A convenient procedure for the solid-phase synthesis of hydroxamic acids on PEGA resins

An efficient method for the solid-phase synthesis of hydroxamic acids is described. The method comprises the nucleophilic displacement of esters immobilized on PEGA resins with hydroxylamine/sodium hydroxide in isopropanol. The hydroxyaminolysis protocol is compatible with a broad range of PEGA-supported peptide and peptidomimetic esters. The methodology was found to be compatible with two new strategies for the synthesis of solid-supported lactams and diketopiperazines, respectively, both relying on the high inter- and intramolecular reactivity of cyclic N-acyliminium ions with electron-rich aromatics and heteroaromatics, ultimately affording hydroxamic acid derivatives in high purities.     

A new method for cleavage of silicon-carbon linkers on glass plate supports with applications to solid-phase syntheses on silica resins

We describe herein a novel and facile method for the cleavage of a silicon-based linker on solid-phase supports such as glass plates or silica resin. The linker was efficiently cleaved by oxidation of the silicon-carbon bond (Tamao-Kumada oxidation) to release the functionalized molecule.     

Traceless solid-phase synthesis of 2-amino-5-alkylidene-thiazol-4-ones

2-Amino-5-alkylidene-thiazol-4-ones bearing two diversity points are prepared by a solid-phase strategy exploiting rhodanine as the starting material. Rhodanine is first loaded on bromo-Wang resin, subjected to Knovenagel condensation with aldehydes, and cleaved off the resin in a traceless manner by means of an amine.     

General methodology for solid-phase synthesis of N-alkyl hydroxamic acids

Polymer-supported N-benzyloxy-2-nitrobenzenesulfonamides 1 were N-alkylated using three different routes: via Fukuyama reaction with alcohols, by N-alkylation with alkylbromides, and by Michael addition reaction with α,β-unsaturated carbonyl compounds. The N-alkylated products prepared on the linker 1b were obtained in excellent purity and yield. The 2-nitrobenzenesulfonyl (Nos) group was cleaved under mild conditions to yield polymer-supported N-alkylated benzyloxyamines. Acylation by carboxylic acids and cleavage with TFA yielded N-alkyl hydroxamic acids.     

Selective synthesis of dehydroamino acids from threonines

Dehydropeptides containing dehydroamino acid (ΔAA) are frequently found in natural resources with important biological activity. Herein, we report the selective synthesis of Z- and E-ΔAbu from l- and l-allo-threonine as starting materials through selenation and oxidative elimination. The detailed reaction mechanism of phosphine-assisted selenoether formation is also discussed.     

Reversible 5′-end biotinylation and affinity purification of synthetic RNA

A reversible biotinylation phosphoramidite was synthesized and incorporated onto the 5′-end of an oligoribonucleotide on a solid phase synthesizer. After cleavage and deprotection, the crude synthetic oligomer mixture was incubated with NeutrAvidin^® coated microspheres, and the failure sequences removed by washing with a buffer followed by treating the microspheres with tetrabutylammonium fluoride to give a high quality unmodified full-length oligoribonucleotide.     

Dual linker with a reference cleavage site for information rich analysis of polymer-supported transformations

Two dual linker systems with specific reference cleavage sites were designed and synthesized to accelerate and simplify development and optimization of reaction conditions for solid-phase synthesis. The dual linker allows simple evaluation of cleavage rate of polymer-supported compounds from the linker and, at the same time, ensures that all resin-bound components are cleaved from the solid support. The dual linker 4 was assembled from two Wang linkers connected by a three carbon spacer. The linker 9 was synthesized using the PAL and HMPB linkers.     

New selenyl linker for solid-phase synthesis of dehydropeptides

A novel linker possessing selenocyanate and masked carboxylic acid was developed for the solid-phase synthesis of dehydropeptides. This linker was used to demonstrate the synthesis of the model compound of RGD-conjugated dehydropeptide.     

Novel route to carboxylic acids via the DCME reaction

Brown's DCME reaction was successfully performed employing B-alkyl-9-oxa-10-borabicyclo[3.3.2]decanes (1) to provide carboxylic acids (2) in good to excellent yields with complete retention of configuration.     

Comparison of activated chromatography resins for protein immobilization

The adsorption of bovine serum albumin (BSA) to an immobilized camelid‐derived antibody fragment was investigated using six different activated resins, of which two are prototypes. The resins differed in base material, coupling chemistry and particle size. The adsorption, washing and desorption stage of the affinity chromatography process were taken into account. Dynamic binding capacities at 10% breakthrough ranged between 0.76 and 4.8 mg BSA/mL resin. The washing volume ranged between 2.9 and 10 column volumes. One of the resins did not concentrate BSA, while the highest concentration was 13‐fold. We present a method to rank and weigh the properties of the resins to find the optimal resin to meet specific requirements. For three of the resins the adsorption flow rate was varied, while the washing and desorption flow rate was kept the same. The dynamic binding capacity decreased with increasing flow rate, as expected. For one resin, the washing volume remained constant, but for the others it decreased with increasing adsorption flow rate. The number of column volumes required to purify a given amount of BSA increases with increasing flow rate, which indicates that higher flow rates do not necessarily speed up the process.     

Determination of carboxylic acids in water by gas chromatography using several detectors after flow preconcentration

A novel analytical method is reported that combines continuous solid-phase extraction and gas chromatography for the determination of 22 carboxylic acids in water. The highly polar and hydrophilic analytes were preferentially sorbed on a mixture of LiChrolut EN-Supelclean ENVI-18 (1:1) sorbent column and eluted with methanol; this extraction process did not require derivatisation. The extract was analysed by gas chromatography coupled to a flame ionisation detector as well as a mass spectrometer with electron impact (EI) or positive chemical ionisation modes. The highest sensitivity was achieved when using MS-EI, with good linearity in calibration curves and low detection limits (2-40ngL(-1)) for 50mL of sample. The entire procedure from raw aqueous sample to a ready-to-inject methanol solution of the acids requires less than 15min. Another benefit of this method is the good accuracy (recoveries between 93 and 102%) and precision (relative standard deviation, 3.4-6.2%), which allows the determination of carboxylic acids in environmental water and in real chlorinated and ozonated drinking water.     

A new versatile linker for the solid-phase synthesis of secondary amines

A novel linker for the solid-phase synthesis of secondary amines based on an intramolecular cyclization was developed. The linker allows for a stepwise built-up of the secondary amines on the support. The feasibility was demonstrated in the parallel synthesis of a small set of different secondary amines.     

Siloxyl ether functionalized resins for chemoselective enrichment of carboxylic acids

Although the carboxylic acid moiety is prevalent in many biologically produced molecules, including natural products and proteins, methods to chemoselectively target this functional group have remained elusive. Generally, strategies that utilize carboxylate nucleophilicity also promote reactions with other nucleophiles such as amines and hydroxyls. A reagent was sought to facilitate the selective isolation of carboxylic acid containing compounds from complex mixtures. Here, the development of siloxyl ether functionalized solid supports is described.     

Novel monodisperse PEG-grafted polystyrene resins: synthesis and application in gel-phase C NMR spectroscopy

A series of novel polystyrene-oligo(oxyethylene) graft copolymers containing monodisperse PEG units (n = 2-12) have been synthesized and examined concerning their applicability for gel-phase ¹³C NMR spectroscopy. A strong correlation between the graft length and the line widths in the gel-phase spectra was observed. By grafting a PEG chain with only eight units, it was possible to obtain results similar to TentaGel resin. Additionally, TOF-SIMS images were recorded in order to evaluate the homogeneity of the resin.     

Development of the traceless phenylhydrazide linker for solid-phase synthesis

The hydrazide group is a new oxidatively cleavable traceless linker for solid-phase chemistry. It can be readily introduced by hydrazide formation between a carboxy-functionalized resin and different substituted hydrazines. In order to achieve high yields in this step, new carboxylic acid resins were developed that are not prone to undesired imide formation upon activation of the carboxylic acid. The polymer-bound acyl hydrazides were successfully employed in various transformations, namely Heck, Suzuki, Sonogashira, and Stille couplings, as well as Wittig and Grignard reactions. Traceless release of the coupling products from the solid support is achieved selectively under mild conditions and in high purity by oxidation of the aryl hydrazides to acyl diazenes with Cu(II) salts or N-bromosuccinimide (NBS) and subsequent nucleophilic attack of the acyl diazene intermediates. Traceless cleavage by oxidation with NBS can be carried out as a two-step process in which stable acyl diazenes are first generated by treatment with NBS in the absence of a nucleophile. After removal of the reagents by simple resin washing, the traceless release is effected by the addition of methanol, which leads to products of high purity without any additional separation steps.     

Polystyrene resins cross-linked with di- or tri(ethylene glycol) dimethacrylates as supports for solid-phase peptide synthesis

Polystyrene resins cross-linked with di(ethylene glycol) dimethacrylate (DEGDMA) and tri(ethylene glycol) dimethacrylate (TEGDMA), DEGDMA-PS and TEGDMA-PS, were synthesized by suspension copolymerization. Four functionalized resins, chloromethyl resin, 4-hydroxymethylphenoxymethyl resin (Wang resin), 4-methylbenzhydrylamine resin (MBHA resin) and 2-chlorotrityl chloride resin, were prepared from DEGDMA-PS and TEGDMA-PS. DEGDMA-PS and TEGDMA-PS showed high reactivity in the functionalization reactions in comparison with Merrifield resin (polystyrene cross-linked with divinylbenzene, DVB-PS). DEGDMA-PS-Wang resin and TEGDMA-PS-Wang resin were used as the solid-phase support for the synthesis of a difficult sequence, the fragment of acyl carrier protein 65-74. The yields of the crude peptide synthesized using DEGDMA-PS-Wang resin, TEGDMA-PS-Wang resin and DVB-PS-Wang resin were 92.3%, 91.6% and 78.8%, respectively. The purities of the crude peptides were 85.7%, 88.1% and 73.3%, respectively.     

An efficient approach for monosulfide bridge formation in solid-phase peptide synthesis

An efficient approach for the synthesis of cyclic peptides containing unnatural thioether side-chain bridges, based on the use of (2S)-9-fluorenylmethyl-2-[(tert-butoxycarbonyl)amino]-4-iodobutanoate and its homologue 5-iodopentanoate, derived from Boc-l-Asp-OFm and Boc-l-Glu-OFm, respectively, is reported. The synthesis was performed by a tandem combination of solid-phase peptide synthesis and microwave-assisted cyclization strategy.     

Facile preparation of new unsymmetrical curcumin derivatives by solid-phase synthesis strategy

Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy.     

A one step derivatization of controlled pore glass for oligonucleotide solid-phase synthesis

A one step anchoring of various diols on bare controlled pore glass (CPG) support via an adsorption mechanism allowed us to synthesize different (oligonucleotide-3′-diol) conjugates with high purity, through standard phosphoramidite chemistry. Diol loading on CPG proved to be efficient and reproducible. This methodology virtually allows the synthesis of any 3′-modified oligonucleotide, using any reporter molecule containing a diol moiety adsorbed on the CPG. Moreover, vicinal diol as glycol or glycerol enabled the release of some part of oligonucleotide-3′-OH.     

Rapid and convenient semi-automated microwave-assisted solid-phase synthesis of arylopeptoids

A facile and expedient route to the synthesis of arylopeptoid oligomers (N-alkylated aminomethyl benz-amides) using semi-automated microwave-assisted solid-phase synthesis is presented. The synthesis was optimized for the incorporation of side chains derived from sterically hindered or unreactive amines and both ortho- and para-substituted arylo-backbones. By utilizing this optimized protocol a complex nonameric arylopeptoid was synthesized in less than 11 h, featuring a novel alternating ortho-, meta-, and para-substituted backbone pattern and a variety of chemically diverse and challenging side chains.