Water-soluble carbodiimide', widely used for peptide coupling, with the major advantage that excess reagent and the urea by-product can be easily removed by washing with dilute acid or water: J. Org. Chem., 26, 2525 (1961); J. Am. Chem. Soc., 87, 2492 (1965). For discussion of the mechanism of peptide coupling with this reagent, see: J. Am. Chem. Soc., 103, 7090 (1981). Often used in conjunction with an additive such as HOBt (1-hydroxybenzotriazole hydrate) to suppress racemization; see, for example: Bull. Chem. Soc. Jpn., 55, 2165 (1982). A two-phase solvent system (dichloromethane-water or isopropyl acetate-water) has been found to give superior results in this type of peptide coupling: J. Org. Chem., 60, 3569 (1995). In a comparative study, submolar quantities HOBt in DMF-water gave good results: Chem. Lett., 1 (1997). For use in the synthesis of cyclic derivatives of 3'-amino-3'-deoxyadenosine-5'-di- and triphosphates, see: Angew. Chem. Int. Ed., 33, 1394 (1994). Promotes various other N-acylation reactions such as the formation of N-acylsulfonamides from primary sulfonamides and N-protected amino acids in the presence of DMAP: Synlett, 1141 (1995).
