Synthesis and characterization of chiral enantiopure bis-chromanones: a Baylis-Hillman approach

Enantiopure bis-chromanones were prepared from (S)-Binol and bromo esters via a Baylis-Hillman approach. Chiroptical studies indicate that the two-naphthyl units of the chromanone system are non-coplanar.     

Structural characterization of a completely alkyl-substituted Al-Sb Lewis acid-base adduct

The Lewis acid-base adduct t-Bu₃Al-SbMe₃ (1), which was synthesized by reaction of equimolar amounts of t-Bu₃Al and trimethylstibine SbMe₃, was characterized by multinuclear NMR (¹H, ¹³C) spectroscopy, elemental analyses as well as by single crystal X-ray diffraction.     

Uragogin and blepharodin, unprecedented hetero-Diels-Alder adducts from Celastraceae species

Uragogin and blepharodin were isolated from Crossopetalum uragoga and Maytenus magellanica, respectively. They represent the first examples of a triterpene-neolignan ester and a heptacyclic arylpropanoid-nor-triterpenephenol, hetero-Diels-Alder adducts built with dioxane bridges. Their proposed biosynthetic route is discussed.     

Synthesis of Naphtho[2,1-b]pyrano Pyrrolothiazole Derivatives through 1,3-Cycloaddition Reaction

Facile synthesis of a series of naphtho[2,1,b]pyrano pyrrolo thiazoles was accomplished in good yields in a one-pot reaction through intramolecular 1,3-dipolar cycloaddition of cyclic azomethine ylides with Baylis–Hillman adducts as dipolarophiles. The protocol is applicable to a wide variety of photochromic and biologically active napthopyrano products. The regio- and stereochemical outcome of the cycloaddition reaction was ascertained by x-ray crystallographic study of one of the cycloadducts.     

Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH₄Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]^? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄]⁺, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^? into a Cl^? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄]⁺ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.     

Observation of the multiple halogenation of peptides in the electrospray ionization source

The chlorination of peptides and proteins is an important posttranslational modification, which is a physiological signature of an enzyme myeloperoxidase and can serve as a potential biomarker of some diseases (Parkinson's disease, Alzheimer's disease, etc.). The quantification of the chlorinated peptides has been very challenging in part due to their low levels and artifacts associated with sample preparation. One of the most convenient and promising methods to detect and investigate the chlorinated peptides in the biological samples is the electrospray ionization (ESI) mass spectrometry coupled to the fragmentation techniques (collision‐induced dissociation and electron capture dissociation/electron transfer dissociation). We have shown that if the chlorine anions are present in the solution, then the peptide can undergo the chlorination during the ESI ionization. The effect was found to depend on the values of electric potentials of metal parts of the ESI interface. It was found that the grounding of ESI syringe results in the formation of an additional electric loop leading to the electrolytic production of Cl₂ and as a consequence the hypochlorous acid inside the ESI needle. Hypochlorous acid reacts with amino groups of peptides and proteins producing chloramine or causing the protein cleavage. In the paper, it is shown on the example of the solution of the several peptides in the presence of HCl that by manipulating the ESI syringe potential, it is possible to create complexes with up to five Cl atoms for sample peptides when the ESI is operated in the positive mode. Copyright © 2015 John Wiley & Sons, Ltd.     

High resolution mass spectrometry based profiling of diet-related deoxyribonucleic acid adducts

Exposure of DNA to endo- and exogenous DNA binding chemicals can result in the formation of DNA adducts and is believed to be the first step in chemically induced carcinogenesis. DNA adductomics is a relatively new field of research which studies the formation of known and unknown DNA adducts in DNA due to exposure to genotoxic chemicals. In this study, a new UHPLC-HRMS(/MS)-based DNA adduct detection method was developed and validated. Four targeted DNA adducts, which all have been linked to dietary genotoxicity, were included in the described method; O⁶-methylguanine (O⁶-MeG), O⁶-carboxymethylguanine (O⁶-CMG), pyrimidopurinone (M1G) and methylhydroxypropanoguanine (CroG). As a supplementary tool for DNA adductomics, a DNA adduct database, which currently contains 123 different diet-related DNA adducts, was constructed. By means of the newly developed method and database, all 4 targeted DNA adducts and 32 untargeted DNA adducts could be detected in different DNA samples. The obtained results clearly demonstrate the merit of the described method for both targeted and untargeted DNA adduct detection in vitro and in vivo, whilst the diet-related DNA adduct database can distinctly facilitate data interpretation.     

铜催化α-重氮酮对硼氢键的不对称插入反应

手性有机硼化合物在有机合成、医药、材料等诸多领域中有广泛的应用,发展该类化合物的高效合成方法一直广受关注.此前,我们发展了过渡金属催化卡宾对硼氢键(B—H)的插入反应,并实现了α-重氮酯对B—H键的不对称插入反应.本文以手性螺环双噁唑啉配体和铜的络合物作为催化剂,首次实现了α-重氮酮对膦-硼烷加合物的B—H键不对称插入反应,获得了较高的收率和高达83%ee的对映选择性.该研究成果是为数不多的以α-重氮酮作为卡宾前体的不对称杂原子氢键插入反应,为手性α-硼取代酮化合物这类新的有机硼化合物的合成提供了有效方法.     

APCI as an innovative ionization mode compared with EI and CI for the analysis of a large range of organophosphate esters using GC‐MS/MS

Organophosphate esters (OPEs) are chemical compounds incorporated into materials as flame‐proof and/or plasticizing agents. In this work, 13 non‐halogenated and 5 halogenated OPEs were studied. Their mass spectra were interpreted and compared in terms of fragmentation patterns and dominant ions via various ionization techniques [electron ionization (EI) and chemical ionization (CI) under vacuum and corona discharge atmospheric pressure chemical ionization (APCI)] on gas chromatography coupled to mass spectrometry (GC‐MS). The novelty of this paper relies on the investigation of APCI technique for the analysis of OPEs via favored protonation mechanism, where the mass spectra were mostly dominated by the quasi‐molecular ion [M + H]⁺. The EI mass spectra were dominated by ions such as [H₄PO₄]⁺, [M–R]⁺, [M–Cl]⁺, and [M–Br]⁺, and for some non‐halogenated aryl OPEs, [M]^+● was also observed. The CI mass spectra in positive mode were dominated by [M + H]⁺ and sometimes by [M–R]⁺, while in negative mode, [M–R]⁻ and more particularly [X]^‐ and [X₂]^‐● were mainly observed for the halogenated OPEs. Both EI and APCI techniques showed promising results for further development of instrumental method operating in selective reaction monitoring mode. Instrumental detection limits by using APCI mode were 2.5 to 25 times lower than using EI mode for the non‐brominated OPEs, while they were determined at 50‐100 times lower by the APCI mode than by the EI mode, for the two brominated OPEs. The method was applied to fish samples, and monitored transitions by using APCI mode showed higher specificity but lower stability compared with EI mode. The sensitivity in terms of signal‐to‐noise ratio varying from one compound to another. Copyright © 2016 John Wiley & Sons, Ltd.     

Improvements in monitoring the N-terminal valine adduct in human globin after exposure to sulfur mustard and synthesis of reference chemicals

The N-terminal valine adduct (HETE-Val) in globin is believed to behave as a long-lived biomarker after exposure to sulfur mustard (HD). Development of a highly sensitive method for monitoring HETE-Val, particularly at low HD exposure levels or for retrospective detection, would be a significant achievement. In this study, by improving the sample preparation method, a sensitive NCI-GC/MS method was established for the analysis of HETE-Val in globin after HD exposure. To optimize and investigate the sample preparation method, all the relevant HETE-Val chemicals were synthesized, purified, and characterized. By carrying out optimized solid phase extraction (SPE) cleanup followed by modified Edman degradation results in a low detection level and clean baseline. The minimum detectable exposure level of human blood (in vitro) to HD is 20 nmol/L (S/N > 3). The interday and intraday precisions of the proposed method were found to be acceptable with less than a 15% relative standard deviation (RSD). A nearly linear dose-effect relationship was observed between HETE-Val and a HD exposure concentration range of 0.1-120 μmol/L. The percentage of HD that reacted with N-terminal valine in globin obtained from human blood (in vitro) was quantified using the proposed method.