Fmoc-Lys-OH · HCl

Fmoc-Lys-OH · HCl is an Fmoc-protected lysine hydrochloride salt in which the α-amino group is masked by the base-labile 9H-fluorenylmethoxycarbonyl (Fmoc) protecting group while the ε-amino side chain remains available for orthogonal protection, functionalization, or selective peptide coupling strategies. The molecule contains the lysine backbone with a stereogenic α-carbon (typically supplied as the L-configuration) and a terminal carboxylic acid suited for amide bond formation after activation. Protonation by the hydrochloride counterion improves handling of the free base form and influences salt stability during synthesis and storage, while the Fmoc carbamate provides predictable deprotection under standard base conditions used in solid-phase peptide synthesis. The presence of a primary ε-amino group enables downstream derivatization to generate protected amino acid derivatives, side-chain conjugates, and lysine-containing peptide building blocks for biochemical and industrial workflows.

1. Peptide Synthesis

Fmoc-Lys-OH · HCl is used as a lysine building block in peptide synthesis where the Fmoc-protected α-amino group supports controlled iterative coupling to a growing peptide chain. The free ε-amino side chain can be selectively protected (for example, via orthogonal amine-protecting groups) or converted into side-chain-functional lysine variants to manage chemoselectivity during assembly. The carboxylic acid participates in standard peptide coupling chemistries after activation, enabling formation of amide linkages while maintaining the L stereocenter for stereochemically consistent peptide frameworks. The resulting lysine-containing peptides and peptide fragments can be applied to structure-activity relationship studies, peptide library construction, and protein-mimetic scaffold generation, aligning lysine side-chain chemistry with peptide science requirements.

2. Side-Chain Functionalization

Fmoc-Lys-OH · HCl supports side-chain functionalization workflows in synthetic organic chemistry and chemical biology by providing a primary ε-amino group for controlled derivatization. The ε-amino functionality can be transformed into protected amines, acylated derivatives, sulfonamides, ureas, carbamates, or conjugation-ready handles while the Fmoc group serves as an orthogonal protection element for the α-amino terminus. Salt formation as the hydrochloride can improve reproducibility of amine reactivity and handling during derivatization steps that precede peptide incorporation. Downstream products include lysine side-chain analogs for bioconjugation chemistry, affinity-tagged peptides, and functional peptide intermediates that retain peptide-coupling compatibility through the preserved carboxyl group.

3. Bioconjugation Chemistry

Fmoc-Lys-OH · HCl is suitable for bioconjugation-oriented intermediate preparation where lysine's ε-amino group enables attachment strategies to biomolecules, linkers, and labeling reagents. The Fmoc-protected α-amino group allows the compound to be incorporated into peptide carriers or to generate defined lysine-containing conjugation motifs with controlled placement of the reactive amine. The carboxyl group provides a handle for conversion into activated esters or amide-forming derivatives that can later connect to targeting ligands or scaffold proteins in a modular manner. Lysine-containing conjugates derived from this building block can be used in chemical biology research to probe molecular recognition, map interaction interfaces, and generate labeled peptide constructs for analytical and mechanistic studies.

4. Protein Engineering

Fmoc-Lys-OH · HCl serves as a chiral amino acid intermediate for protein engineering and peptide-based protein mimicry by enabling incorporation of lysine residues with defined stereochemistry into synthetic segments. The Fmoc protection strategy supports sequential assembly of lysine-containing peptides that can be used as building blocks for recombinant protein fragments, domain mimics, or engineered binding motifs. The ε-amino side chain can be protected or functionalized to tune charge distribution, hydrogen-bonding patterns, and conjugation sites relevant to protein-ligand interaction mapping. Downstream use includes generating defined protein engineering reagents, engineered peptide domains, and site-specific lysine variants that can be applied to mechanistic investigations and biomolecular interaction studies.

5. Pharmaceutical Manufacturing

Fmoc-Lys-OH · HCl is applied in pharmaceutical manufacturing contexts as a protected amino acid input for producing lysine-containing peptide intermediates used in drug substance or drug product manufacturing supply chains. The Fmoc carbamate and carboxylic acid functionality align with established peptide synthesis workflows, supporting scalable preparation of protected peptide building blocks and controlled deprotection/coupling sequences. The hydrochloride salt form can facilitate consistent material handling and can influence the reproducibility of amine activation steps during intermediate preparation. Lysine side-chain chemistry enabled by the ε-amino group supports downstream formation of conjugatable or stability-tuned peptide structures, supporting fine chemical synthesis routes that require predictable protection-group behavior and stereochemically defined amino acid incorporation.

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