Simultaneous assay of four stereoisomers of diltiazem hydrochloride. Application to in vitro chiral inversion studies

Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride (2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5 h nor under visible light for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life of 5 h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem hydrochloride (2S, 3S) was not observed.     

Assay of four stereoisomers of desacetyl diltiazem hydrochloride. Application toin vitro chiral inversion studies

Summary Direct resolution of four stereoisomers of the related compound of diltiazem hydrochloride, namely desacetyl diltiazem hydrochloride, was studied by both normal and reversed-phase chiral HPLC. The four stereoisomers were completely resolved on a Chiralcel OF column. The technique developed was applied to a chiral inversion study of desacetyl diltiazem hydrochloride. This inversion was observed neither in the solid state, in aqueous solution at 100°C for 3 h nor under visible light for 10h, but was observed in aqueous solution under UV irradiation.The (+)-(2S, 3S)-cis-desacetyl diltiazem hydrochloride degraded with a half-life of 1.9 h in aqueous solution under UV and epimerized to (+)-(2R, 3S)-trans-desacetyl diltiazem hydrochloride. Similarly, (+)-(2S, 3S)-cis-desacetyl diltiazem hydrochloride degraded about three times faster than diltiazem hydrochloride. Reverse epimerization of (+)-(2R, 3S)-trans-desacetyl diltiazem hydrochloride to (+)-(2S, 3S)-cis-desacetyl diltiazem hydrochloride was not observed.The overall degradation was the result of two competitive processes, the epimerization and the decomposition of the benzothiazepin ring. The degradation and epimerization rate of (+)-(2S, 3S)-cis-desacetyl diltiazem hydrochloride in solution under UV depended upon the solvent, the aqueous pH, and concentration.     

Chiral discrimination studies of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid by high-performance liquid chromatography and NMR spectroscopy

Chiral discrimination studies using (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) as a chiral selector were performed by high-performance liquid chromatography (HPLC) and NMR spectroscopy. The enantiomers of alanine (Ala) or alanine methyl ester (Ala-ME) were well separated on the chiral stationary phases (CSPs) derived from (+)-18-C-6-TA by HPLC. The chiral selector, (+)-18-C-6-TA, used in the CSP was also applied for the chiral discrimination of the Ala and Ala-ME enantiomers, and it discriminated these enantiomers successfully by NMR spectroscopy. The chemical shift differences (Delta Delta delta) of the alpha-proton of these enantiomers in the presence of an equimolecular solution of 18-C-6-TA were observed to be 0.10 ppm for Ala in methanol-d4 containing 10 mM H2SO4 and 0.11 ppm for Ala-ME in methanol-d4. The observed NMR results agreed with the chromatographic data on the (+)-18-C-6-TA-derived CSP by HPLC in terms of both the elution order and solvents effects.     

Absolute structures of some naturally occurring isopropenyldihydrobenzofurans,remirol, remiridiol,angenomalin, and isoangenomalin

The absolute structures of some naturally occurring chiral 2-isopropenyl-2,3-dihydrobenzofurans, (+)-remirol (1a), (+)-remiridiol (1b), (+)-angenomalin (2), and (+)-isoangenomalin (3), were studied by respective chiral synthesis. Kinetic resolutions of racemic 2-isopropenyl-2,3-dihydrobenzofurans, 2-isopropenyl-4,6-dimethoxy-2,3-dihydrobenzofuran (4), 4-hydroxy-2-isopropenyl-2,3-dihydrobenzofuran-5-carbaldehyde (8), and 2-isopropenyl-6-(MOM)oxy-2,3-dihydrobenzofuran-5-carbaldehyde (11c), by Sharpless dihydroxylation using (DHQ)(2)AQN or (DHQD)(2)AQN gave the corresponding chiral 2-isopropenyl-2,3-dihydrobenzofurans. Chiral (S)-(+)-4 (99% ee, using (DHQD)(2)AQN) was converted to natural remirol (S)-(+)-1a and then to natural remiridiol (S)-(+)-1b. (S)-(+)-8 (97% ee, using (DHQD)(2)AQN) was converted to natural angenomalin (S)-(+)-2. (R)-(-)-11c (>99% ee, using (DHQ)(2)AQN), was converted to natural isoangenomalin (R)-(+)-3. Thus, the absolute structures of natural remirol (+)-1a and remiridiol (+)-1b and angenomalin (+)-2 were determined to be S, and the structure of natural isoangenomalin (+)-3 was R.     

Syntheses of (S)-(+)-trihexyphenidyl hydrochloride and (S)-(+)-procyclidine hydrochloride, two anticholinergics, using (S)-(-)-3-cyclohexyl-3-hydroxy-3-phenylpropanoic acid as chiral synthon

The absolute configuration of the more active (-)-enantiomer of the anticholinergic trihexyphenidyl hydrochloride has been established as (R) by syntheses of (S)-(+)-procyclidine hydrochloride, whose absolute configuration has been established previously, and (S)-(+)-trihexyphenidyl hydrochloride from the same chiral building block, viz. (S)-(-)-cyclohexyl-3-hydroxy-3-phenylpropanoic acid. Both enantiomers of this chiral synthon were prepared by optical resolution of the corresponding racemate, employing (R)- and (S)-1-phenylethylamine, respectively, as resolving agents.     

Assessment of the in-vivo stereochemical integrity of aprepitant based on the analysis of human plasma samples via high-performance liquid chromatography with mass spectrometric detection

Achiral and chiral liquid chromatographic methods utilizing mass spectrometric detection were developed to investigate the possibility of inversion of configuration at any or all of the chiral centers of the neurokinin-1 (NK-1) receptor antagonist, aprepitant (5-[[2(R)-[1(R)-(3,5-bistrifluoromethyl phenyl)ethoxy]-3(S)-(4-fluorophenyl)morpholin-4-yl]methyl]-2,4-dihydro-[1,2,4]triazol-3-one), in-vivo, following administration of the compound to man. A structure such as aprepitant, that contains three chiral centers, may exist in eight stereochemical forms or, more specifically, as four diastereoisomeric pairs of enantiomers. The four diastereoisomers were separated from each other using a ProntoSil C18 AQ HPLC column (4.6 x 100 mm, 3 microm particles) with a mobile phase composed of acetonitrile--water (47:53, v/v%). Detection was via a single quadrupole mass spectrometer that was connected to the HPLC system via an APCI interface. Analysis of post-dose plasma samples under these conditions indicated that only aprepitant and or its enantiomer were present following oral administration of the drug. Aprepitant and its enantiomer were separated using a Chiralcel OD-H HPLC column with a mobile phase composed of hexane-isopropanol (80:20, v/v%); tandem mass spectrometric detection using an APCI interface was employed. Post-dose plasma samples analyzed using the Chiracel column were found to contain only aprepitant. The results of these experiments confirm that the products of inversion of configuration at any or all of the three chiral centers of aprepitant are not detectable in human plasma samples obtained following the administration of the drug.     

Planar chiral dianthranilide and dithiodianthranilide molecules: optical resolution, chiroptical spectra, and molecular self-assembly

Planar chiral dianthranilide (1) was resolved to enantiomers with use of (-)-(1S,4R)-camphanoyl chloride as a chiral derivatizing agent. The (+)-1 enantiomer was assigned the S absolute configuration from the X-ray crystal structure of its N,N'-dicamphanoyl derivative. Optical resolution of dithionodianthranilide (2) was accomplished by inclusion crystallization with (R,R)-1,2-diaminocyclohexane, and the X-ray structure of the corresponding adduct revealed the (-)-2stereoisomer has the R configuration. A slow boat-to-boat ring inversion (DeltaG(++) = 24.1 +/- 0.1 kcal mol(-1)) causes racemization of (+)-1 in solution as manifested by a gradual decrease of the CD spectrum whereas, (-)-2 is configurationally stable at these conditions. The analysis of the CD spectra of the title compounds showed that the n-pi* Cotton effect signs are determined by the helicity of the skewed benzamide and thiobenzamide chromophores. The solid-state structures of the racemic and homochiral forms of 1 and 2 show different self-assembly patterns: the racemate (+/-)-1 prefers the cyclic R(2)(2)(8) hydrogen bond motif, whereas the crystalline DMSO solvates of (+/-)-1 and (+)-1 consist of 1D homochiral hydrogen-bonded assemblies generated by the C(6) motif. In the case of dithionolactams (+/-)-2 and (-)-2 two types of 1D networks were observed: in the racemate they are generated by the centrosymmetric R(2)(2)(8) and R(2)(2)(12) hydrogen bond motifs, whereas the molecules in the homochiral crystals are connected solely with use of the strongly nonplanar R(2)(2)(8) motif.     

Multistate Aggregation-Induced Chiroptical Properties of Enantiopure Disulfide-Mediated Bispyrene Macrocycles

A chiral bispyrene macrocycle designed for exclusive intermolecular excimer fluorescence upon aggregation was synthesized by a double hydrothiolation of a bis-enol ether macrocycle followed by intramolecular oxidation of free thiols. Unusually high stereoselectivity was achieved for the thiol-ene additions under templated conditions and Et₃B/O₂ radical initiation. After enantiomer separation (chiral stationary phase HPLC), aqueous conditions provoked aggregation. Detailed structural evolution was afforded by ECD/CPL monitoring. Three regimes can be observed and characterized by strong modifications in chiroptical patterns under, at, or above a 70 % H₂O : THF threshold. In luminescence, high g_lum dissymmetry factors values were obtained, up to 0.022, as well as a double sign inversion of CPL signals during the aggregation, a behavior rationalized by time-dependent density functional theory (TDDFT) calculations. Langmuir layers of enantiopure disulfide macrocycles were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by AFM and UV/ECD/fluorescence/CPL.     

Novel oxygen chirality induced by asymmetric coordination of an ether oxygen atom to a metal center in a series of sugar-pendant dipicolylamine copperII complexes

Six sugar-pendant 2,2'-dipicolylamine (DPA) ligands (L1-3 and L'1-3) have been prepared. OH-protected and unprotected D-glucose, D-mannose, and D-xylose were attached to a DPA moiety via an O-glycoside linkage. X-ray crystallography of the copper(II) complexes (1-5) with these ligands revealed that the anomeric oxygen atom is coordinated to the metal center in the solid state, generating a chiral center at the oxygen atom. The CD spectra of these copper complexes in methanol or aqueous solution exhibit Cotton effects in the d-d transition region, which indicates that the ether oxygen atoms remain coordinated to the metal center and the oxygen-atom chirality is preserved even in solution. For complexes 1 and 2, the inverted oxygen-atom chirality and chelate-ring conformation in the solid state are well correlated with the mirror-image CD spectra in methanol solution. The concomitant inversion of the asymmetric configuration around the copper center was also observed in a methanol solution of complex 3 and a pyridine solution of complex 2. The square-pyramidal/octahedral copper(II) centers also exhibited characteristic absorption and CD spectra.     

High-performance liquid chromatography study of the enantiomer separation of chrysanthemic acid and its analogous compounds on a terguride-based stationary phase

The direct enantioseparation of chrysanthemic acid [2,2-dimethyl-3-(2-methylpropenyl)-cyclopropanecarboxylic acid] and its halogen-substituted analogues was systematically studied by HPLC using a terguride-based chiral stationary phase in combination with a UV diode array and chiroptical detectors. Isomers with (1R) configuration always eluted before those with (IS) configuration. The elution sequence of cis- and trans-isomers was strongly affected by mobile phase pH, whereas the enantioselectivity remained the same. Conditions for the separation of all the enantiomers were also examined. This method was used for monitor the hydrolytic degradation products of Cyfluthrin (Baythroid) in soil under laboratory conditions.     

Synthesis of chiral glycolurils from (<Emphasis Type="Italic">S</Emphasis>)-(+)- and (<Emphasis Type="Italic">R</Emphasis>)-(-)-1-<Emphasis Type="Italic">sec</Emphasis>-butyl-3-methylurea

Chiral dialkyl- and tetraalkylglycolurils have been obtained using chiral (S)-(+)- and (R)-(-)-1-sec-butyl-3-methylurea as starting materials. The diastereomer (S)-(+)-2,6-di-sec-butyl-4,8-dimethyl-2,4,6,8-tetraazabicyclo[3.3.0]-octane-3,7-dione was separated into stereoisomers, for the higher melting of which the absolute configuration was determined as (S,S,S,S) by X-ray structural analysis.     

手性硫代磷酸及其衍生物的研究(Ⅸ)——O-乙基O-苯基硫代磷酰胺水解反应的立体化学

旋光活性O-乙基O-苯基硫代磷酰氯在碱存在下与伯胺、仲胺或氨反应,得到构型翻转的O-乙基O-苯基硫代磷酰胺.其酸性水解在6mol/L或9mol/L盐酸/二氧六环中进行,得P-N键断裂的构型翻转产物;碱性水解在1mol/L或3mol/LNaOH/二氧六环中进行,得到以OPh为离去基团的构型翻转产物.水解反应机理用三角双锥(TBP)中间体概念得到合理解释.     

从(4R)-羟基-(S)-脯氨酸合成4-取代脯氨酸

叙述了以(4R) 羟基 (S) 脯氨酸为原料进行的几种新型手性催化剂的简便合成方法. (4S) 苯氧基 (S) 脯氨酸 1a由N 乙氧羰基 (4R) 羟基 (S) 脯氨酸甲酯经Mitsunobu反应, C 4构型发生翻转, 水解后得到; (4R) 芳甲氧基 (S) 脯氨酸由N 叔丁氧羰基 (4R) 羟基 (S) 脯氨酸用ArCH2X醚化后脱去N 保护基得到, C 4构型不受影响.     

erythro-1-Naphthyl-1-(2-piperidyl)methanol: synthesis,resolution, NMR relative configuration,and VCD absolute configuration

The erythro isomer of 1-naphthyl-1-(2-piperidyl)methanol 4, an efficient chiral modifier for asymmetric heterogeneous hydrogenation, was obtained as the major isomer (95%) in two steps while the threo isomer can be obtained as the major isomer (67%) in three steps. erythro-4 and threo-4 were resolved on a CHIRALCEL OD-RH column. It has been shown by VCD that the diastereomer determined as the erythro by NMR was indeed the erythro and that the first eluted (-)-enantiomer on CHIRALCEL OD-R or -RH columns has the (1R,2S) configuration. The VCD studies identify the presence of at least five conformers in CDCl(3) solution. Moreover, this (-)-(1R,2S) absolute configuration found by VCD is consistent with the expected stereo-outcome of catalytic hydrogenation of pyruvate into lactate, which supported the (+)-(1S,2R) assignment.     

Stereoselective determination of propafenone enantiomers in transgenic Chinese hamster CHL cells expressing human cytochrome P450

An enantioselective assay for S(+)- and R(-)-propafenone in transgenic Chinese hamster CHL cells expressing human cytochrome P450 was developed. The method involved extraction of propafenone from the S9s incubates, and formation of propafenone diastereomeric derivatives with the chiral reagent 2,3,4, 6-tetra-O-beta-D-glucopranosyl isothiocyanate. Separation and quantitation of diastereomeric propafenone derivatives were carried out in a reverse-phase-HPLC system with UV detection. The assay was linear from 2 to 200 microg/mL for each enantiomer. The analytical method gave average recoveries of 97.5% and 97.0% for S(+)- and R(-)-propafenone, respectively. The limits of detection and quantitation for the method are 0.1 and 2.0 microg/mL for both S(+)- and R(-)-propafenone, respectively. The reproducibility of the assay was good (RSD <10%). The method allowed study of the depletion of S(+)- and R(-)-propafenone in transgenic Chinese hamster CHL cells expressing human cytochrome P450. The stereoselectivity of propafenone phase I metabolism via cDNA-expressed CYP3A4 was observed.     

Chromatographic resolution, solution and crystal phase conformations, and absolute configuration of tert-butyl(dimethylamino)phenylphosphine-borane complex

The enantiomers of tert-butyl(dimethylamino)phenylphosphine-borane complex 2 have been separated by HPLC using cellulose tris-p-methylbenzoate as chiral stationary phase. The borane protection could be removed without racemization and the P-configuration of the free aminophosphine 1 has shown to be stable in solution. Infrared (IR) and vibrational circular dichroism (VCD) spectra have been measured in CD2Cl2 solution for both enantiomers. B3LYP/6-31+G(d) DFT calculations allowed a prediction that complex (S)-2 exists as three conformers in equilibrium and computed population-weighted IR and VCD spectra. Predicted and experimental IR and VCD spectra compared very well and indicate that enantiomer (+)-2 has the S absolute configuration. This assignment has been confirmed by an X-ray diffraction study on a single crystal of (+)-2. The crystal structure of enantiomerically pure 2 appears to be very close to the most stable computed conformer which proved to be predominant in solution.     

Chiral separation of trimetoquinol hydrochloride and related compounds by micellar electrokinetic chromatography using sodium taurodeoxycholate solutions and application to optical purity determination

The chiral separation of trimetoquinol hydrochloride, which is a bronchodilator (Inolin), and three related compounds by micellar electrokinetic chromatography was investigated using a bile salt as a chiral surfactant. Enantiomers of these compounds, except laudanosoline, were successfully separated within 12 min using a separation tube of effective length 500 mm × 0.05 rum i.d. and a 0.05 M sodium taurodeoxycholate solution of pH 7.0. The observed theoretical plate numbers of the peaks were ca. 150000. Chiral recognition was affected by the structure of bile salts, the pH of the buffer solutions used and the structure of the solutes. Of four kinds of bile salts, successful chiral separation was achieved only using sodium taurodeoxycholate solution under neutral conditions. The method was applied to the optical purity determination of trimetoquinol hydrochloride. The effects of surfactant concentrations and some additives to the micellar solution are briefly described.     

A chiral LC‐MS/MS method for the enantioselective determination of R‐(+)‐ and S‐(–)‐pantoprazole in human plasma and its application to a pharmacokinetic study of S‐(–)‐pantoprazole sodium injection

Pantoprazole, a proton pump inhibitor, is clinically used for the treatment of peptic diseases. An enantioselective LC‐MS/MS method was developed and validated for the simultaneous determination of pantoprazole enantiomers in human plasma. Pantoprazole enantiomers and the internal standard were extracted from plasma using acetonitrile. Chiral separation was carried on a Chiralpak IE column using the mobile phase consisted of 10 mm ammonium acetate solution containing 0.1% acetic acid–acetonitrile (28 : 72, v /v). MS analysis was performed on an API 4000 mass spectrometer. Multiple reactions monitoring transitions of m /z 384.1→200.1 and 390.1→206.0 were used to quantify pantoprazole enantiomers and internal standard, respectively. For each enantiomer, no apparent matrix effect was found, the calibration curve was linear over 5.00–10,000 ng/mL, the intra‐ and inter‐day precisions were below 10.0%, and the accuracy was within the range of –5.6% to 0.6%. This method was applied to the stereoselective pharmacokinetic studies in human after intravenous administration of S ‐(–)‐pantoprazole sodium injections. No chiral inversion was observed during sample storage, preparation procedure and analysis. While R ‐(+)‐pantoprazole was detected in human plasma with a slightly high concentration, which implied that S ‐(–)‐pantoprazole may convert to R ‐(+)‐pantoprazole in some subjects.     

高效液相色谱法测定布诺酚的光学纯度

用正相高效液相色谱法配合衍生化法准确地测定了抗炎镇痛药布诺酚的光学纯度。方法的平均标准偏差为０．０６４％,准确度为９９．７１％～１００．２９％。     

Asymmetric intramolecular [2 + 2] photocycloadditions: alpha- and beta-hydroxy acids as chiral tether groups

Chiral alpha- and beta-hydroxy acids such as (S)-lactic acid, (S)-phenyllactic acid, (S)-mandelic acid, or (3R)-3-hydroxybutyric acid have been used as tether groups for intramolecular and diastereoselective [2 + 2] photocycloaddition of 3-oxocyclohexene carboxylic acid derivatives. Total regiocontrol toward the straight adduct and high diastereoselectivities (up to 94%) were observed in the case of butenyl lactate 11. After separation of the two diastereoisomers, cleavage of the chiral tether under basic conditions afforded cyclobutane lactones in good yield and enantiomeric pure form. An X-ray structure has been recorded that confirmed the relative and absolute configuration of the three contiguous stereogenic centers assigned according to CD spectra.