![]() If we choose protecting groups that can be removed selectively (and the carbamate / ester pair qualifies) then we can then deprotect the carbamate, and add a third amino acid. The good news is that we don’t have to stop at the dipeptide. Synthesis of Longer Peptides – Tripeptides and Tetrapeptides No matter how you slice it you’re looking at a low yield (95%) of a single product! Just like the letters A and L can combine to make the words AL and LA, in addition to Ala-Leu (our desired product) we will also get Leu-Ala.įurthermore, since we’re not adding single molecules together but molar quantities (even a millionth of a mole (a “micromole”) has 10 17 molecules in it) we also have the possibility of forming the “homo-dipeptides” AA (Ala-Ala) and LL (Leu-Leu).Īnd that’s just a start. That’s because each amino acid has two reactive termini – an amine and a carboxylic acid – and they can bond together in multiple ways. Well, this will give us some of our desired product. But it won’t do so efficiently! Why not take 1 equivalent each of L-alanine and L-phenylalanine, add a coupling agent like N,N-dicyclohexylcarbodiimide (DCC) and patiently wait for our product to appear? Surveying the methods previously covered to make amides, it might seem simple. ![]() 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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