Diverted Total Synthesis of Promysalin Analogs Demonstrates That an Iron-Binding Motif Is Responsible for Its Narrow-Spectrum Antibacterial Activity

Article abstract of DOI:10.1021/jacs.6b03373

Promysalin is a species-specific Pseudomonad metabolite with unique bioactivity. To better understand the mode of action of this natural product, we synthesized 16 analogs utilizing diverted total synthesis (DTS). Our analog studies revealed that the bioactivity of promysalin is sensitive to changes within its hydrogen bond network whereby alteration has drastic biological consequences. The DTS library not only yielded three analogs that retained potency but also provided insights that resulted in the identification of a previously unknown ability of promysalin to bind iron. These findings coupled with previous observations hint at a complex multifaceted role of the natural product within the rhizosphere.

Full text of DOI:10.1021/jacs.6b03373

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Communication
Diverted Total Synthesis of Promysalin Analogs Demonstrates that an Iron-
Binding Motif is Responsible for its Narrow-spectrum Antibacterial Activity
Andrew D. Steele, Colleen E. Keohane, Kyle W. Knouse,
Sean E. Rossiter, Sierra J. Williams, and William M. Wuest
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b03373 • Publication Date (Web): 20 Apr 2016
Downloaded from http://pubs.acs.org on April 24, 2016
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Journal of the American Chemical Society
Diverted Total Synthesis of Promysalin Analogs Demonstrates that
an Iron-Binding Motif is Responsible for its Narrow-Spectrum Anti-
bacterial Activity
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Andrew D. Steele, Colleen E. Keohane, Kyle W. Knouse, Sean E. Rossiter, Sierra J. Williams, and
William M. Wuest*
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
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Supporting Information Placeholder
Abstract: Promysalin is a species-specific Pseudomonad metabolite with unique bioactivity. To better understand the mode
of action of this natural product, we synthesized sixteen analogs utilizing diverted total synthesis (DTS). Our analog studies
revealed that the bioactivity of promysalin is sensitive to changes within its hydrogen bond network whereby alteration has
drastic biological consequences. The DTS library not only yielded three analogs that retained potency but also provided
insights that resulted in the identification of a previously unknown ability of promysalin to bind iron. These findings cou-
pled with previous observations hint at a complex multi-faceted role of the natural product within the rhizosphere.
Over the past century, groundbreaking discoveries in the
field of antibiotics have resulted in the saving of countless
lives. This can be primarily attributed to their broad-spectrum
HO
N
HO
N
O
O
activity that is ideal for the treatment of a wide range of
bacterial infections but can also result in significant misuse
and unintended side effects.1 For example, recent work from
the Blaser lab strongly suggests that prolonged broad-
spectrum antibiotic exposure early in life can lead to an
increased likelihood of obesity, allergies, and inflammatory
diseases.1 These findings highlight the effect that certain
antimicrobials have on one’s commensal population, resulting
in an altered community dynamic and leading to undesired
outcomes lending credence to the recent call for the
development of narrow-spectrum therapies.
16
esterase
3: R = H
5: R = Me
O
OH
O
O
4
OR
OH
C6H13
H2N
OH
8
C6H13
2
(−)-promysalin (1)
H2N
O
O
acid
What is the structure of promysalin
in the rhizosphere?
• Cyclization occurs at low pH
16
19
O
O
N
O
• Esterases are present in bacteria
O
2a: 16S, 19R
2b: 16S, 19S
Is promysalin a pro-drug?
NO
Figure 1. Structure of promysalin (1) and compounds 2 - 5 in-
volved in our pro-drug hypothesis.
To date very few options currently exist for pathogen-
specific treatments.2 Furthermore, with species-specific
compounds in hand one would also have access to tool
compounds to aid in deconvoluting the complex multispecies
environments present. The recent advances in genetic
sequencing, as exemplified by the human microbiome project,
would allow for the probing of these environments if the
appropriate tools were available.3
siderophore) in P. putida KT2440, and as expected, only one
stereoisomer elicited this phenotype. Siderophores are
essential for the growth of Pseudomonads as they actively
chelate Fe3+ for its end use in enzymatic processes.
Intriguingly, siderophore production is closely linked to
virulence; therefore, inhibiting such a process may yield novel
anti-virulence therapies.8 These initial discoveries prompted us
to initiate a synthetic campaign to elucidate what chemical
moieties are responsible for the species-specific nature of
promysalin.
Our group has been particularly interested in developing
narrow-spectrum agents to combat Pseudomonas aeruginosa
(PA) infections. PA is a Gram-negative pathogen that is
typically found in people with weakened immune systems
and/or hospital settings accounting for an estimated 51,000
infections/year in the United States alone.4 The community,
including our own lab,5 has postulated that the rhizosphere,
which is defined as the immediate area of soil that is directly
influenced by microorganisms and root secretions, is an ideal
environment to discover such compounds as the soil is
teeming with Pseudomonads competing to establish their own
niches. This hypothesis has motivated our interest in the
unique and highly specific Pseudomonad natural product
promysalin (1, Figure 1).
At the outset, we hypothesized two potential mechanisms of
action. First, promysalin may be a “prodrug”, whereby it
would be activated by either an enzyme (i.e. an esterase)
unique to PA or by the physical environment surrounding PA
itself. A second alternative is that the chemical architecture of
the molecule is exquisitely selective for a target harbored by
PA but not present in other bacteria. Our earlier synthetic
studies hinted that the exact three-dimensional shape of the
molecule was key to its biological activity as we observed a
100-200-fold decrease in activity by altering either
stereocenter on the fatty acid fragment. To address these
questions, we constructed a library of sixteen hypothesis-
driven analogs via diverted total synthesis (DTS).9
We recently reported the total synthesis and structural
elucidation of promysalin, which is produced by Pseudomonas
putida (PP), and inhibits the growth of PA at nM
concentrations,6 while Gram-positive bacteria show no
susceptibility.7 Furthermore, during our biological studies we
found that promysalin inhibits the production of pyoverdine (a
Figure 1 depicts the structure of promysalin (1) and the
structures involved in our hypotheses. Enamines are quite
susceptible to acid hydrolysis, and we were curious about the
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Is the hydrogen bond network
important for bioactivity?
B. Salicylate DTS
A. Proline DTS
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R7
R6
R4
R1 R1 R2
R3 R4 R5
R4 R5 R6 R7 R8
R1 R2 R3
n
R1
R5
R8
N
R2
R3
1
OH
-
-
-
-
-
-
-
-
-
-
-
-
-
1
6
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9
C=C
H
H
H
1
1
2
1
1
1
11 OMe
-
HO
N
HO
N
H
H
H
H
H
12
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15 OH
16
-
-
-
OH
-
-
-
OMe
-
-
OH
-
n
O
O
O
OH
H
O
O
O
-
OH
O
OH
O
F
O
C=C
OH
-
OMe
Me
10 C=C
H2N
H2N
H2N
-
OMeOMe
-
-
C6H13
C6H13
C6H13
17* NO2
-
-
O
O
O
en route
to 6-8
en route to
9 and 10
R9
en route
to 11
en route
to 12-16
9
n
R9 = OH, H
n = 1, 2
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TfO
CO2Me
H•HCl
N
n
CO2Me
CO2Me
CO2Me
O
CO2H
O
N
N
N
N
O
R10 = H, 2-OSEM, 3-OSEM,
4-OSEM, 2,6-OSEM,
3,4,5-OMe
R11
O
O
R10
R10
R10
R10
R10
R11 = OH, Cl
O
O
O
O
O
O
C6H13
OH
C6H13
OH
HO
O
N
Xc
Xc
H2N
OH
OTBS
OTBS
OTBS
Bn
en route
to 20
en route
to 19
en route
to 18
en route
to 21
C. Myristate DTS
Highlights of Diverted Total Synthesis:
A
B
X
Y
• Late Stage Derivitization
• 16 Rationally Designed Analogs Constructed
• Longest Linear Sequence 5-8 steps
HO
N
15 C−C
18 C−C
19 C−C
OH OH
O
O
-
O
B
OH OMe
Y
X
20 C−C NH OH
21 C=C OH OH
Reveals key hydrogen bond network!
H2N
A
C6H13
O
Scheme 2. The diverted total synthesis of promysalin analogs to probe the hydrogen-bonding network. Blue wording depicts the
branching points from our previously reported synthesis (for reaction conditions see ref. 6 and SI). Dashes in tables denote where
hydrogens are present. *Compound 17 was prepared by a different route (See SI).
stability of promysalin in low pH environments. Somewhat
surprisingly, we (and others)10 noticed the instability of
promysalin under mildly acidic conditions, which we were
able to attribute to the formation of cyclized products 2a/b.
We wondered if this cyclization event was biologically
relevant, whereby the compound would be dispensed by PP
and would undergo cyclization in the known acidic
environment present around PA.11 However, the cyclized
compounds showed no biological activity. Similarly, it is well
known that bacteria possess enzymes capable of hydrolyzing
esters. Therefore, we questioned if the hydrolyzed fragments
(3 and 4) would be active. We synthesized methyl ester 5 in
lieu of the acid, for cell permeability purposes. Methyl ester 5
and diol 4 were both inactive up to concentrations of 250 µM.
Additionally, we have also recently shown that appending the
acid fragment of promysalin to another myristate-derived
natural product, lyngbic acid, yielded compounds devoid of
activity against PA.12 Taken in sum, it appears that the
cyclization and hydrolysis reactions are synthetic artifacts and
not biologically relevant.
enzymatic or chemical manipulation of the natural product
directly, thus showcasing the power of organic synthesis.
We initially hypothesized that the enamide moiety of
promysalin was responsible for the bioactivity wherein it
would covalently interact with its biological target; therefore,
we postulated that any modification would render the
molecule inactive. We utilized DTS to access five specific
dehydroproline derivatives (Scheme 1, Box A). The synthesis
of the proline, piperidine, and hydroxyproline analogs 6 - 8
was straightforward using standard coupling reactions and
protecting group manipulations. We next exploited the
inherent reactivity of our triflate intermediate via Pd-mediated
coupling reactions to provide access to analogs 9 and 10.
Initial computational models of promysalin highlighted an
intricate intramolecular hydrogen-bonding network resulting
in
a rigidified molecular framework (vide infra). We
hypothesized that this network, composed of the phenol,
hydroxyl, and ester moieties, were therefore critical for
activity. To test this hypothesis we designed analogs varying
these key functionalities (Scheme 1, Box B). The salicylate
fragment was systematically altered in three specific ways: 1)
the position (12 and 13) and presence (14) of the phenol, 2)
the substitution of the phenol with either the corresponding
methyl ether (11) or nitro group (17), or 3) by increasing the
electron density within the ring (15 and 16). In a similar
fashion we sought to probe the role of ester linkage and
secondary alcohol (Scheme 1, Box C). For example, we
envisioned converting the ester to the corresponding amide
(20) to create a hydrolytically more stable analog, albeit one
Based on these results we next sought to leverage DTS to
access a library of analogs to build a structure-activity
relationship (SAR) profile and further test the importance of
the dehydroproline heterocycle. DTS has proven useful in
previous natural product mechanistic studies,13 and in some
cases has provided therapeutically useful analogs, exemplified
by the development of fludelone.14 It should be noted that the
analogs accessed from DTS presented here are inaccessible by
2
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possessing a drastically altered hydrogen-bond network. promoting swarming in PP and inhibiting pyoverdine
1
2
3
4
5
6
7
8
Alkene analog 21 would add rigidity to the scaffold and
potentially stabilize the active conformation. Finally, the
importance of the hydroxyl group was probed by either
methylation (19) or omission (18). The detailed synthetic route
for the analogs library is presented in the Supporting
Information (Scheme S1 and S2).
production. With these questions in mind, we tested the ability
of promysalin to bind iron. Indeed, promysalin tested positive
for Fe3+ chelation on CAS agar at concentrations ranging from
6-100 mM, albeit with reduced affinity when compared to the
known iron chelator EDTA (Figure 2B). Furthermore, Fe3+
chelation was confirmed down to 1 mM using an Iron-CAS
shuttle assay (see Supporting Information).19 These results hint
at the ability of promysalin to act as a siderophore in various
Pseudomonads; however, additional studies are needed to
confirm this role and are currently ongoing in our laboratory.
With a library of sixteen analogs in hand, we evaluated all
of the compounds for inhibitory activity against P. aeruginosa
strains PAO1 and PA14. The data for the active analogs (IC50
< 250 µM) is shown in Table 1 along with the inhibitory data
for the less potent diastereomers of promysalin (for numbering
see Figure 1). The inhibition data supported our initial
hypothesis that the conformation of promysalin is exquisitely
linked to its inhibition of PA. Of our modifications to the
proline structure, fluorination (9) – being the smallest steric
perturbation, was the only compound with equipotency to that
of promysalin. Methylation (10) was slightly tolerated, while
the piperidine (7) and hydroxyproline (8) derivatives were
inactive. To our surprise, proline derivative 6 retained modest
activity, which may hint at an inhibitory mechanism that
involves both structural recognition and covalent binding.
9
10
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H −> F
H −> Me
PA01
4.1
46
PA14
0.067
6.6
n = 2
C6H13
Alkene
H
1 (2R,8R)
n
O
1b (2R,8S)
N
O
O
1c (2S,8S)
90
22
O
H
1d (2S,8R)
33
4.3
6
111
7.7
32
28
Deoxy
O
9
0.019
12
H −> Me
10
11
18
19
21
H
O
The structure of the salicylate moiety was largely
unforgiving in terms of the position (12, 13), substitution (17),
or exclusion of the phenol (14). In addition, adding methoxy
substituents in the presence (15) or absence (16) of the o-
phenol was not tolerated. The only active salicylate analog
was the methyl ether (11), albeit with of an order of magnitude
less potency. In contrast, the side chain analogs all retained
some, if not all activity, with the one exception being the
amide (20). Methylation of the hydroxyl group (19) resulted in
a decrease in potency on par with the methylated-phenol (11).
Rigidifying the side chain by including the alkene (21) led to
an equipotent analog. However, when the secondary alcohol is
removed, providing compound 18, biological activity is fully
retained. At first this result was particularly surprising, as we
postulated that the alcohol was integral to the hydrogen-
bonding network, as evidenced by the difference in activity
between 1 and 1b/c (10-100 fold decrease in potency).
However, when considering our proposed macrocyclic
structure, the implications of epimerization at a hydroxyl
group can lead to drastic bond angle changes, in contrast, 18
can adopt a similar conformation simply by substituting the
amide carbonyl as a Lewis base in place of the alcohol.
Furthermore, the synthesis of 18 requires two less overall
steps, and is more atom-economical, than that of promysalin
as the use of a protecting group and chiral auxiliary is avoided.
H2N
57
6.7
= equipotent
= 10-100x
= 100 - 500x
= >500x
5.8
38
0.035
11
8.3
0.067
Table 1. IC50 values of promysalin diastereomers and active
compounds in μM (compounds with IC50 > 250 μM are not
shown). Values are averages of three independent experiments
(see SI for graphs and experimental details). A color-coded SAR
is provided depicting the fold-decrease in activity (right).
These findings may allude to how the natural product can
elicit its species-specific activity against PA and, furthermore,
the increased selectivity of PA14 over that of PAO1. One
possible mechanism of action of promysalin is through the
inhibition of siderophore transport pathways thereby severely
limiting or inhibiting the organism’s ability to acquire iron.
This particular mechanism is especially intriguing since PA14
significantly differs from PAO1 in its ability to acquire iron.
Rahme and coworkers have recently shown that ybtQ, a
yersiniabactin ABC-transporter (yersiniabactin is a phenolate-
thiazoline siderophore of similar chemical structure to that of
pyochelin), is found in PA14 and is primarily responsible for
its virulence.20
Chemists, and in particular the Miller group, have
beautifully leveraged siderophore transport pathways using
“sideromimetic” compounds whereby antibiotics are coupled
to known siderophores for uptake.21 Conversely, in Nature,
there are only a few reports of biosynthesized iron-binding
molecules that possess antibacterial activity and none have
been conclusively shown to inhibit siderophore transport
systems. However, it seems increasingly likely that within the
rhizosphere this type of process is indeed taking place,
resulting in narrow-spectrum Gram-negative agents. As
mentioned earlier, ferrocin is a compound produced by the
soil-dwelling bacteria Pseudomonas fluorescens YK-310 and
has been shown to inhibit Gram-negative bacteria. In addition
to binding iron, both compounds possess amphiphilic features
that may play a role in their potent activities. Nevertheless, the
promise of highly potent and selective agents against
As mentioned earlier, Pseudomonads are well known to
produce a variety of siderophores in the rhizosphere. A
cursory look at the literature reveals two specific siderophores
with known salicyamide iron-binding motifs, reminiscent of
promysalin: pyochelin15 and pseudomonine16 (Figure 2A).
PQS, the Pseudomonas aeruginosa 4-Quinolone Signaling
Molecule, which regulates virulence in PA, has also been
shown to bind iron.17 Intriguingly, ferrocin,18 another
Pseudomonad siderophore that bears a fatty acid moiety, has
been shown to possess antimicrobial activity specifically
against Gram-negative bacteria, and in particular PA. Based
on these findings, and in light of our bioactivity and modeling
results, we speculated that promysalin might be capable of
binding iron. This hypothesis was reinforced by earlier
findings demonstrating that promysalin is capable of
3
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This work was supported by the National Science Foundation
under CHE-1454116 and Temple University. We thank B.A.
Buttaro (Temple University) for assistance with biological
experiments, G.A. O’Toole (Dartmouth Medical School) for
the generous donation of strains, and Materia, Inc. for olefin
metathesis catalysts.
Pseudomonad Siderophores
A
Amphiphilic Pseudomonad
Antimicrobial
1
2
3
4
5
6
7
8
S
O
S
N
OH
N
H
N
H
N
O
H
N
N
H
O
3
N
O
O
O
NH
HO
O
O
O
O
O
OH
pyochelin
OH
O
REFERENCES
HN
N
3
NH
N
O
O
O
3
HO
(1) Cox, L. M.; Yamanishi, S.; Sohn, J.; Alekseyenko, A. V.;
Leung, J. M.; Cho, I.; Kim, S. G.; Li, H.; Gao, Z.; Mahana,
D.; Rodriguez, J. G. Z.; Rogers, A. B.; Robine, N.; Loke, P.;
Blaser, M. J. Cell 2014, 158, 705.
(2) Maxson, T.; Mitchell, D.A. Tetrahedron 2016, ASAP
DOI:10.1016/j.tet.2015.09.069
(3) The Human Microbiome Project Consortium, Nature 2012,
486, 207.
(4) Pseudomonas aeruginosa in Healthcare Settings. (2014). Re-
O
O
N
O
N
NH
HN
H
9
H
N
O
OH
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
N
HN
ferrocin A
pseudomonine
B
O
O
N
trieved
March
19,
2016,
from
100 50 25 12
6
O
http://www.cdc.gov/hai/organisms/pseudomonas.html
HO
OH
EDTA DMSO
(5) Keohane, C. E.; Steele, A. D.; Wuest, W. M. Synlett. 2015,
26, 2739.
(6) Steele, A.D.; Knouse, K. W.; Keohane, C. E.; Wuest, W. M.
J. Am. Chem. Soc. 2015, 137, 7314.
(7) Li, W.; Santos, P. E.; Matthijs, S.; Xie, G.; Busson, R.; Cor-
nelis, P.; Rozenski, J.; De Mot, R. Chem. & Biol. 2011, 18,
1320.
(8) Overhage, J.; Bains, M.; Brazas, M. D.; Hancock, R. E. W. J.
Bacteriol. 2008, 190, 2671.
O
H2N
(-)-1
promysalin
Figure 2. A) Structures of PA siderophores pyochelin and
pseudomonine, and antimicrobial siderophore ferrocin. Putative
iron-binding atoms are colored red and fatty acid tails in blue. B)
Structure of promysalin with proposed iron contacts shown in red
(left), minimized calculated structure (middle), CAS agar plate
(right). Numbers refer to the concentration (mM) of 10 µL of
promysalin used. EDTA (10 µL of 6 mM) and DMSO (10%) are
used as controls.
(9) Wilson, R. M.; Danishefsky, S. J. J. Org. Chem. 2006, 71,
8329.
(10) Kaduskar, R. D.; Dhavan, A. A.; Dallavalle, S.; Scaglioni, L.;
Musso,
L.
Tetrahedron
2016,
ASAP
DOI:
10.1016/j.tet.2016.03.009.
Pseudomonads warrants further investigation.
(11) Hunter, R. C.; Beveridge, T. J. Appl. Environ. Microbiol.
2005, 2501.
(12) Knouse, K. W.; Wuest, W. M. J. Antibiotics 2016, ASAP
DOI: 10.1038/ja.2016.4.
(13) Szpilman, A. M.; Carreira, E. M. Angew. Chem. Int. Ed. 2010,
49, 9592.
(14) Rivken, A.; Chou, T.; Danishefsky, S. J. Angew. Chem. Int.
Ed. 2005, 44, 2838.
(15) (a) Cox, C. D.; Rinehart, K. L., Jr.; Moore, M. L.; Cook, J. C.,
Jr. Proc. Natl. Acad. Sci. USA 1981, 78, 4256 (b) Schlegel,
K.; Lex, J.; Taraz, K.; Budzikiewicz, H. Z. Naturforsch. C.
2006, 61, 263.
(16) (a) Anthoni, U.; Christophersen, C.; Nielsen, P. H.; Gram, L.;
Petersen, B. O. J. Nat. Prod. 1995, 58, 1786. (b) Sattely, E.
S.; Walsh, C. T. J. Am. Chem. Soc. 2008, 130, 12282. (c)
Wuest, W.M.; Sattely, E.S.; Walsh, C.T. J. Am. Chem. Soc.
2009, 131, 5056.
(17) (a) Pesci, E.C.; Milbank, J.B.J.; Pearson, J.P.; McKnight, S.;
Kende, A.S.; Greenberg, E.P.; Iglewski, B.H. Proc. Natl.
Acad. Sci. USA 1999, 96, 11229. (b) Bredenbach, F.; Geffers,
R.; Nimtz, M.; Buer, J.; Haussler, S. Environ. Microbiol.
2006, 8, 1318.
In conclusion, we have leveraged the power of DTS to
access a sixteen-membered library of rationally designed
synthetic promysalin analogs. The structural diversity has shed
light on the key structural features responsible for the
bioactivity and highlights the importance of the key
functionality within the hydrogen-bonding network (which are
presumably responsible for binding iron). Further, these
findings have led to the discovery of the iron-binding ability of
promysalin, hinting at a secondary role for the natural product
as a rhizosphere siderophore. In light of these results, a
potential mechanism of action via the inhibition of siderophore
transport seems feasible. Current work in our laboratory is
now focused on determining if in fact promysalin is a
siderophore and unequivocally identifying its biological target
and will be reported in due course.
ASSOCIATED CONTENT
Supporting Information
Experimental procedures, characterization data, NMR spectra
and supporting figures. The Supporting Information is availa-
ble free of charge on the ACS Publications website at
DOI:xxxx
(18) Katayama, N.; Nozaki, Y.; Okonogi, K.; Harada, S.; Ono, H.
J. Antibiotics 1993, 46, 65.
(19) Schwyn, B.; Neilands, J.B. Anal. Biochem. 1987, 160, 47.
(20) (a) Haaq, H.; Hantke, K.; Drechsel, H.; Stojiljkovi, I.; Jung,
G.; Zähner, H. J. Gen. Microbiol. 1993, 139, 2159. (b) Choi,
J. Y.; Sifri, C. D.; Goumnerov, B. C.; Rahme, L. G.; Ausubel,
F. M.; Calderwood, S. B. J. Bacteriol. 2002, 184, 952
(21) (a) Wencewicz, T.A.; Moellmann, U.; Long, T. E.; Miller, M.
J. BioMetals, 2009, 22, 633 (b) Starr, J.; Brown, M. F.;
Aschenbrenner, L.; Caspers, N.; Che, Y.; Gerstenberger, B.
S.; Huband, M.; Knafels, J. D.; Lemmon, M. M.; Li, C.;
McCurdy, S. P.; McElroy, E.; Rauckhorst, M. R.; Tomaras, A.
P.; Young, J. A.; Zaniewski, R. P.; Shanmugasundaram, V.;
AUTHOR INFORMATION
Corresponding Author
*wwuest@temple.edu
Notes
The authors declare no competing financial interest
ACKNOWLEDGMENT
Han,
S.
J.
Med.
Chem.
2014,
57,
3845.
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