The anti-
H. influenzae activity of meropenem (
1a) was much higher than those of imipenem (
4), panipenem (
2b) and biapenem (
7). To clarify the major structural features responsible for the anti-
H. influenzae activity of carbapenem compounds, the structure-activity relationship to the anti-
H. influenzae activity was investigated. The anti-
H. influenzae activities of meropenem (
1a) and 1β-methyl-panipenem (
2a) were much higher than those of desmethyl-meropenem (
1b) and panipenem (
2b), respectively. Two carbapenems (
5, 6) and imipenem (
4), that have a strong basic C-2 side chain, showed lower anti-
H. influenzae activity than meropenem (
1a) having a weakly basic C-2 side chain and TV-acetyl thienamycin (
3) having a neutral C-2 side chain, respectively. As a result, we found that the introduction of the 1β-methyl group or the reduction of the basicity (cationic character) of the C-2 side chain increased the antimicrobial activity and bactericidal activity of carbapenems against
H. influenzae due to their increased affinity for PBP-4 and PBP-5.
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