6″-thioether tobramycin analogues: Towards selective targeting of bacterial membranes

Article abstract of DOI:10.1002/anie.201200761

Amphiphilic tobramycin analogues with potent antibacterial activity against tobramycin-resistant bacteria were synthesized. Most analogues were found to be less prone to deactivation by aminoglycoside-modifying enzymes than tobramycin. These compounds tar

Full text of DOI:10.1002/anie.201200761

Angewandte
Chemie
DOI: 10.1002/anie.201200761
Antibiotics
6’’-Thioether Tobramycin Analogues: Towards Selective Targeting of
Bacterial Membranes**
Ido M. Herzog, Keith D. Green, Yifat Berkov-Zrihen, Mark Feldman, Roee R. Vidavski,
Anat Eldar-Boock, Ronit Satchi-Fainaro, Avigdor Eldar, Sylvie Garneau-Tsodikova,* and
Micha Fridman*
Decades of widespread clinical use of the bacterial riboso-
me A-site-targeting aminoglycosides (AGs) enhanced the
evolution of resistance to these antibiotics and reduced their
clinical efficacy.[1] Three modes of action lead to bacterial
resistance to AGs: reduction in the intracellular concentra-
tion of the antibiotics by efflux pump proteins or through
reduced membrane permeability; structural modifications of
the 16S ribosomal RNA that lead to reduced target affinity;
and deactivation by AG-modifying enzymes (AMEs).[1c,2]
AMEs are divided into three families: AG nucleotidyltrans-
ferases (ANTs), AG phosphotransferases (APHs), and AG
acetyltransferases (AACs).[1b,3]
In many cases, AG-resistant bacteria have evolved
combinations of resistance mechanisms, a fact that greatly
increases the challenge of regaining their clinical efficacy
through semisynthetic modifications. In recent years, several
studies demonstrated the potential of exploiting AGs for the
development of cationic amphiphilic antimicrobial agents by
converting part or all of their pseudo-oligosaccharide alcohols
into alkyl or aryl ethers.[4] Some of these amphiphilic
analogues demonstrated improved activities against several
bacterial strains with resistance to the parent AG antibiotics.
In addition to AG-based amphiphiles, several families of
cationic amphiphiles including cationic steroids (cerage-
nins)[5] as well as cationic antimicrobial peptides and pepti-
domimetic compounds[6] have been developed and were
found to possess potent antimicrobial activity. Unlike most
mammalian cell membranes, bacterial membranes are rich in
negatively-charged lipids, such as cardiolipins and phospha-
tidylglycerol, which attract cationic amphiphiles through ionic
interactions,[5] a fact that may be utilized for selective
targeting of bacterial membranes.
[*] Dr. K. D. Green,[+] Dr. S. Garneau-Tsodikova
Department of Medicinal Chemistry and the Life Sciences Institute
University of Michigan
210 Washtenaw Ave, Ann Arbor, MI 48109 (USA)
E-mail: sylviegt@umich.edu
Homepage: http://www.lsi.umich.edu/facultyresearch/labs/gar-
neau
I. M. Herzog,[+] Y. Berkov-Zrihen, Dr. M. Feldman, Dr. M. Fridman
School of Chemistry, Tel Aviv University
Tel Aviv 66978 (Israel)
Herein we report the design, synthesis, and antibacterial
activity of 18 cationic amphiphiles (4a–r) derived from
tobramycin (TOB; Scheme 1A), which is a clinically impor-
tant AG antibiotic that is becoming increasingly compro-
mised by bacterial resistance. We also provide evidence for
the mode of action of these derivatives and for the structural
requirements for targeting bacterial membranes compared to
targeting membranes of red blood cells (RBCs).
E-mail: mfridman@post.tau.ac.il
Dr. R. R. Vidavski, Dr. A. Eldar
Department of Molecular Microbiology and Biotechnology
Faculty of Life Sciences, Tel Aviv University (Israel)
A. Eldar-Boock, Dr. R. Satchi-Fainaro
We chose to modify the 6’’ primary alcohol of TOB and
focused on two groups of lypophilic substituents: 1) aliphatic
moieties including linear alkyl chains ranging from 6 to 22
carbon atoms in length as well as branched and cyclic alkyls,
and 2) substituted aryl rings. The five amino groups of TOB
were protected by Boc groups and the 6’’ primary alcohol was
selectively converted to the corresponding O-trisyl leaving
group to provide compound 2 as reported (Scheme 1A).[7]
Compound 2 was then reacted with each of the 18 aliphatic
and aromatic thiols resulting in the Boc-protected compounds
3a–r in yields ranging from 57 to 94%. Removal of all Boc
protecting groups in neat TFA gave the TFA salts of the 6’’-
thioether TOB derivatives 4a–r with no need for further
purification in yields ranging from 74 to 98%.
Department of Physiology and Pharmacology
Sackler School of Medicine, Tel Aviv University (Israel)
[+] These authors contributed equally to this work.
[**] This work was supported by the Life Sciences Institute and the
College of Pharmacy at the University of Michigan (S.G.-T.), by
a grant from the Firland Foundation (S.G.-T.), and by a National
Institutes of Health (NIH) Grant AI090048 (S.G.-T.). This work was
also supported by a grant from the United States-Israel Binational
Science Foundation (BSF), Jerusalem, Israel (Grant 2008017, S.G.-T.
and M.F.), and by the FP7-PEOPLE-2009-RG Marie Curie Auction:
Reintegration Grants (Grant 246673, M.F.). We thank Profs.
David H. Sherman and Philip C. Hanna (University of Michigan),
Itzhak Ofek and Dani Cohen (Tel Aviv University), Doron Steinberg
(The Hebrew University of Jerusalem), and Paul J. Hergenrother
(University of Illinois at Urbana-Champaign) for the gift of bacterial
strains used herein. We thank Prof. Timor Baasov and Dana Atia-
Gilkin (Shulich Faculty of Chemistry, Technion, Israel Institute of
Technology) for their assistance and guidance with the luciferase
assay.
Compounds 4a–r were screened for their antibacterial
activity against 21 Gram-positive and Gram-negative bacte-
rial strains, and their minimum inhibitory concentrations
(MICs) were determined (Table 1). Amongst the Gram-
positive bacteria were pathogenic strains such as methicillin-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201200761.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
activity was observed for the C14 and C16 chain derivatives 4e
and 4 f, with the most significant effect for 4e, which showed
marked activity against all of the 21 tested strains. The MIC
values of 4e ranged between 0.3 to 18.8 mgmLÀ1 against 19 of
the 21 tested strains: the exceptions were E. faecalis (K) and
S. enterica (U) where only a limited improvement in the
antibacterial activity of 4e as compared to TOB was observed
(MIC of 4e: 75 and 37.5 mgmLÀ1, respectively, and for TOB:
150 mgmLÀ1). The antibacterial activity dropped again for the
C18 and the C22 chain analogues 4g and 4h. With few
exceptions, a general drop in the antibacterial activity was
observed for the 6’’ aromatic thioethers (4k–r). The more
substitution around the aryl ring, the more significant was the
loss of antibacterial activity against the tested strains. For
example, of the aromatic thioether analogues, 4k with the
thiophenyl ring, and 4l with the 4-methyl-thiophenyl ring,
demonstrated the best overall antibacterial activities against
the tested strains. However, a drop in antibacterial activity
was observed for the 2,6-dimethyl-thiophenyl derivative 4m,
and a more significant drop was observed for the 2,4,6-
trimethyl-thiophenyl analogue 4n. Since thioethers may be
susceptible to cellular mediated S-oxidation,[9] we oxidized
two of the most potent thioethers (4d–e) to diastereomeric
mixtures (ca. 4:1 ratio) of the corresponding sulfoxides (5d–e)
and to the sulfones (6d–e; Scheme 1B). The effect of S-
oxidation on the antibacterial activity varied amongst the
tested bacterial strains. A reduction in the antibacterial
activity of both sulfoxide and sulfone analogues as compared
to the parent thioethers was observed for the E. coli BL21
(DE3) strains M–Q and for B. subtilis 168 with AAC(6’)/
APH(2’’)-pRB374 (strain G). In contrast, when tested against
E. faecalis (K) and L. monocytogenes (L), all four S-oxidized
analogues demonstrated improved antibacterial activities
compared to those of the thioethers 4d–e. For most of the
tested strains, S-oxidation did not have a dramatic effect on
the antibacterial activity with MIC values identical or one
double dilution higher than those of the thioethers 4d–e. In
most of the tested strains, MIC values were identical for the
sulfoxides (5d–e) and the corresponding sulfones (6d–e), thus
indicating that the level of S-oxidation has little to no effect
on antibacterial activity.
Scheme 1. A) Synthesis of 18 novel 6’’-thioether TOB derivatives (4a–
r). B) Oxidation of the thioether analogues 3d–e into the correspond-
ing sulfoxides 5d–e and sulfones 6d–e. Boc=tert-butyloxycarbonyl,
DMSO=dimethylsulfoxide, Trisyl=2,4,6-triisopropylbenzenesulfonyl,
pyr=pyridine, TFA=trifluoroacetic acid, mCPBA=meta-chloroperben-
zoic acid.
resistant Staphylococcus aureus (MRSA; strain C) and
vancomycin-resistant Enterococcus (VRE; strain J) that
displayed high levels of resistance to TOB (MIC ꢀ
150 mgmLÀ1). Amongst the Gram-negative were three strains
of E. coli BL21 (DE3) that we cloned with AMEs: the
bifunctional AAC(6’)/APH(2’’), AAC(3)-IV, and the multi-
acetylating Eis, an AAC that confers high levels of resistance
to AGs in extensively drug-resistant (XDR) strains of
Mycobacterium tuberculosis (Mtb)[8] (strains O, P, and Q,
respectively). These three strains had significant to high levels
of resistance to TOB (MICs > 150, = 150, and 18.8 mgmLÀ1,
respectively).
The analogues with linear aliphatic chains 4a–h exhibited
a parabolic pattern of chain-length-dependent antibacterial
activity (Figure S45A in the Supporting Information). Com-
pared to the antibiotic TOB, both the C6 and C8 chain
analogues 4a and 4b demonstrated a dramatic loss of
antibacterial activity, the C10 chain derivative 4c regained
some activity, and the C12 chain analogue 4d demonstrated
potent antibacterial activity against several of the strains with
resistance to TOB. The greatest improvement in antibacterial
To uncover the reasons for the broad spectrum and
improved antimicrobial activity of some of the thioether
analogues, we performed several biological tests. The effect of
compound 4e on the translation of a luciferase reporter gene
was measured in E. coli cell lysates. In lysates of Mycobacte-
rium smegmatis and E. coli, previous studies reported that the
antibiotic TOB inhibited luciferase translation at IC50 values
of approximately 20 nm.[10] In our E. coli cell lysate, TOB
potently inhibited translation (IC50 = (8.9 Æ 1.9) nm), whereas
4e did not reach an IC50 value even at 147 nm (measured using
the free base forms of TOB and 4e), thus suggesting that this
compound does not target the bacterial ribosome as its major
mode of antibacterial activity.
Furthermore, time-of-kill assays performed on S. mutans
UA159 (E) and S. pyogenes (D) revealed that 4e rapidly
conferred bacterial cell death as compared to TOB (Fig-
ure S45B in the Supporting Information). At MIC values of
2.3 mgmLÀ1 for 4e on both strains (75 mgmLÀ1 (S. mutans) or
2
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
18.8 mgmLÀ1 (S. pyogenes) for TOB) no
viable bacteria remained in the sample
treated with 4e after five hours of
incubation with S. mutans and three
hours of incubation with S. pyogenes.
For both of these strains, almost no
reduction in bacterial growth was
observed for TOB after the same incu-
bation time. The results of the luciferase
translation assay and the short time of
kill displayed by 4e suggested that this
compound acts by disrupting the bacte-
rial cell membrane. Additional strong
evidence for the membrane disruption
effect of 4e was obtained by fluorescence
microscopy experiments (Figure 1). Flu-
orescently labeled B. subtilis with con-
stitutive YFP expression (PY79)[11] was
incubated for one hour with 4e or with
TOB at several concentrations. After
one hour of incubation with TOB at
both 2 ꢀ and 8 ꢀ the MIC (2.3 and
9.4 mgmLÀ1, respectively), most of the
bacterial cells in the sample were viable
and maintained good fluorescence. In
contrast, a significant drop in fluores-
cence, which presumably resulted from
the bacterial cell lysis and loss of intra-
cellular content including the YFP, was
evident after the same incubation time
with compound 4e at both 2 ꢀ and 8 ꢀ the
MIC (4.7 and 18.8 mgmLÀ1, respectively).
The selectivity of the 6’’-thioether
derivatives 4b–h towards bacterial mem-
branes was tested by using a hemolysis
assay on both laboratory rat and human
RBCs (Figure 2). The MICs of the most
potent thioether analogues ranged
between 0.3 to 18.8 mgmLÀ1. Hence,
RBC samples were incubated with ana-
logues 4d–f at
a concentration of
75 mgmLÀ1, which is 4–250 times greater
than the MIC range and at 18.8 mgmLÀ1,
which is 1–60 times the MIC range. At
75 mgmLÀ1, TOB as well as compounds
4b and 4c with the linear C8 and
C
10 chains caused no measurable hemol-
ysis of rat and human RBCs. Compound
4d with the C12 chain caused (12.6 Æ
0.6)% hemolysis of rat RBCs and
(7.9 Æ 1.7)% hemolysis of human
RBCs. Both compounds 4e (C14 chain)
and 4 f (C16 chain) caused extensive
hemolysis at 75 mgmLÀ1 with (93.6 Æ
5.5)% and (90.2 Æ 4.5)% of rat RBCs,
and (93.7 Æ 11.1)% and (93.1 Æ 5.1)% of
human RBCs, respectively. Compound
4g (C18 chain) caused (77.2 Æ 7.0)%
hemolysis of rat RBCs and (74.3 Æ
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
(C18 chain) caused (26.3 Æ 1.9)% hemolysis of rat RBCs and
(8.0 Æ 0.8)% hemolysis of human RBCs. At 18.8 mgmLÀ1
compound 4h (C22 chain) caused (4.4 Æ 0.5)% hemolysis of
rat RBCs and no measurable hemolysis of human RBCs.
Although compound 4 f with the C16 chain was one of the
most active TOB analogues against the tested bacterial
strains, it readily disrupted RBC membranes as well. In
contrast, compound 4d (C12 chain) demonstrated potent
antimicrobial activity against several of the TOB-resistant
bacterial strains and caused little to no measurable hemolysis
at the tested concentrations. The hemolysis assay demon-
strated that the length of the aliphatic chain plays a key role in
selective targeting of the bacterial membranes versus those of
RBCs.
Several amphiphilic AGs based on paromomycin were
recently shown to act as inhibitors of the AME APH(3’).[12]
Moreover, amphiphilic AGs can make their way into the
bacterial cell where they are exposed to enzymatic modifica-
tions by AMEs. Modifications by AMEs (O-phosphorylation,
O-adenylation, and N-acetylation) result in a reduction of the
overall positive charge of the parent AG. Hence, modifica-
tions by AMEs may reduce the affinity of amphiphilic AGs to
the negatively-charged bacterial membrane and hamper their
antimicrobial activity. Structural information obtained from
crystallographic studies of several AMEs indicated that the
AG binding pocket is rich in negatively-charged amino acid
residues, such as glutamic and aspartic acids, and that several
water molecules are required to stabilize the interactions
between AGs and the AMEsꢁ binding pockets.[13] We
reasoned that the replacement of the 6’’ primary alcohol of
TOB with hydrophobic residues would interfere with these
hydrophilic binding interactions and reduce the ability of the
enzymes to modify these molecules. To test this hypothesis,
the relative activities of seven different AMEs[14] with
compounds 4a–r as substrates were compared to that with
TOB as substrate (Figure 3). While some of the modified
compounds served as better substrates for some AMEs, in
general a drop in the catalytic activity of the AMEs was
observed in most of the cases. Analogues 4d–f, which
demonstrated the most potent antimicrobial activities, were
also the poorest substrates for all of the tested AMEs.
Hence, bacterial strains that contain the tested AMEs will
have limited to no ability to inactivate analogues 4d–f
through chemical modifications that are catalyzed by these
enzymes. This inability is also true for the S-oxidized
compounds 5d–e and 6d–e, which behaved similarly to their
non-oxidized counterparts 4d–e (Figure S46 in the Support-
ing Information).
Figure 1. Bright-field and epi-fluorescence microscopy. B. subtilis
(PY79) cells carrying the gene for the yellow fluorescent protein (YFP)
under an inducible isopropyl-b-d-thio-galactoside (IPTG) promoter
were treated with TOB at 2.3 mgmLÀ1 (2ꢀ MIC) and 9.4 mgmLÀ1 (8ꢀ
MIC) or with compound 4e at 4.7 mgmLÀ1 (2ꢀ MIC) and 18.8 mgmLÀ1
(8ꢀ MIC).
Figure 2. Hemolysis tests. Human RBCs and rat RBCs were incubated
with TOB or with analogues 4b–h at concentrations of 18.8 mgmLÀ1 or
75 mgmLÀ1 for 1 h at 378C.
9.0)% hemolysis of human RBCs. A significant drop in the
hemolytic activity was observed for compound 4h (C22 chain),
which caused hemolysis of (24.4 Æ 5.8)% of rat RBCs and
(7.1 Æ 0.1)% of human RBCs.
In conclusion, 18 novel 6’’-thioether TOB analogues (4a–
r) and four S-oxidized compounds (5d–e and 6d–e) have been
synthesized and screened for antibacterial activity. The
analogues 4d–f, with linear C12, C14, and C16 chains, demon-
strated potent activity against bacterial strains with high levels
of resistance to TOB. We found evidence that the most potent
analogue 4e targets bacterial membranes and no longer
targets the ribosome as does the parent drug. Hemolysis tests
indicated that it is possible to improve the antibacterial
activity while reducing the undesired hemolytic effect by
altering the length of the aliphatic chain. Finally, thioethers
At 18.8 mgmLÀ1, TOB and analogues 4b–d with the linear
C8, C10, and C12 chains caused no measurable hemolysis of
both rat and human RBCs, and compound 4e (C14 chain)
caused (19.5 Æ 0.3)% hemolysis of rat RBCs and (14.3 Æ
1.7)% hemolysis of human RBCs. Compound 4 f (C16 chain)
demonstrated the maximal hemolytic effect of (40.4 Æ 1.7)%
(rat RBCs) and (25.4 Æ 2.1)% (human RBCs), while 4g
4
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Figure 3. Bar graph showing the relative initial rates of reactions of the listed AMEs with TOB and the 6’’-thioether analogues 4a–r. Rates are
normalized to TOB.
4d–f served as poor substrates for several AMEs, thereby
demonstrating that AMEs have a limited deactivating effect
on these AG analogues. The results reported herein offer
guidelines for the design of amphiphilic AGs that target
bacterial membranes.
[6] a) B. Findlay, G. G. Zhanel, F. Schweizer, Antimicrob. Agents
Chemother. 2010, 54, 4049 – 4058; b) A. Giuliani, A. C. Rinaldi,
Cell. Mol. Life Sci. 2011, 68, 2255 – 2266; c) L. M. Yin, M. A.
Edwards, J. Li, C. M. Yip, C. M. Deber, J. Biol. Chem. 2012, 287,
7738 – 7745.
[7] a) H. Wang, Y. Tor, Bioorg. Med. Chem. Lett. 1998, 8, 3665 –
3670; b) H. Wang, Y. Tor, Angew. Chem. 1998, 110, 117 – 120;
Angew. Chem. Int. Ed. 1998, 37, 109 – 111.
[8] a) W. Chen, T. Biswas, V. R. Porter, O. V. Tsodikov, S. Garneau-
Tsodikova, Proc. Natl. Acad. Sci. USA 2011, 108, 9804 – 9808;
b) K. D. Green, W. Chen, S. Garneau-Tsodikova, ChemMed-
Chem 2012, 7, 73 – 77.
[9] a) M. A. Wynalda, J. M. Hutzler, M. D. Koets, T. Podoll, L. C.
Wienkers, Drug Metab. Dispos. 2003, 31, 878 – 887; b) A. G.
Katopodis, H. A. Smith, S. W. May, J. Am. Chem. Soc. 1988, 110,
897 – 899.
[10] a) S. N. Hobbie, S. K. Kalapala, S. Akshay, C. Bruell, S. Schmidt,
S. Dabow, A. Vasella, P. Sander, E. C. Bottger, Nucleic Acids
Res. 2007, 35, 6086 – 6093; b) S. J. Sucheck, A. L. Wong, K. M.
Koeller, D. D. Boehr, K.-A. Draker, P. Sears, G. D. Wright, C.-H.
Wong, J. Am. Chem. Soc. 2000, 122, 5230 – 5231.
[11] A. Eldar, V. K. Chary, P. Xenopoulos, M. E. Fontes, O. C. Loson,
J. Dworkin, P. J. Piggot, M. B. Elowitz, Nature 2009, 460, 510 –
514.
[12] J. Szychowski, J. Kondo, O. Zahr, K. Auclair, E. Westhof, S.
Hanessian, J. W. Keillor, ChemMedChem 2011, 6, 1961 – 1966.
[13] a) E. Wolf, A. Vassilev, Y. Makino, A. Sali, Y. Nakatani, S. K.
Burley, Cell 1998, 94, 439 – 449; b) L. E. Wybenga-Groot, K.
Draker, G. D. Wright, A. M. Berghuis, Structure 1999, 7, 497 –
507; c) J. Sakon, H. H. Liao, A. M. Kanikula, M. M. Benning, I.
Rayment, H. M. Holden, Biochemistry 1993, 32, 11977 – 11984;
d) W. C. Hon, G. A. McKay, P. R. Thompson, R. M. Sweet, D. S.
Yang, G. D. Wright, A. M. Berghuis, Cell 1997, 89, 887 – 895.
[14] a) K. D. Green, W. Chen, S. Garneau-Tsodikova, Antimicrob.
Agents Chemother. 2011, 55, 3207 – 3213; b) V. R. Porter, K. D.
Green, O. E. Zolova, J. L. Houghton, S. Garneau-Tsodikova,
Biochem. Biophys. Res. Commun. 2010, 403, 85 – 90.
Received: January 27, 2012
Revised: March 8, 2012
Published online: && &&, &&&&
Keywords: aminoglycoside-modifying enzymes · amphiphiles ·
.
antibiotics · glycosides · hemolysis
[1] a) M. Fridman, V. Belakhov, S. Yaron, T. Baasov, Org. Lett. 2003,
5, 3575 – 3578; b) J. L. Houghton, K. D. Green, W. Chen, S.
Garneau-Tsodikova, ChemBioChem 2010, 11, 880 – 902; c) G. D.
Wright, A. M. Berghuis, S. Mobashery, Adv. Exp. Med. Biol.
1998, 456, 27 – 69.
[2] a) S. Magnet, J. S. Blanchard, Chem. Rev. 2005, 105, 477 – 498;
b) M. P. Mingeot-Leclercq, Y. Glupczynski, P. M. Tulkens, Anti-
microb. Agents Chemother. 1999, 43, 727 – 737.
[3] L. P. Kotra, J. Haddad, S. Mobashery, Antimicrob. Agents
Chemother. 2000, 44, 3249 – 3256.
[4] a) M. Ouberai, F. El Garch, A. Bussiere, M. Riou, D. Alsteens,
L. Lins, I. Baussanne, Y. F. Dufrene, R. Brasseur, J. L. Decout,
M. P. Mingeot-Leclercq, Biochim. Biophys. Acta Biomembr.
2011, 1808, 1716 – 1727; b) S. Bera, G. G. Zhanel, F. Schweizer, J.
Med. Chem. 2010, 53, 3626 – 3631; c) I. Baussanne, A. Bussiere,
S. Halder, C. Ganem-Elbaz, M. Ouberai, M. Riou, J. M. Paris, E.
Ennifar, M. P. Mingeot-Leclercq, J. L. Decout, J. Med. Chem.
2010, 53, 119 – 127; d) S. Hanessian, K. Pachamuthu, J. Szychow-
ski, A. Giguere, E. E. Swayze, M. T. Migawa, B. Francois, J.
Kondo, E. Westhof, Bioorg. Med. Chem. Lett. 2010, 20, 7097 –
7101.
[5] R. F. Epand, P. B. Savage, R. M. Epand, Biochim. Biophys. Acta
Biomembr. 2007, 1768, 2500 – 2509.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Antibiotics
I. M. Herzog, K. D. Green,
Y. Berkov-Zrihen, M. Feldman,
R. R. Vidavski, A. Eldar-Boock,
R. Satchi-Fainaro, A. Eldar,
S. Garneau-Tsodikova,*
M. Fridman*
&&&& — &&&&
Amphiphilic tobramycin analogues with
potent antibacterial activity against
tobramycin-resistant bacteria were syn-
thesized. Most analogues were found to
be less prone to deactivation by amino-
glycoside-modifying enzymes than tobra-
mycin. These compounds target the
bacterial membrane rather than the ribo-
some (see picture). The lipophilic residue
of these analogues is key to their anti-
bacterial potency and selectivity towards
bacterial membranes.
6’’-Thioether Tobramycin Analogues:
Towards Selective Targeting of Bacterial
Membranes
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!