Carbodiimide activation

Reduction of uronic acids Uronic acids (UA) were converted to the corresponding neutral sugars (NS) by carbodiimide activation of the carboxyl groups followed by a reduction with NaBD4 according to the method of Kim and Carpita [5]. In order to achieve a complete reduction of the uronic acids the procedure was repeated once. 

Figure 15 Conjugation of a carboxylic add and an amine using the carbodiimide method. The carbodiimide activates the carboxyhc acid to speed up the reaction to the amine. Carbodiimides can be used with nonpolar or polar solvents, including water. Undesirable urea complexes may form as by-products. Details of the reaction are given in Table 3...

Molecules containing phosphate groups, such as the 5 phosphate of oligonucleotides, also may be conjugated to amine-containing molecules by using a carbodiimide-mediated reaction (Chapter 27, Section 2.1). The carbodiimide activates the phosphate to an intermediate phosphate ester similar to its reaction with carboxylates (Chapter 3, Section 1). In the presence of an amine, the ester reacts to form a stable phosphoramidate bond (Reaction 13). 

Biotin-hydrazide also may be used to couple with carboxylate-containing molecules. Hydrazidcs can be coupled with carboxylic acid groups by using the carbodiimide reaction (Chapter 3, Section 1.1). The carbodiimide activates a carboxylate to an o-acylisourea intermediate. Biotin-hydrazide can react with this intermediate via nucleophilic addition to form a stable covalent bond. 

In an extension beyond hetaryl onium salt promoted hemiacetal activation, Ishido and coworkers have reported the carbodiimide activation of hemiacetals [141]. In the method (Scheme 3.13), the hemiacetal donor 1 is treated with a carbodiimide electrophile 83 and copper(I) chloride to provide glycosyl isourea intermediate 85. Highly susceptible to hydrolysis, the isourea 85 was not isolated but could be detected by 13C NMR and IR spectroscopy [142,143], Accordingly, the reaction between intermediate 85 and the glycosyl acceptor (NuH) provides glycoside product 3, along with urea by-product 84. 

Further work with the same dye (7.43) and carbodiimides (7.44 and 7.45) concentrated on this problem of limited efficiency. Cotton fabric padded with the dye phosphonate solution was aftertreated with the carbodiimide dissolved in various alcoholic solutions to avoid hydrolytic decomposition. Under these conditions cyanamide was much more effective than dicyandiamide. With conventional reactive dyes the efficiency of the dye-fibre reaction is limited by competing hydrolysis of the active dye. Although phosphonated or carboxylated reactive dyes do not hydrolyse, their level of fixation is limited by competing hydrolysis of the carbodiimide activator [46]. 

The utility of carbodiimide reagents was too important to consider abandoning them. Instead, it rapidly became obvious that carbodiimide activation could be used to prepare in situ active esters. Numerous nucleophilic additives were discovered and prepared for use in these reactions. The most important of these additives was 1,2,3-benzotriazol-l-ol (HOBt, 1), first reported for use in peptide synthesis by Konig and Geiger in 1970.[2(l As an example of a typical result, 1.2 equivalents of HOBt was added to the DCC coupling of Boc-Leu-Phe-OH to H-Val-OtBu in DMF as a solvent. Less than 1% of the l-d-l epimerized tripeptide was formed. When the reaction was carried out in the absence of HOBt, the amount of l-d-l product formed was 14.3%. Addition of HOBt to DCC reactions converts the intermediate G-acylisourea (2) (and any symmetrical anhydride) into the HOBt active ester 3 (Scheme 8). 

Suitable affinity resins are CNBr-activated Sepharose and similarly activated jV-hydroxysuccimmide ester-based gels with spacer arms. These react with free amino groups on the peptide. If the peptide contains many lysine residues, alternative coupling systems may be used, for example, carbodiimide-activated agaroses. In our experience, however, even peptides with internal lysines make good immunoadsorbents, and we routmely use CNBr-activated Sepharose. 

R. L. Taylor and H. E. Conrad, Stoichiometric depolymerization of polyuronides and glycosaminoglycuronans to monosaccharides following reduction of their carbodiimide-actived carboxyl groups, Biochemistry, 11 (1972) 1383-1388. 

If amino acids with unprotected hydroxyl groups are incorporated, it is better to use carbodiimide activation (such as DIC/HOBt-activation) instead of more reactive procedures to avoid acylation of the hydroxyl-groups. 

Interestingly, reaction of hyaluronic acid with EDC in the presence of primary amines affords only theN-acyl urea derivatives, as proven by C- and N-labeling experiments. Water soluble carbodiimides are also used in the depolymerization of polyuronides via reduction of their carbodiimide activated carboxyl groups. ... 

Monodispersed chitosan conjugated Fe304 nanoparticles are fabricated from chitosan via carbodiimide activation. The nanoparticles are useful for the removal of acid dyes. ... 

Figure 10 Schematic representation of the most common reactions for labeling an amine (a) reaction with isothiocyanate to give a thiourea (b) reaction with a Succinimidil ester to give an amide (c) reaction with a sulfonyl chloride to give a sulfonamide (d) reaction with an aldehyde to give an imine (Schiff s base) and (e) reaction with a carbodiimide-activated carboxylic acid to give an amide.

P riy(ethylene glycol) (PEG) OH, a, NHj, COOH/carbodiimide, active esters, 1-hydroxybenzotriazole, Wittig reagents... 

Treatment with dipyridyldisulfide, carbodiimide activation, thiol-disulfide interchange reactions... 

Because the preferred y carboxyl is more sterically accessible, random carbodiimide activation of folic acid usually yields a 70 30 ratio of y carboxyl a carboxyl-derivatized protein. 

Synthetic lipid (dioctadecyldimethyl ammonium polystyrene and dimyristoylphosphatidyl-ethanolamine) cast from solution onto piezoelectric quartz crystals (5/z, ordered layers) IgG covalently linked to thiolated, carbodiimide-activated gold electrodes on piezoelectric quartz crystals Bitter/sweet compounds anti-IgG [1]... 

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