Protected peptide fragments final protection

Two major synthetic strategies have been applied for the synthesis of S-prenylated peptides as shown in Scheme 1. In the first approach (method A), S-alkylation is performed on the final peptide in a protected or unprotected form.13641 In method B, which has produced better results in terms of overall yield, thiol alkylation is carried out on the cysteine residue or on a small peptide fragment and then the S-prenylated synthons are coupled to the remaining peptide fragment to produce the final products.[45 501 Most of the procedures reported for the synthesis of farnesylated peptide derivatives, can also be applied to the synthesis of geranylgeranylated peptides. 

In order to prepare Asp- or Glu-containing peptide fragments, in which side-chain carboxy groups are unblocked, one method is to introduce aspartic or glutamic acid into the peptide through its A-carboxyanhydride. Another method is to introduce aspartic or glutamic acid with the side chain protected as the benzyl ester and then to remove the benzyl ester by YiJ Pd and finally convert the C-terminal methyl ester into the corresponding hydrazide. 

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