Sulfhydryl-selective, covalent labeling of biomolecules with transition metallocarbonyl complexes. Synthesis of (eta5-C5H5)M(CO)3(eta1-N-maleimidato) (M = Mo, W), X-ray structure, and reactivity studies.
The photochemical reaction of (eta5-C5H5)Mo(CO)3I with maleimide in the presence of diisopropylamine yielded complex (eta5-C5H5)Mo(CO)3(eta1-N-maleimidato) 4 in 52% yield. The single-crystal X-ray structure of this complex was determined and shows unusual interactions between oxygen atoms of the maleimidato ligand and carbon atoms of the cis-CO ligands. The tungsten analogue of 4, (eta5-C5H5)W(CO)3(eta1-N-maleimidato) 5, was synthesized in 37% yield by the reaction of (eta5-C5H5)W(CO)3I with the thallium(I) salt of maleimide. Complexes 4 and 5 reacted with cysteine ethyl ester and glutathione to afford products of the addition of the sulfhydryl group to the ethylenic bond of the maleimidato ligand. The reaction of 4 and 5 with glutathione proceeded faster than the reaction of the analogous complex (eta5-C5H5)Fe(CO)2(eta1-N-maleimidato) (3). However, all these complexes react with glutathione more slowly than N-ethylmaleimide. Complexes 4 and 5 were used for labeling of bovine serum albumin (BSA), enriched in thiol groups by reaction with Traut's reagent. Reaction of thiolated BSA containing 7.4 SH groups with 4 and 5 gave bioconjugates bearing 6.9 and 6.4 metallocarbonyl moieties, respectively. Under the same conditions, reaction with 3 afforded a BSA conjugate containing 7.6 metallocarbonyl moieties. Labeling was presumed to be site-specific, as the number of metallocarbonyl entities matched very well with the initial number of SH groups measured for the thiolated BSA sample. IR spectra of BSA labeled with 4 and 5 show intense nu(C[triple bond]O)) bands (2042 and 1948 cm(-1) in the latter case), enabling sensitive detection of the bioconjugates in biological samples. Complexes 4 and 5 (especially the latter) should be of interest as heavy atom phasing reagents for protein X-ray crystallography.
Rudolf
Bogna
B
Department of Organic Chemistry, University of Lodz, 90-136 Lodz, Narutowicza 68, Poland.
Palusiak
Marcin
M
Zakrzewski
Janusz
J
Salmain
Michèle
M
Jaouen
Gérard
G
D000478:Alkylation; D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D005019:Ethyl Ethers / Q000737:chemistry; D005978:Glutathione / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D012709:Serum Albumin / Q000737:chemistry; D013057:Spectrum Analysis; D013438:Sulfhydryl Compounds / Q000737:chemistry*
D005019:Ethyl Ethers; D009942:Organometallic Compounds; D012709:Serum Albumin; D013438:Sulfhydryl Compounds; D005978:Glutathione; D003545:Cysteine