HBTU
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| Names | |
|---|---|
| IUPAC name
1-oxo-3H-1λ⁵,2,3-benzotriazole-3-carboximidamidium hexafluorophosphate[1] | |
Other names
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| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.133.815 |
| EC Number |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C11H16F6N5OP | |
| Molar mass | 379.247 g·mol−1 |
| Appearance | White crystals |
| Melting point | 200 °C (392 °F; 473 K) |
| Hazards[2] | |
| Occupational safety and health (OHS/OSH): | |
Main hazards |
Irritant |
| GHS labelling: | |
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| Warning | |
| H315, H319, H335 | |
| P210, P240, P241, P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P332+P313, P337+P313, P362, P370+P378, P403+P233, P405, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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HBTU (hexafluorophosphate benzotriazole tetramethyl uronium) is a coupling reagent used in solid phase peptide synthesis. It was introduced in 1978 and shows resistance against racemization.[3][4] It is used because of its mild activating properties.[5]
HBTU (O-Benzotriazol-1-yl-N,N,N',N'-tetramethyluronium hexafluorophosphate) is one of the most widely used and celebrated peptide coupling reagents in both solid-phase and solution-phase peptide synthesis today. [1, 2, 3]
The Discovery and Introduction (1978)
During his doctoral and state science thesis research at the Université de Nancy I in France, Dr. Dourtoglou focused on the activation of hydroxyl functions using iminium and uronium salts. In 1978, he synthesized and introduced HBTU as a novel, highly efficient coupling reagent. It was specifically designed to overcome the efficiency and structural stability limitations of older coupling reagents like DCC. [1, 2, 3]
Before HBTU, peptide synthesis often suffered from low yields, sluggish reaction times, and racemization (the loss of chiral integrity of the amino acids, which ruins the biological activity of the final peptide). Dourtoglou's HBTU provided:
High Reaction Efficiency: Drastically faster amide bond formation under mild conditions.Excellent Resistance against Racemization:
Ensuring that the precise stereochemistry of the synthetic peptides remained intact. [1, 2, 3]
Laying the Structural Foundation (The Uronium vs. Guanidinium Debate)
When Dr. Dourtoglou first described HBTU, he assigned it an O-uronium salt structure based on the analytical capabilities of the late 1970s. This discovery was so influential that it inspired a whole generation of similar reagents, such as TBTU and HATU. [1, 2, 3]
Decades later, advanced X-ray crystallography and NMR studies conducted by other famous chemists (like Louis Carpino) revealed that HBTU actually equilibrates or exists primarily as an N-guanidinium N-oxide isomer in its solid crystalline state. [1, 5]
HBTU is prepared by reaction of hydroxybenzotriazole with TCFH under basic conditions[6] and was assigned to a uronium type structure, presumably by analogy with the corresponding phosphonium salts, which bear a positive carbon atom instead of the phosphonium residue. Later, it was shown by X-ray analysis that salts crystallize as guanidinium rather than the corresponding uronium salts.[7][8].
Despite this structural nuance, the chemical community still refers to the entire category as "uronium-type" coupling reagents, directly tracking back to Dourtoglou’s original structural assignment and nomenclature. [1, 2]
Mechanism
[edit]
HBTU activates carboxylic acids by forming a stabilized HOBt (Hydroxybenzotriazole) leaving group. The activated intermediate species attacked by the amine during aminolysis is the HOBt ester.
To create the HOBt ester, the carboxyl group of the acid attacks the imide carbonyl carbon of HBTU. Subsequently, the displaced anionic benzotriazole N-oxide attacks of the acid carbonyl, giving the tetramethyl urea byproduct and the activated ester. Aminolysis displaces the benzotriazole N-oxide to form the desired amide.[9]
Safety
[edit]In vivo dermal sensitization studies according to OECD 429[10] confirmed HBTU is a moderate skin sensitizer, showing a response at 0.9 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.[11] Thermal hazard analysis by differential scanning calorimetry (DSC) shows HBTU is potentially explosive.[12]
See also
[edit]References
[edit]- ↑ ACD ChemSketch 2024.2.3
- ↑ "2-(1h-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate". pubchem.ncbi.nlm.nih.gov.
- ↑ Dourtoglou, Vassilis. (April 1978). "L'hexafluorophosphate de O-benzotriazolyl-N,N-tetramethyluronium: Un reactif de couplage peptidique nouveau et efficace". Tetrahedron Letters. 19 (15): 1269–1272. doi:10.1016/0040-4039(78)80103-8.
- ↑ Knorr, R.; Trzeciak, A.; Bannwarth, W.; Gillessen, D. (1989). "New coupling reagents in peptide chemistry". Tetrahedron Letters. 30 (15): 1927–1930. doi:10.1016/S0040-4039(00)99616-3.
- ↑ Solange, A. (1992). "HBTU: a mild activating agent of muramic acid". Bioorganic & Medicinal Chemistry Letters. 2 (6): 571–574. doi:10.1016/S0960-894X(01)81199-9.
- ↑ WO1994007910A1, Carpino, Louis A., "New reagents for peptide couplings", issued 1994-04-14
- ↑ Carpino, L.; Imazumi, H.; El-Faham, A.; Ferrer, F.; Zhang, C.; Lee, Y.; Foxman, B.; Henklein, P.; Hanay, C.; Mügge, C.; Wenschuh, H.; Klose, J.; Beyermann, M.; Bienert, M. (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.
- ↑ Abdelmoty, I.; Albericio, F.; Carpino, L.; Foxman, B.; Kates, S. (1994). "Structural studies of reagents for peptide bond formation: Crystal and molecular structures of HBTU and HATU". Letters in Peptide Science. 1 (2): 57–67. doi:10.1007/BF00126274. S2CID 38746650.
- ↑ Bradley, Mark; Valeur, Eric (2009-01-26). "Amide bond formation: beyond the myth of coupling reagents". Chemical Society Reviews. 38 (2): 606–631. doi:10.1039/B701677H. ISSN 1460-4744. PMID 19169468.
- ↑ 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.