Solvent Influence on Cellulose 1,4‐β‐Glycosidic Bond Cleavage: A Molecular Dynamics and Metadynamics Study

We explore the influence of two solvents, namely water and the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc), on the conformations of two cellulose models (cellobiose and a chain of 40 glucose units) and the solvent impact on glycosidic bond cleavage by acid hydrolysis by using molecular dynamics and metadynamics simulations. We investigate the rotation around the glycosidic bond and ring puckering, as well as the anomeric effect and hydrogen bonds, in order to gauge the effect on the hydrolysis mechanism. We find that EmimAc eases hydrolysis through stronger solvent–cellulose interactions, which break structural and electronic barriers to hydrolysis. Our results indicate that hydrolysis in cellulose chains should start from the ends and not in the centre of the chain, which is less accessible to solvent.     

Electrospray ionization mass spectrometry studies of cyclodextrin‐carboxylate ion inclusion complexes

Aqueous solutions containing simple model aliphatic and alicyclic carboxylic acids (surrogates 1–4) were studied using negative ion electrospray mass spectrometry (ESI‐MS) in the presence and absence of α‐, β‐, and γ‐cyclodextrin. Molecular ions were detected corresponding to the parent carboxylic acids and complexed forms of the carboxylic acids; the latter corresponding to non‐covalent inclusion complexes formed between carboxylic acid and cyclodextrin compounds (e.g., β‐CD, α‐CD, and γ‐CD). The formation of 1:1 non‐covalent inclusion cyclodextrin‐carboxylic complexes and non‐inclusion forms of the cellobiose‐carboxylic acid compounds was also observed. Aqueous solutions of Syncrude‐derived mixtures of aliphatic and alicyclic carboxylic acids (i.e. naphthenic acids; NAs) were similarly studied using ESI‐MS, as outlined above. Molecular ions corresponding to the formation of CD‐NAs inclusion complexes were observed whereas 1:1 non‐inclusion forms of the cellobiose‐NAs complexes were not detected. The ESI‐MS results provide evidence for some measure of inclusion selectivity according to the 'size‐fit' of the host and guest molecules (according to carbon number) and the hydrogen deficiency (z‐series) of the naphthenic acid compounds. The relative abundances of the molecular ions of the CD‐carboxylate anion adducts provide strong support for differing complex stability in aqueous solution. In general, the 1:1 complex stability according to hydrogen deficiency (z‐series) of naphthenic acids may be attributed to the nature of the cavity size of the cyclodextrin host compounds and the relative lipophilicity of the guest. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of phase I and II metabolites of the new designer drug α‐pyrrolidinohexiophenone (α‐PHP) in human urine by liquid chromatography quadrupole time‐of‐flight mass spectrometry (LC‐QTOF‐MS)

Pyrrolidinophenones represent one emerging class of newly encountered drugs of abuse, also known as ‘new psychoactive substances’, with stimulating psychoactive effects. In this work, we report on the detection of the new designer drug α‐pyrrolidinohexiophenone (α‐PHP) and its phase I and II metabolites in a human urine sample of a drug abuser. Determination and structural elucidation of these metabolites have been achieved by liquid chromatography electrospray ionisation quadrupole time‐of‐flight mass spectrometry (LC‐ESI‐QTOF‐MS). By tentative identification, the exact and approximate structures of 19 phase I metabolites and nine phase II glucuronides were elucidated. Major metabolic pathways revealed the reduction of the ß‐keto moieties to their corresponding alcohols, didesalkylation of the pyrrolidine ring, hydroxylation and oxidation of the aliphatic side chain leading to n‐hydroxy, aldehyde and carboxylate metabolites, and oxidation of the pyrrolidine ring to its lactam followed by ring cleavage and additional hydroxylation, reduction and oxidation steps and combinations thereof. The most abundant phase II metabolites were glucuronidated ß‐keto‐reduced alcohols. Besides the great number of metabolites detected in this sample, α‐PHP is still one of the most abundant ions together with its ß‐keto‐reduced alcoholic dihydro metabolite. Monitoring of these metabolites in clinical and forensic toxicology may unambiguously prove the abuse of the new designer drug α‐PHP. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of new flavan‐3‐ol monoglycosides by UHPLC‐ESI‐Q‐TOF in grapes and wine

Flavan‐3‐ol monoglycosides, having four aglycons (+)‐catechin, (?)‐epicatechin, (?)‐epigallocatechin and epicatechin gallate monomeric units, are detected for the first time in Vitis vinifera L. cv. Merlot grape seeds and wine. These compounds were analyzed in red wine, seed and skin extracts by electrospray ionization quadrupole time of flight mass spectrometry (MS) in negative mode. Fragment ions derived from retro‐Diels Alder, heterocyclic ring fragmentation, benzofuran forming fragmentation and glycoside fragmentations were detected in targeted MS/MS mode. These compounds were not detected in skins; the comparative study showed evidence that these glycosylated compounds originate only from grape seeds. Our method allows for the identification of these glycosylated compounds based on their exact mass and their specific fragmentation pattern. However, exact glucose position on the monomeric units can not be determined. This work allowed us to partially identify 14 new flavan‐3‐ol monoglycosides, based on the exact mass of the molecular ions and their specific retro‐Diels Alder, heterocyclic ring fragmentation, benzofuran forming fragmentation and glycoside fragmentations. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of 15‐Cyano‐12‐oxopentadecano‐15‐lactone and 15‐Cyano‐ 12‐oxopentadecano‐15‐lactam

15‐Cyano‐12‐oxopentadecano‐15‐lactone was synthesized in 59% total yield starting from 2‐nitrocyclododecanone by Michael addition to acrylaldehyde, followed by reaction with trimethylsilylcyanide, hydrolysis, ring‐expansion, and Nef reaction. A two‐step, one‐pot synthesis of intermediate 2‐hydroxy‐4‐(1‐nitro‐2‐oxycyclododecyl)butanenitrile from 3‐(1‐nitro‐2‐oxocyclododecyl)propanal was developed and the conditions for the Nef reaction were studied. 15‐Cyano‐12‐oxopentadecano‐15‐lactam was synthesized in 40% total yield starting from 2‐nitrocyclododecanone by Michael addition to acrylaldehyde, followed by Strecker reaction, ring‐expansion, and Nef reaction. The conditions for the Strecker and Nef reactions were studied. The structures of the target compounds, intermediates, and by‐product were characterized by IR, ¹H‐ and ¹³C‐NMR, and elemental analysis or MS.     

Study of fragmentation pathways of lithiated α,β‐unsaturated thioesters by electrospray ionization mass spectrometry

The fragmentation pathways of lithiated α,β‐unsaturated thioesters with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in positive ion mode. In mass spectrometry of the α,β‐unsaturated thioesters, Ar‐CH?CH‐CO‐S‐Ph, loss of PhSLi and elimination of a thiophenol were the two major fragmentation reactions of the lithiated molecules. The elemental compositions of all the ions were confirmed by high‐resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR‐MS/MS). The thioesters studied here were para‐monosubstituted on the phenyl ring of cinnamoyl and the electron‐withdrawing groups favored loss of a thiophenol, whereas the electron‐releasing groups strongly favored the competing reaction leading to the loss of PhSLi to form a cinnamoyl cation, Ar‐CH?CHCO⁺. The intensity ratios of the two competitive product ions were well correlated with the σ substituent constants. The mechanisms of these two competing routes were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrospray ionization mass spectrometric analysis of newly synthesized α,β‐unsaturated γ‐lactones fused to sugars

Knowledge of the fragmentation mechanisms of lactones and their behaviour under electrospray ionization (ESI) conditions can be extended to larger and more complex natural products that contain an α,β‐unsaturated γ‐lactone moiety in their structure. Moreover, little is known about the gas‐phase behaviour of α,β‐unsaturated γ‐lactones linked or fused to sugars. Therefore, five α,β‐unsaturated γ‐lactones (butenolides) fused to a pyranose ring, recently synthesized compounds with potential relevance regarding their biological properties, were investigated using ESI‐MS and ESI‐MS/MS in both positive and negative ion modes. Their fragmentation mechanisms and product ion structures were compared. It was observed that two isomers could be unambiguously distinguished in the negative ion mode by the fragmentation pathways of their deprotonated molecules as well as in the positive ion mode by the fragmentation pathways of either the protonated or the sodiated molecule. Fragmentation mechanisms are proposed taking into account the MS/MS data and semi‐empirical calculations using the PM6 Hamiltonean. The semi‐empirical calculations were also very useful in determining the most probable protonation and cationization sites. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of the α‐phenylvinyl cation as a chemical ionization reagent for the differentiation of isomeric substituted phenols in an ITMS

Ion–molecule reactions between the α‐phenylvinyl cation and isomeric naturally occurring phenols were investigated using a quadruple ion trap mass spectrometer. The α‐phenylvinyl cation m/z 103, generated by chemical ionization from phenylacetylene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103]⁺ adduct ions and the trans‐vinylating product ions [M + 25]⁺, which correspond to [M + 103]⁺ adduct after the loss of benzene. Isomeric differentiation of several ring‐substituted phenols was achieved by using collision‐induced dissociation of the [M + 103]⁺ adduct ions. This method also showed to be effective in the differentiation of 4‐ethylguaiacol from one of its structural isomers that displays identical EI and EI/MS/MS spectra. The effects of gas‐phase alkylation with phenylvinyl cation on the dissociation behavior were examined using mass spectrometryⁿ and labeled derivatives. Copyright © 2015 John Wiley & Sons, Ltd.     

Electron ionization and electrospray ionization mass spectrometric study of a series of isomeric N‐chloro(or bromo)benzyl‐substituted (E)‐2′(3′‐ or 4′)‐hydroxy‐4‐stilbazole halides

The electron ionization (EI) mass spectra and electrospray ionization (ESI) mass spectra of a series of isomeric N‐chlorobenzyl‐ and N‐bromobenzyl‐substituted (E)‐2′(3′ or 4′)‐hydroxy‐4‐stilbazole chlorides and bromides (1–12) were recorded. The fragmentation pathways of all of the compounds and the characteristic fragment ions formed by EI‐MS were studied by means of B/E and B²/E constant linked‐scanning techniques. The formation of ions originating from preionization reactions, characteristic of quaternary halides under EI‐MS conditions, such as the elimination of chloro‐ or bromobenzyl halides, dehydrohalogenation or substitution reactions, is explained. As soft ionization methods cause no such degradation reactions, the ESI‐MS spectra of the studied compounds were also obtained for comparison. We thus demonstrated the applicability of EI‐MS even in cases when preionization takes place, as long as such secondary processes are properly accounted for. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrolysis Reaction of N-Phosphoryl-α-, β- and γ-amino Acids Studied by HPLC

The hydrolysis reactions of N-（O,O＇diisopropyl）phosphoryl-L-α-alanine （DIPP-L-α-Ala）, N-（O,O＇diisopropyl）- phosphoryl-D-α-alanine （DIPP-D-α-Ala）, N-（O,O＇-diisopropyl）phosphoryl-β-alanine （DIPP-β-Ala） and N-（O,O＇-diisopropyl）phosphoryl-γ-amino butyric acid （DIPP-γ-Aba）, were studied by HPLC and their hydrolysis reaction kinetic equations were obtained. Under acid conditions, the reaction rate of DIPP-L-α-Ala was close to that of DIPP-D-α-Ala and the same rule was true between DIPP-β-Ala and DIPP-γ-Aba. Meantime, the reaction rate of DIPP-L/D-α-Ala was as 10 times as that of DIPP-β-Ala or DIPP-γ-Aba. Under basic conditions, the hydrolysis reactions of DIPP-β-Ala and DIPP-γ-Aba almost did not take place and the reaction rate of DIPP-L/D-α-Ala was about 1/10 of that under acid conditions. Moreover, theoretical calculation further illuminated the differences of the hydrolysis rate from the view of energy. The results would provide some helpful clues to why nature chose a-amino acids but not other kinds of analogs as protein backbones.     

Gas chromatography coupled to mass spectrometry‐based metabolomic to screen for anabolic practices in cattle: identification of 5α‐androst‐2‐en‐17‐one as new biomarker of 4‐androstenedione misuse

The use of anabolic steroids as growth promoters for meat‐producing animals is banned within the European Union. However, screening for the illegal use of natural steroid hormones still represents a difficult challenge because of the high interindividual and physiological variability of the endogenous concentration levels in animals. In this context, the development of untargeted profiling approaches for identifying new relevant biomarkers of exposure and/or effect has been emerging for a couple of years. The present study deals with an untargeted metabolomics approach on the basis of GC‐MS aiming to reveal potential biomarkers signing a fraudulent administration of 4‐androstenedione (AED), an anabolic androgenic steroid chosen as template. After a sample preparation based on microextraction by packed sorbent, urinary profiles of the free and deglucurono‐conjugates urinary metabolites were acquired by GC‐MS in the full‐scan acquisition mode. Data processing and chemometric procedures highlighted 125 ions, allowing discrimination between samples collected before and after an administration of 4‐AED. After a first evaluation of the signal robustness using additional and independent non‐compliant samples, 17 steroid‐like metabolites were pointed out as relevant candidate biomarkers. All these metabolites were then monitored using a targeted GC‐MS/MS method for an additional assessment of their capacity to be used as biomarkers. Finally, two steroids, namely 5α‐androstane‐3β,17α‐diol and 5α‐androst‐2‐en‐17‐one, were concluded to be compatible with such a definition and which could be finally usable for screening purpose of AED abuse in cattle. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization, and degradation of poly(ethylene‐b‐ε‐caprolactone) diblock copolymer

Poly(ethylene‐b‐ε‐caprolactone) (PE‐b‐PCL) diblock copolymers were synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (CL) with α‐hydroxyl‐ω‐methyl polyethylene (PE‐OH) as a macroinitiator and ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] as a catalyst. Polymerization was conducted in bulk (130–150°C) with high yield (87–97%). Block copolymers with different compositions were obtained and characterized by ¹H and ¹³C NMR, MALDI‐TOF, SAXS, and DSC. End‐group analysis by NMR and MALDI‐TOF indicates the formation of α‐hydroxyl‐ω‐methyl PE‐b‐PCL. The PE‐b‐PCL degradation was studied using thermogravimetric analysis (TGA) and alkaline hydrolysis. The PCL block was hydrolyzed by NaOH (4M), without any effect on the PE segment. Copyright © 2009 John Wiley & Sons, Ltd.     

Combined 1H, 13C and 11B NMR and mass spectral assignments of boronate complexes of D‐(+)‐glucose,D‐(+)‐mannose,methyl‐α‐D‐glucopyranoside,methyl‐β‐D‐galactopyranoside and methyl‐α‐D‐mannopyranoside

Complex formation between N‐butylboronic acid and D ‐(+)‐glucose, D ‐(+)‐mannose, methyl‐α‐D ‐glucopyranoside, methyl‐β‐D ‐galactopyranoside and methyl α‐D ‐mannopyranoside under neutral conditions was investigated by ¹H, ¹³C and ¹¹B NMR spectroscopy and gas chromatography–mass spectrometry (GC–MS) D ‐(+)‐Glucose and D ‐(+)‐mannose formed complexes where the boronates are attached to the 1,2:4,6‐ and 2,3:5,6‐positions of the furanose forms, respectively. On the other hand, the boronic acid binds to the 4,6‐positions of the two methyl derivatives of glucose and galactose. Methyl α‐D ‐mannopyranoside binds two boronates at the 2,3:4,6‐positions. ¹¹B NMR was used to show the ring size of the complexed sugars and the boronate. GC–MS confirmed the assignments. Copyright © 2003 John Wiley & Sons, Ltd.     

The unusual hydrogen‐deuterium exchange of α‐carbon protons in N‐substituted glycine‐containing peptides

Hydrogens connected to α‐carbon (α‐C) of amino acid residues are usually resistant to hydrogen‐deuterium exchange (HDX) unless reaction conditions promote racemization. Although N‐methylglycine (sarcosine) residue has been found in biologically active peptide such as cyclosporine, to the best of our knowledge, the HDX of α‐C protons of this residue was not explored yet. Here, we presented a new and efficient methodology of α‐C deuteration in sarcosine residues under basic aqueous conditions. The deuterons, introduced at α‐C atom, do not undergo back‐exchange in acidic aqueous solution. The electrospray ionization‐MS and MS/MS experiments on proposed model peptides confirmed the HDX at α‐C and revealed the unexpected hydrogen scrambling in sarcosine‐containing peptides. Although the observed HDX of α‐C protons is only successful in N‐acylglycine when the amide possesses a certain degree of alkylation, it offers a new approach to the analysis of sarcosine‐containing peptides such as cyclosporine. Copyright © 2014 John Wiley & Sons, Ltd.     

Mass spectrometric studies of cis‐ and trans‐1a,3‐disubstituted‐1,1‐dichloro‐4‐formyl‐1a, 2,3,4‐tetrahydro‐lH‐azirino[1,2‐a]1,5]benzodiazepines

The mass spectrometric behaviour of four cis‐ and trans‐1a,3‐disubstituted‐1,1‐dichloro‐4‐formyl‐1a,2,3,4‐tetrahydro‐1H‐azirino [1, 2‐a][1,5]benzodiazepines has been studied with the aid of mass‐analysed ion kinetic energy spectrometry and exact mass measurements under electron impact ionization. All compounds show a tendency to eliminate a chlorine atom from the aziridine ring, and then eliminate a neutral propene or styrene from the diazepine ring to yield azirino [1,2‐b][1,3] benzimidazole ions. These azirino [1,2‐a][1,5]‐benzodiazepimes can also eliminate HCl, or Cl plus HCl simultaneously to undergo a ring enlargement rearrangement to yield 1,6‐benzodiazocine ions, which further lose small molecular fragments, propyne or phenylacetylene, with rearrangement to give quinoxaline ions.     

Ring Opening of 2‐(Benzylamino)‐2H‐1,4‐benzoxazin‐3(4H)‐ones and 2‐Bromo‐2H‐1,4‐benzoxazin‐3(4H)‐ones

Substituted 2‐(benzylamino)‐2H‐1,4‐benzoxazin‐3(4H)‐ones are unstable under alkaline and acidic conditions, undergoing opening of the benzoxazinone ring. 2‐Bromo‐2H‐1,4‐benzoxazin‐3(4H)‐ones show similar degradation under alkaline conditions, while replacement of Br at C(2) to give 2‐hydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐ones was observed only under mild alkaline conditions. Mechanisms of ring opening and degradation to 2‐aminophenol derivatives are proposed.     

Diastereoselective Electrophilic Amination of Chiral 1‐Benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one for the Asymmetric Syntheses of α‐Substituted α,β‐Diaminopropanoic Acids

The chiral compounds (R)‐ and (S)‐1‐benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one ((R)‐ and (S)‐ 1 ), derived from (R)‐ and (S)‐asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure α‐alkylated (alkyl=Me, Et, Bn) α,β‐diamino acids (R)‐ and (S)‐ 11 – 13 . The chiral lithium enolates of (R)‐ and (S)‐ 1 were first alkylated, and the resulting diasteroisomeric products 5 – 7 were aminated with ‘di(tert‐butyl) azodicarboxylate’ (DBAD), giving rise to the diastereoisomerically pure (≥98%) compounds 8 – 10 . The target compounds (R)‐ and (S)‐ 11 – 13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence.     

Synthesis and Characterization of New 7‐Substituted 6,14‐Ethenomorphinane Derivatives: N‐{5‐[(5α,7α)‐4,5‐Epoxy‐3,6‐dimethoxy‐17‐methyl‐6,14‐ethenomorphinan‐7‐yl]‐1,3,4‐oxadiazol‐2‐yl}arenamines

In this study, (5α,7α)‐4,5‐epoxy‐3,6‐dimethoxy‐17‐methyl‐6,14‐ethenomorphinan‐7‐carboxylic acid hydrazide ( 5 ) was synthesized by the condensation of methyl (5α,7α)‐4,5‐epoxy‐3,6‐dimethoxy‐17‐methyl‐6,14‐ethenomorphinan‐7‐carboxylate ( 4 ) with NH₂NH₂⋅H₂O. The (5α,7α)‐4,5‐epoxy‐3,6‐dimethoxy‐17‐methyl‐6,14‐ethenomorphinan‐7‐carboxylic acid 2‐[(arylamino)carbonyl]hydrazides 6a – 6q were prepared by the reaction of 5 with corresponding substituted aryl isocyanates, and the N‐{5‐[(5α,7α)‐4,5‐epoxy‐3,6‐dimethoxy‐17‐methyl‐6,14‐ethenomorphinan‐7‐yl]‐1,3,4‐oxadiazol‐2‐yl}arenamines 7a – 7q were obtained via the cyclization reaction of 6a – 6q in the presence of POCl₃. The synthesized compounds have a rigid morphine structure, including the 6,14‐endo‐etheno bridge and the 5‐(arylamino)‐1,3,4‐oxadiazol‐2‐yl residue at C(7) adopting the (S)‐configuration (7α). The structures of the compounds were confirmed by high‐resolution mass spectrometry (HR‐MS) and various spectroscopic methods such as FT‐IR, ¹H‐NMR, ¹³C‐NMR, APT, and 2D‐NMR (HETCOR, COSY, INADEQUATE).     

Change of the favored routes of EI MS fragmentation when proceeding from N1, N1‐dimethyl‐N2‐arylformamidines to 1,1,3,3‐tetraalkyl‐2‐arylguanidines: substituent effects

Although series of N¹, N¹‐dimethyl‐N²‐arylformamidines and of 1,1,3,3‐tetraalkyl‐2‐arylguanidines are structurally analogous and similar electron‐ionization mass spectral fragmentation may be expected, they display important differences in the favored routes of fragmentation and consequently in substituent effects on ion abundances. In the case of formamidines, the cyclization‐elimination process (initiated by nucleophilic attack of the N‐amino atom on the 2‐position of the phenyl ring) and formation of the cyclic benzimidazolium [M‐H]⁺ ions dominates, whereas the loss of the NR₂ group is more favored for guanidines. In order to gain information on the most probable structures of the principal fragments, quantum‐chemical calculations were performed on a selected set. A good linear relation between log{I[M‐H]⁺I [M]^+?} and σ_R⁺ constants of substituent at para position in the phenyl ring occurs solely for formamidines (r = 0.989). In the case of guanidines, this relation is not significant (r = 0.659). A good linear relation is found between log{I[M‐NMe₂]⁺/I [M]^+?} and σ_p⁺ constants (r = 0.993). Copyright © 2010 John Wiley & Sons, Ltd.     

立体选择性合成2-(a-噻吩甲酰基)-3-取代苯基-4-乙氧羰基-5-甲基-反式-2,3-二氢呋喃

溴化(a-噻吩甲酰基)甲基三苯鉮1与3-取代苯甲叉基-2,4-戊二酮 2以碳酸钾为碱,在苯中55℃条件下反应,可以较好的收率、高立体选择性地生成反-2-(a-噻吩甲酰基)-3-取代苯基-4-乙氧羰基-5-甲基-2,3-二氢呋喃3。产物结构均经波谱予以确定。本文还提出了生成产物的可能机理。