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Peptide synthesis involves the fusion of two amino acids through an amide bond. Amino acids possess two or three functional groups capable of undergoing reactions. The objective is the formation of the bond that is desired while avoiding reaction at the other functional groups. The tendency for reaction depends on the electrophilicity or nucleophilicity of the groups. The reactivity of a functional group is suppressed by combining it with a protector that is removable preferably without side reactions. Reaction with functional groups of lesser reactivity is less likely if the activation required for peptide-bond formation is moderate. There are three strategies of protection for synthesis, with the adoption of any one having its own implications and consequences. Protection can be maximal, where all functional groups are blocked; minimal, where only functions that have to be blocked are protected; or intermediate, where some groups are blocked during the bond-forming reaction and then unblocked during the subsequent reaction. Functions that have to be blocked are the amino groups in the component to be activated and sulfhydryls.