Phenacyl esters as a new photocleavable linker in liquid-phase chemistry

PEG-supported 2-methylphenacyl ester as a new photocleavable linker is reported. The photocleavage based on an efficient intramolecular hydrogen abstraction was carried out with 280-366 nm UV irradiation in benzene or methanol to give the corresponding carboxylic acid in high yields and purities. The linker was suitable for aliphatic and aromatic carboxylic acids as well as protected amino acids.     

A new safety-catch protecting group and linker for solid-phase synthesis

The use of two derivatives of 2-methoxy-4-methylsulfinylbenzyl alcohol is demonstrated as a safety-catch protecting group and linker for solid-phase peptide synthesis. The protecting group and linker are stable to TFA and are readily removed under reductive acidolytic conditions.     

A thermally-cleavable linker for solid-phase synthesis

Oxabicyclo[2.2.1]norbornenes constitute a convenient and readily cleaved linker for solid-phase organic synthesis. A simple and inexpensive furfuryl-substituted resin has been shown to capture and release maleimide dienophiles under conditions compatible with intermediate synthetic steps. The synthesis of β-amino, -thiophenoxy, and -hydrazino alcohols by epoxide ring opening, and maleimide-functionalized Leu-enkephalin by standard peptide coupling techniques, are described to illustrate the utility of the solid-phase synthesis methodology.     

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.     

A new phenoxyacetate-based linker system for the solid-phase synthesis of oligosaccharides

[structure: see text]. A novel linker system has been designed, and its first application to solid-phase oligosaccharide synthesis is described. The use of the highly reactive o-nitro-phenoxyacetate linker allows a fast and quantitative cleavage using mild basic conditions. This method combined with the trichloroacetimidate glycosylation exhibits highly promising results as demonstrated for the synthesis of tetrasaccharide 1 (n = 3) containing glucose beta(1 --> 4) and beta(1 --> 6) linkages.     

A triazene-based new photolabile linker in solid phase chemistry

An extension of the T2 linker methodology by showing its applicability as a photocleavable linker is reported. Photocleavage was carried out with 355 nm UV laser irradiation (3ω Nd-YAG) in methanol/diethyl ether and is suitable for protected amino acid derivatives, as well as simple small organic molecules including resin-bound biotin. The linker is stable under a wide range of conditions with the exception of strongly acidic media.     

A bromocoumarin-based linker for synthesis of photocleavable peptidoconjugates with high photosensitivity

A new bromocoumarin-based bi-functional linker was developed for preparing photocleavable peptides and proteins with high photolytic efficiency, which have many potential applications in the study and engineering of biological systems.     

A nonacid degradable linker for solid-phase synthesis

Synthesis and applications of two new nonacid degradable linkers as an alternative to the Wang linker for solid-phase synthesis are described. Resin from linker 2 looks superior to linker 1 in terms of yields for both anchoring of the first building block and cleavage and in terms of higher purity of the final product. Use of linker 2 avoids side reactions associated with the use of Wang resin due to an undesired cleavage during final acid treatment.     

Sequentially photocleavable protecting groups in solid-phase synthesis

[reaction: see text] A sequential solid-phase peptide synthesis was developed using both photolabile linker and protecting groups. The chromatic sequential lability between a tert-butyl ketone-derived linker (sensitive to irradiation at 305 nm) and a nitroveratryloxycarbonyl (NVOC) group (sensitive at 360 nm) was exploited to prepare Leu-Enkephalin in a 55% overall yield. This new strategy allows the preparation of peptides in essentially neutral medium, by avoiding the use of common deprotection reagents such as trifluoroacetic acid or piperidine.     

Synthesis of a new hydrophilic o-nitrobenzyl photocleavable linker suitable for use in chemical proteomics

Linkers currently used in solid phase synthesis are generally short and hydrophobic, limiting their usefulness in biological systems. Herein, we describe a facile synthesis of a long, hydrophilic, o-nitrobenzyl photocleavable linker, suitable for constructing affinity supports for use in chemical proteomics. The rates of photolysis of the linker on exposure to UV light emitting diodes are reported.     

A base-stable dithiomethyl linker for solid-phase synthesis of oligonucleotides

A novel linkage, useful for the synthesis of oligonucleotides is described. The linking function is compatible with all conditions used for oligonucleotide synthesis, orthogonal to all other protecting groups, but regenerates 3′-OH rapidly upon mild reduction under aqueous conditions. This method is employed in the removal of depurinated fragments during the synthesis of oligonucleotides.     

A 'triflate-like' tetrafluoroarylsulfonate linker for multifunctional solid-phase organic synthesis

An arylsulfonate solid-phase linker is suitable for 'traceless' synthesis and Pd(0) catalyzed cross-coupling reactions.     

Studies on the chemical stability and synthetic utility of an oxazolidine linker for solid-phase chemistry

A chemical stability study on the oxazolidine linker system has been carried out using a dual-linker analytical construct within a parallel reaction scan. The study established the compatibility of the oxazolidine platform with a wide range of commonly employed synthetic reaction conditions including nucleophilic, oxidizing, and reducing conditions. The scan was further used to probe and optimize acidic conditions under which the oxazolidine could release the substrate from the solid-support and to identify reagents that could cleave while retaining other acid-labile groups. The solid-phase synthesis of a small molecular array established the utility of oxazolidine aldehyde 1 as a building block for asymmetric chemistry while exploiting the data generated by the reaction scan.     

A fluorinated selenide linker for solid-phase synthesis of n-pentenyl glycosides

[reaction: see text] A fluorine-labeled selenide linker for installing terminal isolated olefins has been synthesized in high overall yield. The resin-bound linker could be glycosylated both with glycosyl trichloroacetimidates and glycosyl fluorides. The linker did not decompose after oxidation with tBuOOH but underwent beta-elimination when it was subjected to heat. This allowed the released n-pentenyl glycoside 15 to be isolated in excellent yield and purity after filtration.     

A novel linker for solid-phase synthesis cleavable under neutral conditions

A novel linker cleavable under neutral conditions has been developed for the solid-phase synthesis of base-labile compounds. The linker is comprised of a 3-azidomethyl-4-hydroxybenzyl alcohol moiety, and the azidomethyl group in the linker is readily converted to an aminomethyl group by treatment with a phosphine reagent in the presence of water to result in an intramolecular cyclization to release the compounds. Using the linker, a base-labile dinucleoside methyl phosphate was synthesized on a highly cross-linked polystyrene (HCP) support and cleaved successfully from the resin without decomposition of the product.     

A new highly versatile handle for chemistry on a solid support: the pipecolic linker

The versatility of the pipecolic linker (Pip-linker) is illustrated by the synthesis of modified amino acids, C-terminal-modified pseudopeptides, and cyclic peptides, through side-chain anchoring of a lysine residue. Introduction of the first residue was easily accomplished and the Pip-linker revealed to be robust enough to support various chemical modifications.     

A new linker for solid-phase synthesis of heparan sulfate precursors by sequential assembly of monosaccharide building blocks

A novel ester type linker which upon cleavage releases the glycans as carbamate protected aminoglycosides was successfully employed in the sequential assembly of L-idose and azido glucose monosaccharide building blocks to heparan sulfate precursors.     

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.     

The preparation of a new "safety catch" ester linker for solid-phase synthesis

A new "safety catch" linker for esters has been synthesized on polystyrene resin. This 2-tert-butoxyphenol resin 10 may be acylated to give a relatively stable ester that will allow nucleophilic chemistry without reaction at the linking ester group. Removal of the tert-butyl group with acid unmasks a highly reactive 2-hydroxyphenyl ester that reacts readily with nucleophiles to cause release of the product from the resin. This sequence has been exemplified by acylating the resin with various bromo acids, carrying out nucleophilic displacements with thiols, phenols, or amines, activating the ester with trifluoroacetic acid and cleaving from the resin with amines to give the (nucleophile) substituted carboxamides in high yield and purity. Kinetic studies with a model ester revealed half-lives for reaction with morpholine of 119 h for the tert-butoxyphenyl ester and 1 min for the corresponding phenol.