摘要:
A select series of 5a-methyl-substituted bicyclomycins (2-10, 34) have been prepared to identify interactions that influence antibiotic binding to the Escherichia coli rho transcription termination factor and to aid in identifying the bicyclomycin binding domain. The regioselective reduction of methyl 5a-bicyclomycincarboxylate C(2'), C(3')-acetonide (13) using lithium triethylborohydride provided 5a-(hydroxy)methylbicyclomycin C(2'),C(3')-acetonide (14). Alcohol 14 served as the key synthetic intermediate in preparing the targeted compounds. Replacing or modifying the terminal hydroxy group in 14 gave the corresponding hydrogen, acyl, halogen, azide, amine, and amide derivatives, which were then treated with trifluoroacetic acid to remove the C(2'),C(3')-acetonide protecting group to give 2-10. The chemical reactivity of 5a-(chloro)methylbicyclomycin (6) with the nucleophile EtSH was compared with bicyclomycin (1). We found that allylic chloride 6 underwent S(N)2 displacement with EtSH, while 1 furnished C(5)-C(5a) exomethylene group modified adducts. suggesting that Ci may serve as a site selective irreversible alkylation probe. Evaluation of 2-6, 8-10, and 34 in rho functional assays showed that 5a-methylbicydomycin (2), 5a-(hydroxy)methylbicyclomycin (3), 5a-[2,6-bis(trifluoromethyl)benzoxy]methylbicyclomycin (5), 5a-(azido)-methylbicyclomycin (8), 5a-(ethylmercapto)methylbicyclomycin (34), and 6 all exhibited inhibitory properties comparable with 1. The activities of these compounds and the remaining bicyclomycins within this series provided information of the structural interactions that occur with drug binding. Finally, we found that 2 displayed comparable antimicrobial activity with 1 in the filter disc assay. Compound 2 is the most biologically active bicyclomycin derivative reported to date.