Fmoc-L-MeArg(Mtr)-OH

Fmoc-L-MeArg(Mtr)-OH is an Fmoc-protected, chiral L-arginine derivative bearing a methyl-substituted guanidino side chain and a methoxytrityl (Mtr) protection on the guanidine functionality. The molecule combines an N-fluorenylmethoxycarbonyl (Fmoc) group for orthogonal base-labile N-deprotection with a side-chain-protected, acid-labile guanidine protecting group, enabling controlled exposure of the cationic arginine motif during peptide assembly. The stereogenic center at the α-carbon and the guanidino substitution pattern influence salt formation, coupling behavior, and subsequent functional group transformations relevant to peptide chemistry and molecular recognition. The presence of protected amine/guanidinium functionality and a carboxylic acid handle positions the compound as a peptide building block and chiral amino acid intermediate for downstream synthesis of arginine-containing analogs.

1. Peptide Synthesis

Fmoc-L-MeArg(Mtr)-OH supports solid-phase and solution-phase peptide coupling workflows where orthogonal protection of the arginine side chain is required. The Fmoc group enables base-mediated N-terminal deprotection, while the Mtr-protected guanidine remains masked under typical coupling and washing conditions to prevent side reactions from the strongly nucleophilic, cationic guanidinium. The methylated arginine side chain can be incorporated to probe steric and electronic effects on backbone interactions, hydrogen bonding networks, and salt-bridge formation in peptide sequences. The resulting protected amino acid can be used to construct arginine-rich peptides, including analogs with altered charge density and conformational preferences, and can be carried through to final deprotection to yield the intended guanidino functionality.

2. Chemical Biology

Fmoc-L-MeArg(Mtr)-OH is suitable for chemical biology studies that require controlled installation of methylated arginine residues into peptide probes and protein-interaction scaffolds. The protected guanidine motif, once deprotected, provides a cationic recognition element that can participate in electrostatic and bidentate hydrogen-bonding interactions, while the methyl substitution can modulate binding geometry and local hydration. The orthogonal Fmoc/Mtr strategy allows sequential functional group exposure, supporting the preparation of peptides used in binding assays, pull-down reagents, and substrate-like probes for enzyme or receptor studies. The methylated arginine residue can also be leveraged in structure-function investigations where guanidinium chemistry is used to interrogate molecular recognition determinants in biomolecular systems.

3. Peptidomimetics And SAR

Fmoc-L-MeArg(Mtr)-OH can be employed in peptidomimetic construction and structure-activity relationship (SAR) studies where arginine guanidinium chemistry is incorporated into constrained or modified scaffolds. The α-carboxylic acid and protected amine enable iterative coupling to generate analog series, while the methylated guanidine can tune hydrophobic contribution and steric profile without removing the core charge-bearing functionality. The Mtr-protected side chain facilitates late-stage guanidine deprotection, supporting synthetic designs that require orthogonality with other protected functional groups on the same scaffold. The resulting arginine-containing analogs can be produced as defined intermediates for SAR mapping, fragment elaboration, and comparative studies of binding or activity trends driven by side-chain substitution patterns.

4. Bioconjugation Chemistry

Fmoc-L-MeArg(Mtr)-OH is relevant to bioconjugation chemistry workflows that require guanidinium-bearing peptide handles for attaching biomolecules through controlled coupling and post-assembly functionalization. The protected guanidine protects the highly reactive cationic site during peptide synthesis, reducing undesired interactions during conjugate assembly steps and enabling purification of defined intermediates. The methylated arginine can influence conjugate solubility and surface charge distribution after final deprotection, which can affect conjugate behavior in aqueous buffers and downstream labeling strategies. The compound can therefore serve as a building block for generating peptide-based linkers, cell-penetrating motif analogs, and affinity tags where arginine-mediated interactions are used to guide biomolecular association.

5. Pharmaceutical Intermediate Preparation

Fmoc-L-MeArg(Mtr)-OH is applicable to pharmaceutical intermediate preparation where protected amino acid derivatives are manufactured and subsequently converted into defined, deprotected building blocks for drug-like peptide or peptidomimetic candidates. The Fmoc group provides a stable N-protection handle for processing and purification, while the Mtr-protected guanidine supports controlled deprotection steps that align with orthogonal synthetic sequences used in fine chemical manufacturing. The methylated arginine side chain can be incorporated into active ingredient intermediates to generate structure-defined cationic motifs that are compatible with downstream coupling, salt formation, and formulation-relevant property tuning. The compound's protected functional group set makes it suitable for scalable synthesis planning, including preparation of amino acid-derived intermediates for subsequent peptide assembly and final deprotection to furnish the target guanidinium-containing fragments.

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