The synthesis of peptides is a cornerstone of modern biochemistry and pharmaceutical research. At the heart of many peptide synthesis strategies, particularly Solid-Phase Peptide Synthesis (SPPS), are protected amino acids. Fmoc-Lys(Boc)-OH, a chemically modified form of the essential amino acid lysine, is a prime example of such a crucial building block. Understanding its chemical properties and how it functions within the SPPS cycle is vital for any scientist or procurement specialist in the field.

Fmoc-Lys(Boc)-OH, chemically designated as Nα-(9-Fluorenylmethyloxycarbonyl)-Nε-tert-butyloxycarbonyl-L-lysine, is designed for efficient and controlled peptide chain assembly. Its structure features two key protecting groups: the Fmoc group attached to the alpha-amino group and the Boc (tert-butyloxycarbonyl) group protecting the epsilon-amino group on the lysine side chain. The Fmoc group serves as the temporary protecting group for the N-terminus of the amino acid, allowing for sequential addition to a growing peptide chain anchored to a solid support. This group is typically removed under mildly basic conditions, often using a solution of piperidine in dimethylformamide (DMF).

The Boc group on the epsilon-amino function of lysine is more robust. It is stable to the basic conditions used for Fmoc removal, meaning it remains in place throughout the multiple cycles of deprotection and coupling required to build a peptide chain. This selectivity is critical; without it, the reactive side-chain amine of lysine could participate in unwanted reactions, leading to side products and reduced yield of the desired peptide. Once the peptide chain has been fully assembled, the Boc group, along with other side-chain protecting groups and the peptide itself, is cleaved from the resin using a strong acid cocktail, commonly containing trifluoroacetic acid (TFA). The presence of scavengers in the cocktail helps to trap reactive carbocations formed during cleavage, preventing damage to sensitive amino acid residues in the peptide.

The physical and chemical properties of Fmoc-Lys(Boc)-OH also contribute to its widespread use. It typically presents as a white to off-white powder, with a melting point in the range of 130-135 °C (with decomposition). Its solubility in common organic solvents used in peptide synthesis, such as DMF, is generally good. The optical activity, usually specified as [α]20/D -12±1° (c=1% in DMF), confirms its L-configuration, which is essential for producing biologically active peptides. For those looking to buy, understanding these specifications helps in selecting a high-quality product from a reputable supplier.

The importance of Fmoc-Lys(Boc)-OH cannot be overstated in the synthesis of peptides containing lysine. Its carefully designed chemical structure facilitates predictable and efficient peptide synthesis, making it a staple in research laboratories and pharmaceutical manufacturing worldwide. When procuring this essential reagent, ensuring a reliable supply of high-purity Fmoc-Lys(Boc)-OH from a trusted manufacturer is key to the success of peptide-based projects.