n detail about the intended use of their blood samples and the way of publishing the obtained results. The Advisory Committee of PUH abiding by the Helsinki Declaration on ethical principles for medical research involving human subjects approved this consent procedure. AcPhe-tRNAPhe charged 
to 80% and a post-translocation complex of poly- 15 / 22 Development of Chloramphenicol Homodimers programmed ribosomes from E. coli K12, bearing tRNAPhe at the E-site and Ac Phe-tRNA at the P-site were prepared, as previously described. The percentage of active ribosomes in AcPhe-tRNA 480-44-4 custom synthesis binding was 75%. Melting points were determined with a Buchi SMP-20 apparatus and are uncorrected. IR spectra were recorded as KBr pellets on a Perkin Elmer 16PC FT-IR spectrophotometer. 1H NMR spectra were obtained at 400.13 MHz and 13C NMR spectra at 100.62 MHz on a Bruker DPX spectrometer. Chemical shifts are reported in units, parts per million downfield from TMS. Electron-spray ionization mass spectra were recorded at 30V, on a Micromass-Platform LC spectrometer using MeOH as solvent. Analytical HPLC was used to determine the purity of final products, confirming ! 95% purity. Analytical RP-HPLC was performed on a Waters system. Elution of the compounds was determined from the absorbance at 254 nm. Compound purity was assessed using a LiChrospher C8 column and a linear gradient of 5%-60% acetonitrile in water over 20 min at a flow rate of 1 ml/min. Flash column chromatography was performed on Merck silica gel 60 and TLC on 60 Merck 60F254 films precoated on aluminium foil. Spots were visualized with UV light at 254 nm and charring agents. All solvents were dried and/or purified according to standard procedures prior to use. All reagents employed in PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19757813 synthesis were purchased from either Aldrich or Alfa-Aesar. CLB and the required dicarboxylic acids, glutaric anhydride and terephthaloyl dichloride were obtained from Aldrich. The synthesis of 1,4-phenylenediacrylic acid PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19754877 and compounds 111 as well as physical and spectra data for the synthesized compounds are presented in S1 Supplemental Procedures. Inhibition of peptide-bond formation by CAM dimers The puromycin reaction, i.e. the reaction between complex C and excess puromycin, was carried out at 25C in buffer A. Under these conditions, the puromycin reaction obeys S C S CS! C0 S K kcat pseudo-first-order kinetics and was analyzed as previously described. In the presence of CAM dimers, biphasic semi-logarithmic time plots were obtained. The slope of the straight line through the origin was seen as the value of the apparent rate constant, kobs, at the early phase of the reaction. Similarly, the slope of the second straight line was taken as the apparent rate constant, kobs, at the late phase of the puromycin reaction. Time-resolved binding of CAM dimers to E. coli ribosomes and characterization of RI and RI complexes by footprinting analysis 70S ribosomes from E. coli were incubated either alone or with each CAM dimer at concentration equal to 50Ki in 100 l of buffer B at 25C, either for 2 s or longer than 10t1/2 min. Chemical modification of complexes RI and R I with DMS, kethoxal, or CMCT, primer extension analysis, and gel electrophoresis of the primer extension products were performed as previously described. The primers used were complementary to the sequences 21022119, 25612578, and 26802697 of 23S rRNA to scan primarily domain V, provided that one of the CAM units in CAM dimers binds within the catalytic center o