Basic Product Introduction

What is Lysine?

Lysine (abbreviated as Lys or K) is a basic, positively charged essential amino acid. Its chemical formula is C₆H₁₄N₂O₂, containing one α-amino group, one α-carboxyl group, and one side-chain ε-amino group. The side-chain ε-amino group is the key feature that distinguishes lysine from other amino acids, giving it unique bifunctional reactivity.

Core Structural Features

The lysine molecule has two amino groups (α-amino and ε-amino), both positively charged at physiological pH. This structure gives lysine the following properties:

Dual reaction sites: Both the α-amino and ε-amino groups can participate in amide bond formation, but with different reactivity. In peptide synthesis, one of the amino groups typically requires selective protection.

Side-chain length: The lysine side chain contains four methylene (-CH₂-) groups, providing a flexible linker that can position functional molecules away from the peptide backbone, reducing steric hindrance.

Positive charge: The lysine side chain is positively charged under physiological conditions, participating in electrostatic interactions and DNA binding in peptides and proteins.

Chiral center: Natural lysine has the L-configuration; D-lysine is used for unnatural peptide synthesis or resistance studies.

Classification of Lysine Derivatives

Based on protection strategies and side-chain modifications, lysine derivatives can be classified into the following categories:

Nα-monoprotected lysine

·Only the α-amino group is protected; the ε-amino group remains free

·Representative products: Fmoc-Lys-OH, Boc-Lys-OH, Z-Lys-OH

·Use: After incorporating lysine into the peptide chain in SPPS, the ε-amino group can be used for subsequent side-chain modifications

Nα,Nε-double protected lysine

·Both α-amino and ε-amino groups are protected with orthogonally removable protecting groups

·Common combinations: Fmoc-Lys(Boc)-OH, Fmoc-Lys(Mtt)-OH, Boc-Lys(Fmoc)-OH, etc.

·Use: Selective deprotection of one protecting group in SPPS for site-specific modification

Side-chain functionalized lysine

·The ε-amino group is conjugated with specific functional groups (e.g., alkyne, azide, biotin, fluorophore)

·Representative product: Nα-Fmoc-Nε-pent-4-ynoyl-L-lysine

·Use: Click chemistry, protein labeling, ADC linkers

Nε-acylated lysine

·The ε-amino group is acylated (e.g., acetylated, biotinylated)

·Representative product: Fmoc-D-Lys(Ac)-OH

·Use: Histone acetylation studies, epigenetics

C-terminal activated lysine derivatives

·The carboxyl group is pre-activated as an active ester (e.g., NHS ester, pentafluorophenyl ester)

·Representative product: Nα-Boc-Nε-2-chloro-Z-lysine NHS ester

·Use: Direct amide bond formation without additional coupling reagents

D-lysine derivatives

·D-type chiral configuration

·Representative products: Boc-D-Lys-OH, Fmoc-D-Lys(Ac)-OH

·Use: Synthesis of protease-resistant peptides, D-peptide drugs

Key Application Areas

1. Solid-Phase Peptide Synthesis (SPPS)

Lysine is one of the most common amino acids in peptide sequences. The protection and deprotection strategies for its side-chain amino group directly impact the efficiency of peptide synthesis.

Standard lysine incorporation: Fmoc-Lys-OH is the most commonly used lysine monomer. In standard Fmoc-SPPS, Fmoc-Lys-OH is used directly for coupling reactions with the ε-amino group remaining free (typically as a salt such as hydrochloride or acetate). After coupling, the ε-amino group does not participate in subsequent steps until final deprotection.

Orthogonal protection strategies: When selective modification on the lysine side chain is required (e.g., introducing PEG, biotin, fluorescent probes), orthogonal protection strategies are necessary. For example, Fmoc-Lys(Boc)-OH: Fmoc protects the Nα (removed by piperidine), Boc protects the Nε (removed by TFA). Through orthogonal deprotection, site-specific modifications can be performed at defined positions in the peptide chain.

Side-chain acylated lysine: Lysine acetylation in histones is an important epigenetic modification. Fmoc-Lys(Ac)-OH can be used directly to synthesize peptides containing acetylated lysine for studying the relationship between histone acetylation and gene expression. The Fmoc-D-Lys(Ac)-OH on the page is D-type acetylated lysine for synthesizing acetylated peptides containing unnatural amino acids.

Steric hindrance management: The flexible side chain of lysine can be long. When incorporating multiple consecutive lysines (e.g., KKKK sequence), coupling efficiency may decrease. In such cases, highly active coupling reagents (such as HATU) can be selected or reaction times can be extended.

2. Click Chemistry and Bioorthogonal Labeling

The lysine side-chain amino group can be modified to alkyne or azide groups, enabling conjugation of various functional molecules via click chemistry (CuAAC or SPAAC).

Alkynylated lysine: The Nα-Fmoc-Nε-pent-4-ynoyl-L-lysine on the page is a typical example. The ε-amino group of this molecule is conjugated with a pent-4-ynoyl group bearing a terminal alkyne. After incorporating this derivative into a peptide chain during SPPS, azide-labeled molecules (such as fluorescent dyes, biotin, PEG chains, drug molecules) can be conjugated via click chemistry.

Azido lysine: Similarly, the ε-amino group can be conjugated with an azide-containing acyl group (e.g., azidoacetyl) for reaction with alkyne-labeled molecules.

Copper-free click chemistry: Using cyclooctyne-containing lysine derivatives (such as DBCO-lysine), rapid reaction with azides can be achieved under copper-free conditions, avoiding copper ion toxicity to biological systems and enabling live-cell labeling.

3. ADC Linkers and Antibody-Drug Conjugates

Antibody-Drug Conjugates (ADCs) consist of three components: antibody, linker, and cytotoxic drug. The lysine side-chain amino group is one of the common sites for conjugating the linker to the antibody.

Lysine-based ADC conjugation: Antibody surfaces contain multiple lysine residues whose ε-amino groups react with activated esters (such as NHS esters) on the linker to form stable amide bonds. The Nα-Boc-Nε-2-chloro-Z-lysine NHS ester on the page is a pre-activated lysine derivative. Its C-terminal NHS ester can directly react with the lysine amino groups on antibodies, while the Nα-Boc and Nε-2-chloro-Z protecting groups protect both amino groups of lysine to prevent self-polymerization.

Heterobifunctional linkers: The dual-amino structure of lysine can be used to design heterobifunctional linkers: one end connects to the antibody via an NHS ester, and the other end connects to the drug molecule via maleimide, click chemistry, or other reactions.

Site-specific conjugation: Through orthogonal protection strategies, a single lysine can be introduced at a specific position in a peptide or protein, enabling site-specific ADC conjugation.

4. Protein Chemical Modification

Lysine labeling: Lysine residues on protein surfaces can be modified with NHS esters to introduce fluorescent probes (such as FITC, Cy dyes), affinity tags (such as biotin), crosslinkers, etc. The advantages are mild reaction conditions (pH 7-9, room temperature); the disadvantage is random modification sites (multiple lysines on the protein surface), resulting in product mixtures.

Site-specific labeling: Through genetic code expansion techniques, unnatural lysine derivatives (such as those containing alkyne, azide, benzophenone, etc.) can be introduced at specific sites in proteins for site-specific labeling.

Protein crosslinking: Homobifunctional crosslinkers (such as DSS, BS³) or heterobifunctional crosslinkers (such as Sulfo-SMCC) crosslink proteins via lysine side-chain amino groups for studying protein-protein interactions.

5. Dendrimers and Polylysine

Poly-L-lysine (PLL) is a cationic polymer formed by the polymerization of lysine, widely used in drug delivery and gene transfection.

Gene delivery vectors: PLL electrostatically binds to negatively charged DNA or RNA to form complexes, protecting nucleic acids from degradation and promoting cellular uptake. Different molecular weights of PLL exhibit varying transfection efficiency and cytotoxicity.

Drug delivery: PLL can serve as a drug carrier, with its side-chain amino groups enabling conjugation of drug molecules, targeting ligands (such as folic acid, RGD peptides), PEG chains, etc.

Cell adhesion coating: PLL is commonly used to coat cell culture dishes, promoting cell attachment and growth through positive charges.

6. Histone and Epigenetics Research

Lysine acetylation is an important form of histone modification, regulating biological processes such as gene transcription and DNA repair.

Acetylated histone peptides: Fmoc-Lys(Ac)-OH can be used to synthesize histone peptides containing position-specifically acetylated lysine for studying the effects of acetylation on chromatin structure and function.

HDAC substrates: Acetylated lysine peptides can serve as substrates for histone deacetylases (HDACs) for enzyme activity assays and inhibitor screening.

Antibody production: Peptides containing acetylated lysine can be used to generate antibodies that specifically recognize acetylated histones.

The Fmoc-D-Lys(Ac)-OH on the page is D-type acetylated lysine for synthesizing acetylated peptides containing D-amino acids, enhancing peptide stability in biological systems for long-term tracking or in vivo studies.

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