Electrospray ionization detection of inherently nonresponsive epoxides by peptide binding

A small organic molecule that is inherently nonresponsive to electrospray analysis, 1,3-butadiene diepoxide, was analyzed via electrospray ionization (ESI) by binding it to various peptides and observing the product at the characteristic mass shift. The epoxide reacted only with peptides with arginines in their sequence, most likely through a base-catalyzed ring opening to form a covalently bound product. A calibration curve linear over 3 orders of magnitude was generated for the butadiene diepoxide/peptide adduct. Several other epoxides were also reacted with the peptide of choice (angiotensin II), and adducts of these epoxides with the peptide were observed as well, demonstrating the versatility of this method for the analysis of small epoxides. This study demonstrates the possibility of assaying epoxides bound to peptides or proteins in biological samples. Furthermore, it demonstrates an important concept that could be applied to other analytical problems in electrospray: the ability to react an analyte that is nonresponsive to electrospray analysis with an analyte well suited for the technique, and accomplish quantitation based on the adduct formed between the two.     

Regio- and stereoselective synthesis of aziridino epoxides from cyclic dienes

Two different routes for the regio- and stereoselective synthesis of aziridino epoxides from cyclic dienes have been explored. The first strategy involves regiospecific aziridination of cyclic diene derivatives and subsequent epoxidation with m-CPBA to yield cis-aziridino epoxides as major products. The second strategy utilizes regiospecific epoxidation of cyclic diene derivatives followed by Sharpless aziridination to provide exclusively trans-aziridino epoxides. Synthesis of both enantiomers of cis-aziridino epoxides from (R)-(-)- and (S)-(+)-carvones are also reported.     

Quantification of Tacrolimus in Human Skin Samples and Ointment by LC-MS

A sensitive and simple liquid chromatography-mass spectrometry method was developed to determine the immunosuppressant tacrolimus in human skin samples after treatment with the commercially available ointment. Utilizing diffusion cell experiments according to Franz, human skin samples were treated with ointment containing tacrolimus and the extraction procedure of the drug was optimized. The analytical assay was performed using an LC system consisting of a reversed phase C₁₈ column and an isocratic mobile phase, coupled with electrospray ionization mass spectrometry. The detection was performed in the positive selected ion monitoring mode. Mycophenolate mofetil was used as internal standard to control the stability of the electrospray ionization. The calibration curve was linear for tacrolimus over the range of 5–1,000 ng mL^?1 (average correlation coefficient of r ² = 0.9941) with a limit of detection (LOD) of 2 ng mL^?1, with a limit of quantification (LOQ) of 5 ng mL^?1 and with a precision of 8.70%. The analytical assay described in this paper was successfully applied in order to quantify tacrolimus in human skin samples as well as in the commercially available ointment.     

Electroepoxidation of natural and synthetic alkenes mediated by sodium bromide

Electroepoxidation of synthetic alkenes (styrene, trans-stilbene and trans-β-methylstyrene) and of some natural terpenes (limonene, terpinolene, geraniol, α-terpinene, γ-terpinene and α-terpineol) mediated by sodium bromide was performed in MeCN:H₂O (4:1) at platinum electrodes. The indirect electrochemical oxidation of the olefins led to the corresponding epoxides in yields ranging from 23% to 79%.     

Isolation from pig liver microsomes, identification by tandem mass spectrometry and in vitro immunosuppressive activity of an SDZ-RAD 17,18,19,20,21,22-tris-epoxide

Macrolide immunosuppressive drugs such as tacrolimus (FK506) and sirolimus (rapamycin) are compounds largely used in modern immunosuppressive therapy and considered as powerful immunosuppressive agents. Some of these molecules are still under clinical development as, for example, SDZ-RAD (40-O-(2-hydroxyethyl)rapamycin), an immunosuppressive drug closely related to rapamycin. SDZ-RAD has a molecular mass of 957.57 Da (C53H83NO14) and shares the same common intracellular receptor as tacrolimus, the FK-506 binding protein (FKBP-12). SDZ-RAD exerts its pharmacological effect by binding to a different effector protein, inhibits the S6p 70-kinase and interrupts a different signal transduction pathway than tacrolimus. Both SDZ-RAD and rapamycin are metabolized mainly by the cytochrome P-450 3A4-dependent mixed function oxygenase enzyme system to hydroxylated and demethylated metabolites. We describe here the isolation from pig liver microsomes of a novel SDZ-RAD metabolite identified by electrospray tandam mass spectrometry as a new SDZ-RAD 17,18,19,20,21,22-tris-epoxide metabolite. The in vitro immunosuppressive activity as measured by the mixed lymphocyte reaction is more or less comparable to that of SDZ-RAD, although its pharmacological mode of action may be different from that classically described for rapamycin.     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

HPLC separation of flavonols, flavones and oxidized flavonols with UV-, DAD-, electrochemical and ESI-ion trap MS detection

The cation-induced or electrochemical oxidation of flavonols has been reported to yield 2-(hydroxybenzoyl)-2-hydroxy-3(2H)-benzofuranone. Two new gradient reversed phase HPLC methods are presented which allow the determination of those oxidized flavonols simultaneously with flavonols and flavones. UV and electrochemical detection are used because of their high sensitivity. Qualitative detection together with quantification of all compounds is achieved with photodiode-array detection. An electrospray ionization ion trap mass spectrometric method is presented for unique identification of the benzofuranones after HPLC separation.     

HPLC separation of flavonols, flavones and oxidized flavonols with UV-, DAD-, electrochemical and ESI-ion trap MS detection

The cation-induced or electrochemical oxidation of flavonols has been reported to yield 2-(hydroxybenzoyl)-2-hydroxy-3(2H)-benzofuranones. Two new gradient reversed phase HPLC methods are presented which allow the determination of those oxidized flavonols simultaneously with flavonols and flavones. UV and electrochemical detection are used because of their high sensitivity. Qualitative detection together with quantification of all compounds is achieved with photodiode-array detection. An electrospray ionization ion trap mass spectrometric method is presented for unique identification of the benzofuranones after HPLC separation.     

Artifacts in amine analysis from anodic oxidation of organic solvents upon electrospray ionization for mass spectrometry

Different phenylenediamines were used to explore anodic oxidation in solution during electrospray ionization (ESI) mass spectrometry analysis. In our experiments, a series of unknown ionic species was detected in the phenylenediamine solutions. Our results propose that reactions of phenylenediamines with species formed by anodic oxidation of typical ESI solvents during the electrospray ionization process such as formaldehyde are producing these peaks. Identification of these compounds inter alia suggests formal alkylation, a reaction not reported so far as a result of electrolytic oxidation in the prospective organic solvents.     

Mild and Efficient Ring Opening of Epoxides Catalyzed by Potassium Dodecatungstocobaltate(III)

Summary. Efficient ring opening of epoxides under mild conditions is reported. Potassium dodecatungstocobaltate(III) trihydrate was used as an efficient catalyst for the alcoholysis and acetolysis of epoxides. Conversion of epoxides to thiiranes was also performed efficiently in the presence of this catalyst.     

含1,2二取代的苯并咪唑配体的Zn(Ⅱ)络合物上化学固定CO2转化为环状碳酸酯

合成了一种新的Zn(Ⅱ)配合物ZnCl2(L1)2] (1) (L1为 2-(2-噻吩)-1-(2-噻吩甲基)-1H-苯并咪唑),并采用NMR和IR光谱、元素分析、ESI-HRMS光谱测定和热重分析等对它进行了表征,其分子结构也由单晶X射线衍射确定.络合物1含有单核四面体Zn(Ⅱ)单元,即所谓的锁定的几何结构,这源自分子中存在弱的分子间S···π和π-π配体间相互作用.通过简易的合成路线即可制得苯并咪唑配体及其与Zn(Ⅱ)配合物.采用CO2与环氧化物耦合生成环状碳酸酯反应考察了1的催化活性,以及反应条件的影响.该配合物在无溶剂条件下可高效催化多种环氧化物的转化,具有较好的转化率,TONs和TOFs.     

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

Electrochemical/electrospray mass spectrometric studies of I- and SCN- at gold and platinum electrodes: direct detection of (SCN)3-

Results on the electrochemistry of I- and SCN- at gold and platinum electrodes using an electrochemical cell coupled to an electrospray mass spectrometer are reported. We demonstrate that our apparatus is capable of these very challenging electrochemical/electrospray experiments and that B(C6H5)4- is a suitable internal standard for negative-ion studies in acetonitrile. With I- at a platinum electrode, we observe well-behaved oxidation to I3-. Experiments on I- at gold electrodes are more complex, showing AuI2- as well as I3-. The AuI2- mass spectrometric ion intensity varies in a complex way throughout the applied electrochemical voltage range studied; we propose that this variation involves the adsorption of I- on the gold electrode surface. In experiments on SCN- from (C4H9)4NSCN at gold electrodes, we observe Au(SCN)2-. Finally, at platinum electrodes, we directly observe (SCN)3-, a species analogous to I3- and (CN)3- that has been previously postulated but unverified. This important finding was confirmed by the isotope pattern and demonstrates the stability of the anion.     

Templates for exploratory library preparation. Derivatization of a functionalized spirocyclic 3,6-dihydro-2H-pyran formed by ring-closing metathesis reaction

The preparation of a novel spirocyclic template from tert-butoxycarbonyl-4-piperidone is reported. The synthesis of N-(tert-butoxycarbonyl)-1-oxa-9-aza-spiro[5.5]undec-3-ene (4) for exploratory library generation involves ketone allylation, etherification, and ring-closing metathesis (RCM) reactions. Epoxidation of the alkene formed in the RCM followed by addition of volatile amines to the epoxides led rapidly to an exploratory library of structurally novel spirocyclic amino alcohols. The addition of amines to epoxides derived from 4 was determined to occur primarily at C3.     

Gas-phase Meerwein reaction of epoxides with protonated acetonitrile generated by atmospheric pressure ionizations

Ethylnitrilium ion can be generated by protonation of acetonitrile (when used as the LC-MS mobile phase) under the conditions of atmospheric pressure ionizations, including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) as well as atmospheric pressure photoionization (APPI). Ethylnitrilium ion ( CH₃ - C o \mathop N⁺ HCH_3 - C \equiv \mathop N\limits^ + H and its canonical form CH₃ - \mathop C⁺ = NHCH_3 - \mathop C\limits^ + = NH) is shown to efficiently undergo the gas-phase Meerwein reaction with epoxides. This reaction proceeds by the initial formation of an oxonium ion followed by three-to-five-membered ring expansion via an intramolecular nucleophilic attack to yield the Meerwein reaction products. The density functional theory (DFT) calculations at the B3LYP/6-311 + G(d,p) level show that the gas-phase Meerwein reaction is thermodynamically favorable. Collision-induced dissociation (CID) of the Meerwein reaction products yields the net oxygen-by-nitrogen replacement of epoxides with a characteristic mass shift of 1 Da, providing evidence for the cyclic nature of the gas-phase Meerwein reaction products. The gas-phase Meerwein reaction offers a novel and fast LC-MS approach for the direct analysis of epoxides that might be of genotoxic concern during drug development. Understanding and utilizing this unique gas-phase ion/molecule reaction, the sensitivity and selectivity for quantitation of epoxides can be enhanced.     

Regioselectivity in the ring opening of epoxides for the synthesis of aminocyclitols from D-(-)-quinic acid

Efficient syntheses of four aminocyclitols are reported. Each synthesis is accomplished in eight steps starting from D-(-)-quinic acid. The key step involves a highly regioselective ring opening of epoxides by sodium azide.     

Conversion of epoxides to 1,3-dioxolanes catalyzed by tin(II) chloride

Anhydrous tin(II) chloride is an efficient catalyst for the reaction of epoxides with acetone to prepare 2,2-dimethyl-1,3-dioxolanes (acetonides) in good to excellent yields. Mono-, di-, and trisubstituted epoxides participate equally well in this diastereospecific reaction. The use of single enantiomer epoxides under the reported conditions results in significant erosion of optical activity.     

Analysis of oxidized epigallocatechin gallate by liquid chromatography/mass spectrometry

(-)-Epigallocatechin gallate (EGCG) of catechins changes from non-colored at around neutral pH to yellow at higher pH region in aqueous solution. The pH-dependent oxidation of EGCG was analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). LC/MS/MS analysis of EGCG and its related compounds, (-)-epicatechin gallate (ECG) and (-)-epigallocatechin (EGC), successfully elucidated the structure relationship of EGCG solution involving the color change reaction at different pH conditions. The oxidation species produced at alkaline pH was detected at a different retention time from EGCG in the chromatograms of the EGCG sample. The oxidation species was found to correspond to M+14 (where M is the molecular weight of EGCG), which has two hydrogen atoms removed and addition of one oxygen atom to the gallyl moiety in the B-ring of EGCG.     

Studies on quinones. Part 40: Synthesis and cytotoxicity evaluation of anthraquinone epoxides and isomerization products

Aerobic oxidation of 1,4,4a,10a-tetrahydro-1,4-alkano-5,10-anthraquinones and thiophene-analogues in dichloromethane-DBU yielded the corresponding dihydroalkanoquinones which, depending on their structures, react with in situ generated hydroperoxide anion to give quinone epoxides and/or hydroperoxides. The calcium hydroxide-induced rearrangement of quinone epoxides yielded furan-containing angular quinones. The cytotoxic activities of quinone epoxides and their isomerization products were evaluated in vitro against normal human lung fibroblasts (MRC-5) and human cancer gastric epithelial cells (AGS).     

Heterogeneous reactions of epoxides in acidic media

Epoxides have recently been identified as important intermediates in the gas phase oxidation of hydrocarbons, and their hydrolysis products have been observed in ambient aerosols. To evaluate the role of epoxides in the formation of secondary organic aerosols (SOA), the kinetics and mechanism of heterogeneous reactions of two model epoxides, isoprene oxide and α-pinene oxide, with sulfuric acid, ammonium bisulfate, and ammonium sulfate have been investigated using complementary experimental techniques. Kinetic experiments using a fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) show a fast irreversible loss of the epoxides with the uptake coefficients (γ) of (1.7 ± 0.1) × 10(-2) and (4.6 ± 0.3) × 10(-2) for isoprene oxide and α-pinene oxide, respectively, for 90 wt % H(2)SO(4) and at room temperature. Experiments using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) reveal that diols are the major products in ammonium bisulfate and dilute H(2)SO(4) (<25 wt %) solutions for both epoxides. In concentrated H(2)SO(4) (>65 wt %), acetals are formed from isoprene oxide, whereas organosulfates are produced from α-pinene oxide. The reaction of the epoxides with ammonium sulfate is slow and no products are observed. The epoxide reactions using bulk samples and Nuclear Magnetic Resonance (NMR) spectroscopy reveal the presence of diols as the major products for isoprene oxide, accompanied by aldehyde formation. For α-pinene oxide, organosulfate formation is observed with a yield increasing with the acidity. Large yields of organosulfates in all NMR experiments with α-pinene oxide are attributed to the kinetic isotope effect (KIE) from the use of deuterated sulfuric acid and water. Our results suggest that acid-catalyzed hydrolysis of epoxides results in the formation of a wide range of products, and some of the products have low volatility and contribute to SOA growth under ambient conditions prevailing in the urban atmosphere.