Efficient synthesis of a bacterial translocase MraY inhibitor

Article abstract of DOI:10.1016/j.tetasy.2008.01.037

The bacterial translocase MraY has recently been demonstrated as a prime target for the development of new antibiotics. We describe a straightforward synthesis of a new inhibitor 1 of this enzyme. The two key steps involve a tandem nucleophilic epoxide ri

Full text of DOI:10.1016/j.tetasy.2008.01.037

Available online at www.sciencedirect.com
Tetrahedron: Asymmetry 19 (2008) 397–400
Efficient synthesis of a bacterial translocase MraY inhibitor
Anthony Clouet,a Christine Gravier-Pelletier,a,* Bayan Al-Dabbag,b
Ahmed Bouhssb and Yves Le Merrera,*
aUniversite´ Paris Descartes, Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques,
`
UMR 8601 CNRS, 45 rue des Saints-Peres, 75006 Paris, France
bEnveloppes Bacte´riennes et Antibiotiques, IBBMC, UMR 8619 CNRS, Univ Paris-Sud, 91405 Orsay, France
Received 6 December 2007; accepted 24 January 2008
Abstract—The bacterial translocase MraY has recently been demonstrated as a prime target for the development of new antibiotics. We
describe a straightforward synthesis of a new inhibitor 1 of this enzyme. The two key steps involve a tandem nucleophilic epoxide ring
opening of C2-symmetrical bis-epoxide and subsequent O-heterocyclisation, followed by O-glycosylation. The in vitro biological
evaluation of 1 at 2 mM showed an 81% of inhibition of the MraY activity. Therefore, congeners of 1 should permit detailed SAR
investigations for the discovery of novel antibacterials.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
has been recently purified to homogeneity5 and tests
allowing high-throughput screening of inhibitors have
been achieved.6
In the context of the world-wide emergence of antibiotic
resistance,1 the bacterial cell wall peptidoglycan is a key
target for antibiotic development. In particular, the
inhibition of new targets having been little exploited is a
challenging objective. Thus, the translocase MraY, which
catalyses (Fig. 1) the first membrane step of peptidoglycan
biosynthesis,2 represents such a target, since it has been
demonstrated to be essential and specific to bacteria,3
and is currently not the target of therapeutic drugs,
notably due to its transmembrane localisation4 making
it difficult to purify and to study. However, this enzyme
This enzyme catalyses the transfer of uridine monophos-
phate-N-acetyl-muramoyl pentapeptide from its precursor
UDP-Mur-N-Ac-pentapeptide onto undecaprenyl phos-
phate, a lipid carrier, resulting in the formation of lipid I.
In an ongoing programme directed towards MraY inhibi-
tion,7 we have already developed the synthesis of com-
pounds8 displaying analogous structures to those of
naturally known inhibitors of that enzyme, such as liposid-
omycins9 and caprazamycins10 (Fig. 2).
OH
O
OH
O
O-
P
-O
O
O
HO
HO
NH
O
8
O
2
O- O-
O
O- O-
AcHN
AcHN
O
N
O
O
O
O
O
O
O
P
P
P
P
O
2
O
8
O
N
Pentapeptide
Pentapeptide
O
O
O
O
NH
HO OH
O-
P
UDP-Mur-N-Ac-pentapeptide
Lipid I
-O
O
O
O
O
HO OH
Figure 1. Enzymatic reaction catalysed by the bacterial translocase MraY.
*
Corresponding authors. Tel.: +33 142862181 (C.G.-P.); tel.: +33 142862176; fax: +33 142868387 (Y.L.M.); e-mail addresses: christine.gravier-
pelletier@univ-paris5.fr; yves.le-merrer@univ-paris5.fr
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.01.037

398
A. Clouet et al. / Tetrahedron: Asymmetry 19 (2008) 397–400
R2
R3O2C
O
N
CO2H
O
N
O
O
O
O
NH
NH
O
NH
N
O
O
O
N
OH
N
O
O
O
O
O
3'
O
O
O
O
O
2
H2N
H2N
H2N
HO
OH
HO
OH
HO
R1
HO
OH
HO
OH
HO
R1 = OH or OSO3H
R2 = lipid side chain
Target pharmacophore 1
Aventis Pharma pharmacophore A
R3 = H (Liposidomycins)
R3 = methyl glucoside (Caprazamycins)
Figure 2. Natural inhibitors of MraY and pharmacophores.
O
Indeed, we have recently described a powerful synthesis of
polyfunctionalised diazepanone rings11 as promising
scaffolds. The work described herein is related to a comple-
mentary approach, aimed at developing a straightforward
access to a pharmacophore from which further modifica-
tions will permit SAR investigations for the discovery of
new antibacterials.
NH
N
O
O
O
O
H2N
HO
HO
OH
HO
OH
O
N
1
NH
This pharmacophore has been designed on the basis of
model studies performed by Aventis Pharma12 and taking
into consideration the superimposing of UDP-Mur-NAc-
pentapeptide, one of the MraY substrates, with two known
inhibitors, liposidomycins and tunicamycins.13 Following
these studies, Aventis developed a synthesis for pharmaco-
phore A, including the common residues to the three com-
pounds, that might represent the minimal part responsible
for activity. With regards to these results, our goal was to
perform an efficient and convergent synthesis of pharmaco-
phore 1.
O
O
O
3
X
N3
+
PO
OP
PO
OP
4
O
O
O
NH
+
N
O
2
PO
OP
H
Figure 3. Retrosynthetic analysis of the target pharmacophore 1.
As compared to the known pharmacophore A, which
retains residues, such as aminoribose and uridine, having
been demonstrated to be crucial for biological activity,14
target 1 presents two differences. Firstly, the introduction
of an extra methylene group between uracil and ribose-like
moieties should improve both the flexibility and stability
towards the hydrolysis of the resulting inhibitor. Indeed,
an enhanced flexibility of such a compound is expected to
help in its positioning within the active site of the enzyme.15
Secondly, related to our strategy, an inversion of the abso-
lute configuration at C2 has been introduced while keeping
in mind that the absolute configuration at this stereogenic
centre in pharmacophore A has been proven to be of weak
importance for biological activity.16 Thus, the targeted
pharmacophore 1 should present the advantage of being
both efficiently synthesised in only a few steps and more
stable with regard to hydrolysis as compared to the Aventis
pharmacophore. Furthermore, it represents an interesting
scaffold for the future development of a library of related
putative inhibitors.
4 activated at its anomeric position and a tandem nucleo-
philic epoxide ring opening of C2-symmetrical bis-epoxide
2 followed by concomitant O-heterocyclisation leading to
3.
Ring opening of 1,2:5,6-dianhydro-3,4-di-O-benzyl-L-iditol
2 (Scheme 1), readily available from D-mannitol,17 by
bis(trimethylsilylated) uracil, in situ prepared from uracil
and N,O-bis[trimethylsilyl] trifluoroacetamide (BSTFA),
was performed in the presence of magnesium(II) perchlo-
rate in refluxing acetonitrile to afford the uridine-like 3 in
46% yield. Its formation results from the regiospecific ring
opening of the first epoxide functionality at the least substi-
tuted side, followed by a subsequent O-heterocyclisation of
the resulting alcoholate on the other epoxide functional-
ity18,19 according to a 5-exo-tet process. Owing to the pres-
ence of the C2-axis of symmetry within the bis-epoxide 2,
the opening of one or the other epoxide function leads to
the same compound.
The second key step involved an O-glycosylation between
the primary alcohol function of 3 and 5-azido-1,5-di-
deoxy-2,3-di-O-ethylpropylidene-1-fluoro-D-ribofuranose
4.20,21 The presence of an isopentylidene group on the a
face of the sugar was intended to promote major glycosyl-
ation on its b face due to the steric hindrance of the a face.
2. Results and discussion
Retrosynthetic analysis towards pharmacophore 1 relies on
two key steps (Fig. 3), which are the O-glycosylation of a
uridine-like compound 3 with an aminoribose derivative

A. Clouet et al. / Tetrahedron: Asymmetry 19 (2008) 397–400
399
O
N
O
O
NH
O
F
NH
N3
NH
4
O
N
H
O
O
O
O
O
O
N
O
O
O
O
N3
BSTFA, CH3CN
HO
NH
BnO
OBn
BF3.OEt2, CH2Cl2
M.S., -60°C
87%
then Mg(ClO4)2, Δ
BnO
OBn
O
O
BnO
OBn
46%
5
2
3
O
N
O
NH
O
N
O
O
O
O
O
H2, Pd, AcOH
72%
TFA, H2O
80%
O
O
H2N
N3
HO
OH
BnO
OBn
HO
OH
HO
OH
1
6
Scheme 1. Synthesis of the pharmacophore 1.
The reaction was performed in the presence of boron
trifluoride etherate and molecular sieves in excess in
CH2Cl2 at À60 °C and led to a 13:1 b:a mixture of the
expected protected pharmacophore 5. The pure b-anomer
could be easily obtained in 87% yield after flash chromato-
graphic separation from its a-anomer. Then, acidic hydro-
lysis of the di-O-ethylpropylidene protective group of 5 was
performed with aqueous trifluoroacetic acid to afford the
corresponding diol 6 in 80% yield. Finally, hydrogenolysis
of the benzyl protecting groups and simultaneous azide
reduction in the presence of Pd black in acetic acid gave
the targeted pharmacophore 1. Careful analysis of 1H
and 13C NMR spectra revealed a partial reduction of the
uracil double bond (15%).22
Acknowledgement
We gratefully acknowledge the European Community for
the financial support of the Eur-INTAFAR integrated
project within the 6th PCRDT framework (contract No.
LSHM-CT-2004-512138) and for a post-doctoral grant to
A.C.
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inhibitors, thereby endowing them with antibacterial prop-
erties. Further work is currently in progress towards this
goal.

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A. Clouet et al. / Tetrahedron: Asymmetry 19 (2008) 397–400
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