2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate
[CAS 94790-37-1]

Identification

• Classification: Biochemical >> Amino acids and their derivatives >> Other protected amino acids
• Name: 2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate
• Synonyms: o-Benzotriazol-1-yl-N,N,N',N'-tetramethyluronium hexafluorophosphate; o-Benzotriazol-1-yl-tetramethyluronium hexafluorophosphate; HBTU
• Molecular Formula: C₁₁H₁₆N₅O.PF₆;C₁₁H₁₆F₆N₅OP
• Molecular Weight: 379.24
• CAS Registry Number: 94790-37-1
• EC Number: 619-076-7
• SMILES: CN(C)C(=[N+](C)C)N1C2=CC=CC=C2[N+](=N1)[O-].F[P-](F)(F)(F)(F)F

Properties

• Melting point: 200 °C (Decomposes) (Expl.)

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H317-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P272-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P333+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H302
Flammable solids	Flam. Sol.	1	H228
Skin sensitization	Skin Sens.	1	H317
Respiratory sensitization	Resp. Sens.	1	H334
Eye irritation	Eye Irrit.	2A	H319
Specific target organ toxicity - single exposure	STOT SE	3	H336

chemBlink Chemical Story

CAS 94790-37-1 is universally known in peptide chemistry as HBTU, a benzotriazole-based coupling reagent widely used in Fmoc solid-phase peptide synthesis. HBTU activates a carboxylic acid so an amino group can attack efficiently to form an amide bond. Literature and commercial references emphasize rapid reactions, high coupling yields and relatively low racemization. A notable structural detail emerged from crystallographic and solution studies: HBTU is better represented by an aminium or guanidinium N-oxide structure than the simple 'uronium' formulation suggested by its traditional name. Repeated solid-phase peptide synthesis demands reliable activation over many cycles, explaining why HBTU became a classic workhorse. Its role is synthetic rather than biological: it facilitates peptide-bond construction and is not intended to remain in the final peptide.

The exact registry identity matters because free forms, salts, hydrates, stereoisomers, metabolites, intermediates and finished medicines can have separate CAS numbers even when their names are closely related. This distinction affects molecular weight, analytical standards, formulation, manufacturing specifications and interpretation of published data. A reliable database story therefore follows the exact substance rather than silently borrowing every property of a related compound.

Structure also shows how chemists use functional groups as deliberate tools. Aromatic and heterocyclic frameworks establish molecular shape and electronics, while amines, hydroxyl groups, carbonyls, carboxyl functions or ionic centers determine reactivity and intermolecular interactions. In multistep synthesis, a compound may be valuable precisely because one position can be transformed selectively while the rest of a complex framework survives.

Modern development is also an analytical-control problem. Researchers must establish identity and purity, distinguish relevant stereoisomers or salt forms, monitor process-related species and define reproducible specifications. These requirements explain why an intermediate, metabolite or reagent can be scientifically important even when it is never administered as an independent medicine.

A Chemical Story must distinguish documented use from structural possibility. A familiar scaffold may suggest an activity, but resemblance is not evidence that the exact CAS substance has been tested or approved for that purpose. Verified history and demonstrated applications therefore take priority over attractive but unsupported extrapolation.

Seen broadly, practical performance emerges from the entire molecular system rather than one recognizable group. Structure, stereochemistry, physical form, synthetic route, metabolism and reaction environment can all determine what a substance actually does. Connecting those molecular details to its documented role is what turns a registry entry into a meaningful chemical story.

The exact registry identity matters because free forms, salts, hydrates, stereoisomers, metabolites, intermediates and finished medicines can have separate CAS numbers even when their names are closely related. This distinction affects molecular weight, analytical standards, formulation, manufacturing specifications and interpretation of published data. A reliable database story therefore follows the exact substance rather than silently borrowing every property of a related compound.

Structure also shows how chemists use functional groups as deliberate tools. Aromatic and heterocyclic frameworks establish molecular shape and electronics, while amines, hydroxyl groups, carbonyls, carboxyl functions or ionic centers determine reactivity and intermolecular interactions. In multistep synthesis, a compound may be valuable precisely because one position can be transformed selectively while the rest of a complex framework survives.

Modern development is also an analytical-control problem. Researchers must establish identity and purity, distinguish relevant stereoisomers or salt forms, monitor process-related species and define reproducible specifications. These requirements explain why an intermediate, metabolite or reagent can be scientifically important even when it is never administered as an independent medicine.

References:
1. Fields CG et al. HBTU in peptide synthesis. Pept Res. 1991;4:95.
2. Abdelmoty I et al. Structural studies of HBTU. Lett Pept Sci. 1994;1:57-67.
3. Sigma-Aldrich. HBTU, CAS 94790-37-1, peptide coupling reagent.

Read more stories