Non-racemic atropisomeric (thio)ureas as neutral enantioselective anion receptors for amino-acid derivatives: origin of smaller Kass with thiourea than urea derivatives

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.

Oxoanion Imprinting Combining Cationic and Urea Binding Groups: A Potent Glyphosate Adsorber

The use of polymerizable hosts in anion imprinting has led to powerful receptors with high oxyanion affinity and specificity in both aqueous and non-aqueous environments. As demonstrated in previous reports, a carefully tuned combination of orthogonally interacting binding groups, for example, positively charged and neutral hydrogen bonding monomers, allows receptors to be constructed for use in either organic or aqueous environments, in spite of the polymer being prepared in non-competitive solvent systems. We here report on a detailed experimental design of phenylphosphonic and benzoic acid-imprinted polymer libraries prepared using either urea- or thiourea-based host monomers in the presence or absence of cationic comonomers for charge-assisted anion recognition. A comparison of hydrophobic and hydrophilic crosslinking monomers allowed optimum conditions to be identified for oxyanion binding in non-aqueous, fully aqueous, or high-salt media. This showed that recognition improved with the water content for thiourea-based molecularly imprinted polymers (MIPs) based on hydrophobic EGDMA with an opposite behavior shown by the polymers prepared using the more hydrophilic crosslinker PETA. While the affinity of thiourea-based MIPs increased with the water content, the opposite was observed for the oxourea counterparts. Binding to the latter could however be enhanced by raising the pH or by the introduction of cationic amine- or Na⁺-complexing crown ether-based comonomers. Use of high-salt media as expected suppressed the amine-based charge assistance, whereas it enhanced the effect of the crown ether function. Use of the optimized receptors for removing the ubiquitous pesticide glyphosate from urine finally demonstrated their practical utility.

Chiral Thioureas-Preparation and Significance in Asymmetric Synthesis and Medicinal Chemistry

For almost 20 years, thioureas have been experiencing a renaissance of interest with the emerged development of asymmetric organocatalysts. Due to their relatively high acidity and strong hydrogen bond donor capability, they differ significantly from ureas and offer, appropriately modified, great potential as organocatalysts, chelators, drug candidates, etc. The review focuses on the family of chiral thioureas, presenting an overview of the current state of knowledge on their synthesis and selected applications in stereoselective synthesis and drug development.

Novel Chiral Bifunctional L-Thiazoline-Thiourea Derivatives: Design and Application in Enantioselective Michael Reactions

Several novel chiral bifunctional L-thiazoline-thiourea derivatives were easily synthesized from commercially available L-cysteine in high yield. These catalysts were subsequently applied to the enantioselective Michael addition of acetylacetone to β-nitrostyrenes. The products with S configuration were obtained in 98% enantiomeric excess (ee) when the L-thiazoline-thiourea derivatives were used. A plausible transition state model is proposed to explain the observed enantioselectivities.

A new chiral electrochemical sensor for the enantioselective recognition of naproxen enantiomers using l-cysteine self-assembled over gold nanoparticles on a gold electrode

A chiral electrochemical sensor for analyzing the enantiomeric composition of chiral compounds is reported.

Chiral enantiopure bis(thio)ureas derived from TADDOL and their carboxylate complexation capacity

New chiral enantiopure ureas and thioureas with (R,R)-TADDOL backbone were synthesized. Bis-(thio)ureas with C2 symmetry were obtained from TADDOL iso(thio)cyanates and bifunctional amino-(thio)ureas from TADDAMINE, respectively. These were tested for carboxylate recognition capacity and the association constant was determined for the most stable complex.

Novel phenyl(thio)ureas bearing (thio)oxothiazoline group as potential BACE-1 inhibitors: synthesis and biological evaluation

We report the synthesis and the β-site amyloid precursor protein cleaving enzyme-1 inhibitory properties of novel phenyl(thio)ureas bearing 2-(thio)oxothiazoline derivatives. A library of analogues was prepared according to specific synthetic schemes and the inhibitory activity was monitored using a fluorescence resonance energy transfer assay. Several analogues show potent inhibitory activities ranging between 1 and 0.01 µM and the activity is related to the NH acidity of the (thio)urea motif. Our results illustrate once again the close relationship between molecular recognition, complexation of the active site in enzymatic system, and organocatalysis utilizing explicit hydrogen bonding.

3-(2-aminophenyl)-4-methyl-1,3-thiazole-2(3H)-thione as an ecofriendly sulphur transfer agent to prepare alkanethiols in high yield and high purity

A new process is described for preparing very pure linear alkanethiols and linear α,ω-alkanedithiols using a sequential alkylation of the title compound, followed by a ring closure to quantitatively give the corresponding 3-methyl[1,3]thiazolo[3,2-a]-[3,1]benzimidazol-9-ium salt and the alkanethiol derivative under mild conditions. The alkanethiol and the heteroaromatic salt are easily separated by a simple extraction process. The intermediate thiazolium quaternary salts resulting from the first reaction step can be isolated in quantitative yields, affording an odourless protected form of the thiols.

A phosphotyrosine-imprinted polymer receptor for the recognition of tyrosine phosphorylated peptides

Hyperphosphorylation at tyrosine is commonly observed in tumor proteomes and, hence, specific phosphoproteins or phosphopeptides could serve as markers useful for cancer diagnostics and therapeutics. The analysis of such targets is, however, a challenging task, because of their commonly low abundance and the lack of robust and effective preconcentration techniques. As a robust alternative to the commonly used immunoaffinity techniques that rely on phosphotyrosine(pTyr)-specific antibodies, we have developed an epitope-imprinting strategy that leads to a synthetic pTyr-selective imprinted polymer receptor. The binding site incorporates two monourea ligands placed by preorganization around a pTyr dianion template. The tight binding site displayed good binding affinities for the pTyr template, in the range of that observed for corresponding antibodies, and a clear preference for pTyr over phosphoserine (pSer). In further analogy to the antibodies, the imprinted polymer was capable of capturing short tyrosine phosphorylated peptides in the presence of an excess of their non-phosphorylated counterparts or peptides phosphorylated at serine.

Detailing hydrogen bonding and deprotonation equilibria between anions and urea/thiourea derivatives

Spectrophotometric and 1H NMR titrations of N-methoxyethyl-N'-(4-nitrophenyl)thiourea (3) by Bu(4-)NOAc show that in DMSO deprotonation of the receptor and formation of a hydrogen-bonded complex with anion proceed simultaneously but in MeCN deprotonation requires the participation of the second acetate anion. The formation constants of hydrogen-bonded complexes were determined from titrations in the presence of added acetic acid, which suppressed deprotonation. These constants together with independently measured stability constants of (AcO)(2)H(-) complexes were employed for a rigorous numerical analysis of titration results in the absence of added acid, which allowed us to determine the equilibrium deprotonation constants as well as pKa values for 3 in both solvents. Although 3 appeared to be a weaker acid than AcOH in both solvents, it can be deprotonated by acetate in dilute solutions when the concentration of liberated acetic acid is low enough. With disubstituted N,N-bis(methoxyethyl)-N'-(4-nitrophenyl)thiourea 4 only deprotonation equilibrium is observed. In contrast, both parent urea derivatives 1 and 2 cannot be deprotonated by acetate anions. Independent of the real type of equilibrium, whether it is a deprotonation or a hydrogen bonding, titration plots always can be satisfactorily fitted to a formal 1:1 binding isotherm. A relationship between apparent "binding constants" and real equilibrium constants of hydrogen bonding association and deprotonation processes is discussed.