Carbodiimides polypeptides

The combination of carboxyl activation by a carbodiimide and catalysis by DMAP provides a useful method for in situ activation of carboxylic acids for reaction with alcohols.10 The reaction proceeds at room temperature. Carbodiimides are widely applied in the synthesis of polypeptides from amino acids. The proposed mechanism for this esterification reaction involves activation of the acid via isourea 28 followed by reaction with another acid molecule to form anhydride... 

Carbodiimides are widely used to mediate the attachment of biomarkers to polypeptides. Examples include carbodiimides with ferrocenyl substituents. Also, peptides are covalently modified with ferrocenecarboxylic acid using EDCCl and N-hydroxy-succinimide to promote the coupling to surface lysines. They also mediate the attachment of substituents to single walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). Also, microdots are attached to virus molecules using a water soluble carbodiimide. The attachment of viral DNA to gold particles is used in the manufacture of a new type of vaccine. 

Linear soluble PEG (polyethylene glycol) is used as a liquid phase in the synthesis of polypeptides. In this case the esterification of the carboxylic acid group of the N-protected amino acids with the terminal - OH groups of PEG can be conducted using DCC or a water soluble carbodiimide to give 684. Reaction of 684 with a different N-protected amino acid produces 685. 

Another polymer supported carbodiimide is PCH20(CH2)3N=C=NC6Hu (PSCDI), designed for optimizing the polymer supported formation of polypeptides." This polymer is used in conjunction with HOBt, the latter being easily removed with a supported carbonate base." ... 

Resin bound carbodiimides are used in the formation of diphenol monomers used in the synthesis of tyrosine derived pseudo polypeptides. ... 

DCC is also used to prereact carboxyl groups with 0-benzylhydroxylamine prior to /8-lactam ring closure. A water soluble carbodiimide in combination with HOBt is used in several steps of the total synthesis of nisin, a pentacyclic polypeptide. Carbodiimides are also used for amide bond formation in the synthesis of the antiviral antibiotic distamycin Similarly, carbodiimides are used in the synthesis of a model depsipeptide lactone related to quinoxaline antibiotics. In the last synthesis, DCC in the presence of pyridine is used in the depsipeptide bond formation. 

Deoxyribonucleosides also lack both the adjacent hydroxyls and free phosphate group in this case, the 5 -hydroxyl has been oxidized to a carboxyl group, which is then linked to a synthetic polypeptide carrier with a water-soluble carbodiimide. This procedure has been described in this series (see Vol. 12B [175]). Two other procedures have been used less ex-... 

The coupling of carboxyl-containing compounds to amino groups of the polypeptide carrier is usually performed with an excess of carboxyl groups and an equivalent amount of the water-soluble carbodiimide around pH 5 at room temperature. In some cases where the hapten is not water soluble, it is usually dissolved in DMF or dioxane. In such cases it is also possible to prepare the hydroxysuccinimide ester using dicyclo-hexylcarbodiimide and couple this ester directly to the carrier. The experimental procedure will be demonstrated by two examples. 

Polymers with intramolecular cross-links have organized spatial structures, and are good models for the tertiary structure of proteins (26,27,1 ). In the studies discussed here poly Glu52Lys33Tyr15 (No. 3) was internally cross-linked with Woodward s reagent K or ionic carbodiimide and fractionated on Sephadex G-100. The number of cross-links in each fraction was determined by amino acid analysis. In addition, the parent polymer was fractionated in the same way to provide standards for comparison with the cross-linked polypeptides. 

Four additional polypeptides have been identified in the membrane sector. One of these, a strongly hydrophobic protein, seems to contain the binding site of dicyclohexyl-carbodiimide, an inhibitor of oxidative phosphorylation, and probably also of oligomycin. These four polypeptides are coded for by the mitochondrial genome, the others by the nuclear genome. 

So that after reaction in an organic solvent, it is possible to remove any unreacted carbodiimide and the urea simply by washing with water. It should be noted that significant racemization, via azlactone formation of the anhydride-like intermediate, can occur during the synthesis of a large peptide (protein) molecule. However, for a smaller polypeptide, this is minimal. 

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