Protein synthesis inhibitors termination

The protein synthesis inhibitors tetracycline, chloramphenicol, and streptomycin all block bacterial protein synthesis. Several eukaryotic translational inhibitors have also been found and they include diphtheria toxin, ricin, and cycloheximide. Puromycin causes premature chain termination in both prokaryotes and eukaryotes by functioning as an aminoacyl tRNA analog. 

In A. vinelandii, C-terminal cleavage occurs in crude extracts after restoration of nickel and requires hours rather than minutes, as is the case in vivo. It does not require de novo protein synthesis and surprisingly is not redox or O2 sensitive. Also, it is not inhibited by well-established inhibitors of metallo- or serine protease families (Menon and Robson 1994). 

The synthesis of the C1-C21 subunit of the protein phosphatase inhibitor tautomycin was accomplished by J.A. Marshall et al. During the last steps of the synthetic sequence, the hydrosilylation of a terminal alkyne afforded a five-membered siloxane that was oxidized by the Fleming-Tamao oxidation. The initially formed end tautomerized to the corresponding methyl ketone. 

The answer is e. (Murray, pp 452-467. Scriver, pp 3-45. Sack, pp 1-40. Wilson, pp 101-120.) Puromycin is virtually identical in structure to the 3 -terminal end of tyrosinyl-tRNA. In both eukaryotic and prokaryotic cells, it is accepted as a tyrosinyl-tRNA analogue. As such, it is incorporated into the carboxy-terminal position ol a peptide at the aminoacyl (A) site on ribosomes, causing premature release of the nascent polypeptide. Thus, puromycin inhibits protein synthesis in both human and bacterial cells. Streptomycin, like tetracycline and chloramphenicol, inhibits ribosomal activity. Mitomycin covalently cross-links DNA, which prevents cell replication. Rifampicin is an inhibitor of bacterial DNA-dependent RNA polymerase. 

More recently, Jacobsen and coworkers have found that epoxides undergo a highly enantioselective ring-opening with TMS-azide when catalysed by (salen)Cr(III) complexes such as (5,5)-4. This asymmetric ring opening shows a second-order rate dependence on catalyst concentration . Applications of the process have included kinetic resolution of terminal epoxides , an efficient synthesis of (/ )-4-(trimethylsilyloxy)cyclopent-2-enone, the dynamic kinetic resolution (equation 11) of epichlorohydrin, an enantioselective route to carbocyclic nucleoside analogues and a formal synthesis (equation 12) of the protein kinase inhibitor 5. 

Inhibitors of late chain initiation (Verrucarin 76), elongation (CHI, Cryptoleurine, Anisomycin) and termination (Trichodermin) of protein synthesis, relax RNA synthesis, whereas inhibitors of early chain initiation (Edeine A+B and MDMP (2-(4-methyl-2-6-dinitroanilino)--N-methylpropionamide)) are ineffective as relaxing agents. ... 

---