Amino acids carbodiimide hydrochloride

Carbodiimides are known to react with primary amines to form guanidines.f In the case of amino acid esters, a subsequent elimination of alcohol is possible with formation of an imino-hydantoin species (Scheme 8). However, these reactions usually require higher temperatures or the occurrence of acid catalysis and therefore can be neglected when unprotonated amino acid derivatives are acylated using carbodiimides. On the other hand, this side reaction becomes more important when protonated amino acids (i.e., amino acid ester hydrochlorides) are coupledf and these byproducts may occur. 

A mixture of 4 -[(methylsulfonyl)amino]-y-oxobenzenebutanoic acid and 1-hydroxybenzotriazole in dimethylformamide (DMF) under nitrogen, is treated with dibutylamine in DMF. The mixture is cooled in an ice bath and l-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) added in portions over 5 min. The mixture is stirred in the cold 1 h and overnight at room temperature. The solvent is removed in vacuo (bath temperature 35°C). The residue is treated with ice and ethyl acetate and the organic layer washed sequentially with 0.5 N monopotassium sulfate, cold 4% NaHC03, cold water and finally brine. The organic solution is dried (Na2S04) and concentrated in vacuo. The N,N-dibutyl-y-oxo-4-[(methylsulfonyl)amino]benzenebutan-amide (crystallized from ethyl acetate-hexane) is obtained. 

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. 

Materials. The following were obtained from commercial sources Swims medium S77, horse serum, and fetal calf serum (Grand Island Biologicals) MTX (Lederle Laboratories) was purified by DEAE cellulose prior to use (11) crystalline BSA, poly-L-lysine (M 35,000), hypoxanthine and thymidine (Sigma Chemical Co.) 1-etnyl-3-(3 -dimethylaminopropyl)carbodiimide hydrochloride (EDC) (Story Chemicals) folinic acid (ICN Pharmaceuticals) Blue Dextran (Pharmacia). The concentrations of the folate derivatives and MTX were determined by their respective extinction coefficients (13). MTX-BSA was synthesized according to a previously described procedure ( ) in which MTX is coupled via a terminal carboxyl group to -amino groups contained in the albumin molecule. 

Acylation of 5-substituted 6//-l,3,4-thiadiazines 172 with the carboxylic group of carboxysulfonamides was mediated by a mixture of A -ethyl-A -(3-dimethylamino propyl)carbodiimide hydrochloride, 1-hydroxybenzotriazole (HOBT), and 4-methylmorpholine in DMF at 5°C to yield l,3,4-thiadiazin-2-yl-2-[(phenylsulfonyl)amino]propan-amides 173 (Equation 22) <2001JME3231>. Analogous dihydroorotic acid derivatives 174 were also prepared. Such... 

An N-protected amino aldehyde can be prepared by Swem oxidation of an N-pro-tected amino alcohol in the presence of an oxidizing agent comprising DMSO and a water-soluble carbodiimide derivative as l-ethyl-3-(3-dimethylaminopropyl)carbo-diimide hydrochloride (EDC) in an organic solvent. The N-protected amino alcohol can be derived from an L-, D-, or L-/D-amino acid, but usually is the N-protected-(S)-a-amino alcohol derived from an N-protected L-amino acid. 

Under the mild reaction conditions (0°C), the second amino acid (carboxyl protected) will not react with DCC, but only with the anhydride-like intermediate. The DCU formed is insoluble in most organic solvents so that most often separation from the product merely involves filtrations. However, it occasionally may be difficult to remove the last trace of DCU by filtration. As such, the use of carbodiimides that are soluble in aqueous solvents may be necessary. One example is l-ethyl-3-(3-dimethylaminopropyl)-carbodi-imide hydrochloride. The urea by-product formed is also water soluble. 

Carbodiimides react with dicarbonyl compounds (or their sulfur analogues) to give imidazoles [48, 49]. When diimmonium salts (19) are treated with guanidines or O-methylisoureas the initial products are 4,5-dihydroimidazoles, but these are readily aromatized by heating in the presence of triethylamine hydrochloride (Scheme 4.3.10). The mildly acidic conditions result in the loss of one of the amino functions from the intermediate [50]. Yields of 2,5-diaminoimidazoles are usually 60-80% overall. 

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