Organic &
Biomolecular Chemistry
COMMUNICATION
Design, synthesis and biological evaluation of a
halogenated phenazine-erythromycin conjugate
prodrug for antibacterial applications†
a
Cite this: Org. Biomol. Chem., 2021,
19, 1483
Received 3rd December 2020,
Accepted 17th January 2021
Hongfen Yang,a Ke Liu, a Shouguang Jinb and Robert W. Huigens III
*
DOI: 10.1039/d0ob02428g
There is a significant need for new antibacterial agents as patho-
Our group has discovered a synthetically tunable series of
genic bacteria continue to threaten human health through the halogenated phenazines (HPs) that demonstrates potent anti-
acquisition of resistance and tolerance towards existing antibiotics. bacterial and biofilm-killing activities against Gram-positive
Over the last several years, our group has been developing a novel pathogens, including: Staphylococcus aureus, S. epidermidis
series of halogenated phenazines that demonstrate potent and Enterococcus faecium.11–15 Several halogenated phenazines
antibacterial and biofilm eradication activities against critical have also shown good to excellent antibacterial activities
Gram-positive pathogens, including: Staphylococcus aureus, against Mycobacterium tuberculosis,12–15 a slow-growing patho-
Staphylococcus epidermidis and Enterococcus faecium. Here, we gen responsible for killing 1.4 million humans worldwide in
report the design, chemical synthesis and initial biological assess- 2019.16 We have produced several HPs that demonstrate anti-
ment of
a halogenated phenazine–erythromycin conjugate bacterial activities with minimum inhibitory concentrations
prodrug 5 aimed at enhancing the translational potential for halo- (MICs) ≤ 0.5 µM against Gram-positive pathogens, which is
genated phenazines as a treatment of bacterial infections.
near the potency of vancomycin. HPs have demonstrated out-
standing biofilm-killing activities with minimum biofilm era-
dication concentrations (MBECs) ≤ 10 µM against S. aureus,
S. epidermidis and E. faecium, whereas front-running methicil-
lin-resistant S. aureus (MRSA) therapies (vancomycin, daptomy-
cin, linezolid) are unable to eradicate Staphylococcal biofilms
at 2000 µM when tested alongside HPs.12–15
Using RNA-seq technology for transcript profiling, we
showed that halogenated phenazine analogue HP-14 eradicates
MRSA biofilms through a rapid induction of iron starvation.17
Halogenated phenazines have a metal-coordinating structural
moiety that forms a stable 5-membered chelate following
binding from the 1-hydroxyl oxygen atom and the adjacent
nitrogen embedded in the phenazine heterocycle, which
allows iron binding and starvation in bacteria. In addition, we
have shown that several HP analogues bind iron(II) using UV-
vis spectroscopy.13–15 Despite this mechanism, halogenated
phenazines have demonstrated excellent cytotoxicity profiles
during our investigations.12–15
Despite significant efforts to treat bacterial infections over the
last century, pathogenic bacteria continue to devastate human
life.1–5 Bacteria are capable of demonstrating incredible resili-
ence to conventional antibiotics during infection as a result of
two distinct biological phenomena, including: (1) antibiotic re-
sistance, and (2) tolerance.5 Bacteria can acquire, or develop,
resistance towards antibiotic threat through well-defined
mechanisms (e.g., mutation of antibacterial target, efflux
pump promoted removal of antibiotics, enzymatic inactivation
of antibiotics).5,6 Currently in the United States, there are
∼2.8 million new cases and >35 000 deaths each year as a
result of antibiotic-resistant bacterial infections.7 In contrast
to acquired resistance, metabolically-dormant persister cells
demonstrate innate tolerance towards all classes of conven-
tional antibiotics.5,8–10 Surface-attached bacterial biofilms
have enriched persister cell populations and are the under-
lying cause of chronic and recurring infections.5,10
In addition to structure–activity relationship (SAR) explora-
tion and mode of action studies, we are working to translate
our HP molecules as therapies against antibiotic-resistant and
-tolerant bacterial infections. Our current aim is to develop
phenol-based prodrug strategies that mitigate the metal-chela-
tion properties of our lead HPs while enhancing physico-
chemical properties (e.g., water solubility).14,15,18 HP-17 is an
analogue we previously reported to demonstrate potent anti-
aDepartment of Medicinal Chemistry, Center for Natural Products,
Drug Discovery and Development (CNPD3), College of Pharmacy,
University of Florida, Gainesville, Florida 32610, USA.
E-mail: rwhuigens@cop.ufl.edu
bDepartment of Molecular Genetics & Microbiology, College of Medicine,
University of Florida, Gainesville, Florida 32610, USA
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0ob02428g
This journal is © The Royal Society of Chemistry 2021
Org. Biomol. Chem., 2021, 19, 1483–1487 | 1483