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(S)-Fmoc-2-amino-3-ethyl-pentanoic acid is a bulky hydrophobic noncanonical amino acid also indexed as N-Fmoc-3-ethyl-L-norvaline. Its side chain is substantially more crowded near the peptide backbone than those of Ala, Abu, Nva, or Leu.
This residue is most useful when steric volume and hydrophobic packing are deliberate SAR variables. The broader role of such residues is discussed in noncanonical amino acids in peptide discovery.
Product Information
| Product Name | (S)-Fmoc-2-amino-3-ethyl-pentanoic acid |
| Catalog No. | AS4034 |
| CAS No. | 1310680-47-7 |
| Molecular Formula | C22H25NO4 |
| Molecular Weight | 367.45 g/mol |
| Building Block Type | Fmoc-protected (S)-3-ethyl-norvaline derivative |
| Primary Applications | Noncanonical peptide SAR; bulky hydrophobic substitutions; constrained side-chain studies; specialized Fmoc-SPPS |
A β-Branched Side Chain Creates Strong Steric Demand
The carbon adjacent to the α-center is highly substituted, which increases local hydrophobic volume and can restrict side-chain conformational freedom. This may alter binding-pocket occupancy or peptide folding, but the effect is target- and position-dependent.
Coupling Can Be More Difficult Than Standard Amino Acids
Steric bulk close to the carboxyl and amino center can slow peptide-bond formation. For sequence-critical work, we prefer monitoring coupling completion and using targeted optimization rather than assuming a standard single coupling will be sufficient.
Stereochemistry Is Part of the Material Identity
The product is the S-configured amino acid. Stereoisomers have the same formula and mass, so CAS identity and chiral documentation matter whenever the biological interpretation depends on stereochemistry.
Procurement and QC
Confirm CAS 1310680-47-7, C22H25NO4, MW 367.45 g/mol, and S configuration. Public supplier records also identify this compound as (S)-Fmoc-2-amino-3-ethylpentanoic acid / N-Fmoc-3-ethyl-L-norvaline.
Procurement and QC Considerations
Sequences containing this or several other hindered residues can be reviewed through custom noncanonical peptide synthesis.
Product Documents
A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.
(S)-Fmoc-2-amino-3-ethyl-pentanoic acid MSDS
Frequently Asked Questions
What is the main reason to use this residue?
It introduces a bulky, β-branched hydrophobic side chain as a defined peptide SAR variable.
Can routine LC-MS prove the S configuration?
No. Mass confirms composition, not enantiomeric identity.
Does steric bulk affect SPPS?
It can. Hindered residues may require optimized activation or repeated coupling depending on sequence context.
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