Automated Solid‐Phase Synthesis and Structural Investigation of β‐Peptidosulfonamides and β‐Peptidosulfonamide/β‐Peptide Hybrids: β‐Peptidosulfonamide and β‐Peptide Foldamers are Two of a Different Kind

Fmoc‐protected β‐aminoethane sulfonylchlorides can be employed for efficient automated solid phase synthesis of β‐peptidosulfonamides and β‐peptidosulfonamide/β‐peptide hybrids containing one or more β‐peptidosulfonamide residues. Thus, Fmoc‐protected β‐aminoethane sulfonylchlorides 5a – c led to the hexa‐β‐peptidosulfonamide 9 and the nona‐β‐peptidosulfonamide 10 . In addition, the β‐peptidosulfonamide/β‐peptide hybrids 13 and 16 , consisting of six and nine β‐residues, respectively, and containing a single β‐peptidosulfonamide unit in the middle, as well as the peptidosulfonamide/β‐peptide hybrid 15 with nine β‐residues, including an N‐terminal β‐peptidosulfonamide residue, were synthesized by automated solid‐phase synthesis. Both CD and NMR spectroscopic measurements did not indicate any helical secondary structure for 9 and 10 . As was shown by CD‐measurements, the β‐peptidosulfonamide residue in the hybrids 13, 15 , and 16 acts as a ‘helix breaker', especially when located in the middle of the hybrid chain ( 13 and 16 ), but, although to a lesser extent, also at the N‐terminus.     

Boron Clusters as a Platform for New Materials: Synthesis of Functionalized o‐Carborane (C2B10H12) Derivatives Incorporating DNA Fragments

A synthetic strategy for functionalization of the three vertices of o‐carborane and the attachment of the obtained triped to the solid support was developed. Further functionalization of the triped with short DNA sequences by automated DNA synthesis was achieved. The proposed methodology is a first example of boron cluster chemistry on a solid support opening new perspectives in boron cluster functionalization.     

Nucleotides,Part LXIX,Synthesis of Phosphoramidite Building Blocks of Isoxanthopterin N8‐(2′‐Deoxy‐β‐D‐ribonucleosides): New Fluorescence Markers for Oligonucleotide Synthesis

The chemical synthesis of isoxanthopterin and 6‐phenylisoxanthopterin N⁸‐(2′‐deoxy‐β‐D ‐ribofuranosyl nucleosides) is described as well as their conversion into suitably protected 3′‐phosphoramidite building blocks to be used as marker molecules for DNA synthesis. Applying the npe/npeoc (=2‐(4‐nitrophenyl)ethyl/[2‐(4‐nitrophenyl)ethoxy]carbonyl) strategy, we used the new building blocks in the preparation of oligonucleotides by an automated solid‐support approach. The hybridization properties of a series of labelled oligomers were studied by UV‐melting techniques. It was found that the newly synthesized markers only slightly interfered with the abilities of the labelled oligomers to form stable duplexes with complementary oligonucleotides.     

Synthesis,Characterization and Thermodynamic Study of the Solid State Coordination Compound Ni(Nic)2·H2O(s)(Nic=Nicotinate)

A novel compound‐monohydrated nickel nicotinate was synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analysis, TG/DTG, and X‐ray powder diffraction technique were applied to characterize the structure and composition of the coordination compound. Low‐temperature heat capacities of the solid coordination compound have been measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 386 K. A solid‐solid phase transition occurred in the temperature range of 328–358 K in the heat capacity curve, and the peak temperature, the molar enthalpy and molar entropy of the phase transition were determined to be T_trs=(356.759±0.697) K, Δ_trsH_m=(13.650±0.408) kJ· mol^?1, and Δ_trsS_m= (38.279±0.086) J·K^?1·mol^?1, respectively. The experimental values of the molar heat capacities in the temperature ranges of 78–328 K and 358–386 K were fitted to two polynomials, respectively. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were calculated and tabulated at the intervals of 5 K.     

Preparation and selective recognition of a novel solid‐phase microextraction fiber combined with molecularly imprinted polymers for the extraction of parabens in soy sample

A prepared molecularly imprinted polymer with ethyl p‐hydroxybenzoate as template molecule was applied for the first time to a homemade solid‐phase microextraction fiber. The molecularly imprinted polymer‐coated solid‐phase microextraction fiber was characterized by scanning electron microscopy and thermogravimetric analysis. Various parameters were investigated, including extraction temperature, extraction time, and desorption time. Under the optimum extraction conditions, the molecularly imprinted polymer‐coated solid‐phase microextraction fiber exhibited higher selectivity with greater extraction capacity toward parabens compared with the nonimprinted polymer‐coated solid‐phase microextraction fiber and commercial fibers. The molecularly imprinted polymer‐coated solid‐phase microextraction fiber was tested using gas chromatography to determine parabens, including methyl p‐hydroxybenzoate, ethyl p‐hydroxybenzoate, and propyl p‐hydroxybenzoate. The linear ranges were 0.01–10 μg/mL with a correlation coefficient above 0.9943. The detection limits (under signal‐to‐noise ratio of 3) were below 0.30 μg/L. The fiber was successfully applied to the simultaneous analysis of three parabens in spiked soy samples with satisfactory recoveries of 95.48, 97.86, and 92.17%, respectively. The relative standard deviations (n=6) were within 2.83–3.91%. The proposed molecularly imprinted polymer‐coated solid‐phase microextraction method is suitable for selective extraction and determination of trace parabens in food samples.     

Synthesis of a Tetrasaccharide Related to the Repeating Unit of the Antigen from Shigella dysenteriae Type 9 in the Form of Its 2‐(Trimethylsilyl)ethyl Glycoside

Abstract

Starting from D‐mannose, D‐galactose and D‐glucosamine hydrochloride, two disaccharide blocks were synthesized. Schmidt's inverse addition technique for trichloroacetimidate was utilized for the construction of a disaccharide with a β‐mannosidic linkage in good yield. The two disaccharides in the appropriate form were then allowed to react in the presence of N‐iodosuccinimide (NIS) and trifluoromethanesulfonic acid (TfOH) to give the tetrasaccharide derivative from which removal of protecting groups gave the desired tetrasaccharide in the form of its 2‐(trimethylsilyl)ethyl glycoside.     

Automated solid‐phase extraction of phenolic acids using layered double hydroxide–alumina–polymer disks

The application of layered double hydroxide–Al₂O₃–polymer mixed‐matrix disks for solid‐phase extraction is reported for the first time. Al₂O₃ is embedded in a polymer matrix followed by an in situ metal‐exchange process to obtain a layered double hydroxide–Al₂O₃–polymer mixed‐matrix disk with excellent flow‐through properties. The extraction performance of the prepared disks is evaluated as a proof of concept for the automated extraction using sequential injection analysis of organic acids (p‐hydroxybenzoic acid, 3,4‐dihydroxybenzoic acid, gallic acid) following an anion‐exchange mechanism. After the solid‐phase extraction, phenolic acids were quantified by reversed‐phase high‐performance liquid chromatography with diode‐array detection using a core–shell silica–C18 stationary phase and isocratic elution (acetonitrile/0.5% acetic acid in pure water, 5:95, v/v). High sensitivity and reproducibility were obtained with limits of detection in the range of 0.12–0.25 μg/L (sample volume, 4 mL), and relative standard deviations between 2.9 and 3.4% (10 μg/L, n = 6). Enrichment factors of 34–39 were obtained. Layered double hydroxide–Al₂O₃–polymer mixed‐matrix disks had an average lifetime of 50 extractions. Analyte recoveries ranged from 93 to 96% for grape juice and nonalcoholic beer samples.     

Synthesis of Peptidoglycan Fragments from Enterococcus faecalis with Fmoc‐Strategy for Glycan Elongation

Peptidoglycan (PGN) is an essential structural component of the bacterial cell wall conferring cell shape, which can be recognized by host‐recognition proteins and receptors as well as bacterial surface proteins. In this work, the PGN partial structures from Enterococcus faecalis that contain a tetrasaccharide and an octasaccharide with a unique heptapeptide were synthesized via an Fmoc‐strategy for elongation of the glycan chains. Namely, a 4′‐O ‐Fmoc‐protected disaccharide was utilized as the key intermediate in this efficient synthetic pathway for preparing various PGN fragments. Both the tetrasaccharide and octasaccharide with the unique heptapeptide were successfully synthesized for the first time.     

Matrix solid‐phase dispersion with chitosan‐zinc oxide nanoparticles combined with flotation‐assisted dispersive liquid–liquid microextraction for the determination of 13 n‐alkanes in soil samples

In this study, chitosan‐zinc oxide nanoparticles were used as a sorbent of miniaturized matrix solid‐phase dispersion combined with flotation‐assisted dispersive liquid–liquid microextraction for the simultaneous determination of 13 n‐alkanes such as C₈H₁₈ and C₂₀H₄₂ in soil samples. The solid samples were directly blended with the chitosan nanoparticles in the solid‐phase dispersion method. The eluent of solid‐phase dispersion was applied as the dispersive solvent for the following flotation‐assisted dispersive liquid–liquid microextraction for further purification and enrichment of the target compounds prior to gas chromatography with flame ionization detection. Under the optimum conditions, good linearity with correlation coefficients in the range 0.9991 < r² < 0.9995 and low detection limits between 0.08 to 2.5 ng/g were achieved. The presented procedure combined the advantages of chitosan‐zinc oxide nanoparticles, solid‐phase dispersion and flotation‐assisted dispersive liquid–liquid microextraction, and could be applied for the determination of n‐alkanes in complicated soil samples with acceptable recoveries.     

Screening of drugs of abuse and toxic compounds in human whole blood using online solid‐phase extraction and high‐performance liquid chromatography with time‐of‐flight mass spectrometry

A novel method for the screening of 151 drugs of abuse and toxic compounds in human whole blood has been developed and validated by online solid‐phase extraction with liquid chromatography coupled to time‐of‐flight mass spectrometry. Analytes were extracted and separated by using a fully automated online solid‐phase extraction liquid chromatography system with total chromatographic run time of 26 min. Time‐of‐flight mass spectrometry screening of 151 drugs of abuse and toxic compounds was performed in a full‐scan (m/z 50–800) mode using an MS^E acquisition of molecular ions and fragment ions data at two collision energies (one was 6 eV and another one was in the range of 5–45 eV). The compounds were identified based on retention times and exact mass of molecular ions and fragment ions. The limit of detection ranged from 1 to 100 ng/mL and the recovery of the method ranged from 6.3 to 163.5%. This method is proved to be a valuable screening method allowing fast and specific identification of drugs in human whole blood.     

Novel Fluoride‐Labile Nucleobase‐Protecting Groups for the Synthesis of 3′(2′)‐O‐Aminoacylated RNA Sequences

With the aim to develop a general approach to a total synthesis of aminoacylated t‐RNAs and analogues, we describe the synthesis of stabilized, aminoacylated RNA fragments, which, upon ligation, could lead to aminoacylated t‐RNA structures. Novel RNA phosphoramidites with fluoride‐labile 2′‐O‐[(triisopropylsilyl)oxy]methyl (=tom) sugar‐protecting and N‐{{2‐[(triisopropylsilyl)oxy]benzyl}oxy}carbonyl (=tboc) base‐protecting groups were prepared (Schemes 4 and 5), as well as a solid support containing an immobilized N⁶‐tboc‐protected adenosine with an orthogonal (photolabile) 2′‐O‐[(S)‐1‐(2‐nitrophenyl)ethoxy]methyl (=(S)‐npeom) group (Scheme 6). From these building blocks, a hexameric oligoribonucleotide was prepared by automated synthesis under standard conditions (Scheme 7). After the detachment from the solid support, the resulting fully protected sequence 34 was aminoacylated with L ‐phenylalanine derivatives carrying photolabile N‐protecting groups (→ 42 and 43 ; Scheme 9). Upon removal of the fluoride‐labile sugar‐ and nucleobase‐protecting groups, the still stabilized, partially with the photolabile group protected precursors 44 and 45 , respectively, of an aminoacylated RNA sequence were obtained (Scheme 9 and Fig. 3). Photolysis of 45 under mild conditions resulted in the efficient formation of the 3′(2′)‐O‐aminoacylated RNA sequence 46 (Fig. 4). Additionally, we carried out model investigations concerning the stability of ester bonds of aminoacylated ribonucleotide derivatives under acidic conditions (Table) and established conditions for the purification and handling of 3′(2′)‐O‐aminoacylated RNA sequences and their stabilized precursors.     

Simultaneous estimation of E- and Z-isomers of guggulsterone in rabbit plasma using liquid chromatography tandem mass spectrometry and its application to pharmacokinetic study

A sensitive and selective liquid chromatography/tandem mass spectrometric method was developed for simultaneous determination of E‐ and Z‐guggulsterone isomers (antihyperlipidemic drug) in rabbit plasma. Both the isomers were resolved on a Symmetry‐Shield C₁₈ (5 µm, 4.6 × 150 mm) column, using gradient elution comprising a mobile phase of methanol, 0.5% v/v formic acid and acetonitrile. With dexamethasone as internal standard, plasma samples were extracted by an automated solid‐phase extraction method using C₁₈ cartridges. Detection was performed by electrospray ionization in multiple reaction monitoring (MRM) in positive mode. The calibration curve was linear over the concentration range of 1.56–200 ng/mL (r² ≥ 0.998) for both analytes. The intra‐day and inter‐day accuracy and precision were within −0.96 to 4.12 (%bias) and 2.73 to 8.00 (%RSD) respectively. The analytes were stable after three freeze–thaw cycles. The method was successfully applied to study steriospecific pharmacokinetics of E‐ and Z‐guggulsterone in NZ rabbit. Copyright © 2011 John Wiley & Sons, Ltd.     

Modification of Guanine with Photolabile N‐Hydroxypyridine‐2(1H)‐thione: Monomer Synthesis,Oligonucleotide Elaboration,and Photochemical Studies

The photochemistry of N‐hydroxypyridine‐2(1H)‐thione (NHPT), inserted as a photolabile modifier at the 6‐position of 2′‐deoxyguanosine or guanosine, has been evaluated. In particular, 6‐[(1‐oxidopyridin‐2‐yl)sulfanyl]‐ ( 1a ) and 6‐[(pyridin‐2‐yl)sulfanyl]‐2′,6‐dideoxyguanosine ( 2a ), novel photolabile derivatives of the natural nucleosides, were synthesized and characterized. The observed photolysis products of 1a in organic solvents could only be rationalized by assuming a rapid equilibrium with the corresponding 6‐[(2‐thioxopyridin‐1(2H)‐yl)oxy] analogue 3a (Scheme 5). Transient spectroscopy of 1a indicated a strong triplet‐excited state suitable for triplet → triplet energy transfer or singlet‐oxygen generation. The NHPT function was stable enough for (slightly modified) automated solid‐phase oligonucleotide synthesis. The utility of the above compounds is discussed, as well as their potential use in photosensitization of reactive oxygen species in DNA.     

Chemical Synthesis and Immunological Evaluation of Helicobacter pylori Serotype O6 Tridecasaccharide O‐Antigen Containing a dd‐Heptoglycan

The development of glycoconjugate vaccines against Helicobacter pylori is challenging. An exact epitope of the H. pylori lipo‐polysaccharide (LPS) O‐antigens that contain Lewis determinant oligosaccharides and unique dd ‐heptoglycans has not yet been identified. Reported here is the first total synthesis of H. pylori serotype O6 tridecasaccharide O‐antigen containing a terminal Le^y tetrasaccharide, a unique α‐(1→3)‐, α‐(1→6)‐, and α‐(1→2)‐linked heptoglycan, and a β‐d ‐galactose connector, by an [(2×1)+(3+8)] assembly sequence. Seven oligosaccharides covering different portions of the entire O‐antigen were prepared for immunological investigations with a particular focus on elucidation of the roles of the dd ‐heptoglycan and Le^y tetrasaccharide. Glycan microarray analysis of sera from rabbits immunized with isolated serotype O6 LPS revealed a humoral immune response to the α‐(1→3)‐linked heptoglycan, a key motif for designing glycoconjugate vaccines for H. pylori serotype O6.     

Synthesis of a Potential 10E4 Tetrasaccharide Antigen Involved in Scrapie Pathogenesis

To test the hypothesis that tetrasaccharide 3 is involved in scrapie pathogenesis, tetrasaccharide derivative 32 functionalized with an amine linker at the reducing end was synthesized. A (2 + 2) glycosylation approach was chosen to furnish the target compound in fully protected form. To investigate its biological role, tetrasaccharide 32 was further functionalized to the corresponding thiol 33 using Traut's reagent. During the course of the synthesis, the N,N‐diacetyl protecting group proved surprisingly labile to radical and acidic conditions.     

Preparation of five high‐purity iridoid glycosides from Gardenia jasminoides Eills by molecularly imprinted solid‐phase extraction integrated with preparative liquid chromatography

Five iridoid glycosides were prepared using molecularly imprinted solid‐phase extraction combined with preparative high‐performance liquid chromatography. Hydrophilic molecularly imprinted polymers were synthesized using α‐1‐allyl‐2‐N‐acetyl glucosamine, which introduced an abundance of hydrophilic groups into the polymers. Using molecularly imprinted solid‐phase extraction as the sample pretreatment procedure, five iridoid glycosides, gardenoside, geniposide, shanzhiside, geniposidic acid, and genipin‐1‐O‐gentiobioside, were selectively enriched from Gardenia fructus extracts. Preparative high‐performance liquid chromatography then provided iridoid glycosides with a purity >98%. The structures were elucidated by using nuclear magnetic resonance spectroscopy, optical rotation and melting point measurements, and mass spectrometry. The results demonstrate that molecularly imprinted solid‐phase extraction combined with preparative high‐performance liquid chromatography was an efficient, rapid, and economical method for the preparation of bioactive compounds from natural products.     

Production of N3 upon Photolysis of Solid Nitrogen at 3 K with Synchrotron Radiation

The photodissociation of gaseous molecular nitrogen has been investigated intensively, but the corresponding knowledge in a solid phase is lacking. Irradiation of pure solid nitrogen at 3 K with vacuum‐ultraviolet light from a synchrotron produced infrared absorption lines of product l‐N₃ at 1657.8 and 1652.6 cm^?1. The threshold wavelength to generate l‐N₃ was determined to be (143.7±1.8) nm, corresponding to an energy of (8.63±0.11) eV. Quantum‐chemical calculations support the formation of l‐N₃ from the reaction N₂+N₂, possibly through an activated complex l‐N₄ upon photoexcitation with energy above 8.63 eV. The results provide a possible application to an understanding of the nitrogen cycle in astronomical environments.     

Solid‐Phase Approach for the Synthesis of 2‐Amido‐1,3,4‐oxadiazoles

A new solid‐phase approach for the synthesis of 2‐amido‐1,3,4‐oxadiazoles has been developed. In this synthesis, hydroxypentyl JandaJel polymer support was treated with excess of oxalyl chloride to give resin‐bound 2‐chloro‐2‐oxoacetate, and this intermediate was then coupled with different hydrazides to give resin‐bound 2‐(N′‐acylhydrazinyl)‐2‐oxoacetate. Intramolecular dehydrative cyclization of resulting resin‐bound linear precursor followed by direct amidation using aluminum amide reagent provided 5‐substituted 1,3,4‐oxadiazoles as 2‐carboxamides. To explore the scope of this reaction sequence, we synthesized a small set of library using a combination of hydrazides and amines, and the desired products were obtained in good to high yields.     

Selective solid‐phase extraction of artificial chemicals from milk samples using multiple‐template surface molecularly imprinted polymers

A novel multiple‐template surface molecularly imprinted polymer (MTMIP) was synthesized using ofloxacin and 17β‐estradiol as templates and modified monodispersed poly(glycidylmethacrylate‐co‐ethylene dimethacrylate) (P_GMA/EDMA) beads as the support material. Static adsorption, solid‐phase extraction and high‐performance liquid chromatography were performed to investigate the adsorption properties and selective recognition characteristics of the polymer templates and their structural analogs. The maximum binding capacities of ofloxacin and 17β‐estradiol on the MTMIP were 9.0 and 6.6 mg/g, respectively. Compared with the corresponding nonimprinted polymer, the MTMIP exhibited a much higher adsorption performance and selectivity toward three quinolones and three estrogens, which are common drug residues in food. The MTMIP served as a simple and effective pretreatment method and could be successfully applied to the simultaneous analysis of multiple target components in complex samples. Furthermore, the MTMIP may find useful applications as a solid‐phase absorbent in the simultaneous determination of trace quinolones and estrogens in milk samples, as the recoveries were in the range 77.6–98.0%. Copyright © 2015 John Wiley & Sons, Ltd.     

Solid‐Phase Synthesis of (Poly)phosphorylated Nucleosides and Conjugates

Succinyl‐cycloSal‐phosphate triesters of ribo‐ and 2′‐deoxyribonucleosides were attached to aminomethyl polystyrene as an insoluble solid support and reacted with phosphate‐containing nucleophiles yielding nucleoside di‐ and triphosphates, nucleoside diphosphate sugars, and dinucleoside polyphosphates in high purity after cleavage from the solid support. Here, reactive cycloSal‐phosphate triesters were used as immobilized reagents that led to a generally applicable method for the efficient synthesis of phosphorylated biomolecules and phosphate‐bridged bioconjugates.