Fmoc-L-Asn(Xan)-OH

Fmoc-L-Asn(Xan)-OH is an Fmoc-protected L-asparagine derivative in which the side-chain amide is modified to an Xan (xanthyl/xanthenyl-type) substituent, yielding a chiral amino acid building block with an N-fluorenylmethoxycarbonyl (Fmoc) group and a protected side-chain functionality. The molecule contains a stereogenic center at the α-carbon (L-configuration) and presents a carboxylic acid handle for peptide coupling while maintaining a masked amide-derived side chain that can be selectively revealed or transformed under controlled conditions. The Xan-bearing side chain typically alters hydrogen-bonding capacity and steric profile relative to native Asn, which can be exploited to tune conformational preferences and recognition in peptide and peptidomimetic scaffolds. The combination of an orthogonally removable N-protecting group (Fmoc) and a modifiable side-chain protecting motif supports downstream synthetic planning for protected amino acid synthesis and iterative peptide construction.

1. Peptide Synthesis

Fmoc-L-Asn(Xan)-OH supports solid-phase and solution-phase peptide synthesis where the Fmoc group enables stepwise N-terminal deprotection and coupling. The free carboxylic acid and the stable, chiral L-amino acid framework participate in standard peptide coupling chemistry to introduce an asparagine-derived residue with a side-chain Xan modification. Side-chain masking can reduce undesired side reactions associated with unprotected amide functionality and can modulate intramolecular hydrogen bonding during chain assembly. Downstream, the resulting peptides can be used as protected intermediates for further functionalization, including controlled side-chain unveiling or conversion to other amide-equivalent motifs.

2. Side-Chain Functionalization

Fmoc-L-Asn(Xan)-OH can be applied to side-chain functionalization strategies that require controlled manipulation of an asparagine-derived position. The Xan-modified side chain provides a handle for orthogonal transformation compared with the Fmoc carbamate, enabling sequential protection/deprotection logic in synthetic sequences. The modified side-chain environment can be leveraged to tune polarity, hydrogen-bonding patterns, and local conformational bias, which are common design variables in peptidomimetics and structure-activity relationship studies. The compound therefore serves as a chiral intermediate for generating amino acid derivatives with altered recognition features and for preparing analog libraries where the Asn position is systematically varied.

3. Chemical Biology Probes

Fmoc-L-Asn(Xan)-OH is suitable for chemical biology workflows that require incorporation of an asparagine-like residue into peptide probes with controlled side-chain reactivity. The Fmoc-protected α-amino group supports incorporation into peptide sequences that can later be processed for labeling, conjugation, or attachment to biomolecular targets. The Xan-bearing side chain can function as a modulator of aqueous solubility and intermolecular interactions, which may influence probe behavior during binding assays or immobilization steps. Downstream use can include preparation of peptide-based reagents for studying molecular recognition, enabling controlled generation of functionalized derivatives after selective side-chain transformation.

4. Peptidomimetics And SAR

Fmoc-L-Asn(Xan)-OH enables peptidomimetic construction where Asn side-chain chemistry is tuned to affect binding interactions and conformational ensembles. The chiral L-configuration and the carboxylic acid functionality allow incorporation into constrained scaffolds, while the Xan modification modulates side-chain hydrogen-bonding and sterics relative to canonical asparagine. The orthogonal protection pattern supports iterative synthesis of analogs for structure-activity relationship studies, including systematic variation at the Asn-equivalent position without perturbing the peptide backbone assembly. The resulting analogs can be used as research-grade intermediates for generating structure-diverse libraries and for downstream analytical characterization of structure-function relationships.

5. Pharmaceutical Intermediate Preparation

Fmoc-L-Asn(Xan)-OH can be employed in pharmaceutical intermediate preparation for manufacturing routes that require protected amino acid derivatives compatible with established peptide-building processes. The Fmoc group provides a robust N-protection strategy that can be removed on demand during controlled sequence assembly, while the Xan-modified side chain supports selective handling of functional-group reactivity during intermediate formation. The presence of a carboxylic acid enables conversion into activated coupling forms and supports integration into longer synthetic sequences used to generate peptide-based or peptide-derived intermediates. Downstream, the compound can serve as a defined stereochemical unit for producing consistent, side-chain-modified amino acid segments used in fine chemical synthesis and applied process chemistry.

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