Structure-Activity Relationship for the Oxadiazole Class of Antibacterials

Article abstract of DOI:10.1021/acsmedchemlett.9b00379

A structure-activity relationship (SAR) for the oxadiazole class of antibacterials was evaluated by syntheses of 72 analogs and determination of the minimal-inhibitory concentrations (MICs) against the ESKAPE panel of bacteria. Selected compounds were further evaluated for in vitro toxicity, plasma protein binding, pharmacokinetics (PK), and a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) infection. Oxadiazole 72c shows potent in vitro antibacterial activity, exhibits low clearance, a high volume of distribution, and 41% oral bioavailability, and shows efficacy in mouse models of MRSA infection.

Full text of DOI:10.1021/acsmedchemlett.9b00379

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Letter
Structure-Activity Relationship for the Oxadiazole Class of Antibacterials
Marc A. Boudreau, Derong Ding, Jayda E. Meisel, Jeshina Janardhanan, Edward
Spink, Zhihong Peng, Yuanyuan Qian, Takao Yamaguchi, Sebastian A. Testero,
Peter I. O'Daniel, Erika Leemans, Elena Lastochkin, Wei Song, Valerie A. Schroeder,
William R. Wolter, Mark A. Suckow, Shahriar Mobashery, and Mayland Chang
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.9b00379 • Publication Date (Web): 03 Oct 2019
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Structure-Activity Relationship for the Oxadiazole Class of Antibacterials
Marc A. Boudreau†, Derong Ding†, Jayda E. Meisel†, Jeshina Janardhanan†, Edward Spink†, Zhihong
Peng†, Yuanyuan Qian†, Takao Yamaguchi†, Sebastian A. Testero†, Peter I. O’Daniel†, Erika Leemans†,
Elena Lastochkin†, Wei Song†, Valerie A. Schroeder‡, William R. Wolter‡, Mark A. Suckow‡, Shahriar
Mobashery†*, and Mayland Chang†*
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†Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556
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‡Freimann Life Sciences Center and Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556
KEYWORDS antibacterials, oxadiazoles, penicillin-binding proteins, structure-activity relationship
ABSTRACT: A structure-activity relationship (SAR) for the oxadiazole class of antibacterials was evaluated by syntheses of 72
analogs and determination of the minimal-inhibitory concentrations (MICs) against the ESKAPE panel of bacteria. Selected
compounds were further evaluated for in vitro toxicity, plasma protein binding, pharmacokinetics (PK), and a mouse model of
methicillin-resistant Staphylococcus aureus (MRSA) infection. Oxadiazole 72c showed potent in vitro antibacterial activity, exhibits
low clearance, a high volume of distribution, 41% oral bioavailability, and shows efficacy in mouse models of MRSA infection.
Antibiotics have been called miracle drugs. Not only have
they saved millions of lives in treatment of infections, they have
also made possible other medical interventions such as surgery,
dialysis, and organ transplantation. The availability of
antibiotics has contributed to the increase in life expectancy in
the United States from 59.7 years in 1930 to 78.8 years in 2010.1
Notwithstanding, emergence of resistance to any antibiotic is
inevitable, threatening viability of any given class of such
With a view to explore the structural space of this class of
antibiotics, we recently reported structure-activity
a
relationship (SAR) of the oxadiazoles against S. aureus5 with a
focus on modifications in ring A. We found that 4-phenol, 4-
chloropyrazole, or 5-indole substitutions were generally
favored at this position (1, 2, and 4–8; Figure 1). These
compounds exhibit minimal-inhibitory concentration (MIC)
values against S. aureus ranging from 0.5 to 4 g/mL.
Furthermore, antibiotic 8 gave excellent efficacy in MRSA-
infected mice comparable to results obtained with linezolid, the
gold standard, and exhibited oral bioavailability and low
toxicity.5-6
agents.
Among
Gram-positive
bacteria,
resistant
Staphylococcus aureus and Enterococci pose the biggest
threat.2 S. aureus is a leading cause of health-related infections.
Every year in the United States more than 80,000 severe
methicillin-resistant S. aureus (MRSA) infections occur,
resulting in 11,285 annual deaths.3 Enterococci cause
infections, including endocarditis, urinary-tract infections, and
wound infections. Over 66,000 Enterococcus infections are
reported every year in the United States, of which 20,000 are
vancomycin-resistant Enterococcus (VRE), resulting in 1,300
deaths.3 The limited pipeline of new antibiotics has exacerbated
the antibiotic-resistance crisis.
We report herein the synthesis and SAR results against S.
aureus of 72 synthetic oxadiazoles with modifications in ring D
(see Figure 1 for ring designations). To enable a comparison to
our previously reported active compounds, we have limited our
discussion in this report to compounds with the aforementioned
ring A modifications. The SAR was established by initial
screening of the synthetic derivatives against the ESKAPE
panel of bacteria. This panel is comprised of Enterococcus
faecium, Staphylococcus aureus, Klebsiella pneumoniae,
Acinetobacter baumannii, Pseudomonas aeruginosa, and
Enterobacter sp., and Escherichia coli. These bacteria account
for the majority of problematic human infections.7 Selected
compounds were further evaluated for in vitro toxicity, plasma
protein binding, pharmacokinetics (PK), and in mouse models
of MRSA infection.
The oxadiazoles are a newly discovered class of non-β-lactam
antibiotics targeting cell-wall biosynthesis.4 These antibiotics
show potent bactericidal activity against difficult-to-treat
Gram-positive bacteria, including MRSA and VRE. They do
not have Gram-negative antibacterial activity. Our initial
studies into this class of antibiotics produced lead compounds
1–3, of which 2 and 3 exhibit 100% oral bioavailability and in
vivo efficacy.4 Further studies on compound 2 suggested
inhibition of the penicillin-binding proteins (PBPs) of S. aureus,
which are responsible for bacterial cell-wall biosynthesis.4
O
O
O
Cl
C
D
N
B
O
N
N
R1
HN
R2
R
R
A
HN
N
N
N
N
O
O
R
R
R
1 = OH, R2 = H
1 = OH, R2 = CF3
1 = NH2, R2 = CF3
R = H
R = CF3
R = F
R = H
R = CF3
1
2
3
4
5
6
7
8
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Figure 1. Structures of oxadiazoles active against S. aureus
1
2
3
4
5
6
7
O
Syntheses of Acyl Chlorides:
Syntheses of
Oxadiazoles :
e
Y
Cl
(COCl)2, DMF, CH2Cl2
Cl
O
OR
O
CO2H
HN
BnO
SOCl2, 
Y
CO2H
CO2H
CO2H
HN
Y
Cl
N
Y
Cl
Acids
9, 10, 11
10
11
9
+
8
9
H2N
Z
Syntheses of N'-Hydroxybenzimidamides:
H2N
HO
Z
Nucleophilic substitution a
N
N
OR
HO
NC
X
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59
60
Ullmann coupling b
NC
ROH
+
X = Halogen
12: X = 4-F
13: X = 4-I
Alcohols
16  48
O
O
R
Pyridine/toluene, 
OR
NH2OH
R
EtOH, 
H2N
HO
Nucleophilic substitution a
OR
14: X = 3-F, 4-F
Pyridine, 
N
55  58 d
OH
Acylation c
+
RX
Z
N
NC
Y
Acid Derivatives & Halides
15
49  54
N
O
Starting Materials
Alcohols
HO
24: R' = 4-COCF3
25: R' = 3-Cl, 4-F
26: R' = 4-F
HO
Acid Derivatives & Halides
N
S
HO
37
NHBoc
HO
46
R'
i
-PrSO Cl
MeSO2Cl
2
Br
NBoc
R'
49
50
51
27: R' = 3-Br
41: R' = NBoc
42: R' = O
43: R' = CH2
HO
HO
HO
N
28: R' = 4-SO2CH3
29: R' = 4-COCH3
30: R' = 2-Br, 4-F
31: R' = 2-Br, 4-OCH3
32: R' = 2-Br, 4-OCF3
33: R' = 2-Br
O
Br
16: R' = 3-F, 4-F
17: R' = 3-Cl, 4-Cl
18: R' = 4-I
19: R' = 4-OCF3
20: R' = 4-Br
21: R' = 3-I
22: R' = 2-I
23: R' = 4-OCH3
O
47
48
38
N
O
Cl
NMe2
NO2
53
52
54
HO
R'
N
4-Cyanophenyl Ethers
R'
OR
34: R' = 2-Br, 4-CF3
35: R' = 2-OH
HO
55: R = Bn 57: R = -Bu
56: R = CH3 58: R = CF3
t
39: R' = NBoc
40: R' = CHNHBoc
44: R' = NBoc
45: R' = NCH3
NC
HO(CH2)3NHBoc
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Figure 2. General synthetic routes to access the 1,2,4-oxadiazoles, and the starting materials used for variations within ring D. aNucleophilic
substitution: NaH/K2CO3, DMSO/DMF, 60 – 100 ºC, overnight; bUllmann coupling: CuI, Cs2CO3, N,N-dimethylglycine·HCl, 1,4-dioxane,
90 ºC, 2 – 5 h ; Acylation: anhydrous pyridine, 0 ºC to rt, 4 – 6 h; Outliers like dibenzo[b,d]furan and dibenzo[b,e][1,4]dioxine are not
listed for simplicity of the graph. Compounds 55 – 58 are 4-cyanophenyl ethers purchased commercially; eAdditional modifications are listed
in Supporting Information.
c
d
Figure 3. Antibacterial activities of the synthetic 1,2,4-oxadiazole derivatives with modifications of ring D. The MIC values (in μg/mL)
measured for S. aureus ATCC 29213, with MIC of active compounds denoted in blue (MIC ≤ 8 μg/mL) and inactive ones in red (MIC > 8
μg/mL).
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against S. aureus. Thus, the 4-phenol derivative 79a was only
The general synthetic routes to the oxadiazoles have been described
previously.4-5 The same approach was used to access the analogs
reported herein, except our focus was on modification of ring D,
which necessitated diversification of the structures at the stage of
the diphenyl ether construction. This was achieved either by direct
nucleophilic substitution and Ullmann coupling reactions of nitriles
12–14 or direct nucleophilic substitution and acylation of 4-
hydroxybenzonitrile 15 (Figure 2). In many cases, ring D variations
could be introduced by using commercially available substituted
phenols (16–48), carboxylic acid derivatives (50, 51, 53 and 54) or
halides (49 and 52). The substituents of several of these analogs
could be used as synthetic handles for further elaboration, the
reactions of which are described in the Supporting Information. In
some cases where ring D was replaced by non-annular substituents,
the requisite ethers were purchased (55–58).
1
2
3
4
5
6
7
8
modestly active (MIC = 16 g/mL), and 2-benzyl alcohol 88a
exhibited no activity. Similarly, benzoic acid derivatives 80a,
81a, and 82a were either poorly active or inactive, and 2-
carboxamide 83a and 2-aniline 84a were inactive. Introduction
of polar substituents onto an aliphatic system also resulted in
compounds with no activity, as observed with 4-
aminocyclohexane derivatives 111a, and 112a. Electron-
withdrawing substituents introduced onto ring D also resulted
in compounds with no activity, as evidenced by 4-benzonitriles
85a and 85b, as well as 4-methylsulfonate 86b and 4-acetate
87b. One exception is 2-nitro derivative 71a, which had an MIC
of 4 g/mL against S aureus.
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Replacement of the phenyl ring at position D with
heteroaromatic systems was also detrimental to activity. Thus,
benzothiazole derivative 106b was modestly active (MIC = 16
g/mL), while pyridine derivative 107a was inactive (MIC
>128 g/mL). We observed a similar trend with heteroaliphatic
ring systems, such as 4-piperidines (108a, 108b, 109b, 110a),
3-piperidines (117a, 117b, 118a, 118b), 3-azetidines (119a), as
well as the pyrrolidines and tetrahydrofuran discussed above.
Finally, we introduced more complex aliphatic amine-
containing ring systems, giving quinuclidine derivatives 120a
and 120b and tropine derivatives 121a and 121b, however,
these exhibited poor activity against S. aureus (MIC ≥32
g/mL).
We established the SAR for the oxadiazoles by screening
them for antibacterial activity against the aforementioned
ESKAPE panel of bacteria. The analogs reported herein show
activity against Gram-positive bacteria. We specifically
focused our attention on the analogs that exhibited activity
against S. aureus (Figure 3).
In general, hydrophobic substituents, and especially halogens,
were well-tolerated in ring D. Addition of an extra fluorine
(59b) or chlorine (69b) at the 3-position retained activity in the
4-chloropyrazole series, as did substitution by two chlorines at
these same positions (60b). Replacement of the fluorine by an
iodine, either at position 4 (61b, 75a), position 3 (74a), or
position 2 (67a) also retained activity overall. The same trend
was observed with introduction of a bromine atom at position 4
(63a) or position 3 (73a). Introduction of a trifluoromethoxy or
methoxy group at position 4 of the ring (62a, 68a) also retained
activity, as did the presence of a 3-trifluoromethyl ketone
substituent (70a). An azide group at any position of the ring also
maintained a favorable MIC against S. aureus (64a, 65a, 66a).
Interestingly, a benzylic bromide at position 2 (76a) or position
3 (77a) of the ring did not result in a noticeable increase in MIC,
but introduction of this substituent at position 4 (89a)
completely abolished activity.
Compounds 59b, 60b, 61b, 62a, 69b, 78a, and 72c were
selected and further evaluated for in vitro toxicity using the
XTT assay with HepG2 cells and hemolysis of red blood cells
(Table 1). Compound 78a, in which the ring D was replaced
with trifluoromethoxy caused 16% hemolysis at a concentration
of 64 µg/mL; no further studies were done with this compound.
Plasma protein binding was between 90% to 99%. Although
high, it is within the range for 43% of the 1500 most frequently
prescribed drugs,8 including many antibiotics on the market
such as daptomycin, oxacillin, teicoplanin, rifampicin, and
clindamycin.9-12 Compounds 59b, 60b, 61b, 62a, and 69b
showed >1% hemolysis or < 35 for the ratio of XTT/MIC and
were not studied further.
We also explored the effect of tethering rings C and D at their
respective 2-positions to form a dibenzofuran, and we found
that the resulting compounds where ring A was a phenol were
inactive when ring D was unsubstituted (93a) or substituted
with a 4-trifluoromethyl group (94a), 4-fluoro (90a), 4-
methoxy (91a), or 4-trifluoromethoxy (92b). Likewise,
expanding the furan portion with a heteroatom to form
dibenzodioxine 105a resulted in loss of activity.
Table 1. In vitro evaluation of oxadiazoles
Human
MIC
µg/mL
plasma
protein
XTT IC50
(μg/mL)
Hemolysis
%
binding %
8a
2
0.5
1
<1
1.3
1.8
3.1
2.1
2.9
16
98.2  3.2
98.9  1.6
97.8  0.3
90.5  0.3
99.8  0.1
91.2  0.6
ND
75.7  7.3
17.7  1.0
17.2  1.0
30.7  0.8
16.9  0.9
21.0  0.9
84.9  0.9
37.0  0.9
Replacing ring D with linear alkyl substituents resulted in
only one active compound, the trifluoromethoxy derivative 78a,
which contains a phenol for ring A. However, changing ring A
to a 4-chloropyrazole (78b) or an indole (78c) resulted in loss
of activity. The reasons for this are not clear at present. Other
alkyl substituents introduced as surrogates for ring D, such as
methyl (96a, 96b) and tert-butyl (97a) gave compounds with
poor activity, as did sulfonates (98a, 99a), alkylcarbamates
(100a) and amines (101a), and amides (102a, 103a, 104a).
59b
60b
61b
62a
69b
78a
72c
1
2
2
1
1
<1
98.8  0.7
We observed that introducing partially or fully saturated
systems at ring D gave compounds with good activity in a few
cases. Introduction of a nitrogen atom to give 3-pyrrolidines
113a and 114b, or of an oxygen atom to give 3-tetrahydrofuran
115a, decreased or abolished the activity. As a general trend,
introduction of hydrogen-bond-donating substituents at ring D
resulted in compounds with decreased antimicrobial activity
aData from Spink et al., reproduced for comparison
Compound 72c was evaluated in a broader panel of Gram-
positive bacteria and compared to the previous lead oxadiazole
8 and the standards vancomycin and linezolid (Table 2).
Oxadiazole 72c showed better activity against MRSA strains
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NRS70, VRS1, and VRS2, and S. haemolyticus, B. cereus, B.
licheniformis, and E. faecalis ATCC 29212 than oxadiazole 8.
1
2
3
Table 2. Activity of oxadiazoles against Gram-positive organisms. MIC in µg/mL.
4
5
Organism
72c
8
vancomycin
linezolid
6
7
8
9
S. aureus ATCC 29213a
S. aureus ATCC 27660 b
S. aureus N315 (NRS70)b
S. aureus NRS100 (COL)b
S. aureus NRS119c
1–2
4
4
2
2
2
2
2
2
2
4–8
16
8
8
4
4
1
2
2
1
2
1
2
1
2
1
1
2–4
1
2
1–2
2
1
1
1
2
4
2
4
4
4
1
1
1
1
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60
32
32
1
1
0.5
1
0.5
0.5
1
1
1
S. aureus NRS120c
1
S. aureus VRS1d
S. aureus VRS2e
64
32
4
4
1
0.5
2
1
128
0.5
128
0.5
S. epidermidis ATCC 35547
S. haemolyticus ATCC 29970
B. cereus ATCC 13061
B. licheniformis ATCC 12759
E. faecalis ATCC 29212a
E. faecalis 201 (Van S)f
E. faecalis 99 (Van R)g
E. faecium 119-39A (Van S)f
E. faecium 106 (Van R)g
E. faecium NCTC 7171
aA quality-control strain to monitor accuracy of MIC testing; bmecA positive, resistant to methicillin, oxacillin,
and tetracycline; susceptible to vancomycin and linezolid; cmecA positive, resistant to ciprofloxacin, gentamicin,
oxacillin, penicillin, and linezolid; dvancomycin-resistant MRSA (vanA) clinical isolate from Michigan;
evancomycin-resistant MRSA (vanA) clinical isolate from Pennsylvania; fvancomycin-susceptible clinical isolate;
gvancomycin-resistant clinical isolate.
1
1
1
Table 3. Pharmacokinetic parameters of 72c in mice
A PK study was conducted with 72c after intravenous (iv) and oral
(po) administration (Figure 4). Oxadiazole 72c had low clearance
8a
72c
Dose 20 mg/kg iv
AUC0–last
(µM∙min/mL)
AUC0–∞ (µM∙min/mL)
CL (ml/min/kg)
Vd (L/kg)
of 7.8 mL/min/kg, a large volume of distribution of 14.2 L/kg, and
a long terminal half-life of 21.1 h after iv administration (Table 3).
Maximum concentration of 1.0 µg/mL was achieved at 2.5 h and
oral bioavailability was 41%. Systemic exposure and oral
bioavailability for 72c were generally lower than the corresponding
parameters for oxadiazole 8. In addition, the half-life for
distribution after iv administration for oxadiazole 8 was shorter
than that for 72c.
1790
3140
2570
7.8
14.2
0.4
3520
5.7
4.7
0.009
9.6
t1/2 dist (h)
t1/2 elim (h)
21.1
Dose 20 mg/kg po
AUC0–last
(µM∙min/mL)
AUC0–∞ (µM∙min/mL)
Cmax (µg/mL)
Tmax (h)
t1/2 abs (h)
t1/2 dist (h)
t1/2 elim (h)
F (%)
718
3060
1040
1.0
2.5
1.3
6.2
4060
2.3
6
0.8
15.9
18.6
97
17.0
41
aData from Spink et al., reproduced for comparison
Oxadiazole 72c was evaluated in the mouse peritonitis
MRSA model of infection. The compound showed efficacy,
with half of the mice surviving after two 20 mg/kg doses of the
compound given iv at 30 min and 7.5 h after infection.
Compound 72c was further evaluated in a mouse neutropenic
thigh MRSA infection model using linezolid-sensitive (NRS70)
and linezolid-resistant (NRS119) MRSA strains (Figure 5). The
efficacy of 72c after a single oral dose at 40 mg/kg was
comparable to that of compound 8, with 1.1-log and 1.5-log
reduction in bacterial count compared to vehicle in the NRS70
Figure 4. Pharmacokinetics of 72c after single iv and po
administration at 20 mg/kg to mice (n=3 mice per time point).
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This work was supported by grants AI090818 (to M.C. and S.M.)
and NRS119 strains, respectively. In the NRS119 study,
bacterial counts after treatment with 72c and 8 were
significantly lower (p < 0.05) than in the linezolid group. Drug
concentrations at 48 h after a single oral 40 mg/kg dose of
compound 8 were 7.6 ± 2.3 µg/g and 6.0 ± 1.2 µg/g in the
NRS70 and NRS119 uninfected thighs, respectively (Table S5),
which corresponded to 3- to 4-fold above MIC. Likewise, levels
of compound 72c were 5.8 ± 1.4 µg/g and 6.4 ± 1.3 µg/g in the
NRS70 and NRS119 uninfected thighs, respectively (Table S5),
6-fold above MIC. The levels of linezolid had dropped
significantly and could not be quantified in the uninfected
thighs. In summary, 72c showed potent in vitro activity against
MRSA, oral bioavailability, and efficacy in mouse models of
MRSA infection.
1
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3
4
5
6
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8
and by AI104987 (to S.M.) from the National Institutes of Health.
YQ is a Ruth L. Kirschstein National Research Service Award
Fellow of the Chemistry-Biochemistry-Biology Interface Program
at the University of Notre Dame, supported by training grant T32
GM075762 from the National Institutes of Health.
ACKNOWLEDGMENT
We thank Pablo Cabrera for assistance with the syntheses of two
analogs.
9
ABBREVIATIONS
AUC, area-under-the curve; iv, intravenous; MIC, minimal-
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60
inhibitory
concentration;
MRSA,
methicillin
resistant
Staphylococcus aureus; PK, pharmacokinetics; po, per os; SAR,
structure-activity relationship; VRE, vancomycin-resistant
Enterococci.
REFERENCES
1. National Center for Health Statistics. National Vital
Statistics
Report.
http://www.infoplease.com/ipa/A0005148.html
2. Rossolini, G. M.; Arena, F.; Pecile, P.; Pollini, S., Update
on the antibiotic resistance crisis. Curr. Opin. Pharmacol.
2014, 18, 56-60.
3. Centers for Disease Control and Prevention. Antibiotic
Resistance Threats in the United States, 2013; 2013.
4. O'Daniel, P. I.; Peng, Z.; Pi, H.; Testero, S. A.; Ding, D.;
Spink, E.; Leemans, E.; Boudreau, M. A.; Yamaguchi, T.;
Schroeder, V. A.; Wolter, W. R.; Llarrull, L. I.; Song, W.;
Lastochkin, E.; Kumarasiri, M.; Antunes, N. T.; Espahbodi,
M.; Lichtenwalter, K.; Suckow, M. A.; Vakulenko, S.;
Mobashery, S.; Chang, M., Discovery of a new class of non-
beta-lactam inhibitors of penicillin-binding proteins with
Gram-positive antibacterial activity. J. Am. Chem. Soc.
2014, 136 (9), 3664-3672.
5. Spink, E.; Ding, D.; Peng, Z.; Boudreau, M. A.; Leemans,
E.; Lastochkin, E.; Song, W.; Lichtenwalter, K.; O'Daniel,
P. I.; Testero, S. A.; Pi, H.; Schroeder, V. A.; Wolter, W. R.;
Antunes, N. T.; Suckow, M. A.; Vakulenko, S.; Chang, M.;
Mobashery, S., Structure-activity relationship for the
oxadiazole class of antibiotics. J. Med. Chem. 2015, 58 (3),
1380-1389.
6. Janardhanan, J.; Meisel, J. E.; Ding, D.; Schroeder, V. A.;
Wolter, W. R.; Mobashery, S.; Chang, M., In Vitro and In
Vivo Synergy of the Oxadiazole Class of Antibacterials
with beta-Lactams. Antimicrob. Agents Chemother. 2016,
60, 5581-5588.
7. Boucher, H. W.; Talbot, G. H.; Bradley, J. S.; Edwards, J.
E.; Gilbert, D.; Rice, L. B.; Scheld, M.; Spellberg, B.;
Bartlett, J., Bad bugs, no drugs: no ESKAPE! An update
from the Infectious Diseases Society of America. Clin.
Infect. Dis. 2009, 48 (1), 1-12.
8. Kratochwil, N. A.; Huber, W.; Muller, F.; Kansy, M.;
Gerber, P. R., Predicting plasma protein binding of drugs: a
new approach. Biochem. Pharmacol. 2002, 64 (9), 1355-
1374.
9. Dykhuizen, R. S.; Harvey, G.; Stephenson, N.; Nathwani,
D.; Gould, I. M., Protein binding and serum bactericidal
activities of vancomycin and teicoplanin. Antimicrob.
Agents Chemother. 1995, 39 (8), 1842-1847.
10. Kochansky, C. J.; McMasters, D. R.; Lu, P.; Koeplinger, K.
A.; Kerr, H. H.; Shou, M.; Korzekwa, K. R., Impact of pH
on plasma protein binding in equilibrium dialysis. Mol.
Pharm. 2008, 5 (3), 438-448.
Figure 5. Efficacy of 72c in a mouse neutropenic thigh MRSA
infection model using (a) NRS70 (linezolid-sensitive) and (b)
NRS119 (linezolid-resistant). Mice (n = 8 per group) were
made neutropenic by administration of cyclophosphamide.
Bacteria (105 cfu) were injected intramuscularly into the right
thigh. A single 40 mg/kg oral dose of vehicle, 72c, 8, or
linezolid was given 1 h after infection. The thighs were
harvested 48 h after infection, homogenized, and plated for
colony counts. Mean ± SEM, *p < 0.05, **p<0.01, ***p<0.001
by Mann-Whitney U test two-paired.
ASSOCIATED CONTENT
Supporting Information
Synthetic procedures and experimental are supplied as Supporting
Information. The Supporting Information is available free of
charge on the ACS Publications website.
AUTHOR INFORMATION
Corresponding Author
* Shahriar Mobashery (mobashery@nd.edu) or Mayland Chang
(mchang@nd.edu)
Author Contributions
MAB, DD, ES, TY, SAT, PIO, and EL synthesized compounds.
YQ conducted some of the MS and NMR work and helped in
preparing the manuscript. JEM, ZP, and WS conducted plasma
protein binding and PK. JEM determined drug concentrations in
plasma and thighs in the mouse neutropenic thigh infection study.
JJ conducted the mouse peritonitis and mouse neutropenic thigh
infection studies and MIC against Gram-positive organisms. E.
Lastochkin conducted MIC against the ESKAPE organisms and in
vitro cytotoxicity. VAS, WRW, and MAS conducted the in-life
portion of mouse peritonitis and PK studies. SM and MC designed
the studies and wrote the manuscript, with contributions of all
authors. All authors have given approval to the final version of the
manuscript.
Funding Sources
ACS Paragon Plus Environment
5

ACS Medicinal Chemistry Letters
11. Lee, B. L.; Sachdeva, M.; Chambers, H. F., Effect of protein
binding of daptomycin on MIC and antibacterial activity.
Antimicrob. Agents Chemother. 1991, 35 (12), 2505-2508.
12. Sargent, P., Oxacillin for injection USP. Oxacillin package
insert. 2013.
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For Table of Contents Use Only
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Structure-Activity Relationship for the Oxadiazole Class of Antibacterials
Marc A. Boudreau†, Derong Ding†, Jayda E. Meisel†, Jeshina Janardhanan†, Edward Spink†,
Zhihong Peng†, Yuanyuan Qian†, Takao Yamaguchi†, Sebastian A. Testero†, Peter I. O’Daniel†,
Erika Leemans†, Elena Lastochkin†, Wei Song†, Valerie A. Schroeder‡, William R. Wolter‡, Mark
A. Suckow‡, Shahriar Mobashery†*, and Mayland Chang†*
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