{{Chembox | Verifiedfields = | Watchedfields = | verifiedrevid = | ImageFile = N-HBTU.svg | ImageAlt = HBTU Structural Formula | ImageSize = 240px | IUPACName = 1-oxo-3''H''-1λ⁵,2,3-benzotriazole-3-carboximidamidium hexafluorophosphate<ref>ACD ChemSketch 2024.2.3</ref> | OtherNames = {{ubl|HBTU|<br>2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate|<br>3-[Bis(dimethylamino)methyliumyl]-3''H''-benzotriazol-1-oxide hexafluorophosphate}} |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 94790-37-1 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 2014894 | EINECS = 619-076-7 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = X5I03TZQ8D | PubChem = 2733084 | InChI = InChI=1S/C11H16N5O.F6P/c1-14(2)11(15(3)4)17-16-10-8-6-5-7-9(10)12-13-16;1-7(2,3,4,5)6/h5-8H,1-4H3;/q+1;-1 | InChIKey = UQYZFNUUOSSNKT-UHFFFAOYSA-N | StdInChI_Ref = | StdInChI = | StdInChIKey_Ref = | StdInChIKey = | SMILES = CN(C)C(=[N+](C)C)ON1C2=CC=CC=C2N=N1.F[P-](F)(F)(F)(F)F }} |Section2={{Chembox Properties | C=11 | H=16 | N=5 | O=1 | P=1 | F=6 | Appearance = White crystals | Density = | MeltingPtC = 200 | BoilingPt = | Solubility = }} |Section3={{Chembox Hazards | MainHazards = Irritant | FlashPt = | AutoignitionPt = | Hazards_ref=<ref>{{cite web |title=2-(1h-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate |url=https://pubchem.ncbi.nlm.nih.gov/compound/2733084#section=Safety-and-Hazards |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref> | GHSPictograms = {{GHS07}} | GHSSignalWord = Warning | HPhrases = {{H-phrases|315|319|335}} | PPhrases = {{P-phrases|210|240|241|261|264|271|280|302+352|304+340|305+351+338|312|332+313|337+313|362|370+378|403+233|405|501}} }} }}
'''HBTU''' ('''h'''exafluorophosphate '''b'''enzotriazole '''t'''etramethyl '''u'''ronium) is a coupling reagent used in solid phase peptide synthesis. It was introduced in 1978 and shows resistance against racemization.<ref>{{Cite journal|title=L'hexafluorophosphate de O-benzotriazolyl-N,N-tetramethyluronium: Un reactif de couplage peptidique nouveau et efficace|last=Dourtoglou|first=Vassilis.|date=April 1978|journal=Tetrahedron Letters |doi=10.1016/0040-4039(78)80103-8|volume=19|issue=15|pages=1269–1272}}</ref><ref>{{Cite journal | doi = 10.1016/S0040-4039(00)99616-3 | title = New coupling reagents in peptide chemistry | year = 1989 | last1 = Knorr | first1 = R. |last2 = Trzeciak | first2 = A. | last3 = Bannwarth | first3 = W. | last4 = Gillessen | first4 = D. | journal = Tetrahedron Letters | volume = 30 | issue = 15 | pages = 1927–1930}}</ref> It is used because of its mild activating properties.<ref>{{Cite journal | doi = 10.1016/S0960-894X(01)81199-9 | title = HBTU: a mild activating agent of muramic acid | year = 1992 | last1 = Solange | first1 = A. | journal = Bioorganic & Medicinal Chemistry Letters | volume = 2 | issue = 6 | pages = 571–574}}</ref>
HBTU is prepared by reaction of hydroxybenzotriazole with TCFH under basic conditions<ref>{{Cite patent|number=WO1994007910A1|title=New reagents for peptide couplings|gdate=1994-04-14|invent1=Carpino|inventor1-first=Louis A.|url=https://patents.google.com/patent/WO1994007910A1/en}}</ref> 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.<ref>{{Cite journal | doi = 10.1002/1521-3773(20020201)41:3<441::AID-ANIE441>3.0.CO;2-N | title = The uronium/guanidinium peptide coupling reagents: Finally the true uronium salts | year = 2002 | last1 = Carpino | first1 = L. |last2 = Imazumi | first2 = H. | last3 = El-Faham | first3 = A. | last4 = Ferrer | first4 = F. |last5 = Zhang | first5 = C. | last6 = Lee | first6 = Y. | last7 = Foxman | first7 = B. | last8 = Henklein | first8 = P. | last9 = Hanay | first9 = C. | last10 = Mügge | first10 = C. | last11 = Wenschuh | first11 = H. | last12 = Klose | first12 = J. | last13 = Beyermann | first13 = M. | last14 = Bienert | first14 = M. | journal = Angewandte Chemie International Edition | volume = 41 | issue = 3 | pages = 441–445 | pmid = 12491372}}</ref><ref>{{Cite journal | doi = 10.1007/BF00126274 | title = Structural studies of reagents for peptide bond formation: Crystal and molecular structures of HBTU and HATU | year = 1994 | last1 = Abdelmoty | first1 = I. |last2 = Albericio | first2 = F. | last3 = Carpino | first3 = L. | last4 = Foxman | first4 = B. |last5 = Kates | first5 = S. | journal = Letters in Peptide Science | volume = 1 | issue = 2 | pages = 57–67| s2cid = 38746650}}</ref>
== Mechanism == left|thumb|upright=1.3|This scheme depicts the general mechanistic steps of HBTU creating an activated ester out of the carboxylate anion of the acid substrate. The deprotination of the carboxylic acid and the aminolysis of the activated ester are not shown. 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.<ref>{{Cite journal|last1=Bradley|first1=Mark|last2=Valeur|first2=Eric|date=2009-01-26|title=Amide bond formation: beyond the myth of coupling reagents|journal=Chemical Society Reviews|language=en|volume=38|issue=2|pages=606–631|doi=10.1039/B701677H|issn=1460-4744|pmid=19169468}}</ref>
== Safety == ''In vivo'' dermal sensitization studies according to OECD 429<ref>{{Cite book |last=OECD |url=https://www.oecd-ilibrary.org/environment/test-no-429-skin-sensitisation_9789264071100-en |title=Test No. 429: Skin Sensitisation: Local Lymph Node Assay |date=2010 |publisher=Organisation for Economic Co-operation and Development |location=Paris |language=en}}</ref> 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.<ref>{{Cite journal |last1=Graham |first1=Jessica C. |last2=Trejo-Martin |first2=Alejandra |last3=Chilton |first3=Martyn L. |last4=Kostal |first4=Jakub |last5=Bercu |first5=Joel |last6=Beutner |first6=Gregory L. |last7=Bruen |first7=Uma S. |last8=Dolan |first8=David G. |last9=Gomez |first9=Stephen |last10=Hillegass |first10=Jedd |last11=Nicolette |first11=John |last12=Schmitz |first12=Matthew |date=2022-06-20 |title=An Evaluation of the Occupational Health Hazards of Peptide Couplers |journal=Chemical Research in Toxicology |language=en |volume=35 |issue=6 |pages=1011–1022 |doi=10.1021/acs.chemrestox.2c00031 |issn=0893-228X |pmc=9214767 |pmid=35532537}}</ref> Thermal hazard analysis by differential scanning calorimetry (DSC) shows HBTU is potentially explosive.<ref>{{Cite journal |last1=Sperry |first1=Jeffrey B. |last2=Minteer |first2=Christopher J. |last3=Tao |first3=JingYa |last4=Johnson |first4=Rebecca |last5=Duzguner |first5=Remzi |last6=Hawksworth |first6=Michael |last7=Oke |first7=Samantha |last8=Richardson |first8=Paul F. |last9=Barnhart |first9=Richard |last10=Bill |first10=David R. |last11=Giusto |first11=Robert A. |last12=Weaver |first12=John D. |date=2018-09-21 |title=Thermal Stability Assessment of Peptide Coupling Reagents Commonly Used in Pharmaceutical Manufacturing |url=https://pubs.acs.org/doi/10.1021/acs.oprd.8b00193 |journal=Organic Process Research & Development |language=en |volume=22 |issue=9 |pages=1262–1275 |doi=10.1021/acs.oprd.8b00193 |issn=1083-6160|url-access=subscription }}</ref>{{clear left}}
==See also== * EDC * HATU * BOP reagent * PyBOP * PyAOP reagent
==References== {{reflist}}
Category:Hexafluorophosphates Category:Peptide coupling reagents Category:Benzotriazoles Category:Dimethylamino compounds Category:Guanidinium compounds