Deprotection Reaction Research Articles

A Dual Wavelength Polymerization and Bioconjugation Strategy for High Throughput Synthesis of Multivalent Ligands.

Structure-function relationships for multivalent polymer scaffolds are highly complex due to the wide diversity of architectures offered by such macromolecules. Evaluation of this landscape has traditionally been accomplished case-by-case due to the experimental difficulty associated with making these complex conjugates. Here, we introduce a simple dual-wavelength, two-step polymerize and click approach for making combinatorial conjugate libraries. It proceeds by incorporation of a polymerization friendly cyclopropenone-masked dibenzocyclooctyne into the side chain of linear polymers or the α-chain end of star polymers. Polymerizations are performed under visible light using an oxygen tolerant porphyrin-catalyzed photoinduced electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) process, after which the deprotection and click reaction is triggered by UV light. Using this approach, we are able to precisely control the valency and position of ligands on a polymer scaffold in a manner conducive to high throughput synthesis.

A Screening Platform to Identify and Tailor Biocompatible Small-Molecule Catalysts.

Interfacing biocompatible, small‐molecule catalysis with cellular metabolism promises a straightforward introduction of new function into organisms without the need for genetic manipulation. However, identifying and optimizing synthetic catalysts that perform new‐to‐nature transformations under conditions that support life is a cumbersome task. To enable the rapid discovery and fine‐tuning of biocompatible catalysts, we describe a 96‐well screening platform that couples the activity of synthetic catalysts to yield non‐canonical amino acids from appropriate precursors with the subsequent incorporation of these nonstandard building blocks into GFP (quantifiable readout). Critically, this strategy does not only provide a common readout (fluorescence) for different reaction/catalyst combinations, but also informs on the organism's fitness, as stop codon suppression relies on all steps of the central dogma of molecular biology. To showcase our approach, we have applied it to the evaluation and optimization of transition‐metal‐catalyzed deprotection reactions.

Total synthesis and anti-inflammatory evaluation of violacin A and its analogues.

A concise total synthesis of an exceedingly potent anti-inflammatory agent violacin A as well as the preparation of thirty analogues of this lead from commercially available orcinol are described. Highlights of our synthetic efforts involve Friedel-Crafts acylation, the regioselective etherification and esterification of phenolic hydroxyl groups, and Baker-Venkatamaran rearrangement to form basic skeleton of violacin A. The deprotection reaction with Pd-catalytic was involved to avoid the elimination of the hemiacetal hydroxyl at C2. In addition, all synthetic compounds were screened for anti-inflammatory activity against nitric oxide (NO) production using lipopolysaccharide (LPS)-induced Raw264.7 cells. A range of violacin A derivatives 11b, 11d, 11f, 12e, 12g, 13g, 17d-g exhibited stronger anti-inflammatory effect than that of violacin A. Notably, halogeno-benzyloxy substituent at C-7 were favourable for anti-inflammatory activities of violacin A derivatives. Additionally, Western blot results indicated halogeno-benzyloxy derivatives inhibited pro-inflammatory cytokines releases correlated with the suppression of NF-κB signaling pathway.

Catalytic Transfer Hydrodebenzylation with Low Palladium Loading

AbstractA highly‐efficient catalytic system for hydrodebenzylation reaction is described. The cleavage of O‐benzyl and N‐benzyl protecting groups was performed using an uncommonly low palladium loading (0.02–0.3 mol%; TON up to 5000) in a relatively short reaction time. The approach was used for a variety of substrates including pharmaceutically important precursors, and gram‐scale deprotection reaction was shown. Transfer conditions together with easy‐to‐make Pd/C catalyst are the key features of this debenzylation scheme.magnified image

A new phenothiazine-based sensor for highly selective, ultrafast, ratiometric fluorescence and colorimetric sensing of Hg2+: Applications to bioimaging in living cells and test strips

A new phenothiazine-based sensor PPM was successfully designed and synthesized, which shows highly selective, ultrafast, naked-eye colorimetric and turn-on ratiometric fluorescence sensing of Hg2+ on the basis of the ICT from phenothiazine to aldehyde. Upon addition of Hg2+, obvious blue fluorescence at 455 nm decreased while green fluorescence at 528 nm enhanced, which exhibits ratiometric fluorescent turn-on response along with a “naked-eye” color change from pale-blue to bright-green. The PPM for highly sensing of Hg2+ with a quite low detection limit (12.5 nM) and a wide pH application range. The sensing mechanism proved to be the Hg2+-triggered thioacetal deprotection reaction was confirmed. Importantly, PPM was successfully employed for highly selective detecting and imaging of Hg2+ in living cells, as well as on paper/TLC-based “naked-eye” colorimetric assay.

Development and radiosynthesis of the first 18 F-labeled inhibitor of monocarboxylate transporters (MCTs).

Monocarboxylate transporters 1 and 4 (MCT1 and MCT4) are involved in tumor development and progression. Their expression levels are related to clinical disease prognosis. Accordingly, both MCTs are promising drug targets for treatment of a variety of human cancers. The noninvasive imaging of these MCTs in cancers is regarded to be advantageous for assessing MCT-mediated effects on chemotherapy and radiosensitization using specific MCT inhibitors. Herein, we describe a method for the radiosynthesis of [18 F]FACH ((E)-2-cyano-3-{4-[(3-[18 F]fluoropropyl)(propyl)amino]-2-methoxyphenyl}acrylic acid), as a novel radiolabeled MCT1/4 inhibitor for imaging with PET. A fluorinated analog of α-cyano-4-hydroxycinnamic acid (FACH) was synthesized, and the inhibition of MCT1 and MCT4 was measured via an L-[14 C]lactate uptake assay. Radiolabeling was performed by a two-step protocol comprising the radiosynthesis of the intermediate (E)/(Z)-[18 F]tert-Bu-FACH (tert-butyl (E)/(Z)-2-cyano-3-{4-[(3-[18 F]fluoropropyl)(propyl)amino]-2-methoxyphenyl}acrylate) followed by deprotection of the tert-butyl group. The radiofluorination was successfully implemented using either K[18 F]F-K2.2.2 -carbonate or [18 F]TBAF. The final deprotected product [18 F]FACH was only obtained when [18 F]tert-Bu-FACH was formed by the latter procedure. After optimization of the deprotection reaction, [18 F]FACH was obtained in high radiochemical yields (39.6±8.3%, end of bombardment (EOB) and radiochemical purity (greater than 98%).

Accessing sequence specific hybrid peptoid oligomers with varied pendant group spacing

The synthesis of β-peptoids (i.e., N-substituted β-alanine oligomers) 10 or more residues in length has proven challenging owing to poor coupling efficiency even after extended reaction times, resulting in the substantial generation of deletion sequences and consequently making purification of the target oligomer challenging. To overcome the limitations of conventional approaches, here we examine a synthetic method to rapidly yield sequence specific β- and γ-peptoids with 4–20 repeat units in high purity via alternating monomer addition and deprotection reactions using Fmoc-protected, N-substituted β-alanine- and γ-aminobutyric acid-based monomers in conjunction with microwave-assisted automated solid phase synthesis. By decoupling the secondary amine generation and the oligomer synthesis, this approach circumvents the relatively low reaction efficiency of primary amine alkylation with halogenated propionic or butyric acid to afford secondary amines while retaining the pendant group chemical diversity offered by α-peptoids. We establish the compatibility of this technique with conventional Fmoc-peptide and ‘submonomer’ peptoid syntheses by fabricating several hybrid oligomer sequences including long β- and γ-peptoid oligomers in addition to hybrid α/β, β/peptide, and α/β/γ-systems, thereby confirming the capacity for this approach to yield oligomers with a backbone spacing of three or more atoms between any two residues. Additionally, we demonstrate that mixtures of aromatic amine- and aldehyde-bearing β-peptoids undergo rapid dynamic covalent assembly to afford oligomeric molecular ladders.

Chemical reaction and diffusion kinetics during laser-induced submillisecond heating for lithographic applications

Reactions in solid-state chemistry are controlled by both underlying chemical reaction rates and temperature-dependent diffusion of reactants and products. Due to distinctly different activation energies, the relative rates of reaction and diffusion may shift dramatically with temperature. In this work, the acid catalyzed deprotection of acid labile groups of model chemically amplified photopolymers was studied to understand the effects of temperature on diffusion-coupled reactions. In these systems, strong acids form during exposure of photoacid generators (PAGs) to ultraviolet radiation and then diffuse and catalyze deprotection reactions. By using very short duration laser-induced heating for the postexposure bake step, the potential reaction temperature range is extended by several hundred degrees compared to traditional thermal processing temperatures. Thermal degradation at these temperatures is avoided by simultaneously reducing the heating time from minutes to submilliseconds. Both diffusion and reaction rates were measured in this high temperature region for three different photoresists combined with two different PAGs, with activation energies of the key processes determined. The interplay of diffusion and reaction rates was also examined by comparing results of high-resolution pattern formation. The best image formation at high temperature was achieved using photoresists with high deprotection rates combined with PAGs exhibiting low diffusivity.

The Design, Synthesis and Preliminary Pharmacokinetic Evaluation of d3-Poziotinib Hydrochloride.

To establish a synthetic route to d3-poziotinib hydrochloride. Treatment of 4-chloro-7-hydroxyquinazolin-6-yl pivalate (1) with d3-methyliodide afforded the etherization product, which reacted with 3,4-dichloro-2-fluoroaniline to generate the key intermediate d3-4-(3,4-dichloro-2-fluorophenylamino)-7-methoxyquinazolin-6-yl pivalate (3). Followed the de-protection reaction, the nucleophilic substitution (SN2) reaction with tert-butyl 4-(tosyloxy)piperidine-1-carboxylate (TSP), and the de-protection reaction of t-butoxycarbonyl (Boc) group, and the amide formation reaction with acrylyl chloride, d3-poziotinib was obtained, which was converted to hydrochloride salt by treatment with concentrated hydrochloric acid (HCl). Starting from a known compound 4-chloro-7-hydroxyquinazolin-6-yl pivalate (1), after 7 steps transformation, d3-poziotinib hydrochloride was obtained with a total yield of 9.02%. The structure of d3-poziotinib hydrochloride was confirmed by 1H-NMR, 13C-NMR, and high resolution (HR)-MS. Meanwhile, the in vitro microsomal stability experiment showed that d3-poziotinib had a longer half time (t1/2 = 4.6 h) than poziotinib (t1/2 = 3.5 h).

Development of Trityl Group Anchored Solubilizing Tags for Peptide and Protein Synthesis.

Recently, solubilizing tag methods (Trt-K and Trt-R method) were developed for the challenging synthesis of peptides/proteins by means of native chemical ligation. In this system, the solubilizing tag can be attached to the Cys side chain by simply mixing the tag-introducing reagent under acidic conditions. The tagged peptides/proteins exhibited high water solubility thanks to the introduction of redundant oligo-Lys/Arg. In the final reaction, the tag can be quickly and cleanly detached by a standard deprotection reaction with trifluoroacetic acid. Herein, the development and application of these methods are described.

Synthesis of C2-Regioselectively Substituted Curdlan Acetate Propionate and the Effect of C2 Substituent on Their Properties

A new C2-regioselective synthetic strategy for Curdlan hetero esters was developed using benzaldehyde to protect the Curdlan C4 and C6 hydroxyl groups as a cyclic acetal structure. After esterification and deprotection reactions, two C2-regioselectively substituted Curdlan acetate propionates, 2-O-acetyl-4,6-di-O-propionyl-Curdlan (CD2Ac46Pr) and 4,6-di-O-acetyl-2-O-propionyl-Curdlan (CD46Ac2Pr), were successfully obtained. Through differential scanning calorimetry and wide-angle X-ray diffraction analysis, the C2 ester was confirmed as the decisive substituent over the melting behavior and crystal structure of Curdlan esters.

Stochastic simulation of pattern formation for chemically amplified resist in electron beam lithography

A molecular scale simulation of the pattern formation process for chemically amplified resist in electron beam lithography based on the stochastic approach is proposed. The initial resist structures are formed by the sequential bonding of the randomly selected monomers. The effects of electron exposure are introduced by the activation of the acid generator which randomly determined according to the absorbed energy distribution in the resist. The absorbed energy distribution is calculated using the Monte Carlo simulation of electron scattering. The effects of the post exposure bake are introduced by the acid diffusion and the polymer deprotection reactions. The fundamental properties, such as quencher concentration dependence, molecular weight dependence, and exposure condition effects on pattern profiles, are well reproduced by the simulation.

Diaminoterephthalate-α-lipoic acid conjugates with fluorinated residues.

Two bifunctional diaminoterephthalate (DAT) fluorescence dyes were prepared in a three-step sequence including one deprotection reaction. One functional unit is α-lipoic acid (ALA) for binding the dye to gold surfaces. It was introduced to the DAT scaffold by an amidation reaction. The other functional unit is a para-(trifluoromethyl)benzyl group for facile detection of the surface-bound material by X-ray photoelectron spectroscopy (XPS). This residue was introduced by reductive amination of the DAT scaffold with the respective benzaldehyde derivative. In one compound (60% yield over three steps) the ALA unit is directly bound to the DAT as a relatively electron-withdrawing amide. In solution (CH2Cl2), this material shows strong fluorescence (quantum yield 57% with emission at 495 nm, absorption maximum at 420 nm). The other compound (57% yield over three steps) possesses a propylene spacer between the ALA and the DAT units for electronic decoupling, thus, bathochromic shifts are observed (absorption at 514 nm, emission at 566 nm). The quantum yield is, however, lower (4%). Self-assembled monolayers on a gold surface of both compounds were prepared and characterized by high-resolution XPS of the C 1s, O 1s, S 2p, N 1s and F 1s emissions. The high signal-to-noise ratios of the F 1s peaks indicated that trifluoromethylation is an excellent tool for the detection of surface-bound materials by XPS.

Simultaneous improvement of permeability and selectivity in enantioselective permeation through solid chiral membranes from a newly synthesized one-handed helical polyphenylacetylene with aldehyde pendant groups by enantioselective reaction

One-handed helical poly(substituted phenylacetylene) having aldehyde groups has been newly synthesized in the membrane state by deprotection reaction of the corresponding poly(substituted phenylacetylene) having dioxolane groups. The permeability of phenylethylamine racemate ((RS)-PEA) of the deprotected membrane showed about five times higher together with the increase of enantioselectivity than that of the corresponding polymer membrane without aldehyde groups. The better performance was attributed to the enantioselective reaction between the aldehyde groups of the membrane with the amino groups in the permeant during the concentration-driven permeation of (RS)-PEA.

Effect of modified di- and trisaccharides on hyaluronidase activity assessed by capillary electrophoresis-based enzymatic assay

The activity of eukaryote hydrolase-type of hyaluronidases was studied using a miniaturized capillary electrophoresis (CE) assay developed in our laboratory. Few nanoliters of reagents are sufficient and no labeling is required for this assay. The effect of natural and original synthetic effectors of hyaluronidase was evaluated. These di- and trisaccharides from linkage region of proteoglycans were synthesized in 30–40 steps from monomeric units using classical protection, deprotection, glycosylation and deoxygenation reactions. The influence of the chain length (di/trisaccharide), the modification type (methoxy/deoxy) and its position (2/4/6) was studied.The inhibition and/or activation percentages were determined at two concentrations of effectors; 0.2 mM and 2 mM. The half maximal effective concentration (EC50) values were evaluated (n = 2) for the most effective inhibitors (∼1 mM) and activators (∼0.2 mM). Results showed that hyaluronidase was mostly inhibited in a concentration-dependent fashion by a deoxy modification and activated by a methoxy modification. Trisaccharides were found to be more effective on hyaluronidase activity than disaccharides. Position 4 was found to be more favorable for hyaluronidase activity than position 6 and the activity in position 2 was negligible. For a better understanding of the enzyme function mode, the inhibition constant (Ki) was also evaluated by CE (Ki ∼ 2 mM). These results are of great interest especially as few activators of hyaluronidase are presented in the literature.

Construction of a novel far-red fluorescence light-up probe for visualizing intracellular peroxynitrite

Peroxynitrite (ONOO-) is an important reactive oxygen species (ROS), which can react with a variety of biologically active species and cause many diseases, such as cancer, neurodegenerative disorders. Herein, we develop a novel far-red fluorescent probe DCM-KA, which is equipping with α-ketoamide moiety caged DCM-NH2. The probe exhibits fluorescence off-on response to ONOO- over other biological interfering analytes by ONOO--induced α-ketoamide deprotection reaction. More importantly, the probe is biocompatible and has been successfully utilized to visualize endogenous ONOO- production in macrophage cell line J774A.1.

Dual-targeting nanoparticles with core-crosslinked and pH/redox-bioresponsive properties for enhanced intracellular drug delivery

Multifunctional nanoparticles (NPs) with high blood-stability, tumor-targeting ability, and stimuli-bioresponsive drug release behaviors are urgently demanded. Herein, folic acid (FA) and galactose (GAL) functionalized, core-crosslinked NPs (CC NPs) with dual-targeting and pH/redox-bioresponsive properties were developed based on amphiphilic FA-poly(6-O-methacryloyl-d-galactopyranose)-b-poly[2-(diisopropylamino) ethyl methacrylate-co-pyridyl disulfide methylacrylate] [FA-PMAgGP-b-P(DPA-co-PDEMA), termed as FA-PMgDP] block copolymers, and then investigated for facilitated hepatoma-targeting delivery of doxorubicin (DOX). A series of PMgDP copolymers were synthesized though two-step RAFT copolymerization followed by acid-induced acetal deprotection reaction. Their well-defined chemical structures and compositions were characterized by 1H NMR and gel permeation chromatography. Nano-sized, non-crosslinked PMgDP NPs (PMgDP NC NPs) with sizes of less than 25 nm in aqueous solution were self-assembled via the solvent exchange method, and PMgDP CC NPs were readily prepared in the presence of dithiothreitol. The drug-loading content of PMgDP CC NPs was up to 15.8% and its entrapment efficiency was 89.0%. In normal physiological conditions, 11.6% of DOX was released from DOX-loaded PMgDP CC NPs at 25 h, whereas in analogous intracellular microenvironment, 95.5% was released at 11 h owing to the acid-induced protonation of tertiary amine and reductive cleavage of disulfide bond in the hydrophobic core. In a cellular uptake study, FA and GAL-mediated, active, dual-targeted DOX-loaded FA-PMgDP CC NPs showed a 3.54-fold increase in cellular uptake efficiency to HepG2 cells compared to that of shown by single GAL-targeted, DOX-loaded PMgDP NC NPs. Results of in vitro cytotoxicity study showed that blank FA-PMgDP CC NPs exhibited good biocompatibility, whereas dual-targeting DOX-loaded FA-PMgDP CC NPs increased cell apoptosis. Therefore, the above results indicated that the well-constructed FA-PMgDP CC NPs with multi-synergistic effect may serve as new nanocarriers in the field of precise hepatoma-targeting drug delivery.

Synthesis of enantiopure 18F-trifluoromethyl cysteine as a structure-mimetic amino acid tracer for glioma imaging.

Although 11C-labelled sulfur-containing amino acids (SAAs) including L-methyl-[11C]methionine and S-[11C]-methyl-L-cysteine, are attractive tracers for glioma positron emission tomography (PET) imaging, their applications are limited by the short half-life of the radionuclide 11C (t1/2 = 20.4 min). However, development of 18F-labelled SAAs (18F, t1/2 = 109.8 min) without significant structural changes or relying on prosthetic groups remains to be a great challenge due to the absence of adequate space for chemical modification.Methods: We herein present 18F-trifluoromethylated D- and L-cysteines which were designed by replacing the methyl group with 18F-trifluoromethyl group using a structure-based bioisosterism strategy. These two enantiomers were synthesized stereoselectively from serine-derived cyclic sulfamidates via a nucleophilic 18F-trifluoromethylthiolation reaction followed by a deprotection reaction. Furthermore, we conducted preliminary in vitro and in vivo studies to investigate the feasibility of using 18F-trifluoromethylated cysteines as PET tracers for glioma imaging.Results: The two-step radiosynthesis provided the desired products in excellent enantiopurity (ee > 99%) with 14% ± 3% of radiochemical yield. In vitro cell study demonstrated that both enantiomers were taken up efficiently by C6 tumor cells and were mainly transported by systems L and ASC. Among them, the D-enantiomer exhibited relatively good stability and high tumor-specific accumulation in the animal studies.Conclusion: Our findings indicate that 18F-trifluoromethylated D-cysteine, a new SAA tracer, may be a potential candidate for glioma imaging. Taken together, our study represents a first step toward developing 18F-trifluoromethylated cysteines as structure-mimetic tracers for PET tumor imaging.

A dual colorimetric and near-infrared fluorescent turn-on probe for Hg2+ detection and its applications

The increasing Hg2+ contamination in environment and ecosystem has gained wide attention and thus demands for its facile and effective detection. In this study, we constructed a new fluorescent probe (E)-2-(2-(3-(1,3-dithian-2-yl)-4-hydroxystyryl)- 4H-chromen-4-ylidene)malononitrile (DCM-Hg) for Hg2+ detection by incorporating the 1, 3-dithiane group to the dicyanomethylene-4H-pyran fluorophore for the first time. This probe can selectively detect Hg2+via the Hg2+-triggered deprotection reaction of thioacetals, which leads to a distinct color change from purple to pink and obvious fluorescence enhancement in the near-infrared (NIR) region. The NIR fluorescence intensity increased linearly with Hg2+ level within the range from 0 to 100 μM and the detection limit of DCM-Hg for Hg2+ was found to be 6.8 × 10−8 mol/L. Moreover, the probe could sense Hg2+ on paper strips and image Hg2+ in living cells with low cytotoxicity, which demonstrates its potential application in environment and biological science.

Photoluminescence of platinum(II) diethynylphenanthroline organometallic complexes with bis-arylethynyl derivatives in solution and solid state

Platinum(II) phenanthroline organometallics, Pt(3,8-Phen≡H)(≡Ph-R)2 (1H–11H), of 11 respective arylethynyl ligands with different substituents: R = H (1H), 4-F (2H), 3-F (3H), 2-F (4H), 4-Me (5H), 4-CF3 (6H), NO2 (7H), 4-COOMe (8H), 4-t-Bu (9H), 3,5-di-CF3 (10H), and 3,5-di-t-Bu (11H) were prepared from our reported complexes, Pt(3,8-Phen≡TMS)(≡Ph-R)2, by a deprotection reaction of a trimethylsilyl group. The luminescence and the DFT calculations of the 11 present organometallics clearly supported the assignment of phosphorescence from the mixed transition of 3MLCT/3LLCT (LLCT = ligand-to-ligand charge transfer) in solution state. In solid state, the emission maximum peak values in the spectra of many complexes in 22 platinum organometallics occurred in the long wavelength area over 700 nm, and their emissions were assigned the phosphorescence from the transition of a metal-metal-to-ligand charge transfer, the so-called 3MMLCT. This is related to the diversity of intermolecular interactions as Pt-Pt and π-π interactions in solid state. On the other hand, the emission peak values in the spectra of some complexes occurred in the short-wavelength area less than 600 nm. The complex Pt(3,8-Phen≡TMS)(≡Ph-3,5-di-CF3)2 showed a particularly strong and vibronic emission, and this phenomenon is presumed to be attributable to the aggregation-induced emission.