2244
M. A. Seefeld et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2241–2244
Table 3. In vitro antibacterial activityof selected inhibitors with
<1 mM S. aureus FabI enzyme activity
Each compound in Table 3 was tested against a FabI
over-expressing strain of S. aureus. Thus, if FabI is an
antibacterial target of a compound, an increase in MIC
relative to the wild type strain would be expected. MIC
values for the compounds in Table 3 showed increases
of 4- to >16-fold, supporting that the mechanism of
action does indeed involve FabI inhibition.
Compd
MIC (mg/mL)a
S. aureus
M. catarrhalis
E. coli
20
22
27
3
30
31
32
0.5
4
4
0.5
1
1
1
1
0.03
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
4
8
8
4
2
8
4
0.06
Conclusion
We have identified potent inhibitors of S. aureus enoyl
acyl carrier protein reductase (FabI) that also demon-
strate whole-cell antimicrobial activityin Gram-positive
and Gram-negative organisms.
33
Triclosan
aMICs were repeated at least twice (nꢅ2) with data variabilityof one
dilution or less.
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account for the steric effects observed in Table 2. The
carbonyl oxygen of inhibitor 3 is apparentlyinvolved in
a
hydroxyl of NAD+ and to the hydroxyl group of Tyr
156 (dashed orange lines). This particular active-site
interaction is analogous to that reported for Triclosan in
which a phenol hydroxyl functions in a similar capacity.8
hydrogen bonding interaction to the 20-ribose
5. Smith, S. FASEB J. 1994, 8, 1248.
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Selected compounds with submicromolar S. aureus
enzyme activity were tested for in vitro antibacterial
activityagainst S. aureus Oxford, Moraxella catarrhalis
1502 and E. coli 7623 AcrABEFD+ organisms (Table
3). The MICs against S. aureus ranged from 0.5 to 4.0
(mg/mL) and corresponded well with FabI enzyme inhi-
bition. Antibacterial activityagainst the Gram-negative
M. catarrhalis strain was observed for the hydroxyl
containing compounds (3, 27, and 30–33). While anti-
bacterial activitywas not observed against E. coli, this
was expected due to the relativelypoor E. coli FabI
enzyme activity of these compounds. The MIC values of
triclosan were lower than we would have predicted
based on the corresponding IC50 levels. The high level
of in vitro potencyfor triclosan maybe the consequence
of having multiple cellular targets,10 and therefore MICs
maynot be exclusivelyattributable to FabI inhibition.
9. Crystallization conditions and structure determination
8a
procedures are similar to previouslypublished results. The
flipping loop of the enzyme is disordered. The crystal structure
˚
has been solved and refined to 2.4 A resolution (R=0.209,
Rf 0.277). The atomic coordinates have been deposited at the
Protein Data Bank (PDB) (accession number 1I30).
10. (a) McDonnell, G.; Pretzer, D. Actions and Targets of
Triclosan. ASM News 1998, 64, 670. (b) Russell, A. D. J. Appl.
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