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Fmoc-Pen(Trt)-OH is an Fmoc-protected penicillamine derivative with the thiol protected as S-Trt. Penicillamine can be viewed as a β,β-dimethyl-substituted cysteine analog, so it retains sulfur functionality while adding substantial steric bulk near the backbone.
For comparison, Fmoc-Cys(Trt)-OH provides the corresponding standard cysteine framework without the two β-methyl substituents.
Product Information
| Product Name | Fmoc-Pen(Trt)-OH |
| Catalog No. | AS2058 |
| CAS No. | 201531-88-6 |
| Molecular Formula | C39H35NO4S |
| Molecular Weight | 613.76 g/mol |
| Building Block Type | Fmoc-protected S-trityl penicillamine |
| Primary Applications | Penicillamine incorporation; thiol-containing peptide design; disulfide engineering; constrained peptide SAR; Fmoc-SPPS |
Why Penicillamine Is Different from Cysteine
The two β-methyl groups make penicillamine more sterically congested than cysteine. This can change local conformation, thiol accessibility, coupling kinetics and disulfide geometry in the final peptide.
Trt Protects the Thiol
S-Trt suppresses premature thiol oxidation during peptide elongation and is removed during final acidic cleavage. After deprotection, the thiol can participate in disulfide formation or site-selective conjugation.
Coupling and Cyclization Can Be Sequence-Dependent
The added β-substitution can make coupling more demanding and can alter the geometry of a disulfide-containing ring. We consider the building block and the intended oxidation/cyclization strategy as one design problem rather than two independent steps.
Procurement and QC
Confirm CAS 201531-88-6, formula C39H35NO4S and MW 613.76 g/mol. Penicillamine stereochemistry and S-Trt protection should be confirmed from the lot-specific structure because routine mass does not establish stereochemical identity.
For disulfide-rich or conformationally constrained sequences containing Pen, synthesis and oxidation conditions should be planned together through custom cyclic or modified peptide synthesis.
Product Documents
A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.
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
How is penicillamine different from cysteine?
Penicillamine has two additional β-methyl groups, increasing steric bulk around the thiol-bearing residue.
What does Trt protect?
Trt protects the thiol sulfur.
Can Pen form disulfide bonds?
Yes, after deprotection, but steric substitution can change disulfide geometry and reaction behavior.
Related Technical Resources
Review common SPPS side reactions