ABSTRACT
Protection is warranted for a number of amino acids that have a reactive functionality on their side chain. Some amino acids (e.g., Asp, Glu, Cys, Arg, Lys, His, Ser, Thr) usually require protection; others (e.g., Asn, GIn, Met, Trp) mayor may not depending on the sequence and length of the synthetic target, the type of chemistry, the coupling and cleavage methods, and the resin being used. Side reactions may occur during both synthesis and deprotection, but with a judicial choice of side-chain protecting groups, many known side reactions can be suppressed or avoided totally. Although this chapter focuses on the side-chain protection of amino acids for peptide synthesis, most of the protecting groups could be used for analogous functional groups found in the growing number of molecules amenable to solidphase chemistry. Although the vast majority of the protected derivatives mentioned in this chapter are commercially available, references for their preparation are given. These citations could be of use for the preparation of uncommon or isotopically labeled amino acids as well as for other types of compounds. This chapter also describes the use of backbone amide protection, which has been shown to aid in a number of different syntheses and to also suppress some known side reactions.
