Lysine

Lysine is the second most common target residue used in the design of TCIs and related covalent ligands. Its appeal lies in its abundance in human proteins, which is approximately three times higher than that of cysteine (5.8% vs. 1.9%). This significantly increases the number of proteins suitable for covalent targeting, especially given that many human proteins lack ligandable cysteine residues. Moreover, it has been suggested that functional lysines have a lower probability of being replaced by mutation, as they often play a crucial role in catalysis by acting as bases or nucleophiles. Additionally, lysines are essential for maintaining the structural integrity of proteins and for regulating post-translational modifications (PTMs). Consequently, targeting lysine has garnered significant interest in recent years.

Through careful selection, we constructed a structural filter containing over 110 electrophilic groups. By analyzing the electrophilic fragments selected by the structural filter, we removed any molecules with trivial or undesirable structural features. Ultimately, we obtained 445 fragment molecules which can target lysine residue and can be used for fragment-based covalent drug discovery.

Recently, significant advancements in tyrosine-targeting electrophiles have primarily occurred in the field of protein-protein interactions (PPIs), where cysteine residues are often underrepresented and novel chemistries are needed to address these interfaces. In this context, tyrosines are frequently more accessible compared to more buried binding sites. Moreover, they are commonly found at "hot spots," which are functional epitopes of PPIs, with 12.3% of the residues consisting of tyrosines. This prevalence is likely due to the hydrophobic nature of tyrosine, its ability to participate in aromatic π-interactions, and its capacity for hydrogen bonding. Beyond PPIs, some progress has also been made in covalent tyrosine targeting in other areas where more commonly addressed side chains are lacking. Even though tyrosine has a slightly lower pKa value compared to the protonated lysine side chain (approximately 10 vs. 10.5 for the unprotected amino acid side chains), significantly less progress has been made in the development of tyrosine-targeted covalent ligands compared to lysine. This is likely due to the reduced flexibility of the tyrosine side chain and the greater steric hindrance of its hydroxy group, which makes it more challenging to adopt suitable reaction geometries.

Through careful selection, we constructed a structural filter containing over 110 electrophilic groups. By analyzing the electrophilic fragments selected by the structural filter, we removed any molecules with trivial or undesirable structural features. Ultimately, we obtained 124 fragment molecules which can target tyrosine residue and can be used for fragment-based covalent drug discovery.

A histone modification, a covalent post-translational modification (PTM) to histone proteins, includes methylation, phosphorylation, acetylation, ubiquitylation, and sumoylation, etc. In general, histone modifications are catalyzed by specific enzymes that act predominantly at the histone N-terminal tails involving amino acids such as lysine or arginine, as well as serine, threonine, tyrosine, etc. The PTMs made to histones can impact gene expression by altering chromatin structure or recruiting histone modifiers. Histone modifications act in diverse biological processes such as transcriptional activation/inactivation, chromosome packaging, and DNA damage/repair. Deregulation of histone modification contributes to many diseases, including cancer and autoimmune diseases.

MCE owns a unique collection of 904 bioactive compounds targeting Epigenetic Reader Domain, HDAC, Histone Acetyltransferase, Histone Demethylase, Histone Methyltransferase, Sirtuin, etc. Histone Modification Research Compound Library is a useful tool for histone modification research and drug screening.

Small molecule covalent inhibitors, or irreversible inhibitors, are a type of inhibitors that exert their biological functions by irreversibly binding to target through covalent bonds. Compared with non-covalent inhibitors, covalent inhibitors have obvious advantages in bioactivity, such that covalent warheads can target rare residues of a particular target protein, thus leading to the development of highly selective inhibitors and achieving a more complete and continued target occupancy in living systems. In recent years, the distinct strengths of covalent inhibitors in overcoming drug resistance had been recognized. However, toxicity can be a real challenge related to this class of therapeutics due to their potential for off-target reactivity and has led to these drugs being disfavored as a drug class. The drug design and optimization of covalent inhibitors has become a hot spot in drug discovery.

MCE Lead-like Covalent Screening Library offers a valuable resource of 1,049 lead-like compounds with commonly used covalent warheads. These warheads, such as acrylamide, activated terminal alkyne, acyloxymethyl ketone, and boronic acid, are capable of reacting with specific amino acid residues, including cysteine, lysine, serine, and histidine. The inclusion of these reactive warheads in the library allows researchers to explore the potential of covalent inhibition, a powerful approach in drug discovery.

Boronic acid and boronic ester represent a relatively novel and promising chemical structure in drug design. Boronic acid exists in an sp²-hybridized state, possessing an empty p-orbital that can act as a Lewis acid to accept lone pairs from heteroatoms (O, N, or S). This Lewis acidity enables it to form reversible covalent bonds with amino acid residues such as lysine, serine, threonine, and histidine. Currently, five FDA-approved drugs containing boronic acid or boronic ester predominantly involve such covalent binding mechanisms in their interactions with target proteins. Furthermore, boronic acid can serve as a bioisostere for carboxylic acids, phosphates, and phenolic groups, utilized to improve pharmacokinetic properties and enhance drug efficacy.

To date, five boron-containing drugs have been approved by the FDA. The unique properties of boronic acids and boronic esters confer significant potential in drug design, with applications spanning cancer therapy (e.g., multiple myeloma), anti-infectives (e.g., fungal infections, tuberculosis), anti-inflammatory treatments (e.g., atopic dermatitis), antibacterial agents (e.g., carbapenem-resistant bacterial infections), and Reactive Oxygen Species (ROS)-responsive prodrugs, among others. The MCE Boronic Acid/Boronic Ester Fragment Library, which contains 1,488 compounds, serves as a valuable tool for the development of boron-containing drugs.

DEL technology enables the simultaneous screening of millions or billions of compounds in a single tube by covalently linking each small molecule with a unique DNA sequence. Traditional DEL screening primarily focuses on identifying non-covalent binding molecules, where interactions with the target are reversible. In contrast, DNA‑encoded covalent library is an ultra‑high‑throughput screening library developed on the basis of conventional DNA‑encoded library technology. It incorporates controllable electrophilic covalent warheads capable of forming irreversible covalent bonds with amino acid residues at the active sites of target proteins, including Cys, Lys, Ser, Tyr, and others. This covalent binding enhances binding affinity, prolongs residence time at the target site, and has the potential to overcome challenges associated with traditional non-covalent inhibitors, such as drug resistance or off-target effects.

Each compound in the library contains both a binding domain and an electrophilic warhead. It first recognizes and binds to the target through non covalent interactions, and then forms a stable covalent bond with key amino acid residues to achieve irreversible inhibition. This library is specifically designed for the discovery of potent, long lasting, and highly selective covalent inhibitors, particularly for undruggable targets such as kinases, GPCRs, proteases, and mutant oncoproteins. Each molecule is uniquely labeled with a DNA barcode for molecular identification and sequencing decoding.

This library is an advanced and highly diverse collection, consists of 35 independent sub-libraries with a total scaleof 14 million compounds, It incorporates over 14 experimentally validated covalent warheads capable of targeting cysteine, lysine, arginine, aspartic acid and glutamic acid. This library is constructed with diverse drug like core scaffolds and integrated controllable covalent warheads, it features structural diversity, reaction spec

Sulfonyl fluoride (-SO₂F) overcomes the bottleneck of target selectivity in traditional covalent warheads through its unique chemical and biological properties, which rely heavily on cysteine (Cys) residues. Featuring high stability and tunable electrophilicity under physiological conditions, it can target a wide range of nucleophilic residues including lysine (Lys), tyrosine (Tyr), serine (Ser), and histidine (His). It offers the advantages of a broader druggable space, lower off-target risks, and long-lasting efficacy, with numerous reported cases in the research of covalent inhibitors, Molecular glue, PROTACs, and chemical biology probe development.

MCE constructs a highly diverse sulfonyl fluoride fragment library based on the reactivity, stability and physiological compatibility of sulfonyl fluoride. The library contains 1000 efficiently synthesized and stable sulfonyl fluoride fragments, which ensure precise reactivity of the warhead and retain sufficient derivatization space for subsequent optimization. Combined with the modular strategy of SuFEx click chemistry, it enables versatile modification of compounds and functionalization of complex molecules, improves the efficiency of structural optimization and rapidly expands druggability, making it suitable for high-throughput probe and custom covalent library construction. It provides an efficient research tool for the development of broad-spectrum covalent inhibitors targeting Lys/Tyr/Ser/His, covalent PROTACs for E3 ligases and chemical biology probe development, meeting the requirements of modern drug research for high throughput, high success rate and high derivatization potential.

This library contains 1,162 sulfonyl fluoride fragments with high structural diversity, favorable drug-like properties and tunable electrophilicity. It is well suited for precise targeting of non-Cys residues and meets the criteria of simple structure and high derivatization potential. It effectively improves