What does bodybuilding, anti-ageing cream and Bleomycin (a cancer drug) have in common? Peptides of course! Peptides are large molecules that are vital to life. If you were to take a protein and break it into smaller pieces, each piece would be called a peptide. Just like proteins, peptides are made of amino acids linked together in a chain-like structure. Whenever you ingest a protein, your body breaks it down to its individual amino acids. It then puts those amino acids back together in a different order to make whatever peptide or protein your body needs. Insulin, for instance, is a peptide that is 51 amino acids long. Your body synthesizes insulin from the amino acids it gets from the proteins you eat.
Peptides and small proteins can be synthesized in a lab as well. Peptide synthesis is a huge market in the pharmaceutical and skin care industry. They’re also used, somewhat shakily, as a steroid substitute by serious athletes and bodybuilders. we’re going to go over the basic steps of how to join amino acids together to make a peptide. The chemistry of peptide synthesis is complex and well beyond the scope of explaining. But the basic steps of making a peptide are not as difficult as you might think.
There are 20 amino acids that occur in nature. They all have the same core — an amine group (NH2) attached to a carboxylic acid (COOH) via a single carbon atom, called an alpha carbon. The thing that gives each amino acid its uniqueness is the functional group called the R group or R side chain, that is also attached to the alpha carbon. When building peptides, the amine group of one amino acid gets attached to the carboxylic acid of the other. The R functional group determines the overall shape, structure and properties of the peptide, as it will form bonds and cause the peptide to fold in on itself. By convention, the NH2 side is drawn and written on the left and the COOH side is on the right. The NH2 side is called the N-Terminus and the COOH side is called the C-Terminus.
In order to make peptides, you start with amino acids obviously. By themselves, they have the consistency of white power and are usually stored in plastic containers. Amino acids used in peptide synthesis need to have some sort of protection on the amine group to prevent unwanted reactions. This is accomplished with a molecule the most common of which is called FMOC. This is important to note because before attaching two amino acids together, we need to remove the FMOC protecting group from the amine side of one, but leave it on the other. Leaving the FMOC on one is necessary to prevent the same amino acid from coupling with itself. For instance, if I wanted to couple A to N, how do I prevent A-A couplings from occurring? Keeping A protected with FMOC ensures we only get an A-N outcome.
The R functional groups need protection as well, but will not be covered in this basic introduction.