Effects of the 1-N-(4-Amino-2 S-hydroxybutyryl) and 6′- N-(2-Hydroxyethyl) Substituents on Ribosomal Selectivity, Cochleotoxicity, and Antibacterial Activity in the Sisomicin Class of Aminoglycoside Antibiotics

Article abstract of DOI:10.1021/acsinfecdis.8b00052

Syntheses of the 6′-N-(2-hydroxyethyl) and 1-N-(4-amino-2S-hydroxybutyryl) derivatives of the 4,6-aminoglycoside sisomicin and that of the doubly modified 1-N-(4-amino-2S-hydroxybutyryl)-6′-N-(2-hydroxyethyl) derivative known as plazomicin are reported together with their antibacterial and antiribosomal activities and selectivities. The 6′-N-(2-hydroxyethyl) modification results in a moderate increase in prokaryotic/eukaryotic ribosomal selectivity, whereas the 1-N-(4-amino-2S-hydroxybutyryl) modification has the opposite effect. When combined in plazomicin, the effects of the two groups on ribosomal selectivity cancel each other out, leading to the prediction that plazomicin will exhibit ototoxicity comparable to those of the parent and the current clinical aminoglycoside antibiotics gentamicin and tobramycin, as borne out by ex vivo studies with mouse cochlear explants. The 6′-N-(2-hydroxyethyl) modification restores antibacterial activity in the presence of the AAC(6′) aminoglycoside-modifying enzymes, while the 1-N-(4-amino-2S-hydroxybutyryl) modification overcomes resistance to the AAC(2′) class but is still affected to some extent by the AAC(3) class. Neither modification is able to circumvent the ArmA ribosomal methyltransferase-induced aminoglycoside resistance. The use of phenyltriazenyl protection for the secondary amino group of sisomicin facilitates the synthesis of each derivative and their characterization through the provision of sharp NMR spectra for all intermediates.

Full text of DOI:10.1021/acsinfecdis.8b00052

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Article
Effects of the 1-N-(4-Amino-2S-hydroxybutyryl) and 6’-N-(2-Hydroxyethyl)
Substituents on Ribosomal Selectivity, Cochleotoxicity and Antibacterial
Activity in the Sisomicin Class of Aminoglycoside Antibiotics
Amr Sonousi, Vikram A Sarpe, Margarita Brilkova, Jochen
Schacht, Andrea Vasella, Erik C. Böttger, and David Crich
ACS Infect. Dis., Just Accepted Manuscript • DOI: 10.1021/acsinfecdis.8b00052 • Publication Date (Web): 30 Apr 2018
Downloaded from http://pubs.acs.org on April 30, 2018
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Effects of the 1ꢀNꢀ(4ꢀAminoꢀ2Sꢀhydroxybutyryl) and 6'ꢀ
Nꢀ(2ꢀHydroxyethyl) Substituents on Ribosomal
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Selectivity, Cochleotoxicity and Antibacterial Activity
in the Sisomicin Class of Aminoglycoside Antibiotics
Amr Sonousi,a Vikram A. Sarpe,a Margarita Brilkova,b Jochen Schacht,c Andrea Vasella,d,* Erik C.
Böttger,b,* and David Cricha,*
a: Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI 48202,
USA
b: Institut für Medizinische Mikrobiologie, Universität Zürich, Gloriastrasse 28/30, 8006 Zürich,
Switzerland
c: Kresge Hearing Research Institute, Department of Otolaryngology, 1150 West Medical Center
Dr, University of Michigan, Ann Arbor, MI 48109, USA
d: Laboratorium für Organische Chemie, ETH Zürich, VladimirꢀPrelogꢀWeg 1ꢀ5/10, 8093
Zürich, Switzerland
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dcrich@chem.wayne.edu
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Syntheses of the 6'ꢀNꢀ(2ꢀhydroxyethyl) and 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl) derivatives of the 4,6ꢀ
aminoglycoside sisomicin and that of the doubly modified 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl)ꢀ6'ꢀNꢀ(2ꢀ
hydroxyethyl) derivative known as plazomicin are reported together with their antibacterial and
antiribosomal activities and selectivities. The 6'ꢀNꢀ(2ꢀhydroxyethyl) modification results in a moderate
increase in prokaryotic/eukaryotic ribosomal selectivity, the 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl)
modification has the opposite effect. When combined in plazomicin the effects of the two groups on
ribosomal selectivity cancel each other out leading to the prediction that plazomicin will exhibit
comparable ototoxicity to the parent and to the current clinical aminoglycoside antibiotics gentamicin
and tobramycin, as borne out by exꢀvivo studies with mouse cochlear exꢀplants. The 6'ꢀNꢀ(2ꢀ
hydroxyethyl) modification restores antibacterial activity in the presence of the AAC(6')
aminoglycosideꢀmodifying enzymes, while the 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl) modification
overcomes resistance to the AAC(2') class, but is still affected to some extent by the AAC(3) class.
Neither modification is able to circumvent the ArmA ribosomal methyltransferaseꢀinduced
aminoglycoside resistance. The use of phenyltriazenyl protection for the secondary amino group of
sisomicin facilitates synthesis of each derivative and their characterization through the provision of
sharp NMR spectra for all intermediates.
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Keywords: Aminoglycosides, StructureꢀActivity Relationship, Aminoglycoside modifying enzymes,
ribosomal methyltransferases, cellꢀfree translation assays
The growing threat to public health posed by the spread of multidrugꢀresistant infectious diseases
necessitates the development of new antibiotic substances.1ꢀ7 This may be achieved either by the
discovery of new classes of antibiotic molecules or by further development of existing antibiotic classes.
The aminoglycoside antibiotics (AGAs) are an attractive starting point for the latter avenue as, with
more than fifty years of development and clinical application, an extensive knowledge of their
mechanism of action, pharmacology, and chemistry provides a strong foundation for rational
development.8ꢀ23 The decades of clinical use have also given rise to extensive resistance to AGAs,
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which is mostly due to the aminoglycosideꢀmodifying enzymes (AMEs) or the ribosomal
methyltransferases (RMTases).24ꢀ29 AMEs can be thwarted by AGA redesign to prevent modification
without compromising antibacterial activity. Indeed, this has long been a strategy in the pharmaceutical
industry and led to a series of semisynthetic AGAs, of which the kanamycin A 1 derivative amikacin 2
was the last to enter the clinic in the early 1990s,19ꢀ22,30,31 and which continues with the sisomicin 3
derivative plazomicin 4 that is currently in phase III clinical trials.32ꢀ34 Plazomicin was designed to
overcome the action of most AMEs, but it is still a target for the RMTases and most notably the G1405
methyl transferases.35 AGA modification can also impact selectivity by reducing affinity for the
eukaryotic ribosomes, particularly the mitochondrial ribosome for which drug affinity underlies the
major side effect of ototoxicity.36ꢀ38 Unfortunately, little is known about the manner in which AGA
modifications affect affinity for and thus selectivity among the bacterial and eukaryotic ribosomes. In
our laboratories, using cellꢀfree translation assays with bacterial wild type ribosomes and hybrid
bacterial ribosomes carrying humanized decoding A sites,39 we have begun to address these issues with
particular emphasis on modification of ring I in the 2ꢀdeoxystreptamine class of AGAs.40ꢀ48
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Continuing our studies of the relation between structure, activity, and selectivity of the AGAs, we report
expedient methods for the synthesis of sisomicin derivatives modified at either or both of the N1 or the
N6'ꢀpositions. These syntheses incorporate phenyltriazene protection of the secondary amino group in
ring III of the parent system facilitating spectral characterization of intermediates, a notable advantage
over the classical carbamateꢀbased protecting schemes. The consequent effective availability of
plazomicin 4, a semisynthetic AGA possessing two previously known individual structural
modifications (the 6'ꢀN (2ꢀhydroxyethyl and the 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl) substituents) of the
parent drug, and of the two individual modifications 10 and 11 enable us to report on the contribution of
these modifications, alone and in combination, to antibacterial activity and ribosomal selectivity. We
further report on exꢀvivo studies with mouse cochlear explants leading to the conclusion that the
cochleotoxicity of plazomicin is comparable to that of typical AGAs including sisomicin 3, gentamicin
5, and tobramycin 6.
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H
6' NH2
N Y
6'
HO 4'
HO
O
I
O
NH2
I
HO
3
NH2
H
O
II
H2N
N X
3
HO
H
O
HO
O 1
II
N X
HO
O1
O III
HO
OH
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O III
HO
NH2
HN
1: Kanamycin A, X = H
OH
2: Amikacin, X = 2S-COCH(OH)(CH2)2NH2
3: Sisomicin, X = Y = H
4: Plazomicin, X = 2S-COCH(OH)(CH2)2NH2
R2
Y = (CH2)2OH
NHR1
O
NH2
I
NH2
3'
O
H2N
3
HO
I
O
NH2
II
NH2
HO
3'
H2N
3
O 1
O
II
NH2
HO
O III
O 1
HO
HO
HN
OH
O III
HO
OH
NH2
5: Gentamicin C1A, C1 and C2
(R1R2 = H = C1A, R1R2 = Me = C1,
R1 = H, R2 = Me = C2)
6: Tobramycin
Results and Discussion
Synthesis
Adopting the use of the Nꢀphenyl triazenes described earlier for the selective protection of secondary
amines in the presence of their primary counterparts, we oxidized the known sisomicin derivative 749ꢀ51
with selenium dioxide in hot pyridine to afford the α,βꢀunsaturated aldehyde 8 in 77% yield.52
Reductive amination of 8 with ethanolamine then afforded derivative 9 in 63% yield, from which the
known sisomicin derivative 1051 was obtained by Staudinger reduction of the azides,53 cleavage of the
triazene with trifluoroacetic acid,49 and purification by ion exchange chromatography over Sephadex
(Scheme 1).
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Scheme 1. Synthesis of 6'ꢀNꢀ(2ꢀhydroxyethyl)sisomicin 10
The preparation of the 1ꢀNꢀ(4ꢀaminoꢀ2(S)ꢀhydroxybutyryl sisomycin 11, a compound previously
described in the patent literature54,55 and characterized as an impurity in plazomicin from the Achaogen
synthesis,56 began with the selective protection of the 6'ꢀNH2 group of sisomicin 3 using 4ꢀnitrobenzyl
Nꢀhydroxysuccinimidyl carbonate33,57 and zinc acetate giving 6’ꢀNꢀ(4ꢀnitrobenzyloxycarbonyl)sisomicin
12 in 75% yield. The amino substituents at positions 2' and 3 were then selectively protected as the Boc
derivatives by temporary protection of the other amines in the form of zinc chelates, resulting in the
formation of 13 in 52% yield.58 Reaction of 13 with a 10 mol % excess of phenyldiazonium
tetrafluoroborate in acetonitrile in the presence of potassium carbonate gave the desired triazene 14 in
88% yield. The remaining amino group was then coupled to NꢀBocꢀ4ꢀaminoꢀ2(S)ꢀhydroxyꢀbutyric acid
(LHABA)59 under standard carbodiimide conditions in the presence of Nꢀhydroxyꢀ5ꢀnorborneneꢀ2,3ꢀ
dicarboximide (HONB),60 and afforded the amide 15 in 89% yield. The 4ꢀnitrobenzyl carbamate group
was then cleaved with aqueous sodium hydroxide in dioxane to yield 70% of the amine 16, which on
treatment with TFA followed by ion exchange chromatography over Sephadex afforded the target 1ꢀ
LHABA sisomicin 11. Alternatively, reductive amination of tertꢀbutyldimethylsilyloxy acetaldehyde
with 16 and sodium triacetoxyborohydride61 gave 17 in 52% yield. This reaction was conducted in the
presence of Hünig’s base62 so as to avoid premature cleavage of the triazene group. Finally, removal of
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the Boc, silyl, and triazene groups from 17 was achieved with 50% trifluoroacetic acid in
dichloromethane and gave plazomicin 4 in 40% yield after purification by chromatography over
Sephadex and lyophilisation (Scheme 2).
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The syntheses of 4, 10, and 11 all feature the use of the phenyltriazene group for the protection of
secondary amines. In addition to the convenient protection of secondary amines in the presence of their
primary counterparts, and because of the absence of the rotamer problems associated with the more
common carbamates, the use of this protecting group affords sharp, wellꢀresolved NMR spectra which
facilitate structural elucidation. We also note that this synthesis affords the opportunity for full
characterization of plazomicin, as the published synthesis provides neither experimental details, nor
characterization data,32 and the patent literature33 reveals only high resolution mass spectrometric
measurements.
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Scheme 2. Synthesis of 1ꢀNꢀLHABA sisomicin 11 and of plazomicin 4
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Antibacterial Screening
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Compounds 10, 11 sisomicin 3 and plazomicin 4 were screened for activity against two methicillinꢀ
resistant clinical isolates of the Gramꢀpositive Staphylococcus aureus (MRSA) and against two clinical
isolates of the Gram negative Escherichia coli (E. coli) from the Diagnostic Division of the Institute of
Medical Microbiology (Table 1). Gentamicin C 5, tobramycin 6 and the structurally unusual apramycin
18, characterized by activity in the presence of most common resistance determinants and low levels of
ototoxicity,40,63,64 were also screened against the same panel for comparison. For both the Gramꢀ
positive and the Gramꢀnegative organisms the installation of the 6'ꢀNꢀ(2ꢀhydroxyethyl) substituent on
sisomicin as in compound 10 results in a modest 2ꢀ4 fold reduction in antibacterial activity, consistent
with our earlier observations on the influence of the same substituent as applied to the 4,5ꢀ
aminoglycoside neomycin B.47,65 Similarly, the 1ꢀNꢀLHABA sisomicin derivative 11 exhibits a small 2ꢀ
4ꢀfold decrease in activity against the same clinical strains of MRSA and E. coli (Table 1). Not
surprisingly, therefore, the combination of both substituents into the single compound plazomicin 4 also
results in a modest decrease in antibacterial activity against wild type MRSA and E. coli (Table 1). The
moderately reduced antibacterial activity of plazomicin, as compared to the parent sisomicin, is
consistent with the literature data.32 Broad antibacterial screening was not conducted as the activity of
plazomicin is widely reported in the literature,32,66ꢀ68 nevertheless all compounds were screened against
a small panel of ESKAPE pathogens (Table 2).
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All compounds were screened for antibacterial activity against a panel of wildꢀtype, recombinant, and
clinical strains of E. coli carrying specific resistance determinants in order to distinguish the influence of
the individual modifications (Table 3). Noteworthy is the fact that the 6'ꢀNꢀ(2ꢀhydroxyethyl)
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modification restores activity to compound 10 in the presence of the aminoglycosideꢀmodifying enzyme
AAC(6')ꢀ1 that causes a very significant drop in the activity of the parent, and of the clinical AGA
tobramycin. This result is consistent with the early indications from Mallams and coworkers,51 and with
application of the same modification to neomycin B and related 4,6ꢀAGAs.69,70 Modification of
sisomicin with the 1ꢀLHABA group 11 largely restores activity in the presence of AAC(3)ꢀI, and is also
effective in protecting against the action of AAC(2′) and AAC(6′)ꢀI (Table 3). Consistent with these
observations, and those of the Achaogen group,32 plazomicin retains most of its activity in the face of
the AAC(2′), AAC(3)ꢀI, and AAC(6')ꢀIAMEs. Most importantly, however, as members of the 4,6ꢀclass
of AGAs, all of these compounds including plazomicin succumb to resistance arising from modification
of the decoding A site of helix 44 of bacterial 16S ribosomal RNA by the RMTase ArmA acting on N5
of G1405.24,35,71ꢀ73 Apramycin 18 on the other hand, despite its moderately lower activity against wildꢀ
type bacteria (Tables 1 and 2), retains full activity in the presence of most resistance determinants
including ArmA (Table 3).
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Table 1. Antibacterial Activities (MIC, ꢁg/mL)a
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8
MRSA
E. coli
AG055
AG038
AG039
AG001
0.5
1ꢀ2
2
9
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Sisomicin
3
0.25
1
0.25
1
0.25
1
6'ꢀ(2ꢀHydroxyethyl)sisomicin 10
1ꢀLHABA sisomicin 11
0.5
2
1
0.5
2
Plazomicin
Gentamicin
4
2
2
5
0.25
0.5ꢀ1
4
0.25
>128
4
1ꢀ2
4ꢀ8
4
0.5
2
Tobramycin
6
Apramycin 18
4
a) All values were determined in duplicate using twofold dilution series.
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Table 2. Activity Against ESKAPE Pathogens (MIC, ꢁg/mL)a
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6
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8
E. coli
K. pneu
(AG215)
0.125
A. baum
E. cloacae
(AG290)
0.25ꢀ0.5
0.5ꢀ1
P. aerug
(AG212)
(AG225)
(AG220)
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Sisomicin
3
0.25ꢀ0.5
0.5
8ꢀ16
1
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6'ꢀ(2ꢀHydroxyethyl)sisomicin 10
1ꢀLHABA sisomicin 11
1
0.5
2ꢀ4
1
0.25ꢀ0.5
0.125
0.5
Plazomicin
Gentamicin
4
1
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0.25
2ꢀ4
0.5ꢀ1
1
0.5ꢀ1
0.5ꢀ1
1
5
0.5ꢀ1
0.25
Tobramycin
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4
0.25ꢀ0.5
1ꢀ2
0.5
0.5
4
Apramycin 18
4
2ꢀ4
a) All values were determined in duplicate using twofold dilution series.
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Table 3. Antimicrobial Data Against Wild Type, Engineered Strains, and Clinical Strains of E. coli Carrying Specific Resistance
Determinants (MIC, ꢁg/mL)a
Strain
Resistance Mechanism
Sisomicin
AG006b AG007b
AG105b
AG036b
AG037b
AG103b
ATCC25922c AG175c
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WT
AAC(3)ꢀI, AAC(2′) ANT(4′,4′′) APH(3′)ꢀIIIa ArmA
WT
0.5
1
AAC(6’)ꢀI
3
≤0.25
16
>64
1
>64
≤0.125
≤0.125
≤0.125
0.25
≤0.125
0.25
>64
>64
>64
>64
>64
>64
2
16ꢀ32
1ꢀ2
1ꢀ2
1ꢀ2
1
6'ꢀ(2ꢀHydroxyethyl)sisomicin 10 0.5
1ꢀLHABA sisomicin 11 0.25
>64
0.25ꢀ0.5
≤0.125
0.25
0.5
1
Plazomicin
Gentamicin
4
0.5
0.25
0.5
4
2ꢀ4
32
2
1
5
64
2
≤0.125
8
≤0.125
0.5
0.5ꢀ1
1
Tobramycin
6
64
Apramycin 18
4ꢀ8
4
4
4
4ꢀ8
nd
a) All values were determined in duplicate using two dilution series. b) Genetically engineered strain from Pasteur Institute. c)
Clinical isolates
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Antiribosomal Activity and Selectivity.
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3
4
5
6
7
8
9
In a series of cellꢀfree translation assays, 6′ꢀNꢀ(2ꢀhydroxyethyl)sisomicin 10, 1ꢀNꢀLHABA sisomicin 11,
plazomicin 4, sisomicin 3, and the comparators gentamicin 5, tobramycin 6, and apramycin 18 were
screened for inhibition of luciferase production by the bacterial ribosome. Inhibitory activities against
hybrid bacterial ribosomes carrying either the complete mitochondrial decoding A site (Wildꢀtype
mitohybrid) or its A1555G mutant (Mutant deafness mitohybrid) (Figure 1), that confers
hypersusceptibility to drugꢀinduced hearing loss, were also determined (Table 4).36,37,39 Selectivities for
the bacterial decoding A site over the wildꢀtype and mutant mitochondrial were then calculated (Table
4).
10
11
12
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18
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60
Figure 1. Decoding A sites of bacterial, human wildꢀtype mitohybrid, and human deafness mitohybrid
ribosomes. The AGA binding pocket is boxed. The bacterial numbering scheme is illustrated for the
AGA binding pocket. Changes from the bacterial ribosome binding pocket are coloured green. The
A1555G mutant conferring hypersusceptibility to AGA ototoxicity is coloured red.
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Table 4. Antiribosomal Activities (IC50 ꢁg/mL)a and Selectivities
1
2
3
Selectivityb
Antiribosomal Activitya
4
5
IC50 ꢁg/mL
6
7
8
9
Mutant
Deafness
Mitohybrid
Wildꢀtype
Mitohybrid
Mutant
Deafness
Mitohybrid
Wildꢀtype
Mitohybrid
Bacterial
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
Sisomicin 3
0.01
0.06
0.01
0.06
0.015
0.02
0.08
9.8
59
4.7
50
9
0.6
6.6
0.25
2.8
0.5
0.5
38
980
983
470
833
600
750
850
60
110
25
6′ꢀ(2ꢀHydroxyethyl)sisomicin 10
LꢀHABA Sisomicin 11
Plazomicin 4
47
Gentamicin 5
33
Tobramycin 6
15
68
25
Apramycin 18
475
a) All values were determined in duplicate using two dilution series. b)
Selectivity
=
eukaryotic/prokaryotic antiribosomal activity
The 6'ꢀ(Nꢀ2ꢀhydroxyethyl) derivative 10 of sisomicin displays largely comparable selectivity to 3 over
the wild type mitochondrial ribosomes and a two fold increase in selectivity over the A1555G mutant
mitochondrial ribosomes, suggestive of modest reduction in ototoxicity and largely consistent with the
influence exerted by this modification in the 4,5ꢀaminoglycoside neomycin B.47 The sisomicin
derivative 11 carrying the 1ꢀNꢀLHABA modification, on the other hand exhibits reduced selectivity over
both the wild type and mutant mitochondrial ribosomes. Thus, at least for sisomicin the 1ꢀNꢀLHABA
modification used to overcome the action of AAC(1) and AAC(3) AMEs attenuates ribosomal
selectivity. The opposing influence of the two modifications on ribosomal selectivity is cancelled by
their combination in plazomicin 4, resulting overall in comparable selectivity to that exhibited by the
parent, and suggesting that plazomicin and sisomicin will display comparable cochleotoxicity. As
reported previously,40 apramycin 18 exhibits excellent selectivity for the bacterial ribosome over both
the human mitochondrial and mutant mitochondrial ribosomes (Table 4).
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Cochleotoxicity.
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2
3
4
5
6
7
8
9
The cochleotoxicity of plazomicin 4, and of comparators tobramycin 5, gentamicin 6, and apramycin
18, was examined using the mouse cochlear explant model, as described previously for apramycin,40 in
24 and 72 h exposures, enabling the measure of µM EC50 values (Table 5).
Table 5. Exꢀvivo Ototoxicity
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
EC50 µM
24 h
75ꢀ150
125ꢀ250
150
72 h
16.4
9.3
Plazomicin 4
Tobramycin 5
Gentamicin 6
Apramycin 18
4.5
3500
85.5
The difference in EC50 values for the 24 and 72 h exposures clearly indicates the importance of
exposure time in these studies. While 24 h exposure requires suprapharmacological drug
concentrations, the longer 72 h period better models the clinical conditions, requiring at least an order of
magnitude less drug to kill 50% of the sensory cells in the explant (EC50). Regardless of exposure time
the data demonstrate that plazomicin has cochleotoxicity comparable to the clinical AGA tobramycin.
The ototoxicity of tobramycin is similar to that of amikacin and sisomicin in an inꢀvivo guinea pig
model,74 and moderately lower than that of gentamicin. This observation is consistent with a
preliminary report by Achaogen suggesting that plazomicin may be less ototoxic than gentamicin in the
guinea pig model,75 albeit only a single relatively low concentration of 80 mg/kgꢀ1 was employed that
does not allow for firm conclusions in this regard. It is clear from Table 5 that plazomicin is
significantly more cochleotoxic than apramycin, a compound that is known to exhibit very low levels of
ototoxicity in the guinea pig model.40
Conclusion.
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The 6'ꢀNꢀ(2ꢀhydroxyethyl) and 1ꢀNꢀ(4ꢀaminoꢀ2Sꢀhydroxybutyryl) modifications of the 4,6ꢀ
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1
2
aminoglycoside sisomicin have been prepared and characterized and demonstrated to have contrasting
influences on the ribosomal selectivity of the parent. Combination of the two modifications in a single
derivative, the experimental drug plazomicin, results in effective cancellation of their effects on
ribosomal selectivity and the prediction that plazomicin will exhibit comparable ototoxicity to the parent
sisomicin and other AGAs in current clinical practice. This conclusion is clearly borne out exꢀvivo
studies with mouse cochlear exꢀplants.
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4
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Acknowledgments. We are grateful to Sven N. Hobbie, University of Zurich for assistance with
microbiology, and Patrice Courvalin, Institut Pasteur, for the gift of engineered strains of E. coli. We
thank the NIH (AI123352) for support of this work, and acknowledge the NSF (MRIꢀ084043) for funds
in support of the purchase of the 600 MHz NMR spectrometer in the Lumigen Instrument Center at
Wayne State University.
Supporting Information. The Supporting Information is available free of charge on the ACS
Publications website at DOI:
Full experimental details and copies of 1H and 13C NMR spectra for all intermediates; 1H and 13C NMR
and 2D NMR spectra for 4, 10, and 11 (PDF)
Current Author Address: Amr Sonousi, Department of Pharmaceutical Organic Chemistry, Faculty of
Pharmacy, Cairo University, Cairo 11562, Egypt.
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Table of Contents Graphic
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OH
NH
O
Ribosomal
selectivity
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NH2
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H2N
O
NH2
OH
NH
HN
HO
O
O
O
HO
OH
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