Fmoc-D-Cys(Mbzl)-OH is an Fmoc-protected D-cysteine derivative bearing an Mbzl (benzyl-protected mercapto) side chain, placing it in the protected amino acid class used for peptide-building blocks. The molecule contains a free carboxylic acid and the N-terminus is masked by the Fmoc group, while the cysteine thiol is converted to a benzyl thioether (Mbzl) to suppress disulfide formation and side reactions during coupling. In solid-phase or solution-phase peptide synthesis, it functions as a chemically protected cysteine unit that provides a masked sulfur handle for later deprotection steps and supports the preparation of peptides containing cysteine-derived motifs for structure-activity studies and analytical characterization.
CAT No: CP26650
CAS No:200354-41-2
Synonyms/Alias:Fmoc-D-Cys(Mbzl)-OH;200354-41-2;Fmoc-S-4-methylbenzyl-D-cysteine;ZINC2560717;6829AH;AKOS025404247;AK187077
Fmoc-D-Cys(Mbzl)-OH is an Fmoc-protected D-cysteine derivative bearing a benzyl-protected thiol side chain (Mbzl) and a stereodefined D-amino acid center. The molecule combines an aromatic fluorenylmethyloxycarbonyl (Fmoc) group for N-protection with a thioether-protected sulfur that can be selectively unmasked or transformed during peptide assembly and downstream chemistry. The carboxylic acid functionality enables incorporation as a C-terminal or side-chain-modified amino acid building block, while the D-configuration supports stereochemical control in peptide analogs and chiral synthetic sequences. The presence of both stable protecting groups and a reactive sulfur handle positioned for later functionalization makes the compound suitable as a chiral amino acid intermediate and protected peptide coupling component.
1. Peptide Synthesis
Fmoc-D-Cys(Mbzl)-OH functions as a protected cysteine building block for solid-phase peptide synthesis and solution-phase peptide coupling where stereodefined D-amino acid incorporation is required. The Fmoc carbamate protects the N-terminus during coupling cycles, while the Mbzl thioether protection strategy maintains sulfur chemoselectivity by suppressing undesired thiol side reactions. The free carboxylic acid participates in standard amide bond formation, enabling controlled placement of the cysteine residue within peptide sequences and peptide fragments. Downstream deprotection and sulfur functionalization can be applied to generate thiol-containing intermediates, thioether-to-thiol conversions, or cysteine-reactive handles for peptide analog construction. The compound's defined stereochemistry and orthogonal protecting-group pattern support reproducible peptide assembly workflows in amino acid chemistry.
2. Bioconjugation Chemistry
Fmoc-D-Cys(Mbzl)-OH can be employed in bioconjugation workflows that require cysteine-derived reactive sites with controlled stereochemistry and protection-state management. The protected sulfur (Mbzl) helps stabilize the reactive side chain during peptide or linker synthesis, while the Fmoc group supports orthogonal deprotection timing to expose the amine for controlled coupling and assembly. The D-cysteine configuration can be used to modulate conformational preferences and protease resistance in conjugate scaffolds, supporting the design of stable peptide-based linkers and labeling reagents. Subsequent thiol generation or sulfur functional group transformation can enable conjugation to maleimide, haloacetamide, disulfide-exchange, or other electrophilic capture chemistries depending on the chosen downstream step. The compound thus serves as a protected amino acid precursor for constructing cysteine-functional biomolecule conjugates and research-grade labeling tools.
3. Peptidomimetics And SAR Studies
Fmoc-D-Cys(Mbzl)-OH supports peptidomimetic construction for structure-activity relationship studies where side-chain positioning and stereochemical inversion are used to tune molecular recognition. The combination of an Fmoc-protected amino group and a sulfur-protected cysteine side chain enables systematic synthesis of peptide analog libraries with consistent protection patterns across variants. The D-configuration at the alpha carbon provides a stereochemical handle for probing how backbone chirality influences binding-site geometry, while the sulfur functionality can be converted into thioether, thiol, or other sulfur-containing motifs to explore electronic and steric effects. The carboxylic acid group ensures compatibility with peptide coupling chemistry for rapid analog generation and fragment assembly. The resulting D-cysteine-containing analogs can be carried forward into SAR-focused biochemical research and molecular design programs that rely on protected amino acid intermediates.
4. Side-Chain Functionalization
Fmoc-D-Cys(Mbzl)-OH is suitable for side-chain functionalization strategies that use cysteine sulfur as a synthetic pivot for generating diverse sulfur-containing derivatives. The Mbzl protection pattern allows the sulfur to remain controlled during peptide bond formation and purification steps, reducing competing oxidation or alkylation pathways that can occur with free thiols. The Fmoc group provides a clean N-protection platform that can be removed under standard deprotection conditions to expose the amino functionality for subsequent conjugation, cyclization, or coupling transformations. After unmasking the sulfur in a downstream sequence, the resulting thiol-equivalent functionality can be directed toward thioether formation, disulfide engineering, or incorporation into sulfur-rich motifs used in synthetic organic chemistry and biochemical probe design. The compound's stereodefined D-cysteine framework supports functional group placement with predictable three-dimensional geometry in amino acid derivative synthesis.
5. Pharmaceutical Intermediate Preparation
Fmoc-D-Cys(Mbzl)-OH can be used as a process-relevant intermediate for manufacturing protected amino acid derivatives and peptide intermediates that incorporate cysteine residues under controlled protection schemes. The Fmoc carbamate and Mbzl thioether protection enable robust handling during multi-step synthetic sequences, supporting reliable protection/deprotection orchestration in fine chemical synthesis. The presence of a single stereogenic center and protected functional groups supports consistent downstream conversion into D-cysteine-containing peptide fragments, linkers, or protected building blocks used in active-ingredient precursor manufacturing. The carboxylic acid group provides a direct coupling handle for forming amide bonds in intermediate assembly routes, aligning with industrial peptide synthesis logic. The compound therefore aligns with industrial chemistry needs for chiral amino acid intermediates and protected peptide building block preparation where stereochemical fidelity and functional-group control are required.
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