In-capillary derivatization and analysis of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with laser-induced fluorescence detection

This paper describes an automatic rapid approach for in-capillary derivatization of ephedrine (E) and pseudoephedrine (PE) and subsequent sensitive determination of the derivatives by micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) detection using 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as fluorescent reagent. The unique feature of this method is the capillary being used as a small reaction chamber, in which the sample, derivatization buffer and reagent solutions were injected directly into the capillary by tandem mode, followed by an electrokinetic step (5 kV, 15s) to enhance the mixing efficiency of analytes and reagent plugs. Standing a specified time of 1 min for reaction, the derivatives were then immediately separated and determined. Several parameters for in-capillary derivatization and subsequent MEKC separation were systematically investigated. Under these optimized conditions, a baseline separation of the two analytes was achieved within 10 min and the derivatization concentration limits of detection were found to be 4.8 ng mL(-1) for E and 1.6 ng mL(-1) for PE, respectively. The method was validated in terms of precision, linearity, accuracy and successfully applied for the determination of the two alkaloids in ephedra herb and its preparations.     

Sensitive determination of ephedrine and pseudoephedrine by capillary electrophoresis with laser-induced fluorescence detection

A CE-LIF method was developed for the separation and sensitive detection of ephedrine and pseudoephedrine after derivatization by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol (NBD-C1). The derivatization and separation conditions were investigated in detail and the optimum conditions were obtained. Under the optimum experiment conditions, good linearity relationships (correlation coefficients: 0.9942 for ephedrine and 0.9970 for pseudoephedrine) between the peak heights and concentrations of the analytes were obtained (0.7-140 microM). The detection limits were 0.16 microM for ephedrine and 0.17 microM for pseudoephedrine, which indicated that the sensitivities were at least ten times improved over those reported in the literature obtained by UV detection. The method was applied to the analysis of ephedrine and pseudoephedrine in ephedra herb plants and preparations with good results.     

Comparative conformational analysis of peptide T analogs

A series of peptide T analogs were investigated within the molecular mechanics framework. In order to determine the role of the aminoacid residues in spatial formation of peptide T the conformational peculiarities of the glycine-substituted analogs were investigated. The conformational profiles of some biologically tested analogs of this peptide were determined independently. The received data permit to assess the active form of this peptide. It is characterized by β-turn at the C-terminal physiologically active pentapeptide fragment of peptide molecule. The received results are important for the investigation of the structure-activity relationship and may be used at design of a rigid-molecule drug against HIV.     

Microemulsion electrokinetic chromatography with laser-induced fluorescence detection for sensitive determination of ephedrine and pseudoephedrine

A selective and sensitive microemulsion electrokinetic chromatography with laser-induced fluorescence detection method was developed for the quantification of ephedrine (E) and pseudoephedrine (PE) derivatized with 4-chloro-7-nitrobenzo-2-oxa-1, 3-diazol. By a series of optimization, a running buffer composed of 20 mM borate + microemulsion (23.3 mM Sodium dodecyl sulfate/180.85 mM 1-butanol/16.4 mM n-heptane) +8% acetonitrile was applied for the separation of the derivatives. A linear relationship for E and PE was obtained in the range of 0.058-11.58 microg.mL(-1) (correlation coefficient: 0.9993 for E, 0.9995 for PE), and the detection limits for E and PE were 5.3 and 3.9 ng.mL(-1). The method was applied to the analysis of the two alkaloids in Chinese traditional herbal preparations with recoveries in the range of 96.9-105.4%.     

Synthesis and conformational analysis of glycomimetic analogs of thiochitobiose

The synthesis of six analogs of N,N′-diacetylchitobiose is reported, including a novel transglycosylation reaction for the preparation of S-aryl thioglycosides. The conformations of the compounds were studied by a combination of NMR spectroscopy and molecular modeling, using force field calculations. In the case of the S-aryl thioglycosides with exclusively S-glycosidic linkages, dihedral angles of the disaccharidic S-glycosidic bonds, Φ′ and Ψ′ and of the S-arylglycoside bonds, Φ and Ψ, were found to be similar, whereas they were different in mixed glycosides and in a thiazoline derivative. An adequate correlation between the calculated H,H-distances of the local minima and the measured NOE contacts was achieved by applying population-weighted averages over participating conformers based on weighted relative energies.     

Separation and determination of ephedrine and pseudoephedrine by combination of flow injection with capillary electrophoresis

A simple, rapid, and accurate method for the separation and determination of ephedrine and pseudoephedrine using direct UV absorbance detection has been developed by the combination of flow injection with capillary electrophoresis for the first time. The buffer solution used is a 40 mM borate solution with the pH adjusted to 9.5 using a 2 M NaOH solution. The linear calibration range is 50 to 1000 microg/mL (r = 0.9996) for both analytes, and the recoveries are 91.2-108.2% for ephedrine and 92.6-107.3% for pseudoephedrine, respectively. The relative standard deviation of the peak area is 1.6% for ephedrine and 1.3% for pseudoephedrine (n = 6) at a concentration of 500 microg/mL, respectively. A series of samples is injected repeatedly without current interruption and subsequent rinsing, and the contents of these two alkaloids in three marketed drugs and the medical plant, Ephedra sinica, are determined with satisfactory results by this method.     

Micellar electrokinetic chromatography with laser-induced fluorescence detection for sensitive determination of ephedrine and pseudoephedrine

A selective and sensitive micellar electrokinetic chromatography method with laser-induced fluorescence detection was developed for the quantification of ephedrine (E) and pseudoephedrine (PE) derivatized with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. After conducting a series of optimizations, a running buffer of 10 mM sodium borate + 16 mM SDS was used for separation of the derivatives. A linear relationship for E and PE was obtained in the range of 0.044-6.6 microg mL(-1) (correlation coefficient: 0.9943 for E, 0.9946 for PE), and the detection limits for E and PE were 0.70 and 0.30 ng mL(-1), respectively. The sensitivity of E and PE was improved by several multiples of ten over those of CZE-LIF method. The method was applied to the analysis of the two alkaloids in ephedra herbal medicine and preparations with recoveries in the range of 98.3-107.1%.     

Tricarbonylchromium(0) promoted stereoselective transformations of ephedrine and pseudoephedrine derivatives

(−)-(1S,2S)-(N,O-Dimethylephedrine)tricarbonyl chromium(0) (6) and (−)-(1S,2R)-(N,O-dimethylpseudoephedrine)tricarbonylchiromium(0) (22) undergo completely stereoselective ortho deprotonation upon treatment with alkyllithium base, followed by addition of an electrophile. In both cases, exclusive removal of the pro-(R)-ortho proton was confirmed by single crystal X-ray structure analyses of the methylated products. Addition of methyllithium onto the ortho-formylated derivative of complex (6) occurs stereoselectively, the stereochemistry of the major product being confirmed by a single crystal X-ray structure determination. The results presented demonstrate an efficient transfer of chirality from a side chain onto the (arene)tricarbonylchromium(0) complex and back to a different side chain.     

Rapid and sensitive determination of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with on-line regenerating covalent coating

A rapid, sensitive and reproducible micellar electrokinetic chromatographic method using hexamethyldisilazane as on-line regenerating covalent coating was developed for the quantification of ephedrine (E) and pseudoephedrine (PE). E and PE were derivatized with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol for laser-induced fluorescence detection. The on-line regenerating covalent coating formed a combinative double coating with the subsequently produced dynamic SDS coating. The total coating can be easily removed and conveniently regenerated on-line. The simple coating procedure was described. By a series of optimization, a running buffer of 20 mm Na(2)B(4)O(7) + 16 mm SDS was applied for the separation of the derivatives. Linear relationships for E and PE were obtained in the range of 0.044-6.60 microg mL(-1) (correlation coefficients: 0.9975 for E, 0.9981 for PE), and the detection limits for E and PE were 1.71 and 0.67 ng mL(-1), respectively. The separation speed, the reproducibility and the sensitivity were much improved over those of other capillary electrophoresis methods more recently reported. The method was applied to the analysis of the two alkaloids in traditional herbal preparations with recoveries in the range 92.8-104.8%.     

Simple HPLC method for detection of trace ephedrine and pseudoephedrine in high-purity methamphetamine

A simple and sensitive HPLC technique was developed for the qualitative determination of ephedrine and pseudoephedrine (ephedrines), used as precursors of clandestine d‐methamphetamine hydrochloride of high purity. Good separation of ephedrines from bulk d‐methamphetamine was achieved, without any extraction or derivatization procedure on a CAPCELLPACK C₁₈ MGII (250 × 4.6 mm) column. The mobile phase consisted of 50 mM KH₂PO₄–acetonitrile (94:6 v/v %) using an isocratic pump system within 20 min for detecting two analytes. One run took about 50 min as it was necessary to wash out overloaded methamphetamine for column conditioning. The analytes were detected by UV absorbance measurement at 210 nm. A sample (20 mg) was simply dissolved in 1 mL of water, and a 50 μL aliquot of the solution was injected into the HPLC. The detection limits for ephedrine and pseudoephedrine in bulk d‐methamphetamine were as low as 3 ppm each. This analytical separation technique made it possible to detect ephedrine and/or pseudoephedrine in seven samples of high‐purity d‐methamphetamine hydrochloride seized in Japan. The presence of trace ephedrines in illicit methamphetamine may strongly indicate a synthetic route via ephedrine in methamphetamine profiling. This method is simple and sensitive, requiring only commonly available equipment, and should be useful for high‐purity methamphetamine profiling. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of analogs of the ergot alkaloids

A number of 3,4,5,6‐tetrahydro‐1H‐azepino[5,4,3‐cd]indole derivatives have been synthesized starting with methyl indole‐4‐carboxylate functionalized at the 3 position.     

On the CH...Cu agostic interaction: chiral copper(II) compounds with ephedrine and pseudoephedrine derivatives

The ephedrine derivative, (H2ceph), yields [Cu(Hceph)2], showing a CH...Cu(II) agostic interaction; while in the analogous compound [Cu(Hcpse)2], with pseudoephedrine (H2cpse), that interaction is absent, despite the fact that these two diasteromers differ only in the orientation of the methyl and phenyl groups: erythro in H2ceph and threo in H2cpse. The X-ray crystal structure of [Cu(Hceph)2], indicates a Cu...HC length of 2.454 A and the theoretical study reveals the formation of a Cu...HC bond since the associated electronic density shows both a bond critical point and a bond ring critical point.     

Synthesis and acute toxicity of some phosphorylated derivatives of ephedrine alkaloids

The results are given of the synthesis and a comparative study of the toxicities of some phosphorylated derivatives of the alkaloids l-ephedrine and d-pseudoephedrine. It has been shown that the introduction of phosphorus- and sulfur-containing fragments considerably lowers the toxicity of the alkaloids. Institute of Organic Synthesis and Coal Chemistry, National Academy of Sciences of the Republic of Kazakhstan, Karaganda. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 406–408, May–June, 1994.     

Synthesis and acute toxicity of some phosphorylated derivatives of ephedrine alkaloids

The results are given of the synthesis and a comparative study of the toxicities of some phosphorylated derivatives of the alkaloids l-ephedrine and d-pseudoephedrine. It has been shown that the introduction of phosphorus- and sulfur-containing fragments considerably lowers the toxicity of the alkaloids.Institute of Organic Synthesis and Coal Chemistry, National Academy of Sciences of the Republic of Kazakhstan, Karaganda. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 406–408, May–June, 1994.     

Oligofuranosides containing conformationally restricted residues: synthesis and conformational analysis

The synthesis of a panel of arabinofuranosyl oligosaccharide analogues (5-13) in which one ring is locked into either the E(3) or OE conformation is described. The E(3)-locked scaffolds 15 and 16 required for the synthesis of 5-10 were prepared in one step from known 1,5-anhydroalditols. A number of routes were explored for the preparation of the OE-locked monosaccharide derivative 17 needed for the preparation of 11-13. The successful synthesis of 17 was achieved in 17 steps from D-arabinose. Subsequent analysis of 5-13 by 1H NMR spectroscopy demonstrated that the locked residue does not exert any detectable influence upon the conformers populated by adjacent conformationally unrestricted furanose rings.     

Synthesis and conformational analysis of 3-hydroxypipecolic acid analogs via CSI-mediated stereoselective amination

A short and efficient stereoselective synthetic approach toward substituted piperidines, involving (2S,3S)-3-hydroxypipecolic acid 1, (2R,3S)-3-hydroxypipecolic acid 3, and their acid-reduced analogs 2 and 4, has been developed. The requisite anti- and syn-1,2-amino alcohols 11 and 12 for the preparation of title four piperidine analogs 1-4 were synthesized via the regioselective and diastereoselective amination of anti- and syn-1,2-dibenzyl ethers 13 and 14 using chlorosulfonyl isocyanate (CSI). As a result, reaction of anti-1,2-dibenzyl ether 13 with CSI afforded exclusively the anti-1,2-amino alcohol 11 with the diastereoselectivity of 49:1 in toluene at −78 °C and syn-isomer 14 gave the syn-1,2-amino alcohol 12 as the major product with the diastereoselectivity of 12:1 in hexane at −78 °C. The result of these reactions could be explained by the neighboring group effect leading to retention of stereochemistry. In addition, conformational changes of trans-piperidine intermediate 9 in terms of the nature of N-protecting groups are described. The conformations of 9 and 24-28 were confirmed by ¹H NMR analysis and NOE correlation. Furthermore, the conformations of piperidines 18 and 23 with hydroxyl methyl substituent at C-2 were investigated by NMR spectroscopy.