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Fmoc-α-Me-L-Asp(OtBu)-OH is an α-methylated L-aspartic acid building block. The α-amino group is Fmoc-protected, the side-chain β-carboxyl is protected as OtBu, and the α-carboxyl remains available for peptide coupling.
Compared with standard Fmoc-Asp(OtBu)-OH, the α-methyl group removes the α-hydrogen and increases steric substitution directly at the peptide backbone.
Product Information
| Product Name | Fmoc-α-Me-L-Asp(OtBu)-OH |
| Catalog No. | AS4260 |
| CAS No. | 1072845-47-6 |
| Molecular Formula | C24H27NO6 |
| Molecular Weight | 425.47 g/mol |
| Building Block Type | Fmoc-protected α-methyl-L-Asp with side-chain OtBu protection |
| Primary Applications | α-Methyl amino-acid peptide SAR; constrained peptide design; noncanonical Fmoc-SPPS; acidic residue analog studies |
Why α-Methylation Matters
α-Methyl residues are often used to reduce local backbone flexibility and probe conformational requirements. The modification can affect protease recognition and target binding, but it can also create a more difficult coupling site.
Asp Side-Chain Protection Remains Conventional
OtBu protects the side-chain β-carboxyl through Fmoc cycles and is removed under final acidic deprotection. This keeps the α-carboxyl available for ordinary chain extension.
Coupling Can Be Sterically Demanding
The α-methyl substituent increases steric congestion around both the amino and carboxyl functions. We recommend checking completion around this residue rather than extending activation time indiscriminately, especially if neighboring residues are also hindered.
Procurement and QC
Confirm CAS 1072845-47-6, C24H27NO6, MW 425.47 g/mol, L/S configuration, α-methyl substitution, and side-chain OtBu protection.
Sequences containing α-methyl residues can be evaluated 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.
Certificates of Analysis (COAs) are batch-specific. Please contact us to request the COA for your product, and we will provide it by email.
Frequently Asked Questions
How is this different from Fmoc-Asp(OtBu)-OH?
It contains an additional methyl group at the α-carbon.
Which Asp carboxyl group is OtBu-protected?
The side-chain β-carboxyl group is protected; the α-carboxyl remains free.
Can α-methylation make coupling harder?
Yes. It increases steric demand at the peptide backbone.
Related Technical Resources
Read about α-methyl and other noncanonical residues