Peptides carbodiimide hydrochloride

Scheme 9. N-Ras peptide synthesis employing choline esters as C-terminal protecting group. EDC 1-ethyl-3 (dimethylamino)propyl-carbodiimide hydrochloride, HOBt 1-hydroxybenzo-tri azole...

Abbreviations used Dde, N-[l-(4,4-dimethyl-2,6-dioxocyclohexadiene)]-ethyl DIEA, diisopropylethylamine DMF, N,N-dimethylformamide EDC, l-Ethyl-3-(3 -dimethylaminopropyl)carbodiimide hydrochloride HOBt, 1-hydroxybenzotriazole NHS, N-hydroxysuccinimide NMP, l-methyl-2-pyrroIidinone PAL, Peptide Amide Linker [5-(4-(9-fluorenylmethyloxycarbonyl) aminomethyl-3,5-dimethoxyphenoxy) valeric acid] PyBOP, Benzotriazole-l-yl-oxy-trispyrrolidino-phosphonium hexafluorophosphate TFA, trifluoroacetic acid. 

Miller, M.M. and Boger, D.S. (2005) Polystyrene-1-ethyl-3-(3 -dimethylaminopropanej-carbodiimide Hydrochloride (PS-EDCI), in Handbook of Reagents for Organic Synthesis, Reagents for Glycoside, Nucleotide and Peptide Synthesis (ed. D. Crich), John Wiley Sons Ltd, Chichester, pp. 529-33. 

Another potential problem with DCC is that at the completion of the reaction some DCU remains in solution with the product, necessitating additional purification. Water-soluble carbodiimide derivatives such as l-Cyclohexyl-3-(2-morpholinoethyl)carbodiimide Metho-p-toluenesulffonate and l-Ethyl-3-(3 -dimethylaminopropyl)carbodiimide Hydrochloride (EDCI) obviate this problem, as they are removed by a simple extraction. Many newer coupling agents have been developed for peptide synthesis and other acylation reactions. These include Benzotriazol-l-yloxytris(dimethylamino)phosphonium Hexafluorophosphate (BOP)," 0-Benzotriazol-l-yl-N,N,N, N -tetramethyluronium Hexafluorophosphate (HBTU)," Bis(2-oxo-3-oxazolidinyl)phosphinic Chloride (BOP-Cl), and (1 //-1,2,3-benzotriazol-1 -yloxy)tris(pyrTolidino)phosphonium hexafluorophosphate (PyBOP). In addition to linear and polymeric amides, lactams of various ring sizes have been synthesized using these methods (eq 1)."... 

Carbodiimides are, in general, useful compounds for effecting certain dehydrative condensations, e.g., in the formation of amides, esters, and anhydrides. These two crystalline water-soluble carbodiimides are especially useful in the synthesis of peptides and in the modification of proteins. The excess of reagent and the co-product (the corresponding urea) are easily separated from products with limited solubility in water. The hydrochloride is best employed in nonaqueous solvents (methylene chloride, acetonitrile, dimethylformamide). The methiodide is relatively stable in neutral aqueous systems, and thus is recommended for those media. 

Also, solid phase synthesis of peptides containing o, )3-didehydroamino acids are common. In this case the carbodiimide affects dehydration to generate the a,)8-didehydroamino acids 686. Eor example, the water soluble carbodiimide EDC hydrochloride (EDCCl) is used in this dehydration reaction, also using CuCl as catalyst. ... 

In view of the rapid reaction of carbodiimides with water they are often used in dehydration reactions. Major examples are the intra- and intermolecular esterification reactions of carboxylic acids, and the formation of peptides from carboxylic acids and protected amino acids. Especially, dicyclohexylcarbodiimide (DCC) or diisopropylcar-bodiimide (DIPCD) are often used in carbodiimide mediated reactions because the corresponding urea byproducts are insoluble in most organic solvents and water, and therefore are readily removed by filtration. Also, water soluble carbodiimides, such as N-ethyl-N -(3-dimethylamino)propylcarbodiimide (EDC) or its hydrochloride (EDCCl, sometimes referred to as EDAC) are often used in these reactions. EDC reacts with carboxyl groups at pH of 4.0-6.0, but loses its reactivity at lower pH. Sometimes solid phase reactions are conducted using carbodiimide terminated linear or crosslinked polymers. 

P-Ser -] P-corticotropin-(l-13)-tridecapeptlde amide (l). The synthesis of I, shown in Fig. 1, was carried out by Dr. M. Brugger. It followed closely the one reported from our laboratory (I5) for the preparation of a-MSH. Use of the carbodiimide method to couple the protected 1-D-serine decapeptide 1-10 with the hydrochloride of the trlpeptide amide 11-15 (15) yielded the protected sequence 1-15 which was purified by column chromatography on silica gel. Removal of the protecting groups by treatment with trifluoro-acetic acid and subsequent ion exchange led to the acetate salt of the free peptide I in pure form. 

The PEG conjugation can also be accomplished directly by activating the polymer in situ with the use of a carbodiimide. In this manner, the carboxylic group of sucdnylated PEG is activated and coupled to various peptides. When organic solvents are used, N,N -diisopropylcarbodiimide (DIG) is the coupling agent of choice. The water-soluble l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) is suitable for reactions in the aqueous phase (Figure 4). 

---