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Cbz-Asp(OtBu)-OH, also known as Z-Asp(OtBu)-OH, is N-Cbz-L-aspartic acid with the side-chain β-carboxyl group protected as a tert-butyl ester and the α-carboxyl group left free for coupling.
It is structurally analogous to Fmoc-Asp(OtBu)-OH at the Asp side chain, but the N-terminal protecting group changes the entire deprotection strategy: Cbz is normally removed reductively, while Fmoc is removed under basic conditions.
Product Information
| Product Name | Cbz-Asp(OtBu)-OH |
| Catalog No. | AS2020 |
| CAS No. | 5545-52-8 |
| Molecular Formula | C16H21NO6 |
| Molecular Weight | 323.34 g/mol |
| Building Block Type | N-Cbz-protected L-aspartic acid side-chain tert-butyl ester |
| Primary Applications | Solution-phase peptide synthesis; protected fragment coupling; Asp-containing intermediates; route development |
Why Protect the Asp Side-Chain Carboxyl
Asp contains two carboxyl groups. Protecting the β-carboxyl as OtBu directs activation toward the free α-carboxyl and limits unwanted side-chain acylation during protected-fragment synthesis.
Cbz and OtBu Provide Mixed Deprotection Logic
Cbz is typically removed by hydrogenolysis or another compatible reductive method, whereas OtBu is acid-labile. This separation can be useful in solution-phase synthesis, but hydrogenation must be compatible with any alkenes, sulfur-containing groups, benzyl-sensitive motifs, or other reducible functionality in the molecule.
Aspartimide Risk Is a Sequence Property
Side-chain OtBu protection does not eliminate every Asp-related side reaction after the residue enters a peptide. In Fmoc-based chain assembly, aspartimide formation can still depend strongly on neighboring residues and repeated base exposure. Researchers planning an Asp-containing sequence can review the SPPS practical guide before selecting a fragment strategy.
Procurement and QC
Confirm CAS 5545-52-8, formula C16H21NO6, MW 323.34 g/mol, L configuration, N-Cbz protection, side-chain OtBu protection, and a free α-carboxyl group. This protection map is the chemically meaningful identity.
For complete Asp-containing peptide projects, Alan Scientific can compare a Cbz-fragment route with standard Fmoc assembly through custom 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
Is Cbz-Asp(OtBu)-OH the same as Fmoc-Asp(OtBu)-OH?
No. The side-chain protection is similar, but Cbz and Fmoc require different N-deprotection chemistry.
Which Asp carboxyl group is protected?
The side-chain β-carboxyl group is protected as a tert-butyl ester; the α-carboxyl remains available for coupling.
How is Cbz usually removed?
Cbz is commonly removed reductively, often by catalytic hydrogenolysis when compatible with the complete molecule.