What do we need to do to make L-Ala-L-Leu ? For simplicity’s sake, we’ll pick two from the “hydrophobic sidechain” group, alanine (Ala) and leucine (Leu), since their sidechains don’t need additional protecting groups. Let’s build a simple dipeptide between two of these amino acids. Synthesis of A Simple Dipeptide Without Protecting Groups (is not advisable!) Of the chiral amino acids, all are S, with the exception of cysteine and selenocysteine (because sulfur and selenium have a higher priority under the CIP system. With the exception of (achiral) glycine, all proteinogenic amino acids are L-amino acids, where the “L-” prefix relates the stereochemistry of the amino acid relative to that of L-glyceraldehyde. In addition to the 20 amino acids directly encoded by the genome, two other amino acids are coded into proteins under special circumstances: selenocysteine (present in eukaryotes, including humans) and pyrrolysine (found only in methane-producing bacteria). Proteinogenic amino acids are the building blocks of proteins. Synthesis, and Nomenclature) that connects two amino acids, as in the “dipeptides” L-phenylalanyl-L-valine (below left) and L-leucyl-L-alanine (below right): ![]() What Are Peptide Bonds?Ī “peptide bond” is an amide linkage (see Amides: Properties. Today we’ll go deeper on how to synthesize the most important amides of all – peptides – with an important contribution from protecting group chemistry. ![]() ![]() Peptide bonds: Forming peptides from amino acids with the use of protecting groups
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