Product Overview

Fmoc-Cys(Trt)-OH (CAS 103213-32-7; catalog AS2487) is an Fmoc-protected L-cysteine building block with trityl protection on the side-chain sulfur. It is used to incorporate cysteine into research peptides prepared by Fmoc solid-phase peptide synthesis. The S-Trt group masks the thiol during chain assembly, while the alpha-carboxyl group remains available for coupling.

Quality Specifications and Ordering

Purity: Alan Scientific supplies Fmoc-Cys(Trt)-OH at >99% purity.

Catalog pack sizes: 25 g, 100 g, 500 g, and 1 kg.

Quality documentation: See Product Documents below for lot-specific COA request details. Review the analytical methods and results reported for the supplied batch.

Quotation: Email [email protected] with AS2487, the pack size, total quantity, delivery destination, and required date. Confirm availability and dispatch lead time before ordering.

Confirm L-cysteine and S-Trt identity. For a supplier-change assessment, specify the stereochemical testing and other acceptance criteria that must be compared between lots.

Cysteine Protection and Stereochemical Control

Fmoc removal exposes the alpha-amino group for elongation while Trt is retained under routine basic deprotection conditions. Appropriate acidic cleavage and deprotection release the cysteine thiol. The final handling strategy must then account for the reactivity of the unprotected sulfur.

Cysteine can be susceptible to epimerization during activation and coupling. Base exposure, activation time, temperature, and sequence context require attention; the purity of the starting building block does not by itself establish the stereochemical purity of the completed peptide. A C-terminal cysteine can also require consideration of the resin and linker strategy.

Disulfide-Containing and Thiol-Functionalized Peptides

Applications include peptides requiring free cysteine thiols, disulfide-containing research constructs, and projects using a defined cysteine conjugation site. Releasing a thiol and forming the intended disulfide are separate operations. Trt removal does not establish correct folding or cysteine pairing.

When a sequence contains several cysteines, define the intended connectivity before synthesis. Stepwise disulfide formation may require different side-chain protections and a dedicated oxidation sequence. For a thiol conjugation project, confirm which cysteine must remain accessible and how unwanted oxidation or reaction at other sites will be controlled.

For cysteine protection and disulfide planning, consult the cysteine discussion in our Fmoc amino acid selection guide before choosing a multi-cysteine protection scheme.

Fmoc-Cys(Trt)-OH and Other Trt-Protected Building Blocks

The presence of Trt does not make different amino-acid derivatives interchangeable. For example, Fmoc-Gln(Trt)-OH uses Trt protection on a glutamine side-chain amide, whereas Fmoc-Cys(Trt)-OH uses Trt protection on cysteine sulfur. Always match the amino-acid residue, protection site and CAS number to the intended sequence.

Product Documents

A MSDS is available for this product to support laboratory handling, storage and safety assessment.

MSDS_Fmoc-Cys-Trt-OH_AS2487

Certificates of Analysis are batch-specific. Please contact us to request a COA, and we will provide it by email.

Frequently Asked Questions

What should I confirm before changing suppliers of Fmoc-Cys(Trt)-OH?

Match chemical identity, S-Trt protection, the specified purity method, and any required stereochemical test before comparing lots. Request the lot-specific COA and evaluate the candidate material in your own synthesis. The >99% building-block specification does not establish final-peptide disulfide connectivity or folding.

Does Fmoc-Cys(Trt)-OH contain a free thiol?

No. The side-chain sulfur is Trt-protected. An appropriate deprotection step is required before the thiol can participate in conjugation or disulfide formation.

Will Trt deprotection produce the correct disulfide bonds?

Not necessarily. Oxidation and folding must be planned and assessed separately, particularly when more than one cysteine pair is present.

Does the building-block COA confirm final-peptide folding?

No. It characterizes the supplied building block within the stated test scope; folding and disulfide connectivity are properties of the finished peptide.

Research Use Only

For research use only. Not for human or veterinary use.