4-Aminothiazolyl analogues of GE2270 A: Antibacterial lead finding

Article abstract of DOI:10.1021/jm101602q

4-Aminothiazolyl analogues of the antibacterial natural product GE2270 A (1) were designed, synthesized, and evaluated for Gram positive bacteria growth inhibition. The aminothiazole-based chemical template was evaluated for chemical stability, and its de

Full text of DOI:10.1021/jm101602q

BRIEF ARTICLE
pubs.acs.org/jmc
4-Aminothiazolyl Analogues of GE2270 A: Antibacterial Lead Finding
Matthew J. LaMarche,*,† Jennifer A. Leeds,‡ JoAnne Dzink-Fox,‡ Karl Gunderson,† Philipp Krastel,§
Klaus Memmert,§ Michael A. Patane,† Elin M. Rann,† Esther Schmitt,§ Stacey Tiamfook,‡ and Bing Wang†
†Global Discovery Chemistry, ‡Infectious Disease Area, Novartis Institutes for Biomedical Research, Cambridge, Massachusetts 02139,
United States
§Natural Products Unit, Novartis Institutes for Biomedical Research, Basel, Switzerland
ABSTRACT: 4-Aminothiazolyl analogues of the antibacterial natural product GE2270 A (1) were designed, synthesized, and
evaluated for Gram positive bacteria growth inhibition. The aminothiazole-based chemical template was evaluated for chemical
stability, and its decomposition revealed a novel, structurally simplified, des-thiazole analogue of 1. Subsequent stabilization of the
4-aminothiazolyl functional motif was achieved and initial structure activity relationships defined.
’ INTRODUCTION
identify compounds with potent antibiotic activity.11 Most notably,
1 and several fermentation metabolites thereof were identified as
potent inhibitors of Gram positive bacterial growth. Fortunately,
large-scale fermentation and isolation of the thiopeptides was possible
in order to further investigate the chemotype as an antibacterial drug-
lead.12 Considering the potent antibiotic activity of the thiopeptide
class of molecules, we embarked on our own drug discovery efforts
with the aim to discover and develop a novel class of antibiotics for
parenteral use.
In view of the chemical instability of the oxazoline-based side
chain of 1 and the previously reported carbon-based side chain
analogues thereof, we envisioned the use of a nitrogen-linked side
chain strategy to prosecute our discovery efforts (5, Scheme 1),
vis ꢀa vis a 4-aminothiazolyl moiety. In 1991, South reported the
chemical instability of 2,5-dichloro, 4-aminothiazolyl rings via
polymerization.13 More recently, others have successfully synthe-
sized and manipulated amides, ureas, and carbamates derived
from 4-aminothiazoles.14 In these reports, the 4-aminothiazole
was synthesized via Curtius rearrangement of an activated
4-carboxylic acid-thiazole derivative. The intermediate isocya-
nate was subsequently trapped by a nucleophile, providing the
requisite amide, carbamate, or urea. To facilitate a thorough SAR
investigation of N-linked thiazolyl side chains of 1, and to
evaluate the chemical stability of this functional motif, we
investigated trapping of the 4-thiazolyl isocyanate as well as
chemistries derived from the 4-aminothiazole.
In 1991, Selva and co-workers from Lepetit Research Institute
reported the structure and antibiotic activity of GE2270 A (1), a
thiopepetide-based natural product isolated from a fermentation
broth of Planobispora rosea.1 The in vitro antibiotic profile against
methicillin resistant staphylococci (MRSA) and vancomycin
resistant enterococci (VRE) was exquisite, with minimum in-
hibitory concentrations <1 μg/mL. Structurally related thiopep-
tide natural products are known in the literature and have been
reported in preclinical drug discovery campaigns. These thiopep-
tides include the Thiostreptons (Figure 1), Nocathiacins,
Amythiamicins (not shown), and the Thiomuracins.2
Thiazolyl actinomycetes metabolites are characterized by their
highly modified, sulfur containing macrocyclic peptide struc-
tures, which possess a tri- or tetra-substituted nitrogen-contain-
ing heterocycle core (circled, Figure 1). Nearly all of the
thiopeptides inhibit bacterial growth by inhibiting protein synth-
esis, however, their cellular targets are distinct. For example, the
structurally complex polycycles of the Nocathiacins and Thios-
treptons bind to the 23s rRNA component of the bacterial 50S
ribosomal subunit at the same site as the L11 ribosomal subunit,
while 1 and the Thiomuracin monocycles target the prokaryotic
chaperone, elongation factor Tu (EF-Tu).3
Recently there has been increased interest in 1. In 2003,
Vicuron, Inc., reported semisynthetic derivatives of 1 intended
for parenteral administration.4 In that report, the previously
described acid-mediated decomposition of the oxazoline side
chain allowed for SAR investigation of carbon-based side chain
analogues.5 One compound was reportedly selected for advance-
ment to the clinic as a topical treatment for acne.6 In addition,
partial and total syntheses of 1 have been achieved by several
academic groups.7 Structural papers8 and solution conformation
studies9 of related natural products have also recently been
reported.
The discovery of antibiotics which act via a novel mechanism
of action remains a pressing unmet medical need in infectious
disease care. Clinical resistance to marketed drugs is becoming
increasingly common.10 Toward this end, a high-throughput
screen of the Novartis compound library was conducted to
’ RESULTS
In a retrosynthetic sense, 4-aminothiazole 5 was envisioned
from the Boc-protected 4-aminothiazole (6, Scheme 1). This
strategic intermediate would from a Curtius rearrangement of
known acid 7,1,4 a derivative of 1. In the forward synthetic
direction, 1 (Scheme 2) was first subjected to acid-catalyzed
rearrangement and basic hydrolysis,4 which afforded acid 7 in high
yield. The resulting 4-thiazolylcarboxylic acid was next activated
with ethylchloroformate to form the ethylacylcarbonate, which was
Received: December 17, 2010
Published: March 15, 2011
r
2011 American Chemical Society
2517
dx.doi.org/10.1021/jm101602q J. Med. Chem. 2011, 54, 2517–2521
|

Journal of Medicinal Chemistry
BRIEF ARTICLE
Scheme 2. Synthesis of 4-Aminothiazole 5
Figure 1. Thiopepetide-based natural products.
Scheme 1. Retrosynthesis of 4-Aminothiazolyl Analogues
Scheme 3. 4-Aminothiazole Decomposition and Proposed
Mechanism
displaced in situ by azide. This three-step, one-pot process
furnished acylazide 9 and also set the stage for the Curtius event.
Interestingly, direct acylazide formation from the carboxylate
utilizing diethylphosphorylazide led to low, irreproducible yields.
In the Curtius rearrangement, the acylazide was heated in tert-
butyl alcohol at 80 °C to furnish the Boc protected 4-aminothia-
zole 6 (43%, 4 steps). Acetylation of the alcohol (i.e., 10, 11)
increased the organic solubility and improved the recovery from
column chromatography. Subsequent deprotection of either 6 or
10 under acidic conditions (TFA or HCl in DCM) afforded the
corresponding 4-aminothiazole salt. Unfortunately, attempts to
obtain the freebase of 5 (or 11) proved challenging. Basic
aqueous workup, chromatography, or storage of the 4-aminothia-
zole freebase (5) led to chemical decomposition (Scheme 3).
The major decomposition product identified was 2-picolinamide
12, the product of likely aminothiazole hydrolysis. Mechanisti-
cally, we speculate that the 4-aminothiazole ring tautomerizes to
afford the thiazol-4(5H)imine (13). Subsequent hydration of the
imine promoted by advantageous water under column chroma-
tography (or via aqueous workup) would provide intermediate
14. Ring-opening leading to amide formation would then afford
intermediate 15. Further hydration of 15 (e.g., 16) and
elimination of 2-mercapto-acetamide would furnish the 2-pico-
linamide, 12. Of note, the synthesis of 2-picolinamide (12) could
also be purposely accomplished under basic aqueous reaction
conditions (Cs2CO3, MeCN, H2O).
2518
dx.doi.org/10.1021/jm101602q |J. Med. Chem. 2011, 54, 2517–2521

Journal of Medicinal Chemistry
BRIEF ARTICLE
To circumvent the 4-aminothiazole hydrolysis and enable the
evaluation of structure activity relationships of amine-based
thiazole linkers, chemical stabilization of the 4-aminothiazole
was necessary. Boc removal via acidolysis revealed the aminothia-
zole salt (Scheme 2: 5, 11), which was successfully stored without
decomposition (room temperature, > 14 days) and used directly
in amidation and sulfonylation reactions (Scheme 4), affording
amide 17 and sulfonamide 18. We surmise that salting, acylation,
or sulfonylation precludes tautomerization and thus prevents the
subsequent hydrolytic decomposition.
1 and novel analogues 6, 12, 17, and 18 were then evaluated in
minimum inhibitory concentration (MIC) assays15 against Gram
positive bacteria (Table 1). Four organisms comprised our
antibacterial screen and included Enterococcus faecalis, Enterococ-
cus faecium, Staphylococcus aureus, and Streptococcus pyogenes. Boc
protected aminothiazole 6 proved significantly less potent
(MICs > 32 μg/mL) than the natural product (1: MICs < 1
μg/mL). The structurally simplified des-thiazolyl 2-picolinamide
12 also failed to retain activity against all organisms. The amide
and sulfonamide analogues (17, 18), however, retained good to
moderate potency (1 > 32 μg/mL) in 3 out of 4 target organisms.
Thus, a stabilized and structurally simplified chemical platform
for further medicinal chemistry optimization had been identified.
’ DISCUSSION AND CONCLUSIONS
4-Aminothiazolyl analogues of the antibiotic natural product
GE2270 A were designed, synthesized, and evaluated for Gram
positive bacterial growth inhibition. An unexpected 4-aminothia-
zolyl decomposition pathway was identified that led to a struc-
turally simplified des-thiazole analogue (12). The chemical
instability of the 4-aminothiazolyl moiety was then con-
trolled by salting, amidation, and sulfonylation, which resulted
in analogues with moderate in vitro potency (17, 18). Because of
the improved chemical stability and promising initial antibacter-
ial results, the 4-aminothiazolyl template was selected for further
medicinal chemistry lead optimization. Furthermore, the 4-ami-
nothiazolyl-based chemical template described herein represents
an original chemotype for antibacterial drug discovery. Indeed, to
combat increasing clinical resistance to marketed antibiotics, the
discovery of innovative chemical scaffolds that address under-
exploited antibacterial mechanisms of action remains a pressing
need in infectious disease care. Thus, the biological activity
exhibited by this unique class of thiopeptides represents a
significant and promising lead for antibiotic drug discovery. In
addition, these lead identification efforts also serve as a reminder
of the importance and relevance of natural product-based,
industrial drug discovery. The details of these continued efforts
will be the subject of additional correspondence.
Scheme 4. 4-Aminothiazole Stabilization
’ EXPERIMENTAL SECTION
NMR: proton NMR spectra were recorded on a Bruker 400 MHz
ultrashield spectrometer. Chemical shifts are reported relative to metha-
nol (δ 3.31), dimethyl sulfoxide (δ 2.50), or chloroform (δ 7.26).
LCMS: compounds were analyzed on an Inertsil ODS-3 column (C18,
50 mm ꢀ 4.6 mm, 3 μm) with a 2 min gradient elution (25%
acetonitrile/H2O/5 mM ammonium formate) and a flow rate of
4 mL/min. HPLC purification utilizes a C8 or C18 column (30 mm
ꢀ 100 mm, 5 μm, brand: Sunfire or XTerra) and 10 mM NH4OH in
40-95%ACN in H2O. LC analysis utilizes an Atlantis brand C18
column (150 mm) with a 20 min gradient elution (0-95% acetonitrile
in water þ0.1% TFA).
Preparation of Acylazide 9. To a solution of the ester (5, 1.5 g,
1.16 mmol) in THF (300 mL) is added 20 mL of H2O and NaOH (60
mg, 1.50 mmol). The reaction is stirred at 60 °C for 1.5 h and monitored
by TLC (10% MeOH/DCM) and LCMS. After completion, the
reaction is concentrated to dryness. The off-white solid is suspended
Table 1. Minimum Inhibitory Concentrations15 (μg/mL) of 1 and Analogues 6, 12, 17, and 18
2519
dx.doi.org/10.1021/jm101602q |J. Med. Chem. 2011, 54, 2517–2521

Journal of Medicinal Chemistry
BRIEF ARTICLE
in toluene (100 mL) and concentrated to dryness (repeat 3ꢀ), which
affords the acid, an off-white solid. The crude solid is stored in vacuo (0.1
Torr) for 12 h. LCMS: Rt = 1.12 min, [M þ H]þ 1125.
Preparation of Amide 17. To a solution of the Boc-amine (6, 10
mg, 0.0083 mmol) in DCM (10 mL) was added TFA (1 mL, 13.46
mmol). The reaction was stirred for 30 min and concentrated. The
resultant yellow foam was dissolved in DCM (10 mL) and concentrated
(repeat 3ꢀ). The crude amine salt was taken on with no further
purification. LCMS: Rt = 1.33 min, [M þ H]þ 1096.0.
The carboxylic acid 7 was suspended in 300 mL of acetone. The flask
was sonicated and the solid scraped down the sides of the flask for
15 min. To this suspension was added TEA (2.0 mL, 14.2 mmol) and
ethylchloroformate (2.0 mL, 20.91 mmol). The precipitate slowly
dissolved. Further sonication and vigorous stirring was used to break
up all particles. After 1 h, the reaction appeared complete via LCMS and
NaN3 (500 mg, 7.69 mmol) was added. The suspension (white/yellow
in appearance) was stirred for 1 h at 60 °C and monitored by LCMS.
Two additional aliquots of NaN3 (500 mg, 7.69 mmol) were added and
the reaction stirred for 20 min. The reaction was concentrated onto SiO2
and purified by flash chromatography (1.5 in. ꢀ 1.5 in. SiO2 column, 3 L
of EtOAc). This afforded 920 mg of crude acyl-azide (6), a white solid.
The crude material was taken on to the next step with no further
purification. LCMS: Rt = 1.55 min, [M þ H]þ 1150.
To a solution of the amine (0.0083 mmol) in pyridine (1 mL) is
added acetic anhydride (0.100 mL, 0.979 mmol). The solution is stirred
at RT for 10 min and poured into a saturated aq solution of sodium
bicarbonate (100 mL). The mixture is extracted with EtOAc (3ꢀ) and
the combined organic extracts are dried over MgSO4, filtered, and
concentrated directly onto SiO2. The crude product is purified by flash
chromatography (gradient elution: 0-5% MeOH/DCM) to afford 6
1
mg of amide (17) as a white solid. H NMR (400 MHz, DMSO-d6 δ
11.14 (br s, 1 H), 9.00 (br d, 1 H), 8.68-8.66 (m, 2 H), 8.59 (s, 1 H),
8.45-8.42 (m, 1 H), 8.40 (d, 1 H), 8.24 (s, 1 H), 8.13 (d, 1 H), 7.80 (s, 1
H), 7.38-7.21 (m, 7 H), 6.01 (br d, 1 H), 5.32-5.17 (m, 3 H), 5.01-
4.99 (m, 1 H), 4.97 (s, 2 H), 4.27 (dd, 1 H), 3.79 (dd, 1 H), 3.38 (s, 3 H),
2.73-2.68 (m, 1 H), 2.46 (d, 3 H), 2.19-2.14 (m, 1 H), 2.10 (s, 3 H),
1.35-1.28 (m, 1 H), 0.87 (d, 3 H), 0.84 (d, 3 H). LCMS: Rt = 1.35 min,
[M þ H]þ1138.0. HRMS [M þ H]þ 1138.2046, calcd 1138.2073.
Preparation of Sulfonamide 18. To a solution of Boc-amine-
acetate (10, 100 mg, 0.081 mmol) in DCM (25 mL) was added TFA (5 mL,
67.3 mmol). The reaction was stirred for 30 min and concentrated. The
resultant yellow foam was dissolved in DCM (10 mL) and concentrated
(repeat 3ꢀ). The crude amine is taken on with no further purification.
LCMS: Rt = 1.45 min, [M þ H]þ1138.0.
Preparation of Boc-amine 6. A suspension of acyl-azide (9, 920
mg) was heated (80 °C) in t-BuOH (100 g). After 2 h complete
dissolution occurred and after 12 h the reaction appeared complete by
LCMS. The solution was concentrated directly onto SiO2 and chroma-
tographed (gradient elution: 50-70% EtOAc/hexanes) which afforded
600 mg (43%, 4 steps) of Boc-amine (6), a white solid. 1H NMR (400
MHz, DMSO-d6) δ 10.38 (br s, 1 H), 9.00 (d, 1 H), 8.70 (app d, 2 H),
8.58 (s, 1 H), 8.44-8.41 (m, 1 H), 8.38 (d, 1 H), 8.23 (s, 1 H), 8.11 (d, 1
H), 7.48 (br s, 1 H), 7.38-7.23 (m, 7 H), 6.02 (br s, 1 H), 5.31-5.18 (m,
3 H), 5.01-5.00 (m, 1 H), 4.97 (s, 2 H), 4.30-4.24 (dd, 1 H), 3.79 (dd,
1 H), 3.38 (s, 3 H), 2.75-2.68 (m, 1 H), 2.47 (d, 3 H), 2.22-2.13 (m, 1
H), 1.49 (s, 9 H), 1.37-1.31 (m, 1 H), 0.87 (d, 3 H), 0.84 (d, 3 H).
LCMS: Rt = 1.72 min, [M þ H]þ 1196. LC: Rt = 17.96 min. HRMS:
1196.2437, calcd 1196.2492.
Step 5, Preparation of Boc-amine-acetate 10. To a solution
of the Boc-amine (6, 540 mg, 0.451 mmol) in DCM (250 mL) was
added acetic anhydride (0.100 mL, 0.979 mmol), pyridine (1.0 mL, 12.4
mmol), and DMAP (20 mg, 0.169 mmol). The reaction stirred for 3 h,
was concentrated directly onto SiO2, and chromatographed (gradient
elution: 50-70% EtOAc/hexanes), which provided 465 mg (83%) of
Boc-amine-acetate (10). 1H NMR (400 MHz, DMSO-d6) δ 10.38 (br s,
1 H), 9.20 (br d, 1 H), 8.79 (br d, 1 H), 8.61 (br d, 1 H), 8.56 (s, 1 H),
8.44-8.41 (m, 1 H), 8.38 (d, 1 H), 8.24 (s, 1 H), 8.11 (d, 1 H), 7.48 (br
s, 1 H), 7.42 (s, 2 H), 7.35-7.29 (m, 6 H), 6.14 (s, 1 H), 5.47 (t, 1 H),
5.31-5.26 (m, 1 H), 5.19 (dd, 1 H), 4.97 (s, 3 H), 4.26 (dd, 1 H), 3.72
(dd, 1 H), 3.38 (s, 3 H), 2.70-2.65 (m, 1 H), 2.59 (s, 3 H), 2.45 (d, 3 H),
2.22-2.14 (m, 1 H), 1.96 (s, 3 H), 1.57-1.50 (m, 1 H), 1.49 (s, 9 H),
0.88 (d, 3 H), 0.84 (d, 3 H). LCMS: Rt = 1.81 min, [M þ H]þ 1238. LC:
Rt = 18.89 min. HRMS: 1238.2559, calcd 1238.2597.
To a solution of the amine (0.081 mmol) in pyridine (5 mL) was
added methanesulfonylchloride (0.050 mL, 0.646 mmol). The solution
was stirred for 30 min and poured into a saturated aq solution of sodium
bicarbonate (100 mL). The mixture was extracted with EtOAc (3ꢀ) and
the combined organic extracts were dried over MgSO4, filtered, and
concentrated directly onto SiO2. The crude acetate was taken on to the
next step without any further purification. LCMS: Rt = 1.42 min, [M þ
H]þ1216.1.
To a solution of the acetate-sulfonamide in MeOH (10 mL) was
added K2CO3 (50 mg, 0.362 mmol). The reaction was stirred 5 min,
concentrated, and purified by HPLC to afford 15 mg of sulfonamide 18.
1H NMR (400 MHz, DMSO-d6 δ 10.62 (br s, 1 H), 9.00 (br d, 1 H),
8.68-8.66 (m, 2 H), 8.58 (s, 1 H), 8.44-8.41 (m, 1 H), 8.37 (d, 1 H),
8.23 (s, 1 H), 8.15 (d, 1 H), 7.39-7.20 (m, 7 H), 7.07 (br s, 1 H), 6.02
(d, 1 H), 5.31-5.18 (m, 3 H), 5.01-4.98 (m, 1 H), 4.97 (s, 2 H), 4.27
(dd, 1 H), 3.77 (dd, 1 H), 3.38 (s, 3 H), 3.12 (s, 3 H), 2.73-2.67
(m, 1 H), 2.58 (s, 3 H), 2.47 (d, 3 H), 2.19-2.13 (m, 1 H), 1.36-1.28
(m, 1 H), 0.87 (d, 3 H), 0.84 (d, 3 H). LCMS: Rt = 1.31 min, [M þ
H]þ1174.0. HRMS [M þ H2O] 1192.1843, calcd 1192.1849.
Preparation of 2-Picolinamide 12. To a solution of Boc-amine
(6, 911 mg, 0.761 mmol) in DCM (100 mL) was added excess TFA
(0.5 mL). The reaction was stirred for 2 h then concentrated from DCM
three times and stored under reduced pressure (0.1 Torr) for 30 min.
The residue was suspended in acetonitrile and H2O (80 mL, 10:1), and
excess Cs2CO3 were added. The reaction was stirred at RT for 72 h and
then concentrated onto silica gel for purification. The compound was
first purified by flash chromatography (0-10% MeOH in DCM),
followed by a second flash chromatography (0-5% MeOH in DCM)
and finally purified by HPLC (20-70% acetonitrile in H2O with 0.1%
TFA), which afforded 33 mg of final compound. 1H NMR (DMSO-d6):
δ 9.00 (d, 1H), 8.80 (s, 1H), 8.73 (d, 1H), 8.68 (d, 1H), 8.62 (s, 1H),
8.41-8.46 (m, 2H), 8.35 (d, 1H), 8.13 (d, 1H), 7.86 (bs, 1H), 7.21-
7.34 (m, 7H), 5.99 (bs, 1H), 5.27-5.32 (m, 1H), 5.18-5.21 (m, 2H),
4.97-5.00 (m, 3H), 4.23-4.29 (m, 1H), 3.75-3.81 (m, 1H), 3.38 (s,
3H), 2.68-2.73 (m, 1H), 2.57 (s, 3H), 2.44 (d, 3H), 2.12-2.17 (m,
1H), 1.22-1.28 (m, 1H), 0.83-0.89 (m, 6H). LC/MS: Rt 1.14 min, [M
þ H]þ1041. LC: Rt = 13.50 min. HRMS: 1041.2062, calcd 1041.2087.
’ AUTHOR INFORMATION
Corresponding Author
*Phone: (617) 871-7729. Fax: (617) 871-4081. E-mail: matthew.
lamarche@novartis.com. Address: 250 Massachusetts Avenue,
Cambridge, MA 02139.
’ ACKNOWLEDGMENT
We thank the Novartis natural products unit for their
collaboration.
’ REFERENCES
(1) Selva, E.; Beretta, G.; Montanini, N.; Saddler, G. S.; Gastaldo, L.;
Ferrari, P.; Lorenzetti, R.; Landini, P.; Ripamonti, F.; Goldstein, B. P.;
Berti, M.; Montanaro, I.; Denaro, M. J. Antibiot. 1991, 44 (7), 693–701.
The structure was later corrected and verified: Tavecchia, P.; Gentili, P.;
2520
dx.doi.org/10.1021/jm101602q |J. Med. Chem. 2011, 54, 2517–2521

Journal of Medicinal Chemistry
BRIEF ARTICLE
Kurz, M.; Sottani, C.; Bonfichi, R.; Selva, E.; Lociuro, S.; Restelli, E.;
Ciabatti, R. Tetrahedron 1995, 51 (16), 4867–4890. For acidic decom-
position, see above.
(2) For a review of thiopeptide natural products see: (a) Bagley, M. C.;
Dale, J. W.; Merritt, E. A.; Xiong, X. Chem. Rev. 2005, 105, 685–714.(b)
Rezanka, T.; Sobotka, M.; Spizek, J.; Sigler, K.Anti-Infect. Agents Med. Chem.,
2006, 5, 187-224. Hughs, R. A.; Moody, C. J. Angew. Chem., Int. Ed. 2007,
46, 2–27. (c) Thiostrepton:Mocek, U.; Zeng, Z.; O’Hagan, D.; Zhou, P.;
Fan, L. D. G.; Beale, J. M.; Floss, H. G. J. Am. Chem. Soc. 1993,
115, 7992–8001. (d) Nocathiocins:Pucci, M. A.; Bronson, J. J.; Barret,
J. F.; DenBleyker, K. L.; Driscotto, L. F.; Fung-Tomc, J. C.; Ueda, Y.
Antimicrob. Agents Chemother. 2004, 48, 3697–3701. Naidu, B. N.; Sor-
ensen, M. E.; Bronson, J. J.; Pucci, M. J.; Clark, J. M.; Ueda, Y. Bioorg. Med.
Chem. Lett. 2005, 15, 2069–2072 and references cited therein. (e)
Amythiomicins:Shiminaka, K.; Kinoshita, N.; Iinuba, H.; Hamada, M.;
Takeuchi, T. J. Antibiot. 1994, 47 (6), 668–674. (f) Thiomuracins:Morris,
R. P.; Leeds, J. A.; Naegeli, H. U.; Oberer, L.; Memmert, K.; Weber, E.;
LaMarche, M. J.; Parker, C. N.; Burrer, N.; Esterow, S.; Hein, A. E.; Schmitt,
E. K.; Krastel, P. J. Am. Chem. Soc. 2009, 131, 5946–5955.
(3) For review of the elongation factors see: Lim, V. I.; Curran, J. F.;
Garber, M. B. J. Mol. Biol. 2005, 351, 470–480. Nilsson, J.; Nissen, P.
Curr. Opin. Struct. Biol. 2005, 15, 349–354.
(4) Clough, J.; Chen, S.; Gordon, E. M.; Hackbarth, C.; Lam, S.;
Trias, J.; White, R. J.; Candiani, G.; Donadio, S.; Romano, G.; Ciabatti,
R.; Jacobs, J. W. Bioorg. Med. Chem. Lett. 2003, 13, 3409–3414.
Malabarba, M.; Cavaleri, M.; Mosconi, G.; Jabes, D.; Romano, G. Patent
WO 2003105881, 2003.
(5) Tavecchia, P.; Kurz, M.; Colombo, L.; Bonofichi, R.; Selva, E.;
Lociuro, S.; Marzorati, E.; Ciabatti, R. Tetrahedron 1996, 52 (26),
8763–8774.
(6) Butler, M. S. Nat. Prod. Rep. 2005, 22, 162–195.
(7) (a) Heckmann, G.; Bach, T. Angew. Chem., Int. Ed. 2005,
44, 1199–1201. (b) Nicolaou, K. C.; Zou, B.; Dethe, D. H.; Li, D. B.;
Chen, D. Y. K. Angew. Chem., Int. Ed. 2006, 45, 7786–7792.
(8) (a) Heffron, S. E.; Jurnak, F. Biochemistry 2000, 39, 37–45. (b)
Heffron, S. E.; Moeller, R.; Jurnak, F. Acta Crystallogr., Sect. D: Biol.
Crystallogr. 2006, D62, 433–438. (c) Parmeggiani, A.; Nissen, P. FEBS
Lett. 2006, 580, 4576–4581.
(9) Lewis, R. J.; Hughs, R. A.; Alcaraz, L.; Thompson, S. P.; Moody,
C. J. Chem. Commun. 2006, 4215–4217.
(10) Poulakou, G.; Giamarellou, H. Expert Opin. Invest. Drugs 2007,
16 (2), 137–155.
(11) A bacterial inhibition screen measuring growth inhibition of S.
aureus at a single concentration was conducted on the entire Novartis
compound archive (>600000 compounds).
(12) GE2270 and fermentation metabolites were isolated from a rare
strain of Actinomycetes, Nonomuraea strain WU8817.
(13) South, M. S. J. Heterocycl. Chem. 1991, 28, 1003.
(14) (a) Larsen, S. D.; Stachew, C. F.; Claire, P. M.; Cubbage, J. W.;
Leach, K. L. Bioorg. Med. Chem. Lett. 2003, 13, 3491–3495.(b) Green, J.;
Miller, A.; Jiminez, J. M.; Marhefka, C.; Cao, J.; Court, J. J.; Bandarage,
U. K.; Gao, K.; Nanthakumar, S., WO2005/103050, 2005.
(15) MIC assays were conducted according to the Clinical and
Laboratory Standards Institute (CLSI).Wikler M. A.; Cockerill F. R.;
Bush K, et al. Methods for Dilution Antimicrobial Susceptibility Tests for
Bacteria that Grow Aerobically; Approved Standard, 8th ed.; Clinical and
Laboratory Standards Institute: Wayne, PA, 2009; Vol. 29, no. 2, CLSI
M07-A8. Bacterial strains included E. faecalis (ATCC 29212), E. faecium
(Prof. Chopra, University of Leeds UK, strain 7130724), S. aureus
(MRSA from Prof. Willinger, isolated from a pharyngeal smear, AKH
Vienna A4.018), S. pyogenes (ATCC BAA-595). Wikler M. A., Cockerill
F. R., Bush K., Performance Standards for Antimicrobial Susceptibility
Testing; Nineteenth Informational Supplement; Clinical and Laboratory
Standards Institute: Wayne, PA, 2009; Vol. 29, no. 3, CLSI M100-S19.
2521
dx.doi.org/10.1021/jm101602q |J. Med. Chem. 2011, 54, 2517–2521