Fmoc-gamma-Glu(OtBu)-Gly-OH (AS4075) is a protected gamma-glutamyl-glycine building block. The supplied structural drawing confirms that the glutamate side-chain gamma-carboxyl forms the amide bond to glycine, while the glutamate alpha-carboxyl is protected as a tert-butyl ester. The glutamate amino group is Fmoc-protected and the glycine carboxyl group remains free.

This connectivity is the defining feature of AS4075. We recommend treating the structure, not molecular mass alone, as the primary identity reference because an alpha-linked Glu-Gly constitutional isomer can have the same molecular formula and molecular weight.

Product Information

What the AS4075 Structure Confirms

In the confirmed AS4075 structure, glycine is attached through the glutamate side-chain carboxyl group. The glutamate alpha-carboxyl is present as a tert-butyl ester rather than as the peptide-bond-forming carboxyl. This orientation distinguishes AS4075 from the conventional alpha-linked Fmoc-Glu(OtBu)-Gly-OH constitutional isomer.

That distinction matters during route design. The preformed gamma-amide bond fixes the unusual linkage before the fragment enters a longer synthesis, while the free glycine carboxyl provides a coupling handle for extension from the C-terminal side.

Protecting-Group Logic

The Fmoc group provides base-labile protection of the glutamate amino function. The tert-butyl ester protects the glutamate alpha-carboxyl under standard Fmoc deprotection conditions and is acid-labile during final cleavage or a separate acid-deprotection step. The glycine carboxyl remains available for activation and coupling.

We consider this orthogonal arrangement especially useful when the gamma linkage must be installed as a defined fragment rather than generated on-resin through selective side-chain manipulation. The exact cleavage sequence should still be planned around the protecting groups present elsewhere in the target peptide.

Gamma-Linked vs Alpha-Linked Glu-Gly

Gamma-linked and alpha-linked Glu-Gly structures can share the same elemental composition and nominal mass while differing in which glutamate carboxyl group forms the amide bond. LC-MS can therefore support molecular-weight confirmation but does not, by itself, establish the linkage topology.

For identity-sensitive work, we recommend retaining the drawn structure in the product record and using lot documentation or an orthogonal structural method when linkage verification is required. A CAS number from the conventional alpha-linked isomer should not be transferred to AS4075 solely because the formula and mass match.

Applications in Peptide Synthesis

AS4075 is suited to research involving gamma-glutamyl motifs, protected gamma-linked peptide fragments and synthetic routes in which a preassembled Glu-Gly side-chain amide is advantageous. The fragment can also support method development for peptides containing non-alpha amide connectivity.

The practical value of the reagent depends on the final sequence. Coupling efficiency, solubility and purification behavior should be assessed in the context of the complete peptide rather than inferred from the protected fragment alone.

Procurement and QC Considerations

For AS4075, molecular formula and LC-MS mass are necessary but not sufficient identity checks. We recommend confirming the structural drawing, molecular weight, assay and lot-specific analytical record together. If the project depends on gamma linkage fidelity, the QC package should preserve evidence that distinguishes the gamma-linked material from its alpha-linked constitutional isomer.

Product Documents

A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.

MSDS_AS4075_Fmoc-gamma-GluOtBu-Gly-OH

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

Which carboxyl group forms the Glu-Gly bond in AS4075?

The supplied structure shows glycine coupled through the glutamate side-chain gamma-carboxyl group. The glutamate alpha-carboxyl is protected as a tert-butyl ester.

Why can LC-MS not distinguish this product from an alpha-linked Glu-Gly isomer?

The two linkage isomers can have the same molecular formula and molecular weight. LC-MS confirms mass but does not determine which glutamate carboxyl group forms the amide bond.

Is the glycine carboxyl group free?

Yes. In the confirmed structure, the glycine carboxyl group is unprotected and available for activation in a subsequent coupling step.

What happens to the tert-butyl ester during peptide synthesis?

The tert-butyl ester is stable to standard Fmoc-removal conditions but is acid-labile. Its removal should be planned with the final cleavage and protecting-group strategy.

Related Technical Resources

Browse related specialty peptide building blocks for nonstandard peptide connectivity.

For sequence-specific projects using gamma-linked residues or protected fragments, explore our custom peptide synthesis with complex building blocks.

Research Use Only.