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HATU

HATU, systematically named O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate, is a highly efficient uronium salt coupling reagent primarily used in organic synthesis for facilitating amide bond formation between carboxylic acids and amines, especially in peptide coupling reactions.^[1] With the molecular formula C₁₀H₁₅F₆N₆OP, a molecular weight of 380.23 g/mol, and CAS number 148893-10-1, it appears as a white to off-white powder with a melting point of 183–185 °C and is soluble in polar aprotic solvents such as DMF and DMSO.^[1] HATU operates by activating carboxylic acids to form active esters, enabling rapid and high-yield couplings under mild conditions, often in the presence of bases like DIPEA or TEA.^[2] Developed by Louis A. Carpino and colleagues in the early 1990s, HATU represents a third-generation advancement in peptide coupling reagents, building on the 1-hydroxy-7-azabenzotriazole (HOAt) additive introduced in 1993 to enhance carbodiimide-mediated reactions.^[3] Its uronium structure, confirmed through X-ray crystallography and NMR studies in 2002, features the true O-connected isomer, which contributes to its stability and reactivity superior to second-generation analogs like HBTU. HATU was first reported in 1994 for its ability to suppress racemization in solid-phase peptide synthesis, particularly with challenging amino acids like histidine, making it a gold standard for both solution- and solid-phase methodologies compatible with Fmoc and Boc strategies.^[5] In practice, HATU excels in synthesizing difficult sequences by providing faster coupling rates and higher purity products with minimal byproducts, though it requires careful handling due to its potential to cause allergic skin reactions.^[6] It is routinely employed in the preparation of therapeutic peptides, natural products, and complex amides, often outperforming phosphonium-based alternatives like PyBOP in yield and stereocontrol.^[7] Ongoing research continues to explore HATU's applications beyond peptides, including in PNA synthesis and acylation of alcohols.^[8]

Chemical Identity

Nomenclature and Formula

HATU, an abbreviation for hexafluorophosphate azabenzotriazole tetramethyl uronium, is the common name for the coupling reagent widely used in organic synthesis, particularly for amide bond formation in peptide chemistry.^[9] Although commonly referred to by the systematic IUPAC name O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (corresponding to the O-uronium isomer), the commercial form is the N-guanidinium isomer with the systematic name 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate.^[10]^[11] The molecular formula of HATU is C₁₀H₁₅F₆N₆OP, with a molar mass of 380.23 g/mol.^[10] It is identified by the CAS registry number 148893-10-1.^[10]

Structure and Tautomers

HATU is an ionic compound consisting of a bulky organic cation paired with a hexafluorophosphate (PF₆⁻) counterion, which provides solubility in polar organic solvents. The core structure of the cation centers on a central carbon atom bonded to two dimethylamino groups (forming the tetramethyluronium-like moiety), a 7-azabenzotriazol-1-yl group, and an oxygen or nitrogen linkage that defines its isomeric forms. This architecture incorporates the 7-azabenzotriazole ring—a fused 1,2,3-triazolo[4,5-b]pyridine system—as a key leaving group component, alongside the electron-withdrawing dimethylaminomethylene unit and the non-coordinating PF₆⁻ anion, which imparts overall stability to the salt.^[11] The key functional groups in HATU include the heterocyclic azabenzotriazole ring, which enhances reactivity through its electron-deficient nature; the tetramethylguanidinium or uronium core, responsible for activating carboxylic acids; and the hexafluorophosphate anion, which balances the positive charge without participating in reactions. These elements collectively enable HATU's role as a coupling agent, with the azabenzotriazole moiety mimicking additives like HOAt to minimize racemization in sensitive substrates.^[11] HATU exhibits constitutional isomerism rather than classical tautomerism, existing in an O-linked uronium form (O-HATU) and an N-linked guanidinium form (N-HATU), which differ in the connectivity of the azabenzotriazole group to the central carbon. In the uronium form, the oxygen atom of the HOAt-derived group links directly to the carbon, rendering it highly electrophilic and reactive; the guanidinium form involves nitrogen linkage, forming a more stable but less reactive structure. Commercial HATU is the guanidinium (N-form), as confirmed by X-ray crystallography and NMR spectroscopy, with characteristic ¹H NMR singlets at δ 3.02 and 3.37 ppm, and IR absorption at 1668.9 cm⁻¹.^[11]^[12] The uronium (O-form) can be synthesized separately using base-free conditions with potassium salts of the aza-hydroxybenzotriazole, but it spontaneously isomerizes to the guanidinium form in the presence of tertiary amines or other bases, a process monitored by IR spectroscopy showing a shift from 1711.5 cm⁻¹ to 1668.9 cm⁻¹. This isomerization is irreversible under typical peptide synthesis conditions, with no observable equilibrium favoring the uronium form; the guanidinium isomer is thermodynamically preferred and constitutes the active species in standard applications, though the pure O-form demonstrates superior coupling efficiency when accessible.^[11]

Physical and Chemical Properties

Appearance and Solubility

HATU appears as a white to off-white crystalline solid or powder, though some samples may appear light brown.^[13]^[14]^[1] This compound has a reported melting point of 183–185 °C, with decomposition upon melting, though differential scanning calorimetry (DSC) indicates an onset of thermal decomposition at 161 °C.^[1]^[14]^[15] The polar nature of HATU's structure contributes to its solubility profile, making it highly soluble in polar aprotic solvents such as DMF and DMSO (e.g., up to 200 mg/mL in DMSO).^[13] It shows solubility in acetonitrile but is insoluble in water and non-polar solvents like hexane.^[14]^[16] HATU is hygroscopic and requires storage in a cool, dry place to avoid moisture absorption.^[17]^[1]

Stability and Reactivity

HATU exhibits good chemical stability under standard ambient conditions and at room temperature, making it suitable for typical laboratory use when properly handled.^[18] However, its thermal stability is limited at elevated temperatures; differential scanning calorimetry (DSC) analysis reveals an onset of decomposition at 161 °C with a substantial exothermic energy release of -1131 J/g, which can result in explosive decomposition if the material is heated under confinement or in the presence of ignition sources.^[15] Hazardous decomposition products under such conditions include carbon oxides, nitrogen oxides, phosphorus oxides, and hydrogen fluoride.^[18] As a uronium salt, HATU is moisture-sensitive and can hydrolyze in aqueous media to form inactive byproducts such as urea and HOAt, necessitating avoidance of water exposure during handling.^[19] In terms of general reactivity, HATU functions as a potent electrophile, primarily intended for activating carboxylic acids through nucleophilic attack at the central carbon of its uronium moiety. It is incompatible with strong oxidizing agents, which may trigger violent reactions.^[18] Strong nucleophiles or bases can react with the uronium group, potentially leading to degradation.^[20] To minimize degradation, HATU is best stored under desiccated, cool conditions (2–8 °C), using tightly sealed containers to protect against moisture and heat.^[18]

Synthesis

Preparation from HOAt and TCFH

HATU is synthesized in the laboratory through the reaction of 1-hydroxy-7-azabenzotriazole (HOAt) with tetramethylchloroformamidinium hexafluorophosphate (TCFH) in the presence of a base such as triethylamine. This method involves the direct formation of the uronium salt by activating the hydroxyl group of HOAt.^[21] The procedure typically employs dry dichloromethane as the solvent under a nitrogen atmosphere. HOAt and TCFH are combined in equimolar amounts (e.g., 1.5 mmol each), with a slight excess of triethylamine (1.1 equiv) added to neutralize the HCl byproduct. The mixture is initially cooled to 0°C for 30 minutes to control the exothermic reaction, then stirred at room temperature for 1.5 hours. A white precipitate forms, which is collected by filtration.^[21] Further purification is achieved by recrystallization from acetonitrile-ether (twice) or by silica gel chromatography, yielding HATU as a white solid. Typical yields range from 69% in standard protocols to 82% under optimized conditions with careful exclusion of moisture.^[21] The reaction mechanism proceeds via nucleophilic attack by the oxygen of HOAt on the electrophilic carbon of the formamidinium moiety in TCFH, facilitated by deprotonation of HOAt under basic conditions. This displaces chloride ion, generating the tetramethyluronium cation bound to the azabenzotriazolyl group, with hexafluorophosphate (PF₆⁻) serving as the counterion. Byproducts include HCl (neutralized by base).^[21] The overall transformation can be represented as:

\ce{HOAt + (Me2N)2C=Cl^+ PF6^- + Et3N -> [HOAt-C(NMe2)2]^+ PF6^- + Et3NH^+ Cl^-}

where HATU is the uronium salt [ \ce{(7-azabenzotriazol-1-yloxy)-C(NMe2)2^+ PF6^-} ].^[21] This remains the primary laboratory preparation method, though variations using other bases like imidazole have been reported.^[21]

Commercial Availability and Alternatives

HATU is widely available from established chemical suppliers, including Sigma-Aldrich and Thermo Scientific (incorporating the former Alfa Aesar portfolio), where it is offered in purities typically exceeding 97%, such as ≥97% or ≥98.0% by CHN analysis.^[1]^[12]^[22] These suppliers provide HATU in a range of quantities, from 1 g vials suitable for academic and small-scale research to 100 g or larger packs for industrial or high-volume applications. As of November 2025, at small scales, HATU is costly, with prices ranging from $70 to $100 per gram depending on purity and supplier, reflecting its specialized role in organic synthesis. Bulk procurement significantly reduces expenses, often to 50–70% of small-scale pricing or less upon request, making it more viable for large-scale peptide manufacturing.^[1]^[12] HATU is not classified as a controlled substance under major regulatory frameworks, such as those administered by the DEA or Health Canada, and is treated as a standard research chemical. It requires handling in accordance with general laboratory safety protocols, including the use of gloves and ventilation due to its potential as a skin and eye irritant.^[6]^[23] Common commercial alternatives to HATU include other uronium- and phosphonium-based coupling reagents, such as HBTU (O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate) and COMU (O-(1-cyano-2-ethoxy-2-oxoethylideneaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate), both available from suppliers like Sigma-Aldrich and Bachem with comparable purities above 97% and pricing structures that follow similar small-scale versus bulk economics. Additional options encompass PyBOP (benzotriazole-1-yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate) and TBTU, which are also readily sourced in gram to kilogram quantities for analogous synthetic needs.^[24]

Mechanism of Action

Uronium vs. Iminium Forms

HATU exists in two tautomeric forms: the uronium form, characterized by an O-linked structure where the positively charged central carbon is bonded to the oxygen atom of the 7-azabenzotriazol-1-yl moiety, and the iminium form (also known as the guanidinium form), featuring an N-linked arrangement. The uronium form serves as the more reactive electrophile, making it the preferred species for carboxylic acid activation in coupling reactions due to its enhanced electrophilicity at the central carbon. The O-uronium structure was confirmed by X-ray crystallography. In contrast, the iminium form is less reactive and arises via base-catalyzed rearrangement of the uronium tautomer, with the nitrogen linkage reducing the electrophilic character of the central carbon. The isomerization from O- to N-form is induced by tertiary amines and is not readily reversible. HATU is isolated and characterized as the O-uronium form, which predominates under anhydrous conditions without base, supporting efficient reactivity in typical peptide synthesis. Spectroscopic evidence confirms the presence and distinction of these tautomers, particularly through nuclear magnetic resonance (NMR) analysis. For instance, ¹H NMR spectra exhibit distinct chemical shifts for the N-methyl groups: the uronium form shows a singlet around 3.24 ppm, while the iminium form displays two singlets at 3.02 ppm and 3.37 ppm, reflecting differences in the electronic environment of the tetramethyluronium moiety. These characteristic signals allow for identification and monitoring of the tautomeric forms in solution.

Role in Amide Bond Formation

HATU serves as a key coupling reagent in amide bond formation by activating carboxylic acids to enable efficient nucleophilic attack by amines, particularly in peptide synthesis. In the activation step, HATU reacts with a carboxylic acid in the presence of a base, such as N,N-diisopropylethylamine (DIPEA), to form an active 7-azabenzotriazole ester (HOAt ester) intermediate. This process involves the carboxylate anion displacing the tetramethyluronium group from HATU, generating the reactive ester and tetramethyluronium hexafluorophosphate as a byproduct.^[25]^[26] Subsequently, the amine nucleophile attacks the carbonyl carbon of the active ester, displacing the HOAt leaving group and forming the desired amide bond while regenerating HOAt. The overall mechanism can be represented as:

\text{RCOOH} + \text{HATU} + \text{R'NH}_2 + \text{base} \rightarrow \text{RCONHR'} + \text{HOAt} + \text{tetramethylurea} + \text{PF}_6^-

This pathway ensures rapid and selective amide formation under mild conditions.^[25]^[26] To further optimize the reaction and suppress racemization (epimerization) during peptide coupling, HATU can be employed with additives such as 1-hydroxybenzotriazole (HOBt) in some cases. These additives help stabilize the active intermediate and minimize side reactions, particularly with chiral amino acids. The reaction is typically conducted in polar aprotic solvents like dimethylformamide (DMF) at room temperature, promoting high reactivity without requiring elevated temperatures.^[25]^[26] HATU-mediated couplings achieve high efficiency, routinely delivering yields of 90-99% with minimal epimerization, making it superior to earlier reagents for challenging substrates. This performance stems from the electron-withdrawing nature of the azabenzotriazole moiety, which enhances the electrophilicity of the active ester.^[26]

Applications

Peptide Coupling in Synthesis

HATU serves as a primary coupling reagent for forming amide bonds between protected amino acids in peptide synthesis, activating the carboxylic acid group to facilitate nucleophilic attack by the amine component. This process is central to both solid-phase peptide synthesis (SPPS) and solution-phase methods, enabling the assembly of peptides from individual amino acid units. In SPPS, particularly within Fmoc and Boc strategies, HATU is employed to couple incoming Fmoc- or Boc-protected amino acids to the growing peptide chain anchored on a resin support. Typical protocols involve 3-5 equivalents of HATU relative to the resin loading, combined with 6-10 equivalents of a base such as N,N-diisopropylethylamine (DIPEA), in solvents like dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP). Reactions proceed at room temperature for 30-120 minutes, ensuring high yields while minimizing side reactions.^[7] In solution-phase peptide synthesis, HATU excels in fragment coupling, where larger peptide segments are joined. It is typically used at 1-2 equivalents relative to the carboxylic acid, with 2-3 equivalents of DIPEA, in DMF at 0-25°C for 15-60 minutes, promoting rapid and selective amide formation. This approach is particularly valuable for synthesizing longer peptides or when scaling up production beyond automated SPPS capabilities. HATU's mechanism involves the formation of an active ester intermediate, as detailed in the section on its role in amide bond formation, which enhances reactivity without excessive heating.^[27]^[7] Compared to older reagents like dicyclohexylcarbodiimide (DCC), HATU offers significant advantages, including superior suppression of racemization during coupling, especially for urethane-protected amino acids in Fmoc/Boc chemistries, with epimerization levels often below 1% under optimized conditions. It is also highly compatible with sterically hindered amino acids, such as N-methylated or β-branched residues, enabling efficient incorporation where DCC fails due to slower activation and higher byproduct formation. These properties stem from HATU's azabenzotriazole-derived structure, which provides milder activation and better solubility in polar solvents.^[27]^[3] Despite these benefits, HATU has limitations, notably the generation of byproducts such as tetramethylurea and hexafluorophosphate salts, which can complicate purification in solution-phase reactions due to their fluorous nature and solubility. Excess HATU may also lead to guanidine side products if not carefully controlled. An illustrative protocol for solution-phase coupling involves treating a carboxylic acid (1 equiv) with the amine (1.1 equiv), HATU (1.1 equiv), and DIPEA (2 equiv) in DMF at room temperature for 30 minutes, yielding the amide in high purity after standard workup.^[24]^[7]

Use in Drug Discovery and Other Reactions

HATU plays a pivotal role in drug discovery by facilitating the rapid synthesis of peptidomimetics and small-molecule drugs through efficient amide bond formation, enabling the exploration of diverse chemical spaces for therapeutic leads.^[28] In medicinal chemistry, it supports the construction of peptidomimetic scaffolds that mimic protein-protein interactions, accelerating the development of orally bioavailable candidates targeting challenging biological targets.^[28] Additionally, HATU is widely employed in library screening methodologies, such as DNA-encoded libraries (DELs), where it promotes high-yield on-DNA amide couplings for generating amide-based hit compounds, often achieving conversions superior to alternative reagents like DMTMM in sterically hindered scenarios.^[29] As of 2024, HATU has been integrated into the synthesis of proteolysis targeting chimeras (PROTACs) for targeted protein degradation, where it is preferred for amidation steps due to reduced racemization risks.^[30] In 2025, studies have repurposed HATU for guanylation of amines, expanding its utility beyond amides to synthesize guanidines for potential catalytic and medicinal applications.^[31] Beyond peptide linkages, HATU enables versatile applications in other reactions, including esterifications and amide formations involving non-amino acid components. For instance, it mediates the esterification of nucleosides to solid-phase supports, providing high efficiency in oligonucleotide synthesis workflows.^[32] In amide synthesis, HATU couples carboxylic acids with diverse amines, such as those derived from non-amino acid structures, to form key intermediates in organic synthesis.^[33] It also supports siRNA conjugations by enabling rapid solution-phase amide bond formation between amine-modified siRNAs and carboxylic acids, allowing the incorporation of lipophilic or functional groups without prior activation, thus streamlining the preparation of therapeutic conjugates.^[34] Furthermore, HATU facilitates one-pot diamide constructions from dicarboxylic acids and amines at ambient temperature, offering a streamlined route to symmetrical diamides used in pharmaceutical intermediates.^[35] HATU's stereospecificity is particularly valuable in maintaining chirality during the assembly of complex molecules, such as tubulysin analogs and natural product derivatives, where it minimizes racemization in amide couplings involving chiral centers.^[36] In tubulysin syntheses, for example, HATU-mediated dipeptide formations preserve the stereochemistry of key fragments like tubuvaline, enabling the production of potent antimitotic agents without epimerization.^[37] Recent post-2020 advances have integrated HATU into green chemistry protocols for peptide and conjugate synthesis, emphasizing reduced solvent use through alternative media like dipropyleneglycol dimethylether or binary mixtures that maintain high coupling efficiency while minimizing environmental impact.^[38] These variants align with sustainability goals in pharmaceutical manufacturing by lowering solvent volumes and enabling recyclable systems without compromising reactivity.^[39] In macrocyclization and cross-coupling setups, HATU consistently delivers high yields, often exceeding 85%, as demonstrated in the cyclization of chiral polyamines from natural building blocks, where it outperforms other reagents under dilute conditions.^[40] This reliability supports the scalable synthesis of macrocyclic drug candidates, enhancing their potential in therapeutic applications.^[41]

History and Development

Invention by Carpino

HATU, or O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, was invented by Louis A. Carpino at the University of Massachusetts Amherst as a potent coupling reagent for peptide synthesis.^[42] Carpino developed HATU to improve upon the performance of earlier reagents like HBTU, which, while effective, suffered from slower coupling rates and higher tendencies toward racemization during amide bond formation.^[5] Specifically, HATU was designed to leverage the enhanced reactivity of HOAt-based active esters, providing a more efficient alternative for activating carboxylic acids in the presence of amines.^[5] The compound was first reported in a 1994 communication in Tetrahedron Letters, where Carpino and colleagues detailed its preparation and utility, along with other HOAt-derived uronium salts such as HAMTU and HAPipU.^[5] Initial experiments demonstrated HATU's superior suppression of racemization in solid-phase peptide synthesis compared to HBTU, particularly in model systems prone to epimerization.^[5] HATU's invention fell under Carpino's broader portfolio of patents on uronium salts for acylation reactions, with key coverage in U.S. Patent 5,580,981, filed in 1993 and granted in 1996, which encompasses azahydroxybenzotriazole derivatives and their uronium counterparts for amide and ester formation.^[42] This patent emphasized the structural modifications that enable these salts to outperform prior art in reactivity and selectivity, solidifying HATU's foundational role in advancing coupling agent technology.^[42]

Evolution and Improvements

In the early 2000s, HATU gained recognition as a third-generation coupling reagent, valued for its superior efficiency in minimizing racemization during amide bond formation compared to earlier phosphonium-based agents like BOP.^[43] This period also saw the introduction of cost-effective analogs such as HCTU (O-(6-chlorobenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate), developed in 2002 by Luxembourg Bio Technologies to provide reactivity intermediate between HBTU and HATU while reducing expenses in large-scale peptide synthesis. HCTU enabled faster couplings with lower racemization in difficult sequences, making it a practical alternative for industrial applications without compromising yield.^[44]^[45] In the early 2000s, investigations into HATU's structural tautomerism—specifically the equilibrium between its uronium and iminium forms—provided deeper insights into its reactivity, confirming that the O-bound uronium isomer predominates and enhances coupling efficiency.^[46] Concurrently, microwave-assisted protocols emerged to accelerate HATU-mediated couplings, reducing reaction times from hours to minutes while maintaining high purity in solid-phase peptide synthesis (SPPS). For instance, semi-automated microwave systems allowed couplings at 50–75°C with HATU/HOAt, achieving up to 95% yields for sequences prone to aggregation, as demonstrated in syntheses of cyclotides and difficult peptides.^[47]^[48] In the 2020s, efforts toward greener HATU protocols focused on sustainable solvents and recyclable supports to minimize environmental impact. Bio-based solvents like Cyrene replaced DMF in HATU couplings, enabling amide formations with comparable efficiency and facilitating easier recycling of reaction mixtures. Additionally, integration with recyclable polymeric supports in flow-based SPPS allowed repeated use of HATU-activated resins, reducing waste by up to 80% in iterative syntheses. HATU's role has since become standard in automated synthesizers, with over 10,000 citations in peptide literature underscoring its ubiquity in high-throughput production of therapeutic peptides.^[49]^[50]^[45] Key challenges, including byproduct toxicity from HOAt decomposition, have been addressed through additive optimizations such as Oxyma Pure, which suppresses hazardous benzotriazole formation while preserving HATU's stereoselectivity and yielding safer, non-explosive residues. These enhancements have broadened HATU's applicability in scalable, eco-conscious syntheses.^[7]^[24]

Safety and Handling

Health Hazards

HATU is classified as a strong skin sensitizer, capable of inducing allergic contact dermatitis upon repeated or prolonged dermal exposure. This primary hazard arises from its uronium structure, which can react with skin proteins to form haptens that trigger immune responses, leading to symptoms such as redness, itching, and blistering. Occupational exposure in laboratory settings, particularly among peptide chemists, has been linked to such sensitization, with cases progressing from mild irritation to severe reactions if contact persists.^[6] Toxicity studies indicate low acute oral toxicity, with an LD₅₀ greater than 2,000 mg/kg in rats, suggesting it is not highly lethal via ingestion in single doses. Respiratory sensitization is reported, manifesting as allergy or asthma-like symptoms including coughing and shortness of breath if inhaled, particularly in dusty environments.^[6]^[51]^[6] Documented occupational cases highlight the risks, including a 2019 report of anaphylaxis in a researcher after repeated exposure to HATU and similar uronium coupling agents during peptide synthesis, underscoring the potential for life-threatening sensitization. These incidents emphasize the importance of protective measures to mitigate exposure. A 2024 case of occupational airborne allergic sensitization to the related uronium salt HBTU involved progressive symptoms including rash, blisters, and eczema-like skin inflammation on the face and neck.^[52]^[53] The main exposure routes for HATU include dermal contact, which occurs during weighing, transfer, or spills of the solid powder, and inhalation of airborne dust generated from handling the hygroscopic material. Its physical form as a fine, off-white powder facilitates dust generation, increasing inhalation risks in poorly ventilated areas. To prevent adverse effects, handling should involve nitrile gloves, protective clothing, and operations within a fume hood.^[6] Genotoxicity assessments show that HATU is non-mutagenic, as demonstrated by negative results in the Ames bacterial reverse mutation test conducted under GLP conditions following OECD guidelines. This indicates no DNA-damaging potential in standard assays, though chronic exposure concerns remain centered on sensitization rather than carcinogenicity.^[54]

Storage and Disposal

HATU should be stored in tightly sealed containers under an inert atmosphere such as nitrogen at temperatures between 2-8°C to prevent moisture ingress and maintain stability, with a typical shelf life of 2-3 years under these conditions.^[18]^[13] It is hygroscopic and sensitive to humidity, so desiccation is essential to avoid degradation.^[16] During handling, HATU must be used in well-ventilated areas or under a fume hood to minimize inhalation of dust or vapors, and skin contact should be avoided by wearing nitrile gloves, which provide adequate protection against permeation.^[18]^[55] For spill response, absorb the material with an inert absorbent like vermiculite, then clean the affected area with soap and water; if necessary, neutralize residues with a mild base before disposal to mitigate any irritant effects.^[56]^[57] As a hazardous substance, HATU disposal requires treatment as chemical waste, either through incineration in an approved facility equipped with afterburners and scrubbers, in full compliance with local environmental regulations such as those from the U.S. Environmental Protection Agency (EPA).^[18]^[57] For transportation, dry HATU is classified as a flammable solid under UN 1325 (Class 4.1, Packing Group III) and adherence to general chemical shipping protocols.^[18]^[58]

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### Physical Properties of HATU (445460)
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In stock $6 deliveryHATU, or Hexafluorophosphate Azabenzotriazole Tetramethyl Uronium, is a reagent used in peptide coupling to form a coupling reaction.
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O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate ; Molecular Weight. 380.23 g/mol. Computed by PubChem 2.2 (PubChem release 2025.09.15).
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HATU - 99%, high purity , CAS No.148893-10-1 ; H109327-5g, 5g. 2 ; H109327-10g, 10g. 3 ; H109327-25g, 25g. 3 ; H109327-100g, 100g. 3.Missing: formula | Show results with:formula
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[27]
Rational Strategy for Designing Peptidomimetic Small Molecules ...
The development of small-molecule drugs targeting PPIs remains an important challenge. The current mainstream method of small-molecule drug discovery ...
[28]
Synthesis and Applications of Peptides and Peptidomimetics in Drug ...
Jan 30, 2023 · Over 40 cyclic peptide drugs are currently in the drug market and an average of around one new drug enters the market. Natural cyclic peptides ...
[29]
Highly efficient on-DNA amide couplings promoted by micelle ... - NIH
Jun 22, 2021 · Amide couplings are the most commonly used reaction in synthesis of screening libraries and also in DELs. The ability to carry out highly ...
[30]
Dose–Response Activity-Based DNA-Encoded Library Screening
Aug 21, 2023 · The 2-cycle library was constructed using high-yielding, DNA-compatible amide bond formation, which minimized synthesis variability (21) and ...
[31]
Rapid Esterification of Nucleosides to Solid-Phase Supports for ...
Uronium reagents (HATU or HBTU) gave the best results with the HQDA linker arm, while the bromophosphonium (BrOP or PyBrOP) reagents were best with the succinyl ...
[32]
Direct formation of amide/peptide bonds from carboxylic acids
Feb 28, 2023 · Technology for generating especially important amide and peptide bonds from carboxylic acids and amines that avoids traditional coupling reagents is described.
[33]
Rapid HATU-Mediated Solution Phase siRNA Conjugation
Conditions for facile solution-phase amide conjugation of amine-modified siRNA with a diverse set of carboxylic acid partners using the coupling reagent HATU ...Missing: diamide constructions
[34]
Efficient One-pot HATU Mediated Coupling of Dicarboxylic Acid and ...
Aug 7, 2025 · Conclusion: Among various coupling reagents scrutinized, HATU was proven to be 'gold standard' to accomplish one-pot synthesis of diamides.
[35]
Total Synthesis and Biological Evaluation of Natural and Designed ...
Aug 6, 2025 · ... HATU and HOAt furnished dipeptides 31 (55% yield) and. 32 (54% yield) ... and Tb33 in overall yields of 39−91%. The synthesis of tubulysin ...
[36]
[PDF] The Development and Scale-Up of an Antibody Drug Conjugate ...
Aug 1, 2017 · This compound had initially been coupled in the SPPS using HATU/TMP, but following an evaluation of the reaction the coupling was changed to ...
[37]
Dipropyleneglycol Dimethylether, New Green Solvent for Solid ... - NIH
Jun 20, 2023 · We report the use of dipropyleneglycol dimethylether (DMM), a well-known green solvent with low human toxicity following oral, inhalant, and dermal exposure.Missing: post- | Show results with:post-
[38]
Greening the synthesis of peptide therapeutics: an industrial ...
Nov 24, 2020 · The uronium-based coupling reagents gave poor purities both in 2-MeTHF and CPME on both resins. In another study by Albericio and co-workers, ...
[39]
Synthesis of chiral nine and twelve-membered cyclic polyamines ...
Mar 27, 2019 · We found that best macrocyclization yields of up to 85% were obtained using HATU as peptide coupling reagent and a dilution of 1 g L−1 in ...
[40]
Macrocyclization as a Source of Desired Polypharmacology ...
Nov 2, 2021 · Macrocyclization as a Source of Desired Polypharmacology. ... 85% yield. (g) DCM/TFA, 0 °C to rt, quantitative yield. (h) HATU, HOAt in DMF, rt.
[41]
US5580981A - Azahydroxybenzotriazoles and derivatives thereof ...
For example, HOAt or 1-hydroxy-7-azabenzotriazole in the presence of an amino acid or peptide ester, is converted to its anion, which is colored. As coupling ...
[42]
HATU：a third-generation coupling reagent - ChemicalBook
Jul 3, 2024 · HATU, the N-guanidium salt of HOAt, is a third-generation coupling reagent used in small and peptide synthesis, causing amine acylation.
[43]
(PDF) HCTU and TCTU. New coupling reagents: Development and ...
Aug 7, 2025 · It is one of the reagents most frequently used for coupling reactions in aqueous solutions or other protic solvents like alcohols [45,46] HATU ...
[44]
Low-Cost, Fast, Conventional Peptide Synthesis With HCTU and ...
Jun 22, 2008 · In 1993, Carpino introduced the activator O-(7- azabenzotriazole-1-yl)-N,N,N′N′-tetramethyluronium hexafluorophosphate (HATU), which was ...
[45]
(PDF) The Uronium/Guanidinium Peptide Coupling Reagents
Oct 28, 2025 · These O isomers (O-HBTU and O-HATU) are more efficient coupling reagents than the N isomers.
[46]
Microwave accelerated high speed solution synthesis of peptides ...
Aug 6, 2025 · The chemical synthesis of peptides employing HATU/HOAt as a coupling agent under microwave irradiation has been described.
[47]
Semi‐automated microwave‐assisted SPPS: Optimization of ...
Mar 11, 2010 · In this article, a new, flexible semi-automated instrument for the application of precise microwave heating in solid-phase peptide synthesis is ...
[48]
Cyrene as a Bio-based Solvent for HATU Mediated Amide Coupling
The solvent Cyrene has been used successfully in HATU mediated coupling reactions to make small molecule amides including dipeptides. 53 Cyrene can also be used ...
[49]
Greening the synthesis of peptide therapeutics: an industrial ... - NIH
Greening peptide synthesis involves solvent substitution, recycling, and reduction, focusing on solvent substitution and reduction for large-scale industrial ...
[50]
[PDF] SAFETY DATA SHEET - Fisher Scientific
Jul 16, 2012 · hexafluorophosphate; O-(7-Azabenzotriazol-1-yl)-N,N,N·,N·-tetramethyluronium ... Melting Point/Range. 189 - 191 °C / 372.2 - 375.8 °F.
[51]
Anaphylaxis Induced by Peptide Coupling Agents: Lessons Learned ...
Dec 18, 2019 · We present a case study of anaphylaxis induced by three uronium coupling agents, HATU, HBTU, and HCTU, as a cautionary note for researchers who handle peptide ...
[52]
Peptide bond-forming reagents HOAt and HATU are not mutagenic ...
Our data show that HOAt and HATU-common pharmaceutical synthesis reagents-are not mutagenic, and can be treated as ordinary drug impurities.
[53]
None
### Summary of Section 10: Stability and Reactivity (HATU MSDS)
[54]
https://pubmed.ncbi.nlm.nih.gov/26840011/
[55]
[PDF] Material Safety Data Sheet - HATU, 99% - Cole-Parmer
Boiling Point: Not available. Freezing/Melting Point:183 - 185 deg C. Decomposition Temperature:Not available. Solubility: Not available. Specific Gravity ...
[56]
[PDF] SAFETY DATA SHEET - Thermo Fisher Scientific
Melting Point/Range. 189 - 191 °C / 372.2 - 375.8 °F. Softening Point. No data available. Boiling Point/Range. No information available. Flammability (liquid).