H-L-Arg-OtBu*2HCl

H-L-Arg-OtBu*2HCl is an L-arginine tert-butyl ester hydrochloride salt in which the α-carboxyl group is protected as an OtBu ester and the guanidinium side chain is present as a protonated, chloride-associated functionality. The molecule retains a defined stereocenter at the α-carbon (L-configuration) and provides a highly basic, strongly hydrogen-bonding guanidine moiety that participates in salt formation, ion-pairing, and selective protection/deprotection logic during peptide assembly. The tert-butyl ester can be removed under acid-promoted conditions to regenerate the free carboxylic acid for coupling, while the guanidinium group is maintained in a cationic state that can be used directly for guanidine-compatible transformations or for controlled deprotection strategies in downstream synthesis. The overall salt form improves handling of the basic amino acid derivative and supports its role as a chiral, peptide-ready intermediate for arginine incorporation and side-chain functional manipulation.

1. Peptide Synthesis

H-L-Arg-OtBu*2HCl is applied in peptide synthesis workflows where arginine must be introduced as a protected amino acid building block for controlled amide bond formation. The protected amino acid ester format (OtBu) supports sequential coupling chemistry by enabling C-terminal activation after ester deprotection, while the L-configuration preserves stereochemical fidelity at the α-carbon. The guanidinium side chain, stabilized as a hydrochloride salt, can be carried through coupling steps and then managed via acid/base conditions that align with guanidine deprotection or guanidine-to-derivative conversion strategies. Downstream peptide construction can therefore proceed toward arginine-rich sequences, including synthesis of protected peptide intermediates and peptide fragments used for further elongation or for analytical standard preparation. The compound's salt-stabilized guanidinium functionality makes it compatible with peptide science routes that require reliable handling of strongly basic side chains.

2. Protected Amino Acids

H-L-Arg-OtBu*2HCl functions as a protected amino acid derivative for synthetic planning in which orthogonal protection of the carboxyl group is required while maintaining the arginine side chain in a defined protonation state. The tert-butyl ester provides a removable C-terminal protecting group that can be converted back to a carboxylic acid for subsequent peptide coupling, esterification, or conversion to activated derivatives. The guanidinium group's cationic character facilitates predictable salt behavior and can guide selection of coupling conditions that minimize side reactions associated with free, strongly basic amino acids. The resulting intermediate utility extends to preparation of protected arginine-containing fragments, chiral building blocks for fragment condensation, and stepwise assembly of amino acid derivatives where stereochemistry and functional-group compatibility are critical. Such protected amino acid chemistry aligns with industrial intermediate preparation and fine chemical synthesis strategies that rely on controlled deprotection windows.

3. Chemical Biology Labeling

H-L-Arg-OtBu*2HCl is suitable for chemical biology and biomolecule labeling efforts that require arginine-containing motifs for receptor-binding mimics, cell-penetrating peptide analogs, or affinity handles. The guanidinium side chain can serve as a recognition element for molecular interactions and can be leveraged for conjugation schemes that preserve charge distribution in labeled constructs. The protected carboxylate ester can be transformed into carboxyl-activated intermediates for attachment to linkers, surfaces, or reporter-bearing moieties while maintaining the L-arginine stereochemical signature. The hydrochloride salt form supports reproducible handling during derivatization steps that involve aqueous-compatible coupling or ion-pairing-based purification strategies. Downstream, labeled arginine-containing peptides and peptide-like probes can be generated for biochemical assays, pull-down experiments, and molecular interaction studies that depend on guanidine-mediated binding features.

4. Peptidomimetics And SAR Studies

H-L-Arg-OtBu*2HCl can be employed in peptidomimetic construction and structure-activity relationship studies where arginine's guanidinium functionality is used to tune binding, permeability, and electrostatic complementarity. The compound's side-chain guanidine provides a handle for designing analogs that maintain strong hydrogen-bonding and salt-bridge formation patterns while varying the backbone or terminal groups. The OtBu ester protection supports modular synthesis of analog libraries by enabling conversion to activated carboxylic acid derivatives for fragment coupling, scaffold diversification, or incorporation into non-natural peptide-like frameworks. Stereochemical control at the α-carbon helps maintain consistent spatial orientation of the guanidinium group relative to the backbone in analog series. This makes the intermediate applicable to SAR-driven synthesis planning, where controlled arginine incorporation supports iterative generation of structure-defined compounds for analytical characterization and comparative studies.

5. Pharmaceutical Manufacturing Intermediates

H-L-Arg-OtBu*2HCl is relevant to pharmaceutical manufacturing and process chemistry as a chiral arginine-based intermediate for producing protected peptide intermediates and amino acid derivatives used in active ingredient synthesis routes. The OtBu ester offers a process-compatible protecting group strategy for managing C-terminal functionality during sequential transformations, enabling conversion to free carboxylic acid for activation and coupling downstream. The guanidinium hydrochloride salt form supports stable storage and controlled reactivity of the highly basic side chain, which can be important for reproducible batch processing and consistent intermediate quality. The compound can be incorporated into upstream peptide fragment manufacturing where arginine-rich sequences require predictable handling of charged functional groups. Downstream utility includes preparation of peptide building blocks, activated acid intermediates, and defined chiral components used for scale-up of fine chemical synthesis and peptide-based intermediate generation.

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