Microwave‐Assisted Solid‐Phase Synthesis of Antifreeze Glycopeptides

Microwave‐assisted solid‐phase synthesis allows for the rapid and large‐scale preparation and structure–activity characterization of tandem repeating glycopeptides, namely monodispersed synthetic antifreeze glycopeptides (syAFGPs, H‐[Ala‐Thr(Galβ1,3GalNAcα1→)‐Ala]_n‐OH, n=2–6). By employing novel AFGP analogues, we have demonstrated that of the monodispersed syAFGP_n (n=2–6, degree of polymerization, DP=2–6, M_w=1257–3690 Da), syAFGP₅ (DP=5, M_w=3082 Da) and syAFGP₆ (DP=6, M_w=3690 Da) exhibit the ability to form typical hexagonal bipyramidal ice crystals and satisfactory thermal hysteresis activity. Structural characterization by NMR and CD spectroscopy revealed that syAFGP₆ forms a typical poly‐L ‐proline type II helix‐like structure in aqueous solution whereas enzymatic modification by sialic acid of the residues at the C‐3 positions of the nonreducing Gal residues disturbs this conformation and eliminates the antifreeze activity.     

Microwave‐Assisted One‐Pot Synthesis of Substituted 3‐Bromoimidazo[1,2‐a]pyridines and Imidazoheterocycles

Herein, an efficient, one‐pot microwave‐assisted synthesis of a diverse set of 3‐bromoimidazo[1,2‐a]pyridines is being reported with good yields (40–85%). The method involves electrophilic aromatic bromination using bromodimethylsulfonium ion generated in situ via oxidation of HBr salt by DMSO. This methodology was also applied to the synthesis of related imidazoheterocycles. Copyright © 2014 HeteroCorporation     

Microwave‐Assisted Palladium‐Catalyzed Direct Arylation of 1,4‐Disubstituted 1,2,3‐Triazoles with Aryl Chlorides

Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively.     

Microwave‐Assisted Expedite Synthesis of 2‐Phenylimidazo[1,2‐a]pyridylquinoxalin‐2(1H)‐ones

An efficient methodology has been developed for the synthesis of quinoxalin‐2(1H)‐one derivatives of 2‐phenylimidazo[1,2‐a]pyridines by microwave‐irradiated Hinsberg heterocyclization between 2‐phenylimidazo[1,2‐a]pyridine‐3‐glyoxalates and o‐phenylenediamine using either montmorillonite K‐10 or Yb(OTf)₃ as catalysts. Montmorillonite K‐10 was proven to be an efficient catalyst for the heterocyclization reaction between sterically hindered glyoxalate and o‐phenylenediamine only under microwave conditions. The use of Yb(OTf)₃/tetrahydrofuran was also found to be an effective catalyst for the above chemical transformation among a series of Lewis acids screened under microwave conditions; however, comparatively lesser yields were obtained as compared with the use of montmorillonite K‐10.     

Microwave‐Assisted Synthesis of Spiro‐Isoxazolidines

Solvent‐free synthesis of spiro‐isoxazolidines (exclusively endo‐diastereoisomers) through [3 + 2] cycloaddition of N‐cyclohexylidene N‐phenyl nitrones with cyclic dipolarophiles under microwave irradiation is described.     

Microwave‐Assisted Synthesis of Associative Hydrogels

In the present paper, the microwave (MW)‐assisted synthesis of hydrogel forming polymers based on poly(acrylic acid) ( 1 ) is described. The polymer analogous condensation reaction between adamantyl moieties bearing free amino groups and poly(acrylic acid) ( 1 ) was carried out simply by mixing both components and subsequent use of MW protocol. The mixture was irradiated for 20 min without the addition of solvents or coupling agents. Aqueous solutions of the sodium salts of the obtained hydrophobically modified poly(acrylic acid)s showed a very high viscosity due to the intermolecular association of the hydrophobic side chains and the resulting formation of physical networks. By the addition of randomly methylated β‐cyclodextrin (RAMEB), the rheology of these systems could be influenced significantly.

     

Reactions of Polymer‐Supported α‐Selenoaldehydes with Grignard Regents. A Facile Solid‐Phase Stereoselective Synthesis of (E)‐1,2‐Disubstituted Ethenes

Polymer‐supported α‐selenoaldehydes easily obtained by reaction of polymer‐supported 4‐(phenylseleno)morpholine with aldehydes react with Grignard reagents to form polymer‐supported β‐hydroxyalkyl selenides, which were treated with thionyl chloride/triethylamine leading to (E)‐1,2‐disubstituted ethenes in good yields.     

Facile Microwave‐Assisted Solid‐Phase Synthesis of Highly Fluorescent Nitrogen–Sulfur‐Codoped Carbon Quantum Dots for Cellular Imaging Applications

Carbon quantum dots (CQDs) have recently attracted significant attention for both their fundamental science and technological applications as a new class of fluorescent zero‐dimensional nanomaterials with a size below 10 nm. However, the reported methods of synthesis were generally less suitable for the large‐scale production of the CQDs with high‐fluorescent quantum yield (QY). In the paper, a novel one‐pot microwave‐assisted drying synthesis approach was presented to prepare CQDs with high QY of 61.3 % for the first time. The production yield of CQDs was 35±3 % in weight. The as‐prepared CQDs were characterized by various techniques such as TEM, AFM, XRD, XPS, FTIR spectroscopy, UV/Vis absorption spectroscopy, and fluorescence spectroscopy. The results showed that the high QY of CQDs was largely attributed to the dual doping of nitrogen and sulphur into CQDs. Such CQDs were then used as live‐cell imaging reagents due to their high QY, good water dispersibility, fine biocompatibility, high photostability, and low cytotoxicity.     

Synthesis of 1,2‐Disubstituted Carbocyclic Nucleoside Analogues of Cytidine

The synthesis of new 1,2‐disubstituted, five‐ or six‐ring‐carbocyclic nucleoside analogues of cytidine, compounds 1 and 2a – d , are described. These compounds were obtained by aminolysis, starting from the corresponding uracil derivative, via nucleophilic displacement of a triazolyl (Scheme 1) or a (2,4,6‐triisopropylphenyl)sulfonyl (TPS) group (Scheme 2) at 4‐position of the pyrimidine ring.     

Efficient Solid‐Phase Synthesis of pppRNA by Using Product‐Specific Labeling

A novel solid‐phase synthesis and purification strategy for 5′‐triphosphate oligonucleotides by using lipophilic tagging of the triphosphate moiety is reported. This is based on triphosphate synthesis with 5′‐O‐cyclotriphosphate intermediates, whereby a lipophilic tag, such as decylamine, is introduced during the ring‐opening reaction to give a linear gamma‐phosphate‐tagged species. This method enables the highly efficient synthesis of 5′‐triphosphorylated RNA derivatives and their gamma‐phosphate‐substituted analogues and will especially facilitate the advancement of therapeutic approaches that make use of 5′‐triphosphate oligonucleotides as potent activators of the cytosolic immune sensor RIG‐I.     

Conventional and Microwave‐Assisted Synthesis of Benzimidazole Derivatives and Their In Vitro Inhibition of Human Cyclooxygenase

A large series of 1,2‐diaryl‐benzimidazole and 2‐aryl‐1H‐benzimidazole derivatives were synthesized with slight differences using both microwave irradiation and conventional heating methods. Usually higher yields and time reactions reduction were obtained with the former method. All compounds were assayed for their in vitro ability to inhibit human cyclooxygenases, and most of them showed an encouraging inhibitory activity and isoform selectivity in the micromolar range.     

Microwave‐Assisted Solvent‐Free Synthesis of Ipsapirone

The currently applied synthetic methods of serotonin receptor ligands belonging to the group of long‐chain arylpiperazines, including ipsapirone, require the use of toxic solvents and comprise numerous synthetic steps. Moreover, the reaction yield does not exceed 60% in the majority of cases. These factors lead to an increased energy consumption and negatively impact the environment. This paper describes a more environmentally friendly method of ipsapirone synthesis that we decided to use. Ipsapirone was obtained in two different methods. The first method involved N‐alkylation of bromobutyl saccharin with 1‐(2‐pyrimidyl)piperazine dihydrochloride, while the second was a one‐pot method. Neither of these requires the use of toxic and expensive solvents. A shortened synthesis time, not exceeding 10 min due to the use of microwave radiation, is also another advantage of these methods. The yield of the final product, ipsapirone, was 85% and 67% in the first and the second method, respectively. We also attempted to obtain ipsapirone using saccharin and arylpiperazine salt (method III) as starting materials, but to no avail in the tested conditions. As described herein, the green chemistry method for ipsapirone synthesis is rapid, cost‐effective, and environment friendly.     

Solid‐Phase Organic Synthesis of 1,4‐N‐Vinyl‐ and 1,4‐N‐Allyl‐Triazoles with the Sulfonate Linker

Polymer‐supported 2‐azidoethyl sulfonate and 3‐azidopropyl sulfonate reagents have been developed and applied to the solid‐phase organic synthesis of 1‐vinyl‐ and 1‐allyl‐1,2,3‐triazoles, respectively, by CuI‐mediated azide‐alkyne cycloadditions and subsequent cleavage from the polymer support through elimination reaction promoted by DBU. The advantages of this new synthetic method include simple operation and high yield of the products, as well as good stability of the reagents.