Understanding protease catalysed solid phase peptide synthesis

A protease (thermolysin) was used to directly synthesise a number of dipeptides from soluble Fmoc-amino acids onto a solid support (PEGA1900) in bulk aqueous media, often in very good yields. This shift in equilibrium toward synthesis is remarkable because for soluble dipeptides in aqueous solution hydrolysis rather than synthesis is observed. Three possible reasons for the equilibrium shift were considered: (i) using a solid support makes it easy to use an excess of reagents, so mass action contributes towards synthesis; (ii) reduction in the unfavourable hydrophobic hydration of the Fmoc group within the solid support compared with the free amino acid in solution and (iii) suppression of the ionization of amino groups linked to the solid phase due to mutual electrostatic repulsion. It was found that under the conditions studied the second effect was most important.     

A novel peptide synthesis using fluorous chemistry

Three new fluorous supports for peptide synthesis, i.e., the trialkoxybenzhydryl-type (6), the Wang-type (7) and the tert-butyl-type support (8), were prepared. A bioactive peptide TRH was easily synthesized by an Fmoc strategy using the benzhydryl-type fluorous support with fluorous chemistry.     

Just add water: a new fluorous capping reagent for facile purification of peptides synthesized on the solid phase

A novel fluorous capping reagent is introduced to facilitate purification during solid-phase peptide synthesis (SPPS). Reagent 1 is a trivalent iodonium salt that reacts vigorously with free amines to deliver a long-chain fluoroalkyl group. It has been used to tag all unreacted amines following the peptide coupling step in SPPS. The resulting fluoroalkylated amine is no longer able to couple in further peptide coupling steps and is also stable to standard peptide synthesis conditions. Deletion products are removed using flash fluorous chromatography to yield the pure, full-length peptide.     

Design and synthesis of a multi-detachable benzhydrylamine-resin for solid phase peptide synthesis

Peptides with C-terminal α-carboxamides were synthesized from a multi-detachable benzhydrylamine-resin containing a Boc-(4-acetoxy)benzhydryl-amine handle of unambiguous origin. The peptides bound to the new resin are stable to trifluoroacetic acid, but are cleavable by hydrogen fluoride, base and nucleophiles to give unprotected or protected peptide fragments.     

N-Terminal peptide aldehydes as electrophiles in combinatorial solid phase synthesis of novel peptide isosteres

N-Terminal peptide aldehydes were synthesized on a solid support and utilized as electrophiles in nucleophilic reactions in order to furnish novel and diverse peptide isosteres. The aldehyde moiety of the peptide was synthesized by coupling a protected aldehyde building block to the peptide and deprotecting it quantitatively in less than 3 min. It was found that protection of the two succeeding amide nitrogens was necessary in order to avoid reaction between the aldehyde and backbone amides. The N-terminal peptide aldehydes were successfully reacted in the following way: (a) reductive amination with a large variety of amines, leading to N-alkyl-gamma-aminobutyric peptide isosteres positioned centrally in the peptide; (b) reductive amination with amino esters, leading to N-terminal 2,5-diketopiperazine peptides; (c) Horner-Wadsworth-Emmons olefination, leading to unsaturated peptide isosteres positioned centrally in the peptide; and (d) Pictet-Spengler condensations, leading to tetrahydro-beta-carbolines either positioned centrally in a peptide or fused with a diketopiperazine ring in the N-terminus of the peptide.     

A faster solid phase peptide synthesis method using ultrasonic agitation

Solid phase-supported synthesis is a widely used strategy in peptide chemistry. A factor which limits the product purity is the individual stages yields. Here, we reported that the use of ultrasonic agitation allows to reduce tenfold the time of synthesis in the Fmoc strategy and improve the purity of the final product. Our method is a promising alternative to traditional synthetic methods and microwave synthesizers.     

Zinc chloride-catalyzed chloromethylation of resins for solid phase peptide synthesis

Zinc chloride has been found to catalyze chloromethylation of resins for solid phase peptide synthesis, producing low levels of chloromethylation more accurately and under more convenient conditions than does SnCl₄. The preparation of a stable solution of the ZnCl₄ catalyst in THF is described, and data are presented detailing the effects of varying temperature, time, and the concentrations of catalyst and chloromethyl methyl ether on the chloromethylation reaction.     

Deprotection of 2-nitrobenzenesulfonamides using fluorous and solid phase reagents

The 2-nitrobenzenesulfonyl group was efficiently removed from primary and secondary amines as well as amides with a perfluorinated thiol under mild conditions. The resulting perfluorinated byproduct was removed via a solid phase extraction through perfluorinated silica gel making this a fast and simple procedure for parallel deprotection.     

Microwave-assisted guanidinylation in solid phase peptide synthesis: comparison of various reagents

The guanidinylation of a peptide chain on a polymeric support under microwave conditions using derivatives of thioureas—S-alkylisothioureas, pyrazole-carboxamidine, and guanidine as guanidinylating reagents is described. The best results are obtained with N,N′-di-Z-S-methylisothiourea and N,N′-di-Z(2-Cl)-S-methylisothiourea. It is found that guanidinylation with reagents containing Boc groups is accompanied by side reactions.     

亲水性二苯甲胺树脂制备及用于肽合成研究

通过反相悬浮共聚合成了含酯基的聚丙烯酰胺树脂, 再经乙二胺取代和两步缩合反应引入二苯甲胺功能基团。讨论了反应条件对各步反应的影响。测定了该载体与几种保护氨基酸的缩合率并合成了模型肽。缩合率和模型肽的纯度都令人满意。     

Synthesis of 2-hydroxyethylsulfonyl-methyl-substituted polystyrenes and their application in solid phase peptide synthesis

2-Hydroxyethylsulfonylmethyl-substituted polystyrenes are obtained from Merrifield's chloromethylated, cross-linked copolymer, by treatment with sodium 2-hydroxyethylmercaptide in liquid ammonia, followed by oxidation with m-chloroperbenzoic acid. Boc-amino acids can be esterified with the polymer, using dicyclohexylcarbodiimide in dichloromethane. Further condensations are possible via conventional procedures. Protected peptide derivatives, thus prepared, can be detached from the resin by brief treatment with a base. A high elimination rate was observed when the cleavage was performed with a 0.1 M solution of sodium hydroxide containing methanol and a limited amount of water. In the absence of methanol only trace amounts of the product were liberated.     

An amine-derivatized, DOTA-loaded polymeric support for Fmoc solid phase peptide synthesis

An amine-derivatized DOTA has been used to modify the surface of a polymeric support for conventional solid phase peptide synthesis (SPPS) following standard Fmoc chemistry methods. This methodology was used to synthesize a peptide-DOTA conjugate that was demonstrated to be a PARACEST MRI contrast agent. Therefore, this synthesis methodology can facilitate Fmoc SPPS of molecular imaging contrast agents.     

A new environment-sensitive fluorescent amino acid for Fmoc-based solid phase peptide synthesis

A new 4-(N,N-dimethylamino) phthalimide-based environment-sensitive fluorescent building block for solid phase peptide synthesis, has been synthesized and incorporated into peptides. Peptides incorporating this residue show great potential for biological applications in sensing protein/protein interactions.     

Conversion of NGurethane protected arginine to ornithine in peptide solid phase synthesis

It is shown that Di-Adoc or Boc as guanidino protecting groups do not prevent the acylation and the subsequent conversion of arginine to ornithine in Fmoc solid phase peptide synthesis.