Bile Salt Hydrolase Activity-Based Probes for Monitoring Gut Microbial Bile Acid Metabolism

Bile acids are bioactive metabolites that are biotransformed into secondary bile acids by the gut microbiota, a vast consortium of microbes that inhabit the intestines. The first step in intestinal secondary bile acid metabolism is carried out by a critical enzyme, bile salt hydrolase (BSH), that catalyzes the gateway reaction that precedes all subsequent microbial metabolism of these important metabolites. As gut microbial metabolic activity is difficult to probe due to the complex nature of the gut microbiome, approaches are needed to profile gut microbiota-associated enzymes such as BSH. Here, we develop a panel of BSH activity-based probes (ABPs) to determine how changes in diurnal rhythmicity of gut microbiota-associated metabolism affects BSH activity and substrate preference. This panel of covalent probes enables determination of BSH activity and substrate specificity from multiple gut anerobic bacteria derived from the human and mouse gut microbiome. We found that both gut microbiota-associated BSH activity and substrate preference is rhythmic, likely due to feeding patterns of the mice. These results indicate that this ABP-based approach can be used to profile changes in BSH activity in physiological and disease states that are regulated by circadian rhythms.

Tuning Green Explosives through SNAr Chemistry

Reactivity and regioselectivity of SNAr-type fluorine substitution with azide in polyfluoronitrobenzenes was studied both theoretically and experimentally. The obtained polyazidonitrobenzene derivatives were extensively characterized by NMR, IR, HPLC, X-ray, and DFT methods. It was found that the substitution with the azide nucleophile occurs first at the para- and the ortho-positions to the NO2-group and that transazidation reactions also occur here. Thermal decomposition of prepared azidonitrobenzenes was studied both in controlled (kinetic decay) and uncontrolled (explosion) modes. In case of the controlled thermal decomposition of ortho-azidonitrobenzenes, benzofuroxans were found as major products of the reaction unless another azido group was adjacent to the furoxan moiety. The bursting power of azidonitrobenzenes was found to rise gradually with the number of the azide substituents in the aromatic ring.

Chemical biology tools to probe bacterial glycans

Bacterial cells are covered by a complex carbohydrate coat of armor that allows bacteria to thrive in a range of environments. As a testament to the importance of bacterial glycans, effective and heavily utilized antibiotics including penicillin and vancomycin target and disrupt the bacterial glycocalyx. Despite their importance, the study of bacterial glycans lags far behind their eukaryotic counterparts. Bacterial cells use a large palette of monosaccharides to craft glycans, leading to molecules that are significantly more complex than eukaryotic glycans and that are refractory to study. Fortunately, chemical tools designed to probe bacterial glycans have yielded insights into these molecules, their structures, their biosynthesis, and their functions.

Simulating Non-Adiabatic Dynamics of Photoexcited Phenyl Azide: Investigating Electronic and Structural Relaxation en Route to the Formation of Phenyl Nitrene

Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N-N bond separation to be accompanied by synchronous changes in the azide N-N-N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

Photocatalytic Generation of Trifluoromethyl Nitrene for Alkene Aziridination

N-Trifluoromethylated organics may be applied in drug design, agrochemical synthesis, and materials science, among other areas. Yet, despite recent advances in the synthesis of aliphatic, cyclic and heterocyclic N-trifluoromethyl compounds, no strategy based on trifluoromethyl nitrene has hitherto been explored. Here we describe the formation of triplet trifluoromethyl nitrene from azidotrifluoromethane, a stable and safe-to-use precursor, by visible light photocatalysis. The addition of CF3 N to alkenes via biradical intermediates afforded previously unknown aziridines substituted with trifluoromethyl group on the nitrogen atom. The obtained aziridines were converted into either N-trifluoromethylimidazolines, via formal [3+2] cycloaddition with nitriles, mediated by a Lewis acid, or into N-trifluoromethylaldimines, via ring opening and aryl group migration mediated by a strong Brønsted acid. Our findings open new opportunities for the development of novel classes of N-CF3 compounds with possible applications in the life sciences.

Lewis Acid Supported Nickel Nitrenoids

Metalation of the polynucleating ligand F,tbs LH6 (1,3,5-C6 H9 (NC6 H3 -4-F-2-NSiMe2 t Bu)3 ) with two equivalents of Zn(N(SiMe3 )2 )2 affords the dinuclear product (F,tbs LH2 )Zn2 (1), which can be further deprotonated to yield (F,tbs L)Zn2 Li2 (OEt2 )4 (2). Transmetalation of 2 with NiCl2 (py)2 yields the heterometallic, trinuclear cluster (F,tbs L)Zn2 Ni(py) (3). Reduction of 3 with KC8 affords [KC222 ][(F,tbs L)Zn2 Ni] (4) which features a monovalent Ni centre. Addition of 1-adamantyl azide to 4 generates the bridging μ3 -nitrenoid adduct [K(THF)3 ][(F,tbs L)Zn2 Ni(μ3 -NAd)] (5). EPR spectroscopy reveals that the anionic cluster possesses a doublet ground state (S =1 / 2 ${{ 1/2 }}$ ). Cyclic voltammetry of 5 reveals two fully reversible redox events. The dianionic nitrenoid [K2 (THF)9 ][(F,tbs L)Zn2 Ni(μ3 -NAd)] (6) was isolated and characterized while the neutral redox isomer was observed to undergo both intra- and intermolecular H-atom abstraction processes. Ni K-edge XAS studies suggest a divalent oxidation state for the Ni centres in both the monoanionic and dianionic [Zn2 Ni] nitrenoid complexes. However, DFT analysis suggests Ni-borne oxidation for 5.

Dearomative Ring-Fused Azafulleroids and Carbazole-Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage

Herein, we report divergent additions of 2,2'-diazidobiphenyls to C60 and Sc3 N@Ih -C80 . In stark contrast to that of the previously reported bis-azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7-6-5-membered ring system in the case of C60 . In contrast, the corresponding reaction with Sc3 N@Ih -C80 switches to the C-H insertion pathway, thereby resulting in multiple isomers, including a carbazole-derived [6,6]-azametallofulleroid 3 and a [5,6]-azametallofulleroid 4 and an unusual 1,2,3,6-tetrahydropyrrolo[3,2-c]carbazole-derived metallofullerene 5, whose molecular structures have been unambiguously determined by single-crystal X-ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole-derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]-isomer 4 to the [5,6]-isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]- and [6,6]-isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies.

Growing Impact of Intramolecular Click Chemistry in Organic Synthesis

Click Chemistry, a modular, rapid, and one of the most reliable tool for the regioselective 1,2,3-triazole forming [3+2] reaction of organic azide and terimal alkyne is widely explored in various emerging domains of research ranging from chemical biology to catalysis and medicinal chemistry to material science. This regioselective reaction from a diverse range of azido-alkyne scaffolds has been well performed in both intermolecular as well as intramolecular fashions. In comparison to the intermolecular metal (Cu/Ru/Ni) variant of 'Click Chemistry', the intramolecular click tool is little addressed. The intramolecular click chemistry is exemplified as a mordern tool of cyclization which involves metal-catalyzed (CuAAC/RuAAC) cyclization, organo-catalyzed cyclization, and thermal-induced topochemical reaction. Thus, we report herein the recent approaches on intramolecular azide-alkyne cycloaddition 'Click Chemistry' with their wide-spread emerging applications in the developement of a diverse range of molecules including fused-heterocycles, well-defined peptidomemics, and macrocyclic architectures of various notable features.

Photoinduced Metallonitrene Formation by N2 Elimination from Azide Diradical Ligands

Transition-metal nitrides/nitrenes are highly promising reagents for catalytic nitrogen-atom-transfer reactivity. They are typically prepared in situ upon optically induced N2 elimination from azido precursors. A full exploitation of their catalytic potential, however, requires in-depth knowledge of the primary photo-induced processes and the structural/electronic factors mediating the N2 loss with birth of the terminal metal-nitrogen core. Using femtosecond infrared spectroscopy, we elucidate here the primary molecular-level mechanisms responsible for the formation of a unique platinum(II) nitrene with a triplet ground state from a closed-shell platinum(II) azide precursor. The spectroscopic data in combination with quantum-chemical calculations provide compelling evidence that product formation requires the initial occupation of a singlet excited state with an anionic azide diradical ligand that is bound to a low-spin d8 -configured PtII ion. Subsequent intersystem crossing generates the Pt-bound triplet azide diradical, which smoothly evolves into the triplet nitrene via N2 loss in a near barrierless adiabatic dissociation. Our data highlight the importance of the productive, N2 -releasing state possessing azide ππ* character as a design principle for accessing efficient N-atom-transfer catalysts.

A Physical Organic Approach towards Statistical Modeling of Tetrazole and Azide Decomposition

Nitrogen atom-rich heterocycles and organic azides have found extensive use in many sectors of modern chemistry from drug discovery to energetic materials. The prediction and understanding of their energetic properties are thus key to the safe and effective application of these compounds. In this work, we disclose the use of multivariate linear regression modeling for the prediction of the decomposition temperature and impact sensitivity of structurally diverse tetrazoles and organic azides. We report a data-driven approach for property prediction featuring a collection of quantum mechanical parameters and computational workflows. The statistical models reported herein carry predictive accuracy as well as chemical interpretability. Model validation was successfully accomplished via tetrazole test sets with parameters generated exclusively in silico. Mechanistic analysis of the statistical models indicated distinct divergent pathways of thermal and impact-initiated decomposition.

Sulfonyl-PYBOX Ligands Enable Kinetic Resolution of α-Tertiary Azides by CuAAC

We report the first highly selective kinetic resolution of racemic α-chiral azides via Cu-catalyzed azide-alkyne cycloaddition (CuAAC). Newly developed pyridine-bisoxazoline (PYBOX) ligands, bearing a C4 sulfonyl group, enable effective kinetic resolution of racemic azides derived from privileged scaffolds such as indanone, cyclopentenone, and oxindole, and their asymmetric CuAAC to afford α-tertiary 1,2,3-triazoles with high to excellent ee values. DFT calculations and control experiments reveal that the C4 sulfonyl group decreases the Lewis basicity of the ligand and increases the electrophilicity of the copper center for better recognition of azides, and functions as a shielding group to make the chiral pocket of the catalyst more effective.

Comprehensive Review on Natural Pharmacophore Tethered 1,2,3-Triazoles as Active Pharmaceuticals

The privileged 1,2,3-triazole scaffold is drawing researcher's attention due to its widespread applications in diverse fields such as drug discovery (eg. carboxyamidotriazole), organic synthesis (click-reaction template), polymeric materials (eg. triazolamer), supramolecular receptors (eg. triazolophane), fluorescent materials (eg. metal-organic frameworks) and agricultural sectors (eg. fungicides), etc. Various 1,2,3-triazole persuasion modules are also currently available in the market that have multiple assets such as active pharmaceuticals and agricultural purposes. Owed to the highly consistent and firmest synthesis approach i.e. click reaction of various azides and acetylene derivatives by copper (I)-catalyzed 1,3-dipolar cycloaddition (CuAAC), highly functionalized 1,2,3-triazoles are prepared in scalar yields for drug discovery. Given the importance of 1,2,3-triazole chemistry, the present review focuses specifically on the synthesis of structurally diverse 1,2,3-triazoles linked to natural pharmacophores and their biological importance. Furthermore, the dual/multi-pharmacophores assimilated 1,2,3-triazoles have listed interesting biological activities that could be valuable as future drug leads. In addition, this comprehensive review can serve as a template for the development of new diverse scaffolds that will ensure for newl therapeutic approaches for the existing myriad diseases and disorders.

Azide-modified Nucleosides as Versatile Tools for Bioorthogonal Labeling and Functionalization

Azide-modified nucleosides are important building blocks for RNA and DNA functionalization by click chemistry based on azide-alkyne cycloaddition. This has put demand on synthetic chemistry to develop approaches for the preparation of azide-modified nucleoside derivatives. We review here the available methods for the synthesis of various nucleosides decorated with azido groups at the sugar residue or nucleobase, their incorporation into oligonucleotides and cellular RNAs, and their application in azide-alkyne cycloadditions for labelling and functionalization.

Synthesis of Isocryptolepine-Triazole Adducts and Evaluation of Their Cytotoxic Activity

Eighteen hybrid compounds between 8-bromo-2-fluoro-isocryptolepine (4) and 1,2,3-triazole were synthesized via azide rearrangement-annulation reaction. Compound 4 underwent regioselective N-propargylation and click reaction to form 8-bromo-2-fluoro-isocryptolepine-triazole hybrids 11 which were evaluated for cytotoxic activity. Compound 11 c containing 1-anisyltriazole was the most effective in inhibiting HepG2, HuCCA-1 and A549 cell lines (IC₅₀ values of 1.65-3.07 μM) while compounds 11 a (1-phenyltriazole), 11 j (1-para-CF₃ -benzyltriazole) and 11 l (1-meta-Cl-benzyltriazole) were potent inhibitors of HuCCA-1, HepG2 and A549 cell lines, respectively. Moreover, 11 l showed the lowest cytotoxicity to normal human kidney cell line. Compounds 11 c and 11 l provided improvement of cytotoxic activity over 4. Compounds 4, 11 c and 11 l were selected to investigate their mechanisms of action. The results showed that 4 could induce G2/M cell cycle arrest and was involved in the upregulation of p53 and p21 proteins. However, the mechanisms of growth inhibition by 11 c and 11 l were associated with G0/G1 cell cycle arrest and mediated by induction of oxidative stress.

Solvent-Dependent Reactivity and Photochemistry of Dinuclear and Mononuclear Platinum(IV) Azido Triazaolato Complexes

Reaction between the platinum(IV) azido complex trans,trans,trans-[Pt(py)2(N3)2(OH)2] (1) and 1,4-diphenyl-2-butyne-1,4-dione 2 in MeCN produces the intermediate peroxide-bridged dimeric platinum(IV) azido triazolato species (5), which has been characterised by X-ray crystallography. However, if the reaction between 1 and 2 is conducted in MeOH it results in decomposition. Over time in MeCN, dimer (5) converts into mononuclear complexes trans,trans,trans-[Pt(py)2(N3)(triazole)(OH)2] (3 a/3 b), which are in dynamic exchange. If resuspended in protic solvents (MeOH,H2O), 3 a/3 b undergo a slow (22 d) irreversible rearrangement to a cyclised platinum(IV) species 4 which contains a formally N,O-chelated ligand. Conversion of 3 a/3 b to 4 in d 4-MeOH can be accelerated (384x) by irradiation with visible light, although continued irradiation also produces N3 . and OH. radicals, and the [4-N3]+ species can be readily detected by ESI-MS. Solvent choice significantly effects both the cycloaddition reaction between 1 and 2, and the stability of the resultant complexes.

Chemoenzymatic route to stereodefined 2-(azidophenyl)oxazolines for click chemistry

Aryl-substituted esters of a racemic diprotected 2-azido-1-alkanol were submitted to the Staudinger/aza-Wittig reaction in order to assess scope and establish conditions for their cyclization to the corresponding 2,4,5-trisubstituted oxazolines. Following the cyclization study, the (2R,3R)-antipode of the azidoalkanol was obtained in high ee by incubation of the corresponding racemic azidoacetate with pig liver esterase (PLE). The p-nitrobenzoate of the enantioenriched 2-azido-1-alcohol was cyclized by the Staudinger/aza-Wittig to give the corresponding (4R,5R)-disubstituted-2-(4-nitrophenyl) oxazoline. Selective reduction of the nitrophenyloxazoline to the corresponding aminophenyloxazoline using aluminum amalgam followed by direct azidation of the 2-(4-aminophenyl) moiety provided the corresponding (4R,5R)-2-(4-azidophenyl) oxazoline derivative. The azidophenyl oxazoline was reacted with a proven click partner 4-ethynylfluorobenzene under copper/sodium ascorbate mediation to provide the click triazole product in high yield.

Applicability of aluminum amalgam to the reduction of arylnitro groups

An array of arylnitro compounds with various functionality were treated with freshly-prepared aluminum amalgam in THF/water solution and resulted in the corresponding arylamines. The Al(Hg)-mediated reductions are relatively rapid with consumption of the amalgam and disappearance of starting material occurring over 20-30 minutes. The workup of the reductions involves only removal of the insoluble by-products by filtration followed by concentration. Only in some cases is chromatography required to secure the pure product. The desired arylamines are furnished in quantities of 25-100 mg, which in some cases, could be taken on to the next reaction without further purification. Reductions of 4-nitrobenzyl derivatives of carbohydrates or nucleosides were selective in affording the corresponding 4-aminobenzyl products. To show applicability in click chemistry, selected aminobenzyl products are directly azidated to yield products that were then used in click reactions to afford the corresponding 1,2,3-triazoles.

Fast phosphine-activated control of protein function using unnatural lysine analogues

Effective, general methods for conditionally activating proteins in their native biological environments are highly useful for biological studies. Since phosphines and azides are not found in pro- and eukaryotic cells, the Staudinger reduction can function as an excellent small molecule-controlled switch for protein activation. This methodology involves site-specifically incorporating azidobenyl-lysine analogues into proteins in live cells. When placed at a crucial position, these unnatural side chains block protein function until a phosphine trigger is added. We discuss methods for expressing caged proteins in bacterial and mammalian cells in high yields, and activating the proteins with an optimized phosphine trigger. We also discuss important considerations for safe and effective synthesis of these molecules. This methodology was used to translocate proteins to the nucleus and to turn-on a protein post-translational modification (SUMOylation) in living cells.

Part 1-Azides, Porphyrins and Corroles

Azides and porphyrinoids (such as porphyrin and corrole macrocycles) can give rise to new derivatives with significant biological properties and as new materials' components. Significant synthetic approaches have been studied. A wide range of products (e.g., microporous organic networks, rotaxane and dendritic motifs, dendrimers as liquid crystals, as blood substitutes for transfusions and many others) can now be available and used for several medicinal and industrial purposes.

Theoretical study of the 1,3-DC reaction between fluorinated alkynes and azides: Reactivity indices, transition structures, IGM and ELF analysis

DFT/B3LYP/6-31 + g(d,p) calculations were performed and reactivity indices, transition structures theory were applied to elucidate the molecular mechanism of the reaction between fluorinated alkynes and different azides. The process of cycloaddition operates through a one-step mechanism and an asynchronous transition states. Examination of the energy profile in the gas phase show two possible 1,4 and 1,5 addition channels for amid, the former is preferred. Furthermore, the Parr functions have used to elucidate the reaction's regioselectivity. It was noted that the addition of solvent (DMSO) does not affect the regioselectivity of the reactions. Analysis of charge transfer in the transition structures shows a moderate polar character for the majority of the studied reactions. Moreover, the independent gradient model based on promolecular density (IGM) has been used to evaluate the asynchronicity of the formation of the two new sigma bonds. Finally, the ELF calculation has been performed to clearly describe the formation of the previous bonds along the IRC path.

On the Winstein rearrangement: equilibrium and mechanism

Allylic azides are underutilized in organic synthesis when compared to other organic azides or other allylic functionality. This is likely because allylic azides rearrange at room temperature, resulting in a potentially complex mixture of azides. This rearrangement has been termed the Winstein rearrangement. Understanding the mechanism and basic principles governing the allylic azide equilibrium may aid in developing applications for these molecules based on either alkene or azide functionalization. Presented herein is a compilation of the key observations regarding the nature of the allylic azide rearrangement. Mechanistic considerations are explicitly addressed with key examples from the literature.

Convenient Entry to 18F-Labeled Amines through the Staudinger Reduction

Fluorine-18 possesses outstanding decay characteristics for positron emission tomography (PET) imaging. Therefore, it is ideally suited for clinical applications. As such, improved strategies to incorporate fluorine-18 into bioactive molecules are of utmost importance. Indirect 18F-labeling with amino-functionalized synthons is a convenient and versatile approach to synthesize a broad variety of PET tracers. Herein, we report a method to convert 18F-labeled azides to primary amines by means of the Staudinger reduction. Aliphatic and aromatic 18F-labeled azides were converted into the corresponding amines with high conversion yields. The method was easily automated. From a broader perspective, the applied strategy results in two useful synthons from a single precursor and thus increases the flexibility to label diverse chemical scaffolds with minimal synthetic effort.

Synthesis of camphecene derivatives using click chemistry methodology and study of their antiviral activity

A series of seventeen tetrazole derivatives of 1,7,7-trimethyl-[2.2.1]bicycloheptane were synthesized using click chemistry methodology and characterized by spectral data. Studies of cytotoxicity and in vitro antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells of the compounds obtained were performed. The structure-activity relationship analysis suggests that to possess virus-inhibiting activity, the compounds of this group should bear oxygen atom with a short linker (C2-C4), either as a hydroxyl group (18, 19, 29), keto-group (21) or as a part of a heterocycle (24). These compounds demonstrated low cytotoxicity along with high anti-viral activity.

Metal-Catalysed Azidation of Organic Molecules

The azide moiety is a desirable functionality in organic molecules, useful in a variety of transformations such as olefin aziridination, C-H bond amination, isocyanate synthesis, the Staudinger reaction and the formation of azo compounds. To harness the versatility of the azide functionality fully it is important that these compounds be easy to prepare, in a clean and cost-effective manner. Conventional (non-catalysed) methods to synthesise azides generally require quite harsh reaction conditions that are often not tolerant of functional groups. In the last decade, several metal-catalysed azidations have been developed in attempts to circumvent this problem. These methods are generally faster, cleaner and more functional-group-tolerant than conventional methods to prepare azides, and can sometimes even be conveniently combined with one-pot follow-up transformations of the installed azide moiety. This review highlights metal-catalysed approaches to azide synthesis, with a focus on the substrate scopes and mechanisms, as well as on advantages and disadvantages of the methods. Overall, metal-catalysed azidation reactions provide shorter routes to a variety of potentially useful organic molecules containing the azide moiety.

Azidoimidazolinium Salts: Safe and Efficient Diazo-transfer Reagents and Unique Azido-donors

2-Azido-1,3-dimethylimidazolinium chloride (ADMC) and its corresponding hexafluorophosphate (ADMP) were found to be efficient diazo-transfer reagents to various organic compounds. ADMC was prepared by the reaction of 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and sodium azide. ADMP was isolated as a crystal having good thermal stability and low explosibility. ADMC and ADMP reacted with 1,3-dicarbonyl compounds under mild basic conditions to give 2-diazo-1,3-dicarbonyl compounds in high yields, which were easily isolated in virtue of the high water solubility of the by-products. ADMP showed high diazo-transfer ability to primary amines even in the absence of metal salt such as Cu(II). Using this diazotization approach, various alkyl/aryl azides were directly obtained from their corresponding primary amines in high yields. Furthermore, naphthols reacted with ADMC to give the corresponding diazonaphthoquinones in good to high yields. In addition, 2-azido-1,3-dimethylimidazolinium salts were employed as azide-transfer and migratory amidation reagents.

1,2,3-Triazole-based inhibitors of Porphyromonas gingivalis adherence to oral streptococci and biofilm formation

The development and use of small-molecule inhibitors of the adherence of Porphyromonas gingivalis to oral streptococci represents a potential therapy for the treatment of periodontal disease as these organisms work in tandem to colonize the oral cavity. Earlier work from these laboratories demonstrated that a small synthetic peptide was an effective inhibitor of the interaction between P. gingivalis and Streptococcus gordonii and that a small-molecule peptidomimetic would provide a more stable, less expensive and more effective inhibitor. An array of 2-(azidomethyl)- and 2-(azidophenyl)-4,5-diaryloxazoles having a full range of hydrophobic groups were prepared and reacted with substituted arylacetylenes to afford the corresponding 'click' products. The title compounds were evaluated for their ability to inhibit P. gingivalis' adherence to oral streptococci and several were found to be inhibitory in the range of (IC₅₀) 5.3-67μM.

Synthesis of new saccharide azacrown cryptands

New cryptands including bis-azacrown and saccharidic moieties in their structure were prepared in several steps by applying Staudinger-aza-Wittig reaction (SAW). Syntheses have been started from cheap, easily available commercial compounds such as D-glucose, D-cellobiose and D-lactose subsequently transformed into their derivatives in fairly good yields (60-65%) and suitable to give desired final cryptands by direct SAW coupling reactions.

Oxazoles for click chemistry II: synthesis of extended heterocyclic scaffolds

New routes to 2, 4, 5-trisubstituted oxazoles were established whereby the substitution pattern was established by the structure of the starting nonsymmetrical acyloins. 2-Chloromethyl-4, 5-disubstituted oxazoles were prepared by refinements of an earlier described process whereby chloroacetyl esters of symmetrical and non-symmetrical acyloins were cyclized using an ammonium acetate/acetic acid protocol. After substitution is effected, the azide moiety is then installed by substitution under mild conditions. While dibrominated and iodinated phenyloxazoles are required for further synthetic elaboration, the cyclization reaction was found to be very sensitive to the relative positions of the halogens in the starting materials.

Synthesis of 1H-1,2,3-triazole linked aryl(arylamidomethyl) - dihydrofurocoumarin hybrids and analysis of their cytotoxicity

A series of 2-(4-R-triazolyl)substituted 3-oxo-2,3-dihydrofurocoumarins have been synthesized by a regioselective cycloaddition of 2-azidooreoselone 1 or 2-azido-9-[(4-methylpiperazin-1-yl)methyl]oreoselone 2 with various alkynes in the presence of Cu(II)/ascorbate in water/methylene chloride reaction medium. The structure of 2-azidooreoselone was established by X-ray structure analysis. The cytotoxicity of 2-substituted dihydrofurocoumarins was determined against three cancer cell lines (CEM-13, MT-4, U-937) using the conventional MTT assays. Among the tested molecules, most of the analogs displayed better cytotoxic activity then the parent natural furocoumarin peucedanin 3. The activity and selectivity to the cell line increased even further in the series of 2-(4-{2,3-dihydrobenzo[b][1,4]dioxine}triazolyl)-3-oxo-2,3-dihydrofurocoumarins and 2-(4-aryltriazolyl)-3-oxo-2,3-dihydrofurocoumarins having the (4-methylpiperazin-1-ylmethyl) substituent in the 9-th position. The most active compound 20 contain the 4-hydroxy-3-methoxybenzamidomethyl substituent in the 4-th position at the triazole ring of 2-(triazol-1-yl)dihydrofurocoumarins. The obtained 2-triazolyl substituted dihydrofurocoumarins were studied as inhibitors of phosphodiesterase (PDE-4B) using docking experiments. As a result of virtual screening 3 compounds are selected based on minimum binding energy. The interactions of the most active compound and amino acid residues in the binding site were studied.

Influence of azide incorporation on binding affinity by small papain inhibitors

In order to develop affinity-based biosensor platforms, appropriate ligands with a functional handle for immobilization onto a biosensor surface are required. To this end, a library of papain inhibitors was designed and synthesized, containing different azide linkers for subsequent immobilization by 'click' chemistry, in this particular case by copper-free, strain-promoted azide-alkyne cycloaddition (SPAAC). Furthermore, a molecular docking study was performed to obtain a better insight as to at which position such azide handles could be tolerated without affecting binding affinity. Although the azide moiety is small, in some cases its introduction strongly influenced the binding affinity. For one class of inhibitors a swapped binding mode was proposed to explain the results. In addition, a specific site for linker introduction was identified, which did not significantly affect the binding affinity.

Preparation of azidoaryl- and azidoalkyloxazoles for click chemistry

A series of azidoaryl- and azidoalkyl(diphenyl)oxazole scaffolds were warranted for biofilm inhibition studies. Cyclization of azidoaryl- or azidoalkyl esters of benzoin with ammonium acetate in acetic acid gives 2-azidoaryl- or 2-azidoalkyl-4,5-diphenyloxazoles. The azidoaryl esters are prepared from the corresponding azidocarboxylic acids/acid chlorides while the azidoalkyl esters are prepared from the corresponding haloalkyl esters.

Transition Metal Complexes with Organoazide Ligands: Synthesis, Structural Chemistry, and Reactivity

A drastically enhanced stability is observed for organoazides (RN₃ ) in the presence of Cu²⁺ or Pd²⁺ when the azido group is included in a ligand system chelating the transition metal ions. X-ray structure analysis of such complexes (the structure of a cyclohexaneazide palladium complex is depicted) confirms that the alkylated nitrogen atom of the N₃ moiety is coordinated to the transition metal center.