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HATU
Names
	IUPAC name 1-[Bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate
Identifiers
CAS Number	148893-10-1 ;
3D model (JSmol)	Interactive image;
ChemSpider	8061830;
ECHA InfoCard	100.103.434
PubChem CID	9886157;
UNII	B93RIH1T7E ;
CompTox Dashboard (EPA)	DTXSID201026946 DTXSID30933498, DTXSID201026946 ;
	InChI InChI=1S/C10H15N6O.F6P/c1-14(2)10(15(3)4)17-16-9-8(12-13-16)6-5-7-11-9;1-7(2,3,4,5)6/h5-7H,1-4H3;/q+1;-1 Key: JNWBBCNCSMBKNE-UHFFFAOYSA-N; InChI=1/C10H15N6O.F6P/c1-14(2)10(15(3)4)17-16-9-8(12-13-16)6-5-7-11-9;1-7(2,3,4,5)6/h5-7H,1-4H3;/q+1;-1 Key: JNWBBCNCSMBKNE-UHFFFAOYAG;
	SMILES CN(C)C(=[N+](C)C)On1c2c(cccn2)nn1.F[P-](F)(F)(F)(F)F;
Properties
Chemical formula	C10H15F6N6OP
Molar mass	380.235 g·mol−1
Appearance	White crystalline solid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

HATU (Hexafluorophosphate Azabenzotriazole Tetramethyl Uronium) is a reagent used in peptide coupling chemistry to generate an active ester from a carboxylic acid. HATU is used along with Hünig's base (N,N-diisopropylethylamine), or triethylamine to form amide bonds. Typically DMF is used as solvent, although other polar aprotic solvents can also be used.^[1]

History

HATU was first reported by Louis A. Carpino in 1993 as an efficient means of preparing active esters derived from 1-hydroxy-7-azabenzotriazole (HOAt).^[2] HATU is commonly prepared from HOAt and TCFH under basic conditions^[3] and can exist as either the uronium salt (O-form) or the less reactive iminium salt (N-form). HATU was initially reported as the O-form using the original preparation reported by Carpino; however, X-ray crystallographic and NMR studies revealed the true structure of HATU to be the less reactive guanidinium isomer.^[4] It is, however, possible to obtain the uronium isomer by preparing HATU using KOAt in place of HOAt and working up the reaction mixture quickly to prevent isomerisation.

Reactions

HATU is commonly encountered in amine acylation reactions (i.e., amide formation). Such reactions are typically performed in two distinct reaction steps: (1) reaction of a carboxylic acid with HATU to form the OAt-active ester; then (2) addition of the nucleophile (amine) to the active ester solution to afford the acylated product.

The reaction mechanism of carboxylic acid activation by HATU and subsequent N-acylation is summarised in the figure below. The mechanism is shown using the more commonly encountered and commercially available iminium isomer; a similar mechanism, however, is likely to apply to the uronium form. In the first step, the carboxylate anion (formed by deprotonation by an organic base [not shown]) attacks HATU to form the unstable O-acyl(tetramethyl)isouronium salt. The OAt anion rapidly attacks the isouronium salt, affording the OAt-active ester and liberating a stoichiometric quantity of tetramethylurea. Addition of a nucleophile, such as an amine, to the OAt-active ester results in acylation.

The high coupling efficiencies and fast reaction rates associated with HATU coupling are thought to arise from a neighbouring group effect brought about by the pyridine nitrogen atom, which stabilises the incoming amine through a hydrogen-bonded 7-membered cyclic transition state.^[5]

Because of the extraordinary coupling efficiency of HATU, it has often been used for intramolecular amidation (coupling of a carboxylic acid and an amine of the same molecule). For example, the formation of cyclo-tetrapeptides through the head-to-tail reaction of linear tetrapeptides assisted by HATU has been reported.^[6]

Safety

HATU has been shown to induce allergic reactions.^[7] In vivo dermal sensitization studies according to OECD 429^[8] confirmed HATU is a moderate skin sensitizer, showing a response at 1.2 wt% in the Local Lymph Node Assay (LLNA) placing it in Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Dermal Sensitization Category 1A.^[9] Thermal hazard analysis by differential scanning calorimetry (DSC) shows HATU is potentially explosive.^[10]

References

^ "Amine to Amide (Coupling) - HATU".
^ Carpino, Louis A (1993). "1-Hydroxy-7-azabenzotriazole. An efficient peptide coupling additive". Journal of the American Chemical Society. 115 (10): 4397–4398. doi:10.1021/ja00063a082.
^ WO1994007910A1, Carpino, Louis A., "New reagents for peptide couplings", issued 1994-04-14
^ Carpino, Louis A; Imazumi, Hideko; El-Faham, Ayman; Ferrer, Fernando J; Zhang, Chongwu; Lee, Yunsub; Foxman, Bruce M; Henklein, Peter; Hanay, Christiane; Mügge, Clemens; Wenschuh, Holger; Klose, Jana; Beyermann, Michael; Bienert, Michael (2002). "The Uronium/Guanidinium Peptide Coupling Reagents: Finally the True Uronium Salts". Angewandte Chemie International Edition. 41 (3): 441–445. doi:10.1002/1521-3773(20020201)41:3<441::AID-ANIE441>3.0.CO;2-N. PMID 12491372.
^ Carpino, Louis A; Imazumi, Hideko; Foxman, Bruce M; Vela, Michael J; Henklein, Peter; El-Faham, Ayman; Klose, Jana; Bienert, Michael (2000). "Comparison of the Effects of 5- and 6-HOat on Model Peptide Coupling Reactions Relative to the Cases for the 4- and 7-Isomers†,‡". Organic Letters. 2 (15): 2253–2256. doi:10.1021/ol006013z. PMID 10930256.
^ Müntener, Thomas; Thommen, Fabienne; Joss, Daniel; Kottelat, Jérémy; Prescimone, Alessandro; Häussinger, Daniel (16 April 2019). "Synthesis of chiral nine and twelve-membered cyclic polyamines from natural building blocks" (PDF). Chemical Communications. 55 (32): 4715–4718. doi:10.1039/C9CC00720B. ISSN 1364-548X.
^ McKnelly, Kate J.; Sokol, William; Nowick, James S. (2020-02-07). "Anaphylaxis Induced by Peptide Coupling Agents: Lessons Learned from Repeated Exposure to HATU, HBTU, and HCTU". The Journal of Organic Chemistry. 85 (3): 1764–1768. doi:10.1021/acs.joc.9b03280. ISSN 0022-3263.
^ OECD (2010). Test No. 429: Skin Sensitisation: Local Lymph Node Assay. Paris: Organisation for Economic Co-operation and Development.
^ Graham, Jessica C.; Trejo-Martin, Alejandra; Chilton, Martyn L.; Kostal, Jakub; Bercu, Joel; Beutner, Gregory L.; Bruen, Uma S.; Dolan, David G.; Gomez, Stephen; Hillegass, Jedd; Nicolette, John; Schmitz, Matthew (2022-06-20). "An Evaluation of the Occupational Health Hazards of Peptide Couplers". Chemical Research in Toxicology. 35 (6): 1011–1022. doi:10.1021/acs.chemrestox.2c00031. ISSN 0893-228X. PMC 9214767. PMID 35532537.
^ Sperry, Jeffrey B.; Minteer, Christopher J.; Tao, JingYa; Johnson, Rebecca; Duzguner, Remzi; Hawksworth, Michael; Oke, Samantha; Richardson, Paul F.; Barnhart, Richard; Bill, David R.; Giusto, Robert A.; Weaver, John D. (2018-09-21). "Thermal Stability Assessment of Peptide Coupling Reagents Commonly Used in Pharmaceutical Manufacturing". Organic Process Research & Development. 22 (9): 1262–1275. doi:10.1021/acs.oprd.8b00193. ISSN 1083-6160.