1- Cyclohexyl-3- carbodiimide hydrochloride

We have found that 1-ethyl (3,3-dimethylaminopropyl)carbodiimide hydrochloride generally gives better yields of product than does another water-soluble carbodiimide, 1-cyclohexyl 3-morpholinoethyl carbodiimide hydrochloride. This is particularly true when the dimethyl sulfoxide is not redistilled before use. The use of dimethyl sulfoxide that has been redistilled under reduced pressure is recommended for all oxidation reactions. Prolongation of the oxidation reaction leads to a decreased yield of aldehyde product. After 24 hr, the yield of TFA Pheal is 36% before, and 27% after, crystallization from hexane. 

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)."... 

The most widely used carbodiimides are N,N -dicyclohexylcarbodiimide (DCC) and the water soluble N-ethyl-NL(3-dimethylamino)propylcarbodiimide (EDC) and its hydrochloride salt (EDCCl). Also, analogs of DCC, such as the fluorescent N-cyclohexyl-N -(l-pyrenyl)carbodiimide (PCD) and the paramagnetic N-cyclohexyl-N -(2,2,6,... 

Coupung, dehydrative Bis-o-phenylene pyrophosphite. N,N -Carbonyldiimidazole. N,N -Carbonyl-J-triazine. l-Cyclohexyl-3-(2-morpholinomethyl)-carbodiimide. 1,1-Di-chlorodiethyl ether. Dicyclohexylcarbodiimide. Diethyl chlorophosphonate. Diethyl-cyanamide. Diethyl ethylenepyrophosphite. N-(3-Dimethylaminopropyl)-N -ethylcarbo-diimide hydrochloride. Diphenylketene p-tolylamine. Ethoxyacetylene. l-Ethyl-3(3 -di-methylaminopropyllcarbodiimide hydrochloride. Ethylene chlorophosphite. N-Ethyl-S-phenyliioxazolium-3 -sulfonate. N-Hydropyridine. N-Hydroxyphthalimide. N-Hydroxy-piperidine, N-Hydroxysuccinimide. Phenylphosphorodi-d-imidazolate). 

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