP1 and OPM-2 cells.

Nanospheres with Tunable Size and Chirality from Helical Polymer–Metal Complexes

A new family of nanospheres is made by complexation of divalent metals (i.e., Ca(2+), Ba(2+)) and poly(phenylacetylene) polymers bearing α-methoxyphenylacetic acid (MPA) pendants with high content of the cis isomer responsible for their helical structures. The resulting helical polymer-metal complex (HPMC) nanospheres present two interesting properties: (a) their diameter can be tuned to different sizes, to growth or to shrink, by changing the metal ion or the polymer/metal ion ratio, and (b) the helicity on the surface and the interior of the particle can be tuned to any of the two helical senses (M or P) by selection of the metal ion. The role of the solvent, the metal ion, and the helicity of the polymer in the aggregation are discussed. The ability of these nanospheres to encapsulate is demonstrated with examples.

Evaluation of (R)-(−)-α-methoxy phenyl acetic acid as a chiral shift reagent for resolution and determination of R and S enantiomers of modafinil in bulk drugs and formulations by 1H NMR spectroscopy

(R)-(-)-α-Methoxy phenyl acetic acid, (S)-(-)-1,1'-(2-naphthol), and (R)-(+)-α-methoxy-α-trifluoromethyl phenyl acetic acid were evaluated as chiral shift reagents (CSRs) for (1)H NMR spectroscopic resolution and determination of R and S enantiomers of modafinil (MDL) in bulk drugs and formulations. Effects of the nature of CSR and the weight ratio of substrate to shift reagent on enantiomeric discrimination were investigated. Intramolecular and intermolecular hydrogen bonding interactions between the drug and the CSR seem to be the driving force for desired resolution. A mechanism was proposed to explain the interactions between (R, S)-enantiomers of MDL and (R)-(-)-α-methoxy phenyl acetic acid. The method was validated and applied successfully to determine the enantiomeric purity of MDL in tablet formulations.

First isolation of disubstituted cis-5,6-dihydro-1,10-phenanthrolines. lipase-mediated resolution of cis- and trans-phenoxy alcohol isomers and assignment of absolute stereochemistry via cd and nmr spectroscopy

5,6-Dihydro-1,10-phenanthrolines can display axial and central chirality. In conjunction with the ligating properties of the diimino moiety, this class of compounds is of great interest to applications in supramolecular chemistry. We report the first preparation of cis-5,6-dihydro-1,10-phenanthroline derivatives by reacting triphenyl borate with the corresponding epoxide precursor. We found that solvent and temperature choice determined the stereoselectivity of the epoxide opening giving rise to the cis (14:1 dr) or trans (99:1 dr) product. Racemates of each stereoisomeric mixture, cis- and trans-phenoxy alcohol, were separated via highly enantioselective transesterifications with lipase PSCI from Burkholderia cepacia (97% ee, E > 200). Stereochemical assignments were carried out using CD and X-ray analyses in conjunction with NMR studies of α-methoxy-α-(trifluoromethyl)phenylacetic acid and α-methoxyphenylacetic acid esters.