title: Inhibition of the peptidyltransferase acceptor site by 2'(3')-O-cycloleucyl- and alpha-aminoisobutyryl derivatives of cytidylyl-(3'-5')adenosine.
abstract: 2'(3')-O-(N-Benzyloxycarbonylcycloleucyl)adenosine (1a) was prepared by esterification of 5'-O-(4-methoxytrityl)adenosine with N-benzyloxycarbonylcycloleucine in the presence of dicyclohexylcarbodiimide and subsequent deprotection in acidic medium. The compound 1a was separated into pure 2'- and 3'-isomers using HPLC; these isomers were found to undergo an easy interconversion. Compound 1a was coupled with N-dimethylaminomethylene-2',5'-di-O-tetrahydropyranylcytidine 3'-phosphate in the presence of dicyclohexylcarbodiimide to give, after subsequent deblocking, cytidylyl(3' leads to 5')2'(3')-O-cycloleucyladenosine (1c). Compound 1c, as well as the related cytidylyl(3' leads to 5')2'(3')-O-(alpha-aminoisobutyryl)adenosine (1d), inhibited the peptidyltransferase catalyzed transfer of an AcPhe residue to puromycin in the Ac[14C]Phe-tRNA . poly(U) . 70 S E. coli ribosome system. A half of the maximum inhibition of AcPhe-puromycin formation (at 10(-5) M puromycin) was achieved at 9.5 . 10(-6) M of compound 1c and 9 . 10(-5) M of compound 1d, respectively. The inhibition of the puromycin reaction by compound 1d shows a mixed-type of inhibition kinetics. Further, none of the compounds 1c and 1d was an acceptor in the peptidyltransferase reaction. Both compounds 1c and 1d inhibited the binding of C-A-C-C-A[14C]Phe to the A site of peptidyltransferase in a system containing tRNAPhe . poly(U) . 70 S E. coli ribosomes, in which compound 1d was a much stronger inhibitor than 1c. These results indicate that the derivatives such as compounds 1c and 1d which contain an anomalous amino acid with a substituent in lieu of alpha-hydrogen can interfere with the peptidyltransferase A site; however, they are not acceptors in the peptidyltransferase reaction probably due to a misfit of the alpha-substituent.
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D000227:Adenine Nucleotides / Q000494:pharmacology*; D000621:Aminoisobutyric Acids / Q000031:analogs & derivatives / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects*; D003864:Depression, Chemical; D004926:Escherichia coli / Q000378:metabolism*; D010458:Peptidyl Transferases / Q000378:metabolism*
chemical_list: D000227:Adenine Nucleotides; D000621:Aminoisobutyric Acids; D000217:Acyltransferases; D010458:Peptidyl Transferases