$516.00 - $1550.00
Fmoc-Cys(Mtt)-OH is an L-cysteine derivative with Fmoc protection on the alpha-amino group and 4-methyltrityl (Mtt) protection on sulfur. Mtt is more acid-labile than standard Trt protection and can therefore support selective cysteine unveiling under carefully controlled conditions.
This difference is the reason to choose Mtt. If cysteine only needs to remain protected until final cleavage, a standard Trt-protected cysteine may be simpler. Mtt becomes valuable when the thiol must be exposed earlier for orthogonal chemistry.
Product Information
| Product Name | Fmoc-Cys(Mtt)-OH |
| Catalog No. | AS2095 |
| CAS No. | 269067-38-1 |
| Molecular Formula | C38H33NO4S |
| Molecular Weight | 599.74 g/mol |
| Building Block Type | Fmoc-protected S-Mtt-L-cysteine |
| Primary Applications | Selective cysteine deprotection; orthogonal thiol chemistry; disulfide engineering; site-selective conjugation; Fmoc-SPPS |
Mtt Versus Trt on Cysteine
Fmoc-Cys(Trt)-OH is a conventional cysteine building block for global acid deprotection. Fmoc-Cys(Mtt)-OH is selected when a more acid-labile sulfur protecting group is needed for staged deprotection.
Selective Thiol Chemistry
After controlled Mtt removal, the cysteine thiol can be used for conjugation, disulfide formation or other site-selective transformations while other protected residues remain intact. The complete protecting-group map should be checked because 'mild acid' is relative to the other acid-labile groups present.
Cysteine Racemization Still Matters
Changing the sulfur protecting group does not eliminate alpha-carbon stereochemical risk. Activation conditions, base and preactivation time can all affect cysteine racemization. The broader issue is discussed in Alan Scientific's guide to common SPPS side reactions.
Disulfide and Cyclic Peptide Planning
For peptides that require controlled disulfide or side-chain cyclization, selective cysteine protection should be chosen together with the order of oxidation and purification. See peptide cyclization strategies for the design implications.
Procurement and QC Considerations
Confirm CAS 269067-38-1, C38H33NO4S, MW 599.74 g/mol, L configuration and S-Mtt identity. For multi-cysteine peptides, orthogonal protection can be evaluated during custom cysteine-rich 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
What does Mtt protect?
Mtt protects the cysteine sulfur.
Why use Mtt instead of Trt?
Mtt is more acid-labile and can support staged thiol deprotection.
Can Fmoc-Cys(Mtt)-OH be used for disulfide engineering?
Yes, when the full orthogonal protecting-group and oxidation strategy is designed accordingly.
Related Technical Resources
Compare standard Fmoc-Cys(Trt)-OH
Review peptide cyclization strategies