1-Hydroxybenzotriazole
[CAS# 2592-95-2]

Identification

• Classification: Biochemical >> Amino acids and their derivatives >> Other protected amino acids
• Name: 1-Hydroxybenzotriazole
• Synonyms: HOBt; N-Hydroxybenzotriazole; 1-Hydroxy-1H-benzotriazole; 1-Hydroxybenzotriazole anhydrous
• Molecular Formula: C₆H₅N₃O
• Molecular Weight: 135.12
• CAS Registry Number: 2592-95-2
• EC Number: 219-989-7
• SMILES: C1=CC=C2C(=C1)N=NN2O

Properties

• Melting point: 156-159 °C
• Refraction index: 1.45

Safety Data

• Hazard Symbols: GHS01 Danger
• Risk Statements: H203
• Safety Statements: P210-P230-P240-P250-P264+P265-P280-P305+P351+P338-P337+P317-P370+P380-P372-P373-P401-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Explosives	Expl.	1.3	H203
Eye irritation	Eye Irrit.	2	H319
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Flammable solids	Flam. Sol.	2	H228
Flammable solids	Flam. Sol.	1	H228
Desensitized Explosives	Des. Expl.	2	H207

Discovery and Applications

1-Hydroxybenzotriazole (HOBt) is an essential organic compound that is widely used in peptide synthesis and other organic reactions. Known for its effectiveness in promoting coupling reactions, HOBt has become a must-have in synthetic chemistry laboratories.

1-Hydroxybenzotriazole was first introduced in the mid-20th century when researchers were seeking more efficient methods for peptide bond formation. The compound has a chemical formula of C6H5N3O and features a hydroxyl group on the benzotriazole ring attached to one of the nitrogen atoms. This structure imparts unique reactivity, particularly in activating the carboxyl group for nucleophilic attack.

HOBt is a crystalline solid that typically appears as white to light beige crystals. It is slightly soluble in water but more soluble in organic solvents such as dimethylformamide (DMF) and dichloromethane (DCM). Its stability and solubility in these solvents make it ideal for a variety of organic reactions.

The primary application of HOBt is in peptide synthesis, where it plays a key role in promoting the formation of amide bonds. During peptide synthesis, amino acids are joined together to form a peptide chain, a process that requires activation of the carboxyl group of one amino acid to react with the amine group of another amino acid. HOBt is used in conjunction with coupling agents such as dicyclohexylcarbodiimide (DCC) or N,N'-diisopropylcarbodiimide (DIC) to increase the efficiency and yield of these coupling reactions.

HOBt reacts with the carboxyl group of an amino acid in the presence of a coupling agent to form an active ester. This ester is more reactive toward nucleophilic attack by the amine group of another amino acid, thus promoting the formation of the peptide bond. One of the key advantages of using HOBt in peptide synthesis is its ability to minimize racemization. Racemization, the conversion of L-amino acids to their D-isomers, can impair the biological activity of the peptide. HOBt stabilizes reaction intermediates, reduces the potential for racemization, and ensures the integrity of the synthesized peptide.

In addition to peptide synthesis, HOBt is used in a variety of other organic synthesis applications due to its ability to activate carboxyl groups and promote nucleophilic substitution reactions. HOBt is used to synthesize esters and amides from carboxylic acids and alcohols or amines. The active ester intermediate formed by HOBt makes these reactions more efficient and selective. HOBt can be used to promote cyclization reactions, which are essential in the synthesis of heterocyclic compounds and natural product analogs.

Although HOBt is a valuable reagent, it must be handled with care as explosive peroxides may form upon prolonged exposure to air. Proper storage in sealed containers away from heat and light is essential to maintain its stability. In addition, appropriate safety measures should be followed when handling HOBt, such as wearing gloves and goggles.

References

2013. Solid-Phase Peptide Synthesis: An Introduction. Methods in Molecular Biology.
DOI: 10.1007/978-1-62703-544-6_1

2013. Synthesis of C-Terminal Peptide Thioesters Using Fmoc-Based Solid-Phase Peptide Chemistry. Methods in Molecular Biology.
DOI: 10.1007/978-1-62703-544-6_8

1997. Limitations of the Coupling of Amino Acid Mixtures for the Preparation of Equimolar Peptide Libraries. Molecular Diversity.
DOI: 10.1023/a:1009602707067