Nitrodibenzofuran:A One- and Two-Photon SensitiveProtecting Group That Is Superior to Brominated Hydroxycoumarin forThiol Caging in Peptides

摘要

Photoremovable protecting groups are important for a wide range of applications in peptide chemistry. Using Fmoc-Cys(Bhc-MOM)-OH, peptides containing a Bhc-protected cysteine residue can be easily prepared. However, such protected thiols can undergo isomerization to a dead-end product (a 4-methylcoumarin-3-yl thioether) upon photolysis. To circumvent that photoisomerization problem, we explored the use of nitrodibenzofuran (NDBF) for thiol protection by preparing cysteine-containing peptides where the thiol is masked with an NDBF group. This was accomplished by synthesizing Fmoc-Cys(NDBF)-OH and incorporating that residue into peptides by standard solid-phase peptide synthesis procedures. Irradiation with 365 nm light or two-photon excitation with 800 nm light resulted in efficient deprotection. To probe biological utility, thiol group uncaging was carried out using a peptide derived from the protein K-Ras4B to yield a sequence that is a known substrate for protein farnesyltransferase; irradiation of the NDBF-caged peptide in the presence of the enzyme resulted in the formation of the farnesylatedproduct. Additionally, incubation of human ovarian carcinoma (SKOV3)cells with an NDBF-caged version of a farnesylated peptide followedby UV irradiation resulted in migration of the peptide from the cytosol/Golgito the plasma membrane due to enzymatic palmitoylation. Overall, thehigh cleavage efficiency devoid of side reactions and significanttwo-photon cross-section of NDBF render it superior to Bhc for thiolgroup caging. This protecting group should be useful for a plethoraof applications ranging from the development of light-activatablecysteine-containing peptides to the development of light-sensitivebiomaterials.