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| Product Name | Fmoc-Asp(OtBu)-OH |
|---|---|
| Synonyms | Fmoc-L-aspartic acid 4-tert-butyl ester; Nα-Fmoc-L-aspartic acid β-tert-butyl ester |
| Catalog No. | AS2486 |
| CAS Number | 71989-14-5 |
| Molecular Formula | C23H25NO6 |
| Molecular Weight | 411.45 g/mol |
| SMILES | CC(C)(C)OC(=O)C[C@@H](C(=O)O)NC(=O)OCC1C2=CC=CC=C2C3=CC=CC=C13 |
| Storage Temperature | Cool, dry place (≤25°C) |
| Appearance | White powder |
| Melting Point | 145–160°C |
| Specific Rotation | -24° ± 2.5° (c=1 in DMF) |
| Functional Groups | Fmoc-protected α-amino group; tert-butyl-protected side-chain β-carboxyl group; free α-carboxylic acid |
| Primary Application | Fmoc solid-phase peptide synthesis (SPPS) |
Product Overview
Fmoc-Asp(OtBu)-OH (CAS 71989-14-5; catalog AS2486) is an Fmoc-protected L-aspartic acid building block with its side-chain beta-carboxyl group protected as a tert-butyl ester. The alpha-carboxyl group remains available for peptide coupling. This protection pattern is used to incorporate Asp into conventional Fmoc/tBu solid-phase peptide synthesis.
Quality Specifications and Ordering
Purity: Alan Scientific supplies Fmoc-Asp(OtBu)-OH at >99% purity.
Catalog pack sizes: 25 g, 100 g, 500 g, and 1 kg.
Quality documentation: See Product Documents below for lot-specific COA request details. Review the analytical methods and results reported for the supplied batch.
Quotation: Email [email protected] with AS2486, the pack size, total quantity, delivery destination, and required date. Confirm availability and dispatch lead time before ordering.
Confirm that OtBu protects the side-chain carboxyl group, not the alpha-carboxyl group. Define reagent impurity requirements separately from final-peptide acceptance criteria.
Side-Chain Protection and Aspartimide Formation
The tert-butyl ester masks the Asp side-chain acid during chain assembly, but does not make an Asp-containing sequence immune to aspartimide formation. Susceptibility depends on neighboring residues and the conditions experienced by the growing peptide, including cumulative exposure to base.
An Asp-Gly motif means Asp followed by Gly when the sequence is written from the N-terminus to the C-terminus. Such motifs deserve particular attention during route development. Where necessary, the full synthesis strategy may require changes to deprotection conditions or a different building-block approach rather than simply repeating the same coupling.
For the relationship between sequence context, aspartimide, and epimerization, see our guide to common side reactions in SPPS.
Applications and Analytical Considerations
Fmoc-Asp(OtBu)-OH is used for Asp-containing research peptides, acidic sequence motifs, and analogue studies involving the aspartate side chain. In routes requiring selective side-chain activation or lactam formation before global cleavage, the protection strategy must permit access to the intended carboxyl group.
Final peptide assessment should distinguish chemical identity from a nominal molecular mass. Backbone-linked and side-chain-linked isomers can share the same mass, so an intact-mass match alone does not prove the absence of Asp-related isomerization. The appropriate method depends on the impurity question being investigated.
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. To request a COA, email [email protected] with the product name and catalog number. If you already have the material, include the lot number shown on the label. The SDS provides safety and handling information and does not replace the lot-specific COA.
Frequently Asked Questions
Should I change the building-block purity grade to resolve impurities in an Asp-Gly sequence?
Fmoc-Asp(OtBu)-OH is supplied at >99% purity, but that specification does not prevent process-related aspartimide formation. Review the impurity profile and synthesis conditions before choosing between a raw-material change, a process adjustment, or a different protection strategy.
Does OtBu protection prevent all aspartimide formation?
No. It protects the side-chain carboxyl during assembly, but susceptible sequences can still undergo base-associated side reactions.
Is Fmoc-Asp(OtBu)-OH intended for selective side-chain coupling on resin?
Not automatically. The complete protection and linker scheme must allow the chosen side-chain acid to be exposed without unwanted deprotection or release.
Research Use Only
For research use only. Not for human or veterinary use.