benzofurans and 3-nitrodibenzofuran

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 farnesylated product. Additionally, incubation of human ovarian carcinoma (SKOV3) cells with an NDBF-caged version of a farnesylated peptide followed by UV irradiation resulted in migration of the peptide from the cytosol/Golgi to the plasma membrane due to enzymatic palmitoylation. Overall, the high cleavage efficiency devoid of side reactions and significant two-photon cross-section of NDBF render it superior to Bhc for thiol group caging. This protecting group should be useful for a plethora of applications ranging from the development of light-activatable cysteine-containing peptides to the development of light-sensitive biomaterials.

Topics: Antineoplastic Agents; Benzofurans; Cell Line, Tumor; Cell Membrane; Coumarins; Cysteine; Cytosol; Farnesyl-Diphosphate Farnesyltransferase; Female; Golgi Apparatus; Halogenation; Humans; Indicators and Reagents; Ovarian Neoplasms; Peptides; Photochemical Processes; Photons; Solid-Phase Synthesis Techniques; Sulfhydryl Compounds

Nitrodibenzofuran (NDBF) groups are used as photolabile "caging" groups to temporarily mask the Watson-Crick interaction of dA and dC residues. They show improved masking capabilities and are photodeprotected 12 times more efficiently than 1-(o-nitrophenyl)-ethyl (NPE) caging groups in these positions. Furthermore, NDBF groups can be removed wavelength-selectively in the presence of NPE groups. This will allow more complex (un)caging strategies of oligonucleotides--beyond the usual irreversible triggering.

Topics: Benzofurans; DNA; Molecular Structure; Oligonucleotides; Photochemical Processes; Spectrophotometry, Ultraviolet

Mutagenicities of 3-nitrodibenzofuran and 3-aminodibenzofuran were examined using Salmonella typhimurium TA98 and TA100. Strong mutagenicity was found in both compounds. The mutagenic potency of 3-nitrodibenzofuran was approximately 3.5-fold stronger in TA98 and twice stronger in TA100 than that of benzo[a]pyrene. Mutagenicity of 3-aminodibenzofuran was observed under metabolic activation and was 10 times stronger in TA98 and about 5 times stronger in TA100 than that of benzo[a]pyrene.

Topics: Benzofurans; Mutagenicity Tests; Mutagens; Salmonella typhimurium