Vilon is lysine and glutamate. Two residues. It is the shortest thing in this catalog and it is a useful object lesson in how little the word "peptide" constrains.

Why they are cheap

One coupling cycle instead of forty. Almost no deletion sequences to purify away, because there is almost nowhere for a deletion to happen. Yields that a forty-residue synthesis would never see. The price difference between the short end of this shelf and the long end is not margin; it is work.

The Khavinson series

Several of the short peptides here — vilon, testagen, pinealon, vesugen — come from a Russian research program into very short peptide sequences, and they are related by construction: vilon is KE, vesugen is KED, testagen is KEDG. Each is the one before it with a residue added.

What gets harder, not easier

• Analysis. A dipeptide is small, polar and poorly retained on a reversed-phase column, so the method that resolves a forty-mer beautifully may barely separate this from the solvent front.
• Mass confirmation. At two hundred and seventy-five grams per mole there is a great deal else in that region of the spectrum.
• Net peptide content. Counter-ions are a much larger fraction of the dry weight when the peptide itself is tiny, so the gap between label weight and peptide weight is at its widest here.