General Approach to Protection and Amide-Bond Formation

5 GENERAL APPROACH TO PROTECTION AND AMIDE-BOND FORMATION 

FIGURE 1.5 General approach to protection and amide-bond formation. Pg1, Pg2, Pg3, Pg4, and Pg6 may be identical, similar, or different. Pg5 must be different from Pg1, Pg2, and Pg4. Pg5 must be removable by a different mechanism (i.e., orthogonal to the other protectors) or be much less stable than the others to the reagent used to remove it. 

G Barany, RB Merrifield. A new amino protecting group removable by reduction. 

Chemistry of the dithiasuccinoyl (Dts) function, (orthogonal systems) J Am Chem 

When forming a bond, the nature of the substituent at the carboxyl function of the residue providing the amino group is irrelevant to the reaction that is, it may be a protector or the nitrogen atom of an amide or peptide bond. In contrast, the nature of the substituent on the amino function of the residue providing the carboxyl group 

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