Syntheses and biological evaluations of highly functionalized hydroxamate containing and N-methylthio monobactams as anti-tuberculosis and β-lactamase inhibitory agents

Article abstract of DOI:10.1039/c5md00340g

Both the resurgence of tuberculosis (TB) and antibiotic resistance continue to threaten modern healthcare and new means of combating pathogenic bacterial infections are needed. The syntheses of monobactams possessing hydroxamate and N-methylthio functionality are described, as well as their anti-TB, in vitro β-lactamase inhibitory, and general antimicrobial evaluations. A number of compounds exhibited significant anti-TB and β-lactamase inhibitory activity, with MIC values in the range of 25 to <0.19 μM against Mycobacteria tuberculosis (M. tb), and K_i values in the range of 25-0.03 μM against purified NDM-1 and VIM-1 lystate metallo β-lactamases. This work suggests that these scaffolds may serve as promising leads in developing new antibiotics and/or β-lactamase inhibitors.

Full text of DOI:10.1039/c5md00340g

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Syntheses and Biological Evaluations of Highly Functionalized
Hydroxamate Containing and N-Methylthio Monobactams as
Anti-Tuberculosis and β-Lactamase Inhibitory Agents.
Received
Accepted
Mark W. Majewski,a Kyle D. Watson,a Sanghyun Cho,b Patricia A. Miller,a Scott G. Franzblau,b and
Marvin J. Millera*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Both the resurgence of tuberculosis (TB) and antibiotic resistance continue to threaten modern healthcare and new means
of combating pathogenic bacterial infections are needed. The syntheses of monobactams possessing hydroxamate and N-
methylthio functionality are described, as well as their anti-TB, in vitro β-lactamase inhibitory, and general antimicrobial
evaluations. A number of compounds exhibited significant anti-TB and β-lactamase inhibitory activity, with MIC values in
the range of 25 to < 0.19 µM against Mycobacteria tuberculosis (M.tb), and Ki values in the range of 25-0.03 µM against
purified NDM-1 and VIM-1 lystate metallo β-lactamases. This work suggests that these scaffolds may serve as promising
leads in developing new antibiotics and/or β-lactamase inhibitors.
Introduction
available class B inhibitor.5 In an effort to help address this
Over the past 20 years, the antibiotic depository has become
less effective as a result of both antibiotic overuse and an increase
in pathogenic bacterial resistance. Most notably, tuberculosis (TB)
and the ESKAPE pathogens have posed great challenges in regards
to effective treatments. TB is a highly infectious disease and the
second major cause of death as the result of a bacterial infection
worldwide.1 TB, caused by Mycobacterium tuberculosis (M.tb),
typically targets the lungs and can be easily transmitted among
individuals. On average, there is a new case of TB each second2
and, although most are latent infections, the active cases of TB
continue to grow, approaching 10 million as of 2010.3 The EsKAPE
bacteria refer to the six most common bacteria found in hospital
settings (Enterococcus faecium, Staphylococcus aureus, Klebsiella
pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa,
Enterobacter species) and pose a threat to health care due to the
incredible rate at which these strains can become resistant to
antibiotics. The aforementioned pathogens have been especially
characterized by their remarkable ability to develop resistance to a
myriad of antibiotics because of the many mechanisms developed:
limited permeability, efflux pumps, and β-lactamases being the
most well known.4 Among these defense mechanisms, the β-
lactamases, notably class B metallo enzymes, have garnered
considerable attention especially since there is no clinically
situation, we have recently become interested in developing
hydroxamate-containing monocyclic β-lactams (monobactams) and
substituted azetidinones with different peripheral functionality and
evaluating their activity against M.tb and a panel of β-lactamase
enzymes in vitro. Herein we report on the syntheses and biological
assessments of these intriguing compounds.
Among the major classes of antibacterial agents available, the
β-lactam family continues to persist, still making up the majority of
the antibiotic market today (Figure 1).6 Although this family has
undergone evolution in attempts to address microbial resistance,
this class still remains a mainstay in the never ending microbial war.
Classically, β-lactam antibiotics work by inhibiting the formation of
peptidoglycan cross-linkages in the bacterial cell wall.7
Maintenance of this peptidoglycan layer is accomplished by
transpeptidase enzymes. Here, the β-lactam acts as a mimic of the
normal substrate for the enzymes during the cross-link formation,
ultimately forming an acyl-enzyme intermediate that is sterically
blocked, thus leading to inhibition.8
Reports of β-lactam compounds with potent anti-TB activity,
however, have been scarce. Certain classic β-lactams can exhibit
anti-TB activity when administered in combination with clavulanate,
a β-lactamase inhibitor (Figure 2, 1).9-10 Furthermore, monobactam
alkylthiols and halogen substituted aromatic monobactams have
also demonstrated intrinsic activity (Figure 2, 2-3).11-12 In general,
β-lactams have not been widely used in TB therapy for three major
reasons: issues with permeability of the cell wall of M.tb, the
persistent threat of inactivation by β-lactamases, and poor activity
in vivo.13
a Department of Chemistry and Biochemistry, University of Notre Dame, Notre
Dame, IN, 46556, USA
b Institute for Tuberculosis Research, College of Pharmacy, MIC 964, Rm. 412,
University of Illinois at Chicago, IL, 60612, USA
a. Corresponding Author:
* mmiller1@nd.edu Tel: 1-574-631-7571 Fax:1-574-631-6652.
Electronic Supplementary Information (ESI) available: [Synthetic Procedures and
Characterization Data]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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protected forms for extended use, and electron deficient aromatic
rings may not only aid in passage through the thick cell wall of M.tb,
but also potentiate activity. These features are summarized in
Figure 3. Our lab has already demonstrated that the incorporation
of both hydroxamates and more lipophilic cyclic hydroxamates into
cephalosporins led to potential new anti-microbial agents.21
Furthermore, the incorporation of alkylthio groups at the
monobactam nitrogen has produced a fascinating new class of anti-
cancer and anti-S. aureus agents.22 Herein we describe the
syntheses of hydroxamate and N-methylthiol monobactams and
their biological evaluations.
COOH
O
N
H
N
H
N
H
N
N
S
Ph
H2N
O
O
S
N
O
O
SO3H
COOH
Aztreonam
Penicillin G
NH2
NH2
H
N
H
N
H
N
H
N
S
S
Ph
O
O
HO
O
O
COOH
COOH
Cefalexin
Amoxicilin
COOH
HO
N
H
N
H2N
OH
O
N
O
O
COOH
Nocardicin A
Figure 1. Representative β-lactam Antibiotics.
Figure 3. Key Features of Featured Monobactams.
Results and Discussion
The syntheses and anti-TB evaluation of the necessary
hydroxamate precursors are reported elsewhere.23 Once in hand,
these hydroxamates were then reacted with
a variety of
azetidinones to give an initial set of monobactams, first those
devoid of functionality at the C-3 position (Schemes 1-3).
Hydroxamates 1-3 were added to 4-acetoxy-2-azetidinone, under
similar conditions employed by Clauss24 with other nucleophiles, to
give racemic monobactams 4, 7a-c, and 9a-b. Intermediate 4 was
both N-thiolated with 2-(methylthio)isoindoline-1,3-dione25 and
also separately silylated with TBSCl to give 5 and 6, respectively.
Monobactams 7a-c and 9a-b were also N- thiolated to give 8a-c and
10a-b in good yields.
Figure 2. Some Reported β-Lactams with Anti-TB Activity.
Although there are many treatments for TB (i.e. isoniazid,
rifampin, etc.), there still remain many issues with these current
regimens such as long treatment duration, drug toxicity,
detrimental drug-drug interactions, and resistance.14 Over the last
decade, however, a number of promising new compounds have
been reported that have demonstrated potent activity against M.tb.
These are highlighted by delamanid and bedaquiline, the latter
recently approved for clinical use.15 Additionally, others such as
nitroimidazoles (specifically PA-824),16 benzothiazinones (BTZs,
specifically BTZ-043),17 imidazopyridines,18 and acrylic acid ethyl
ethers19 all have recently been reported as potent anti-TB agents.
With the history of hydroxamates as useful enzyme inhibitors,20
it was of interest to see if the combination of hydroxamates with
monobactams would lead to a new class of medicinal agents.
Specifically, we were interested in the incorporation of more
lipophilic hydroxamates and electronically varied aromatic rings
into these monobactam scaffolds. As mentioned previously, one of
the challenges in TB therapy is the penetrability of drugs, the result
of the lipophilic cell wall of M.tb. Thus, we hypothesized that
monobactams without its normal acidic sulfonate group at the
nitrogen, in combination with lipophilic hydroxamates, including
Scheme 1. Racemic Syntheses of 3-Unsubstituted Monobactams.
2 | J. Name., 2012, 00, 1-3
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1. NaOEt, 0°C
1. NaOEt, 0°C
O
2.
OAc
RO
2.
O
O
TBSO
H
O
N
OAc
BnO
H
BnO
HO
NH
TBSO
O
OR
N
Ph
H
N
Ph
N
NH
R1
NH
EtOH
O
H
1 M HCl
3
4
NH
O
1
R1
NH
12
EtOH, 48%
DMF, 47%
O
O
2a-c
7a R = Bn, R1 = NO2, 44%
7b R = Bn, R1 = OEt, 23%
7c R = Allyl, R1 = NO2, 60%
11
O
O
O
BnO
H
TBSO
N SMe
O
N
N
Ph
SMe
RO
N
O
O
N
11
11
N
Et3N, 40°C
DCM, 77%
Et3N, 40°C
DCM
O
R1
SMe
13
O
S Me
8a R = Bn, R1 = NO2, 57%
8b R = Bn, R1 = OEt, 85%
8c R = Allyl, R1 = NO2, 90%
O
HO
TBSO
H
N
Ph
Pd/C, H2
NH
14
Scheme 2. Racemic Syntheses of Monobactams with Varied
Aromatic Electronics
EtOAc, 81%
O
Scheme 4. Syntheses of Monobactams with a Carbapenam Side
Chain.
Scheme 5 illustrates the syntheses of hydroxamate-containing
monobactams with the phenylacetamido sidechain. This synthetic
sequence started with the degradation of penicillin G29 to ultimately
give the appropriately functionalized azetidinone. Thus, once
generated from penicillin G, 15 was then subjected to ozonolysis
and methanolysis to give key azetidinone 16. This intermediate was
N-thiolated to give 17 and also reacted with hydroxamate 1 to give
monobactam 18. Again, the expected trans stereochemistry was
verified with NMR homo decupling analyses. Lastly, 18 was N-
thiolated to yield product 19.
Scheme 6 illustrates the preparation of hydroxamate containing
monobactams containing the phenoxyacetamido, or penicillin V
sidechain. The initial chemical transformations here are analogous
to those in Scheme 5. Thus, penicillin V potassium salt was
degraded with mercuric acetate in acetic acid, subjected to
ozonolysis, and finally methanolysis to give key azetidinone 20. This
azetidinone was then separately reacted with N-((tert-
Scheme 3. Racemic Syntheses of Monobactams with 3-nitro-5-
(trifluoromethyl) aromatic group
We then turned our attention to synthesizing compounds that
did possess established β-lactam sidechains, specifically,
compounds with the hydroxyethyl, phenylacetamido, and
phenoxyacetamido sidechains. Based on classic precedent, we
hypothesized that these moieties may be needed to potentiate
activity.26 As shown in Scheme 4, 1 was added to (2R, 3R)-3-((R)-1-
((tert-butyldimethylsilyl)oxy)ethyl)-4-oxoazetidin-2-yl acetate27 to
give 11 in modest yield. The expected trans stereochemistry
between the C-3 and C-4 hydrogens was verified using homo
decoupling NMR experiments and the fact that β-lactam protons
give distinctively different coupling values depending on whether
they are cis or trans to each other.28 Next, was to remove the silyl
protecting group. In most cases, a fluoride source, such as TBAF is
employed for this conversion. However, in our hands none of the
various sources of fluoride worked. Rather, stirring 11 in 1 M HCl
with careful monitoring produced 12. Additionally, intermediate 11
was N-thiolated to give 13 and then also subjected to standard
hydrogenolysis conditions to give hydroxamic acid 14.
butyldimethylsilyl)oxy)benzamide
and
three
additional
hydroxamates to give 21 and highly functionalized monobactams
23a-c, respectively. To confirm the expected trans relationship
between the C-3 and C-4 hydrogens, homo decoupling experiments
were conducted on 23b. Lastly, N-thiolation of 23a-b yielded 24a-b.
This journal is © The Royal Society of Chemistry 20xx
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H
N
All compounds synthesized were then subjected to biological
evaluations. Displayed in Table 1 are MIC data for select
compounds against M.tb in the microplate alamar blue assay
(MABA).30 As demonstrated, a number of compounds exhibited
notable media-dependent activity against M.tb with differences in
MIC values from different media being attributed to factors such as
compound solubility, carbon source and media age.31 With regards
to monobactams devoid of functionality at the C-3 position
(Scheme 1), we saw that the more lipophilic and electron deficient
the compound, generally the more active it was against M.tb. This
observation can be highlighted by comparing the activities of
compounds 5-10.
OAc
Ph
Hg(OAc)2
1. O3, -78 C
2. (CH3)2S
DCM, 50%
3. MeOH, 48h
rt, 50%
Penicillin G
O
N
AcOH, 85°C
O
H
15
O
H
H
N
N
SMe
Ph
OAc
N
O
OAc
SMe
Ph
O
O
O
NH
N
Pyridine, 40°C
DCM, 44%
O
17
16
O
BnO
H
O
Compounds that possessed hydroxyethyl functionality at C-3 led
to some interesting observations. Based on the results for 3-
unsubstituted compounds, it was surprising that 11 did not exhibit
noticeable anti-TB activity, despite this compound possessing both
lipophilic benzyl and TBS groups. Hypothesizing that the TBS group
may need to be removed in order to activate the compound, we
carried out the TBS removal (Scheme 4); however, 12 was inactive
as well. This further solidified the notion that factors other than
significant lipophilicity were crucial for the activity of these
compounds. Furthermore, it was observed that once 11 was N-
thiolated, the product obtained (13) demonstrated good activity
against M.tb in both types of media utilized. In this case, it can be
inferred that the methylthio substituent is important for activity
with this set of compounds.
Ph
N
Ph
1. 1M NaOH, 0°C
N
OBn
Ph
N
O
16
2.
H
NH
O
DMK, 39%
1
18
O
O
O
BnO
N
H
N
SMe
Ph
N
Ph
N
O
Et3N, 40°C
DCM, 81%
O
SMe
19
Scheme 5. Syntheses of Monobactams with Penicillin G Side Chain.
H
N
H
N
1. Hg(OAc)2
AcOH, 85 C
Table 1. MIC Determinations (μM) for Select Compounds Against
H
N
OAc
NH
S
PhO
PhO
M.tb (H37Rv) in the Microplate Alamar Blue (MABA) Assay
O
O
2. O3, -78 C
3. Me2S, -78 C to rt
O
O
COOK
Compound 7H12a
GASb
Compound 7H12a
GASb
4. MeOH, rt, 48h, 71%
Penicillin V
20
5
6
>50
17.86
0.28
14
17
>50
47.65
>100
47.33
5.93
>50
10.67
6.05
O
TBSO
H
1. NaH (60%), 0°C
O
PhO
49.20
>100
>100
>100
44.72
23.38
>100
>100
10.26
N
Ph
2.
Ph
N
OTBS
N
H
O
7b
8a
8b
9a
10a
11
12
13
49.32
24.23
34.78
30.27
5.92
18
NH
21
DMF/DCM
27%
O
19
11.56
<0.195
>50
23a
O
R2O
O
R
H
24a
6.00
PhO
N
N
R
OR2
N
1. 1M NaOH
0°C
H
O
24b
>100
64.14
NH
2. 20, DMK
O
R1
>100
>100
0.753
BTZ-043
Rifampin
<0.004 <0.004
0.05 0.04
R1
22a R2 = Bn
R = R1 = H
22b R2 = Allyl
23a
23b
23c
30%, R2 = Bn
R = R1 = H
50%, R2 = Bn, R = NO2
R1 = CF3
33%, R2 = Allyl, R = NO2
R1 = CF3
a7H12 = 7H9 medium + casitone, palmitric acid, albumin, and
R = NO2, R1 = CF3
catalase
bGAS = glycerol-alanine salts medium
O
O
BnO
R
H
N
N SMe
O
PhO
N
For compounds with penicillin G and V sidechains installed, we
saw that having the phenoxyacetamido, or penicillin V sidechain,
generated compounds with increased anti-TB activity. This can be
readily illustrated by comparing the activities of 19 with 24a and 18
with 23a. Overall, it was most intriguing that such anti-TB activity
was seen considering these monobactams lack a classic ionizable
group normally assumed to be necessary for antibiotic activity. An
interesting trend seen among all compounds evaluated was that N-
23a-b
O
N
Et3N, 40°C
DCM, 84%
O
SMe
R1
24a
, 30%, R = R1 = H
24b
, 82%, R = NO2, R1 = CF3
Scheme 6. Syntheses of Monobactams with Penicillin V Side Chain.
4 | J. Name., 2012, 00, 1-3
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thiolation often generated compounds with some measurable that 9-(2-amidoethenylthio)-9-deoxy derivatives of clavulanic acid
degree of anti-TB activity. First reported by Turos, N-alkylthio β- acted as good inhibitors of TEM-1 and staphylococcal β-
lactams have emerged as a new class of β-lactam scaffolds which lactamases.36
Furthermore, mercaptoacetic acid thiol acid
have demonstrated excellent bacteriostatic activity against S. derivatives were reported as potent inhibitors of the B. cereus
aureus and MRSA, in addition to anti-cancer and fungal activity. metallo enzyme.37 It was proposed that active substrates were
Turos has shown that these β-lactams exhibited their bacteriostatic hydrolyzed by the enzyme, releasing the thiol component which
activity against S. Aureus by in vivo transfer of the N-thiol group to then formed a covalent bond with the active site cysteine. Another
coenzyme A, ultimately disrupting essential fatty acid mercaptocarboxylate inhibitor; however, was shown to interact
biosynthesis.32 However, to our knowledge, there have not been with IMP-1 metallo β-lactamase from P. aeruginosa via two key
any reports on the extension of N-thiolated β-lactams as anti-TB interactions: direct coordination of the sulfur to the Zn in the active
agents.
site, and binding in the hydrophobic pocket.38 To the best of our
knowledge, there are no reports of thiol-containing monobactams
that act as potent and/or selective inhibitors of β-lactamases in the
literature. Lastly, it was intriguing that none of the compounds in
this report possessed an ionizable group, such as a carboxylate or -
SO3, normally required for antibacterial and/or β-lactamase
inhibitory activity. However based on the above precedent and
discussions, it seems to not be required.
The second evaluation performed was the Kirby-Bauer
antibacterial agar diffusion assay.33 It was seen that a number of
compounds targeted Gram-positive bacteria, especially M. vaccae,
with notable zones of inhibition in the range of 20-37 mm (see
supporting information). Based on the aforementioned anti-TB
activity, this result was not unexpected since both M.tb and M.
vaccae bacterial strains are from the same genus. However, it
should be noted that a number of the most potent TB agents Table 2. In vitro Screenings of Select Compounds against β-
reported herein (6, 13, and 24a) were not very active in the agar Lactamases
studies. We also determined minimum inhibitory concentration
(MIC) values for compounds of interest. Notably, both compounds
9a and 10b exhibited MICs of 6.25 μM against M. vaccae.
CTX-M-14 Oxa-48
NDM-1
VIM-1
Enzyme
Class
(Purified) (Purified) (Purified)
(Lysate)
A
D
B
B
Lastly, all compounds were screened against a broad panel of β-
lactamases in vitro at and using protocols established by Rempex
pharmaceuticals. Our studies included enzymes from all four
classes (A, B, C, and D). Here, synthesized compounds were
incubated with purified enzyme (or lysate) for 10 min, then an
enzyme substrate was added, and the optical density of the wells
against time was measured and Ki values determined,34 with
pertinent results illustrated in Table 2. For studies with metallo β-
lactamase NDM-1, imipenem was utilized as the enzyme substrate
while for all other enzymes, nitrocefin was employed. Overall, we
observed that many of the monobactams acted as good β-
lactamase inhibitors, with activity noted against a broad range of
enzymes screened. Highlighted among these results was the broad
spectrum of inhibition that compounds 8c and 19 exhibited.
Azetidinone 8c, seen as one of the most active compounds in β-
lactamase inhibition screenings showed inhibitory activity against
CTX-M-14, NDM-1, and VIM-1 with calculated Ki values of 0.64,
0.03, and 22.7 μM, respectively. Compounds 6, 18, 19, and 24a
were of outstanding interest, as a result of their activity against
both M.tb and β-lactamases. With these encouraging results, we
then tested all compounds for synergy with various β-lactam
antibiotics against drug resistant, β-lactamase producing strains.
However, interestingly we saw that the combinations were inactive.
Compound
Ki (μM)
6
7b
7c
>160
>160
>160
>160
>160
0.64
>160
>160
0.25
>160
0.40
0.32
0.05
>160
>160
>160
>160
1.72
>160
>160
>160
>160
>160
1.93
>160
>160
>160
0.97
0.07
0.03
>160
0.04
>160
>160
>160
>160
>160
0.07
0.96
0.06
0.15
>160
>160
>160
>160
>160
22.7
8a
8b
8c
9b
10b
11
12
13
14
18
19
21
24a
24b
>160
59.27
>160
>160
>160
>160
>160
2.86
>160
>160
>160
>160
>160
>160
1.95
>160
>160
>160
31.2
>160
>160
When looking for trends from the data set in Table 2, it seemed
apparent that N-thiolation was quite important in potentiating
activity against the class B metallo β-lactamases. As ready
examples, when comparing activities against class B enzymes, the
conversion from 7b to 8b, 7c to 8c, and 23b to 24b all resulted in
the conversion of an inactive compound to a potent inhibitor of
NDM-1. The interesting exception was compound 13, whose
activity was directed specifically at CTX-M-14 despite bearing the
methylthio substituent. Further, silyl removal to give 12 resulted in
an inactive compound.
Oxa-48: Oxacillinase β-Lactamase; NDM-1: New-Delhi
Metallo β-Lactamase; VIM-1: Verona Integron-Encoded
Metallo β-Lactamase
Conclusions
To close, we have synthesized a library of highly functionalized
monobactams and have subjected them to antimicrobial testing.
Many compounds exhibited notable anti-TB activity (MIC values
10.65 to <0.195 μM) and selective β-lactamase inhibitory activity (Ki
Thiol containing compounds as inhibitors of β-lactamases are
well established in the literature.35 For example, it has been shown
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values in the range 20 to 0.03 μM) against purified enzymes. 13. Chambers, H.F.; Turner, J.; Schecter G.F.;, Kawamura, M.;
Although at this stage of our studies the exact target(s) and/or Hopewell, P.C. Antimicrob. Agents Chemother. 2005, 49, 2816-2821.
general mode of action remain unknown, these compounds may 14. Zumla, A.; Nahid, P.; Cole, S. T. Nat. Rev. 2013, 12, 388-404.
serve as scaffolds against both TB and β-lactamases.
15. Wong, E. B.; Cohen, K. A.; Bishai, W. R. Trends Microbiol. 2013,
21, 493-501.
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Author Information
Corresponding Author
* mmiller1@nd.edu Tel: 1-574-631-7571 Fax:1-574-631-6652.
17. Makarov, V.; Manina, G.; Mikusova, K.; Möllmann, U.; Ryabova,
O.; Saint-Joanis, B.; Dhar, N.; Pasca, M. R.; Silvia, B.; Lucarelli, A. P.;
Milano, A.; De Rossi, E.; Belanova, M.; Bobovska. A.; Dianiskova, P.;
Kordulakova, J.; Sala, C.; Fullam, E.; Schneider, P.; McKinney, J. D.;
Brodin. P.; Christophe, T.; Waddell, S.; Butcher, P.; Albrethsen, J.;
Rosenkrands, I.; Brosch, R.; Nandi, V.; Bharath, S.; Gaonkar, S.;
Shandil, R. K.; Balasubramanian, V.; Balganesh, T.; Tyagi, S.; Grosset,
J.; Riccardi, G.; Cole, S. T. Science, 2009, 324, 801-804.
18. Moraski, G. C.; Markley, L. D.; Cramer, J.; Hipskind, P. A.;
Boshoff, H.; Bailey, M. A.; Alling, T.; Ollinger, J.; Parish, T.; Miller, M.
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Author Contributions
This manuscript was written through contributions of all authors.
M.W.M. synthesized and characterized all compounds and wrote
both this report and the supporting information section. K.D.W.
performed β-lactamase screenings, IR characterization, and assisted
with decoupling experiments. S.C. performed the MABA assay,
P.A.M. performed MIC and diffusion assays. All authors have given
approval to the final version of the manuscript.
Acknowledgements
19. Kabir, M. S.; Namjoshi, O. A.; Verma, R.; Polanowski, R.; Krueger,
S. M.; Sherman, D.; Rott, M. A.; Schwan, W. R.; Monte, A.; Cook, J.
M. Bioorg. Med. Chem. 2010, 18, 4178-4186.
We acknowledge the University of Notre Dame, and the NIH (NIH-
2R01-AI054193 and NIH-T32GMO75782) for support of this work.
We acknowledge Rempex Pharmaceuticals for providing β-
20. a) Flipo, M.; Beghyn, T.; Charton, J.; Leroux, V. A.; Deprez, B. P.;
Deprez-Poulain, R. F. Bioorg. Med. Chem. 2007, 15, 63-76. b) Irwin,
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M. J. Bioorg. Med. Chem. Lett. 2015,
lactamase enzymes for screening during
a CBBI supported
internship at Rempex by K.D.W. We acknowledge Nonka Sevova
(Mass Spectrometry and Proteomics Facility, UND) for mass
spectroscopic analyses, the ND Energy Materials Characterization
Facility for use of IR instrumentation, and the Lizzadro NMR
facilities for use of NMR instrumentation. M.W.M acknowledges an
ECK Global Health Fellowship (2014-2015, UND). K.D.W.
acknowledges a CBBI Fellowship (2013-2015, UND).
http://dx.doi.org/10.1016/j.bmcl.2015.04.099
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Described are the syntheses and evaluations of hydroxamate containing and Nꢀmethylthiolated
monobactams as a class of potent βꢀlactamase inhibitors.