So the reaction basically forms this product, as shown. Now, if you want to know what the reaction mechanism is in this particular reaction, I'll link you above and you can check that reaction mechanism out. So what's the entire point of step one? Well, we want to label that initial amino acid. Why do we want to label it? Well, because in the second step, what we're going to do is we're going to basically cleave this peptide bond that is holding this Allen amino acid and this Arginine amino acid.