Protect the carboxyl group of leucine as its benzyl ester.Coupling of the two amino acids is achieved by N,N′-dicyclohexylcarbodiimide (DCCI)-promotedamide bond formation between the free amino group of leucine benzyl ester and the free carboxylgroup of Z-protected alanine.Both the benzyloxycarbonyl protecting group and the benzyl ester protecting group may be removedby hydrogenolysis over palladium. This step completes the synthesis of Ala-Leu.27.18As in the DCCI-promoted coupling of amino acids, the frst step is the addition of the Z-protectedamino acid to DCCI to give an O-acylisourea.This O-acylisourea is attacked by p-nitrophenol to give the p-nitrophenyl ester of the Z-protectedamino acid.27.19To add a leucine residue to the N terminus of the ethyl ester of Z-Phe-Gly, the benzyloxycarbonylprotecting group must frst be removed. This can be accomplished by hydrogenolysis.C6H5CH2OCNHCHCNHCH2COCH2CH3H2NCHCNHCH
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This note was uploaded on 10/03/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.