Microwave-assisted Solid-phase Synthesis Research Articles

Microwave-assisted solid-phase synthesis of hydantoin derivatives

A microwave-assisted synthesis of 3,5- and 1,3,5-substituted hydantoins starting from various resins for solid-phase combinatorial chemistry has been developed. The hydantoins were synthesized from pre-loaded resins with amino acids via treatment with isocyanate or phenylisocyanate and subsequent intramolecular cyclization. Both reactions were performed under microwave irradiation. We studied the cyclative cleavage leading to hydantoin compounds dependent on the nature of the amino acid and the nucleofuge properties of the resin.

Microwave-assisted solid phase synthesis of Imatinib, a blockbuster anticancer drug

An expeditious, high yield and convenient synthesis of Imatinib was carried out on an aldehydic, super acid-sensitive resin, through an efficient, microwave-assisted synthetic protocol. The high versatility of the reaction scheme may enable the straightforward preparation of libraries of potential protein kinase inhibitors endowed with large molecular diversity.

A Convenient Microwave-Enhanced Solid-Phase Synthesis of Difficult Peptide Sequences: Case Study of Gramicidin A and CSF114(Glc)

Taking into account that microwave technology applied to SPPS is proposed as a valid support to the enhancement of efficiency of coupling reactions in short times, we compared the efficacy of a new automatic monomode microwave instrument versus a traditional automatic peptide synthesizer in the synthesis of different difficult peptide sequences. We verified that microwave-assisted solid phase synthesis is convenient, in terms of yield, purity, and time consumed to prepare two peptides which were previously shown to be difficult to obtain by conventional strategy, i.e., the antibiotic Gramicidin A and a glycopeptide.

Microwave-assisted solid-phase synthesis of pseudopeptides containing reduced amide bond

Procedures were developed for reducing the reaction time and improving the yield of reductive alkylation in solid phase pseudopeptide synthesis by utilizing microwave irradiation. We chose dipeptides containing the reduced amide bond ψ[CH 2NH] as a model system and optimized the microwave assisted reductive alkylation reaction in solid phase pseudopeptide synthesis using Fmoc chemistry. Under the optimized condition, the reductive alkylation reaction used for incorporating the reduced amide bond into the dipeptides was completed in only 8.5 min, whereas the normal reductive alkylation reaction required a total of 300 min. The purity and yield of the various dipeptides containing the reduced amide bond synthesized in this way are better than those achieved using the reductive alkylation method without microwave irradiation. We chose α helical peptides, which are known as a difficult sequence to synthesize, and incorporated the reduced amide bond by the microwave-assisted reductive alkylation reaction. We successfully synthesized pseudopeptides containing the reduced amide bond as a major product by using the novel microwave-assisted method, whereas the same products were obtained as a minor product when using the reductive alkylation method without microwave irradiation.

Construction and Structural Characterization of Versatile Lactosaminoglycan-Related Compound Library for the Synthesis of Complex Glycopeptides and Glycosphingolipids

We have established a facile and efficient protocol for the preparative-scale synthesis of various compound libraries related to lactosaminoglycans: cell surface oligosaccharides composed of N-acetyllactosamine as a repeating disaccharide unit, based on chemical and enzymatic approaches. Substrate specificity and feasibility of a bacterial glycosyltransferase, Neisseria meningitidis beta1,3-N-acetylglucosaminyltransferase (LgtA), were investigated in order to synthesize various key intermediates suited for the construction of mammalian O-glycopeptides and glycosphingolipids containing poly-N-acetyllactosamine structures. Recombinant LgtA exhibited the highest glycosyltransferase activity with strongly basic conditions (pH = 10, glycine-NaOH buffer) and a broad range of optimal temperatures from 20 to 30 degrees C. Interestingly, it was found that LgtA discriminates L-serine and L-threonine and functions both as a core-1 beta1,3-N-acetylglucosaminyltransferase and core-2 beta1,3-N-acetylglucosaminyltransferase toward Fmoc-Ser derivatives, while LgtA showed only core-2 beta1,3-N-acetylglucosaminyltransferase activity in the presence of Fmoc-Thr derivatives. Combined use of LgtA with human beta1,4-galactosyltransferase allowed for controlled sugar extension reactions from synthetic sugar amino acids and gave synthetic lactosaminoglycans, such as a decasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (6), and a dodecasaccharide derivative, Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 3)Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Ser-OH (9). A partially protected pentasaccharide intermediate, GlcNAcbeta(1 --> 3)Galbeta(1 --> 4)GlcNAcbeta(1 --> 6)[Galbeta(1 --> 3)]GalNAcalpha1 --> Fmoc-Thr-OH (11), was applied for the microwave-assisted solid-phase synthesis of a MUC1-related glycopeptide 19 (MW = 2610.1). The findings suggest that this sugar extension strategy can be employed for the modification of lactosyl ceramide mimetic polymers to afford convenient precursors for the synthesis of various glycosphingolipids.

Improved Synthesis of Cationic Pyridinium‐Substituted Indolizines.

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Optimized Synthesis of Hydrogen-Bond Surrogate Helices: Surprising Effects of Microwave Heating on the Activity of Grubbs Catalysts

This manuscript discusses microwave-assisted solid-phase synthesis of hydrogen-bond surrogate based alpha-helices and analogues by ring-closing metathesis (RCM). Microwave-mediated RCM allows access to a greater variety of amino acid residues in the macrocycles in shorter reaction times and higher yields compared to conventional heating. Surprisingly, we discovered that the Grubbs II catalyst is highly active under the influence of microwaves but catalytically dead under oil-bath conditions for the metathesis of these peptide bisolefins. [reaction: see text]

Microwave-Assisted Solid-Phase Synthesis of 2,5-Diketopiperazines: Solvent and Resin Dependence

Solid-phase synthesis of diketopiperazines (DKPs) was preformed using various combinations of resins (polystyrene, TentaGel, ArgoGel, and PEGA) and solvents (toluene, tert-butyl alcohol, water, and toluene/2-butanol (1:4, v/v). The DKPs were synthesized from solid-phase bound dipeptides via intramolecular aminolysis. Both thermal and microwave-assisted solid-phase synthesis of DKPs gave high yields of products independently of resin and organic solvent used; however, only the PEGA resin resulted in high yields of DKPs in water independent of heating method. The short reaction times, high yields, and the possibility to run reactions in water when an appropriate resin is used makes the microwave-assisted solid-phase synthesis the method of choice. The method should be suitable for solid-phase synthesis of diketopiperazine-based libraries.

Improved Synthesis of Cationic Pyridinium-Substituted Indolizines

This paper describes the optimization of the synthesis of pyridinium-substituted indolizines. Different conditions, solution and solid-phase synthesis were used for the key step of [3+2] cycloaddition. The best yields and shortest reaction time were obtained by microwave-assisted solid-phase synthesis.

Construction of Highly Glycosylated Mucin-Type Glycopeptides Based on Microwave-Assisted Solid-Phase Syntheses and Enzymatic Modifications

A MUC1-related glycopeptide having five core-2 hexasaccharide branches (C330H527N46O207, MW = 8450.9) was synthesized by a new strategy using a combination of microwave-assisted solid-phase synthesis (MA-SPGS) and enzymatic sugar elongation. Synthesis of a key glycopeptide intermediate was best achieved in a combination of PEGA [poly(ethylene glycol)-poly-(N,N-dimethylacrylamide) copolymer] resin and MA-SPGS using glycosylated amino acid building blocks with high speed and high purity. Deprotection of the glycopeptide intermediate and subsequent glycosyltransferase-catalyzed sugar elongations were performed for generation of the additional diversities with the sugar moieties of glycopeptides using beta1,4-galactosyltransferase (beta1,4-GalT) and two kinds of alpha2,3-sialyltransferases [ST3Gal III; alpha2,3-(N)-SiaT and ST3Gal II; alpha2,3-(O)-SiaT]. These reactions proceeded successfully in the presence of 0.2% Triton X-100 to convert the chemically synthesized trisaccharide glycans to disialylated hexasaccharide.

Microwave-assisted solid-phase oligosaccharides synthesis reaction and scavenging activity of synthetic product to free radical

Using phosphoric acid as the catalyst and glucose as substrate, microwave-assisted solid-phase bioactive oligosaccharide synthesis was studied. The optimum reaction conditions were that microwave power output of 800 W, microwave irradiation time 10 min, adding 30% water to initiate reaction, adding 10% heteropoly acid A as the catalyst. The yield ratio of product was 76.56%. The product was characterized with HPLC. The component and proportion of synthetic oligosaccharides included glucose 49.25%, maltose 10.10%, isomaltose 21.78%, maltotriose 2.15%, panose 10.08%, isomaltotriose 5.16%, tetrasaccharide and pentasaccharides 1.61%. Free radical scavenging test demonstrated that synthetic oligosaccharides possessed property of scavenging oxygen and hydroxyl free radical.

Rapid solid-phase peptide synthesis using thermal and controlled microwave irradiation

A rapid and efficient microwave-assisted solid-phase synthesis method is described for the preparation of the nonapeptide WDTVRISFK, using conventional Fmoc/Bu(t) orthogonal protection strategy. The synthesis protocol is based on the use of cycles of pulsed microwave irradiation with intermittent cooling of the reaction during the removal of the Fmoc protecting group and during the coupling. The desired nonapeptide was obtained in highest yield and purity by employing MicroKan technology. The chemical reactions were carried out in a single-mode microwave reactor, equipped with a fiber-optic probe to monitor the reaction temperature continuously.

Annulation of Primary Amines to Piperazines and Diazaspirocycles Utilizing α-Methyl Benzyl Resin

The microwave-assisted solid-phase synthesis of piperazines, 3,9-diazaspiro[5.5]undecanes and 2,9-diazaspiro[5.5]undecanes is reported. The synthesis relies on the direct annulation of primary amines with resin-bound bismesylates. Critical to the success of this chemistry was the development of alpha-methyl benzyl carbamate resin linker. This resin permits the cleavage of the heterocycles under mildly acidic conditions, free of contaminating linker-derived N-alkylated byproducts.

Synthesis of 2,4-disubstituted thiazole combinatorial unit on solid-phase: microwave assisted conversion of alcohol to amine monitored by FT-IR

Microwave-assisted solid-phase synthesis of the 2,4-disubstituted thiazole 3 on Merrifield Resin is described. The hydroxyl moiety was converted to amine in five steps - including coupling and cleavage - within a total reaction time of 2 hours and 26% overall yield. The entire solid-phase synthesis was efficiently monitored by FT-IR/KBr pellets and allows potential use in combinatorial chemistry.

Solid Phase Synthesis of Aminochalcones

A microwave-assisted solid phase synthesis of aminochalcones via the Claisen–Schmidt condensation reaction between resin-bound p-aminoacetophenone and aromatic aldehydes was described.

Microwave-assisted solid-phase synthesis (MASS): parallel and combinatorial chemical library synthesis.

The use of microwave technology in solid-phase organic synthesis has attracted much attention in recent years. The combination of solid support, either as a medium for chemical synthesis or as a carrier for organic reagents, with microwave heating offers several advantages over conventional techniques. Rapid and elevated heating of reaction mixtures can induce the completion of chemical transformations in minutes while several hours or days may be required for the same chemistry under conventional conditions. With decreased time of exposure to high temperatures and lessened thermal degradation, microwave accelerated chemistries often deliver products of higher purity when compared to conventional heating techniques. Several chemical syntheses on solid-phase employing microwave irradiation have been reported in the literature. The reagents, solvents, and equipment selected for microwave-mediated synthesis are important contributors to the success of the chemical transformation. Owing to the timesavings in performing chemical synthesis under microwave irradiation, the technique has become an emerging partner in solid-phase organic synthesis.

Microwave-assisted solid-phase synthesis of phthalimides.

[reaction: see text] A traceless solid-phase synthesis of substituted phthalimides is proposed. The target compounds are obtained within minutes by a microwave-assisted cyclative cleavage in good yields and excellent purities.

Microwave-assisted solid-phase synthesis of peptoids.

Microwave irradiation reduces the reaction time for the solid-phase synthesis of peptoids. Under these conditions, coupling of each residue requires only 1 min. The purity and yields of peptoids synthesized in this way are as good as or better than those achieved using standard methods. [reaction: see text]

Microwave-assisted solid-phase synthesis (MASS) of 2,6,9-trisubstituted purines

In an attempt to discover a high-throughput method for the synthesis of 2,6,9-trisubstituted purines, it was found that microwave irradiation was beneficial in accelerating the nucleophilic displacement of halogens by amines at the C-2 position of the purine nucleus. A method for microwave-assisted solid-phase synthesis (MASS) of 2,6,9-trisubstituted purines is presented.

ChemInform Abstract: Microwave-Assisted Solid-Phase Synthesis of Cephalosporin Derivatives with Antibacterial Activity.

The reaction of heterocyclic acids with 7-amino-cephalosporanic acid adsorbed on basic alumina under microwave irradiation afforded the N-acylated cephalosporin analogues in satisfactory yield. All compounds were tested for their antibacterial activity; some of them showed significant antibacterial properties. Cefotaxime and cephalothin were used as reference drugs.