Molecular recognition properties of peptide mixtures obtained by polymerisation of amino acids in the presence of estradiol

In this paper we show that the carbodiimide-induced polymerisation of amino acid mixtures in aqueous medium and in presence of estradiol produces the mixtures of peptides with an average molecular weight of 2-6 kDa that are characterised by possessing molecular recognition properties towards estradiol. After the removal of the templating molecule, the binding properties of the peptide mixtures were studied using spectrophotometric and immunochemical methods. The experimental results show the presence of molecular recognition behaviour for all the peptide mixtures obtained by polymerisation in presence of estradiol, with affinity constant values between 0.44×10⁹ and 6.6×10⁹ M⁻¹, while the same mixtures obtained without estradiol show lower affinity constant values between 2.2×10⁶ and 1.3×10⁹ M⁻¹. The molecular recognition behaviour was found to be highly selective, as the binding constants of peptides towards the structural homologues testosterone and progesterone are lower than three orders of magnitude. Peptide fractions separated by ion-exchange chromatography show the same molecular recognition properties, with affinity constant values between 3.2×10⁶ and 7.1×10⁹ M⁻¹. Similarities and differences between this polymerisation technique and the molecular imprinting technique are briefly discussed.     

Copper-mediated synthesis of N,N''''-diarylhydrazines from boronic acids

N,N0-Diarylhydrazines have been prepared via the reaction of N-Boc-aryl hydrazines with boronic acids mediated by copper acetate. This mild reaction condition tolerates the presence of a variety of functional groups.     

A new type of boronic acid fluorescent reporter compound for sugar recognition

Fluorescent boronic acids that change fluorescent properties upon carbohydrate binding are very useful for the preparation of fluorescent sensors for sugars. Herein we report 5-quinolineboronic acid (5-QBA) that shows significant fluorescent property changes through a unique pK_a-switching mechanism upon binding a diol in aqueous solution.     

Enantioselective rhodium-catalysed addition of boronic acids using C2-symmetric aryl diphosphite ligands

The enantioselective rhodium-catalysed conjugate addition of aryl boronic acids to dehydroalanine derivatives has been successfully carried out in the presence of C₂-symmetric aryl diphosphite ligand (R,R,R-4) to prepare unnatural amino acid esters. The products have been obtained in up to 72% ee and with good isolated yield.     

Highly efficient fluorescent sensing for α-hydroxy acids with C3-symmetric boronic acid-based receptors

Two boronic acid-based fluorescent chemosensors in C₃ symmetry have been prepared with a facial method. These compounds show remarkable ability to recognize α-hydroxycarboxy acids and sugar acids over most saccharides. The fluorescence intensity of the receptors decreased obviously upon adding the α-hydroxy acids in a pH 8.71 buffer of methanol-water, which can be explained with the internal charge-transfer (ICT) mechanism.     

Water works: an efficient palladium-catalyzed cross-coupling reaction between boronic acids and bromoacetate with aminophosphine ligand

Water greatly restrained the formation of self-coupling of boronic acids in a palladium-catalyzed cross-coupling reaction between boronic acids and ethyl bromoacetate with an aminophosphine ligand; good to excellent yields of cross-coupling product were obtained.     

Catalytic enantioselective aryl transfer: asymmetric addition of boronic acids to aldehydes using pyrrolidinylmethanols as ligands

Pyrrolidinylmethanols, easily accessible from readily available (S)-proline, were applied in zinc-catalyzed addition of arylboronic acids to aromatic aldehydes; the reaction was found to proceed in excellent yields and high enantioselectivities (up to 98% ee).     

Visible light induced oxidative hydroxylation of boronic acids

We report herein a visible light-induced aerobic oxidative hydroxylation of boronic acids. The reaction employed 7H-benzo[c]thioxanthen-7-one as metal-free catalyst and dimethyl carbonate as green solvent. Scale-up experiment was achieved using 0.1?mol% catalyst in a good yield with column-free purification. This reaction showed great green chemistry features and potential in synthetic applications.     

Evidence for strong heterodimeric interactions of phenylboronic acids with amino acids

Strong heterodimeric interactions of phenylboronic acids with l-proline or betaine are evident in the solid state. The interaction energy is over 23 kcal/mol (at MP2/6-31+G^∗).     

A mild and efficient copper-catalyzed N-arylation of unprotected sulfonimidamides using boronic acids

An efficient and low cost copper catalyzed system for N-arylation of sulfonimidamides has been developed. The reaction proceeds at room temperature under base free conditions. Various N-aryl, N-heteroaryl, and N-cyclopropyl sulfonimidamides were obtained in good to excellent yields.     

Remarkably selective recognition of iodobenzene derivatives by a macrocyclic bis-Pt(II) metallohost

We designed and synthesized self‐assembled bis‐Pt^II dimer 1? 4 BF₄ with quino[8,7‐b][1,10]phenanthroline as an extended π‐face contact area, which acts as the first artificial receptor with high affinity toward iodinated aromatic compounds significantly based on noncovalent iodine ??? aromatic‐plane interactions in a “side‐on” fashion. Despite their structural similarity to a previously reported metallohost 2 ⁴⁺ that bears 2,2′:6′,2′′‐terpyridine units, a dramatic change in selectivity toward substituted benzene derivatives was observed for 1 ⁴⁺. ¹H NMR spectroscopic titration revealed a high affinity of 1 ⁴⁺ towards haloarenes, with exceptionally large association constants for 2‐iodophenol (K_a=16 000 M ^?1) and 1,2‐diiodobenzene (K_a=21 000 M ^?1), which are 93‐ and 140‐fold higher, respectively, than the values obtained for 2 ⁴⁺. In addition, 1 ⁴⁺ showed a remarkably high affinity and selectivity toward 2,6‐diiodophenol (K_a=35 000 M ^?1), which is an important substructure of the thyroid hormone T₄. X‐ray crystallography and theoretical calculations strongly suggest that “side‐on” iodine ??? aromatic‐plane interactions and π–π stacking contribute to the strong 1,2‐diiodobenzene and 2,6‐diiodophenol binding. The results obtained here give unique and valuable insight into the nature of halogen atom interactions in their “side‐on” region with an electropositive aromatic plane, which may provide useful guidance for designing artificial receptors for iodinated biomolecules.     

Magnesium promoted autocatalytic dehydrogenation of amine borane complexes: A reliable,non-cryogenic,scalable access to boronic acids

Owing to the unusual reactivity of dialkylamine-borane complexes, a methodology was developed to simply access boronic acids. The intrinsic instability of magnesium aminoborohydride was tweaked into a tandem dehydrogenation borylation sequence. Proceeding via an autocatalytic cycle, amineborane dehydrogenation was induced by a variety of Grignard reagents. Overall, addition of the organomagnesium species onto specially designed dialkylamine-borane complexes led to a variety of boronic acids in high yields. In addition, the reaction can be performed under Barbier conditions, on a large scale.     

A novel redox-sensitive protecting group for boronic acids, MPMP-diol

A new boronic acid protecting group, 1-(4-methoxyphenyl)-2-methylpropane-1,2-diol (MPMP-diol), has been developed. Both protection and deprotection can be accomplished under mild conditions with quantitative conversions. The deprotection can be carried out using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).     

Pd-catalyzed addition of boronic acids to vinylogous imines: a convenient approach to 3-sec-alkyl substituted indoles

A convenient approach to 3-sec-alkyl substituted indoles was developed via palladium-catalyzed addition of arylboronic acids to vinylogous imines generated in situ from sulfonylindoles under mild conditions.     

Metal-free electrophilic fluorination of alkyl trifluoroborates and boronic acids

Secondary alkyl trifluoroborates undergo facile electrophilic fluorination under mild conditions to afford the corresponding benzylic fluorinated adducts in excellent yield.     

Facile and effective approach for oxidation of boronic acids

This present work illustrates facile and effective approach for oxidation of boronic acids using environmentally benign dimethyl carbonate (DMC) as a solvent with H₂O₂ as an oxidant at room temperature. In contrast to previous reaction reports, which make use of metal catalyst, hazardous reagent and oxidants that creates environmental concern. This method provides good to excellent yield of products and showed better tolerance towards various functional groups present on boronic acids. Moreover, this developed process is an alternative in terms of inexpensive, non toxic and easy reaction conditions.     

Microwave-assisted cross-coupling of 3-chloro-2-pyrazolines and 3-chloro-1-phenyl-1,4,5,6-tetrahydropyridazine with aryl boronic acids

3-Chloro-1-phenyl-2-pyrazoline and 3-chloro-1-phenyl-1,4,5,6-tetrahydropyridazine were coupled with aryl boronic acids in good yields under microwave heating conditions (140 °C, 5 min).     

Boronic acid-based fluorescent receptors for selective recognition of thymine glycol

Thymine glycol is the major oxidation product of thymine. The amount of thymine glycol present within cellular DNA is one marker of the extent of oxidative damage, and chemosensors for thymine glycol have therefore a number of potential applications. In continuation of our studies devoted to the detection of modified nucleosides, we report herein our results toward the fluorescence detection of thymine glycol at both the nucleoside and the oligonucleotide levels using boronic acid sensors. These receptors show significant fluorescence enhancements and high selectivities in aqueous conditions upon binding with thymine glycol.     

Highly selective capture of nucleosides with boronic acid functionalized polymer brushes prepared by atom transfer radical polymerization

The nucleoside or modified nucleoside level in biological fluids reflects the pathological or physiological state of the body. Boronate affinity absorbents are widely used to selectively extract nucleosides from complex samples. In this work, a novel functionalized absorbent was synthesized by attaching 4‐mercaptophenylboronic acid to gold nanoparticles on modified attapulgite. The surface of the attapulgite was modified by poly(acryloyloxyethyltrimethyl ammonium chloride) by atom transfer radical polymerization, creating many polymer brushes on the surface. The resultant material exhibited superior binding capacity (30.83 mg/g) for adenosine and was able to capture cis‐diol nucleosides from 1000‐fold interferences. Finally, to demonstrate its potential for biomolecule extraction, this boronate affinity material was used to preconcentrate nucleosides from human urine and plasma.     

Chiral donor photoinduced-electron-transfer (d-PET) boronic acid chemosensors for the selective recognition of tartaric acids, disaccharides, and ginsenosides

A modular approach was proposed for the preparation of chiral fluorescent molecular sensors, in which the fluorophore, scaffold, and chirogenic center can be connected by ethynyl groups, and these modules can easily be changed to other structures to optimize the molecular sensing performance of the sensors. This modular strategy to assembly chiral sensors alleviated the previous restrictions of chiral boronic acid sensors, for which the chirogenic center, fluorophore, and scaffold were integrated, thus it was difficult to optimize the molecular structures by chemical modifications. We demonstrated the potential of our new strategy by the preparation of a sensor with a larger scaffold. The photoinduced electron‐transfer (PET) effect is efficient even with a large distance between the N atom and the fluorophore core. Furthermore, the rarely reported donor‐PET (d‐PET) effect, which was previously limited to carbazole, was extended to phenothiazine fluorophore. The contrast ratio, that is, PET efficiency of the new d‐PET sensor, is increased to 8.0, compared to 2.0 with the previous carbazole d‐PET sensors. Furthermore, the ethynylated phenothiazine shows longer excitation wavelength (centered at 380 nm) and emission wavelength (492 nm), a large Stokes shift (142 nm), and high fluorescence quantum yield in aqueous solution (Φ=0.48 in MeOH/water, 3:1 v/v). Enantioselective recognition of tartaric acid was achieved with the new d‐PET boronic acid sensors. The enantioselectivity is up to 10 (ratio of the binding constants toward D ‐ and L ‐tartaric acid, k_D/k_L). A consecutive fluorescence enhancement/decrease was observed, thus we propose a transition of the binding stoichiometry from 1:1 to 1:2 as the analyte concentration increases, which is supported by mass spectra analysis. The boronic acid sensors were used for selective and sensitive recognition of disaccharides and glycosylated steroids (ginsenosides).