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CAS 2592-95-2 Racemization-Suppressing Coupling Additive Racemization-Suppressing Coupling Additive

HOBt (1-Hydroxybenzotriazole, anhydrous)

IUPAC: 1H-1,2,3-Benzotriazol-1-ol View on PubChem
CAS NUMBER
2592-95-2
MOL. FORMULA
C6H5N3O
MOL. WEIGHT
135.12 g/mol
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Scientific Overview

HOBt forms a reactive HOBt-ester intermediate with the activated carboxylic acid, which reacts efficiently with amine nucleophiles under mild conditions while substantially reducing epimerization at chiral centers compared to uncatalyzed carbodiimide coupling. The anhydrous form is used specifically in moisture-sensitive reactions where the ~12% water content of the commercial monohydrate would be problematic.

HOBt (1-Hydroxybenzotriazole, anhydrous) is a benzotriazole-derived coupling additive that suppresses racemization during carbodiimide-mediated amide and peptide bond formation, one of the most widely used additives in classical peptide synthesis.

Full Technical Data
Chemical Name 1-Hydroxybenzotriazole, anhydrous (HOBt)
CAS Number 2592-95-2
IUPAC Name 1H-1,2,3-Benzotriazol-1-ol
Molecular Formula C6H5N3O
Molecular Weight 135.12 g/mol g/mol
Boiling Point >344.6°C at 760 mmHg
Flash Point 162.2°C
Reaction Scheme
2-Nitrochlorobenzene (or 2-Nitroaniline route)
Hydrazine
NA
1-Hydroxybenzotriazole (HOBt), anhydrous
NA
Commercial Applications

Solid-Phase Peptide Synthesis

Standard racemization-suppressing additive used alongside carbodiimide or uronium-based coupling reagents.

Small-Molecule Amide Coupling

Used broadly in API and building-block synthesis for controlled, low-epimerization amide bond formation.

Activated Ester Generation

Forms HOBt-active esters used as isolable intermediates in multi-step API synthesis.

Analytical/Process Reference Standard

Used as a process-related reference material for HOBt-mediated synthetic route impurity profiling.

Market Therapeutic Focus
RACEMIZATION-SUPPRESSING COUPLING ADDITIVE PHARMACEUTICAL MANUFACTURING PEPTIDE THERAPEUTICS API PROCESS CHEMISTRY ORGANIC SYNTHESIS INTERMEDIATES CRO/CDMO
Scientific Literature

Mutagenic Impurities in 1-Hydroxybenzotriazole (HOBt)

Authors: Treitler, D.S. et al.

Org. Process Res. Dev.

DOI: 10.1021/acs.oprd.9b00308

Explosive Properties of 1-Hydroxybenzotriazoles

Authors: Wehrstedt, K.D. et al.

J. Hazard. Mater.

DOI: 10.1016/j.jhazmat.2005.05.044

HBTU-Mediated 1-Hydroxybenzotriazole (HOBt) Conjugate Addition: Synthesis and Stereochemical Analysis

Authors: Mali, S.M. et al.

Org. Biomol. Chem.

DOI: 10.1039/C4OB01claa
Peer Queries & FAQs
Why use the anhydrous form of HOBt instead of the monohydrate?
The commercial monohydrate contains roughly 11.7% bound water, which can interfere with moisture-sensitive coupling reactions; the anhydrous grade avoids introducing that water into the reaction.
Are there any safety considerations specific to HOBt?
Yes, dry HOBt is classified as having explosive properties under confinement or mechanical shock, so it is typically handled and shipped wetted or in solution and stored per hazard-specific guidance.
How does HOBt reduce racemization during peptide coupling?
It intercepts the highly reactive O-acylisourea intermediate formed by the carbodiimide, converting it to a less racemization-prone HOBt active ester before the amine coupling step occurs.
What is the recommended storage condition?
Store in sealed containers in a cool, dry location, protected from light, moisture, and mechanical shock or excessive heat given its explosive-hazard classification when fully dry.

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