The first total synthesis of lipid II: The final monomeric intermediate in bacterial cell wall biosynthesis

Article abstract of DOI:10.1021/ja017386d

Bacterial peptidoglycan is composed of a network of β-[1,4]-linked glyan strands that are crosslinked through pendant peptide chains. The final product, the murein sacculus, is a single, covalently closed macromolecule that precisely defines the size and

Full text of DOI:10.1021/ja017386d

Published on Web 03/14/2002
The First Total Synthesis of Lipid II: The Final Monomeric
Intermediate in Bacterial Cell Wall Biosynthesis
Michael S. VanNieuwenhze,* Scott C. Mauldin, Mohammad Zia-Ebrahimi,
Brian E. Winger,‡ William J. Hornback, Shankar L. Saha,# James A. Aikins, and
Larry C. Blaszczak*
Contribution from DiscoVery Chemistry Research and the Department of Pharmaceutical and
Analytical Chemistry, Lilly Research Laboratories, A DiVision of Eli Lilly and Company,
Lilly Corporate Center, Indianapolis, Indiana 46285
Received October 25, 2001
Abstract: Bacterial peptidoglycan is composed of a network of â-[1,4]-linked glyan strands that are cross-
linked through pendant peptide chains. The final product, the murein sacculus, is a single, covalently closed
macromolecule that precisely defines the size and shape of the bacterial cell. The recent increase in bacterial
resistance to cell wall active agents has led to a resurgence of activity directed toward improving our
understanding of the resistance mechanisms at the molecular level. The biosynthetic enzymes and their
natural substrates can be invaluable tools in this endeavor. While modern experimental techniques have
led to isolation and purification of the biosynthetic enzymes utilized in peptidoglycan biosynthesis, securing
useful quantities of their requisite substrates from natural substrates has remained problematic. In an effort
to address this issue, we report the first total synthesis of lipid II (4), the final monomeric intermediate
utilized by Gram positive bacteria for peptidoglycan biosynthesis.
Introduction
anchor for introduction of the pentapeptide side chain. The
peptide side chain is then incorporated via sequential addition
Potent and notably nontoxic cell wall biosynthesis inhibitors
have dominated treatment regimens for management of bacterial
infections in both hospital and outpatient settings for more than
fifty years.1 Glycopeptide antibiotics (e.g., vancomycin) and
â-lactams, two of the most broadly used classes of antibiotics,
derive their antibacterial activity through inhibition of key steps
in the cell wall biosynthesis cascade.1 Recently, however,
resistance of bacteria to these antibiotics has reached an alarming
level2 and has begun to erode their once dependable clinical
efficacy. Augmentation of the cell wall active antibacterial
pharmacopeia is urgently needed.
Bacterial peptidoglycan consists of a network of â-[1,4]-
linked carbohydrate polymers that are cross-linked via pendant
peptide chains.3 This process is believed to occur in three distinct
stages (Scheme 1). The initial stages of the biosynthetic cascade
occur within the bacterial cytoplasm and begin with the
elaboration of UDP-N-acetylglucosamine 1. First, an enolpyru-
vyl transferase (MurA) and an NADPH-dependent reductase
(MurB) introduce the C(3)-lactyl residue that serves as the
of L-Ala, D-Glu, L-Lys (or meso DAP4), and D-Ala-D-Ala in a
series of reactions mediated by ATP-dependent amino acid
ligases (MurC-F). The final product of this sequence, UDP-N-
acetylmuramylpentapeptide (Park nucleotide 25), then enters the
second stage of the bacterial cell wall biosynthetic cascade that
takes place at the cytoplasmic surface of the bacterial cell
membrane.
In the second stage, a pyrophosphate exchange reaction,
catalyzed by MraY, couples Park nucleotide to a membrane-
anchored C55 lipid carrier. This reaction occurs with concomitant
ejection of UMP and provides undecaprenylpyrophosphoryl-
MurNAc-pentapeptide 3 (lipid I). Subsequently, MurG catalyzes
the transfer of N-acetylglucosamine (GlcNAc) fron UDP-
GlcNAc to the C(4)-hydroxyl group of the lipid-linked MurNAc-
pentapeptide. The product of this transformation, lipid II 4, is
the final monomeric intermediate utilized in bacterial cell wall
biosynthesis.6 In some Gram-positive bacteria, lipid II may be
further modified via attachment of 1-5 amino acid residues to
the terminal amino group of the lysine residue. These additional
residues are frequently glycines, although organisms incorporat-
ing L-serine, L-threonine, and other amino acids are known.2,7
* Address correspondence to this author. E-mail: msv@lilly.com.
‡ Department of Pharmaceutical and Analytical Chemistry.
# Current address: MediChem Research, Inc., 12305 S. New Avenue,
Lemont, IL 60439.
(1) Gale, E. F.; Cundliffe, E.; Reynolds, P. E.; Richmond, M. H.; Waring, M.
J. The Molecular Basis of Antibiotic Action, 2nd ed.; Wiley-Interscience:
New York, 1981.
(4) In Gram negative bacteria, meso-diaminopimelic acid (meso-DAP) is
incorporated in place of L-Lys (see ref 3).
(5) Park, J. T. J. Biol. Chem. 1952, 194, 877.
(2) Review: Chu, D. T. W.; Plattner, J. J.; Katz, L. J. Med. Chem. 1996, 39,
3853.
(6) In Scheme 1, lipid II is shown with a glutamine residue in the pentapeptide
side chain replacing glutamate as shown in the lipid I precursor. In some
bacterial cells, for example, Streptococcus pneumoniae, a glutamine residue
is present in lipid II. Experiments have shown lipid I and lipid II (D-Glu)
are substrates for an ATP-dependent amidation reaction. See: Siewert, G.;
Strominger, J. L. J. Biol. Chem. 1968, 243, 783.
(3) (a) Rogers, H. J.; Perkins, H. R.; Ward, J. B. Biosynthesis of Peptidoglycan;
Chapman and Hall, Ltd.: London, 1980. (b) Ho¨ltje, J.-V. Microbiol. Mol.
Bio. ReV. 1998, 62, 181. (c) Bugg, T. D. H.; Walsh, C. T. Nat. Prod. Rep.
1992, 199.
9
3656
J. AM. CHEM. SOC. 2002, 124, 3656-3660
10.1021/ja017386d CCC: $22.00 © 2002 American Chemical Society

The First Total Synthesis of Lipid II
A R T I C L E S
Scheme 1. Biosynthesis of Lipid II and Its Conversion into Peptidoglycan6
The last stages of bacterial cell wall biosynthesis are
extracytoplasmic. These processes are polymerization of the lipid
II intermediate 4 into â-[1,4]-linked glycan strands having an
N-acetylglucosaminyl-N-acetylmuramic acid (NAG-NAM) re-
peating unit, transpeptidations that extend and cross-link the
pendant muramyl peptides of adjacent strands, and carboxypep-
tidations that modify the peptides. The final product, called the
murein sacculus, is a single covalently closed macromolecule
that precisely defines the size and shape of a bacterial cell.3
Cell wall (peptidoglycan) biosynthetic enzymes and their
natural substrates can be invaluable tools in studies directed
toward understanding resistance mechanisms at the molecular
level, or toward the search for newer and more effective agents.
While modern biochemistry and molecular genetics techniques
have been used to secure the cell wall biosynthesis enzymes in
substantial quantity, acquisition of their respective substrates
in useful quantities from natural sources has remained prob-
lematic. These substances generally occur in small concen-
trations within the bacterial cell.8 In our total synthesis of
undecaprenylpyrophosphoryl-MurNAc-pentapeptide (lipid I,
3),9,10 we demonstrated that chemical synthesis can provide a
powerful solution to this difficult problem.
been estimated to be 1000-2000 molecules per cell in Escheri-
chia coli.11,12 Second, complete separation of the miniscule
amount of 4 from relatively large amounts of cellular lipid, and
membrane, components is tedious at best. Typically, the desired
material is followed through purification by scintillation after
precursing of the culture with radiolabeled components.11,13
Isolated yields of 4 are low14 which, when coupled with the
low copy numbers per cell, present difficult technical challenges
for its isolation in sufficient quantities to enable detailed
mechanistic studies.
Despite the inherent challenges, we chose to extend our
program in the development of practical syntheses of cell wall
biosynthetic intermediates to include lipid II. A recent report
by Walker disclosed a route to lipid II that utilized MurG and
UDP-GlcNAc for the biosynthetic conversion of lipid I into lipid
II.15 We now report the first chemical synthesis of lipid II (4),
the final monomeric intermediate utilized in bacterial cell wall
biosynthesis.16,17
Retrosynthetic Analysis
The diversity of structural elements resident in lipid II present
several significant challenges for total synthesis. The central
Our recent studies in peptidoglycan biosynthesis required a
supply of lipid II 4. Isolation of lipid II from bacteria presents
several formidable challenges. First, the total pool of 4 present
in a bacterial cell culture is very small indeed; the amount has
(11) Van Heijenoort, Y.; Go´mez, M.; Derrien, M.; Ayala, J.; van Heijenoort, J.
J. Bacteriol. 1992, 174 (11), 3549.
(12) Although these data are taken from a gram-negative organism (E. coli),
the copy numbers are illustrative of the low cellular concentration of lipid
II.
(7) Schleifer, K. H.; Kandler, O. Bacteriol. ReV. 1972, 36, 407.
(8) Kohlrausch, U.; Ho¨ltje, J.-V. FEMS Microbiol. Lett. 1991, 78, 253 and
references therein.
(13) See, for example: (a) Umbreit, J. N.; Strominger, J. L. J. Bacteriol. 1972,
112, 1306. (b) Nakagawa, J.; Tamaki, S.; Tomioka, S.; Matsuhashi, M. J.
Biol. Chem. 1984, 259, 13937. (c) Bro¨tz, H.; Bierbaum, G.; Leopold, K.;
Reynolds, P. E.; Sahl, H.-J. Antimicrob. Agents Chemother. 1998, 42, 154.
(14) For example, Umbreit and Strominger reported yields of 2% (ref 12a). A
cell-free system (ref 11) has been reported that has provided improved yields
of lipid II (12-18%).
(9) VanNieuwenhze, M. S.; Mauldin, S. C.; Zia-Ebrahimi, M.; Aikins, J. A.;
Blaszczak, L. C. J. Am. Chem. Soc. 2001, 123, 6983.
(10) A total synthesis of UDP-MurNAc-pentapeptide (Park nucleotide) 2 has
also been reported by a group at Eli Lilly and Company. See: Hitchcock,
S. A.; Eid, C. N.; Aikins, J. A.; Zia-Ebrahimi, M.; Blaszczak, L. C. J. Am.
Chem. Soc. 1998, 120, 1916.
(15) Ye, X.-Y.; Lo, M.-C.; Brunner, L.; Walker, D.; Kahne, D.; Walker, S. J.
Am. Chem. Soc. 2001, 123, 3155.
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J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002 3657

A R T I C L E S
VanNieuwenhze et al.
Scheme 2. Retrosynthetic Analysis for Lipid II
this chemically sensitive allylic diphosphate linkage must
withstand.
Second, the anticipated acid sensitivity of the anomeric
diphosphate dictated the use of base-cleavable protective groups
for all functional groups that are unmasked after its installation.
As a result, acetate was chosen to block the hydroxyl groups
of the disaccharide core, trifluoroacetate was chosen to mask
the ꢀ-amino group of L-lysine, and methyl ester was chosen to
protect the carboxylic acid moiety of the terminal D-alanine
residue. Global deprotection could then be accomplished by
exposure to hydroxide ion as the final step in the synthesis.18
In analogy to our lipid I total synthesis,9 our initial discon-
nection reveals disaccharyl pentapeptide 5 and undecaprenyl
monophosphate 6.19 Disaccharyl pentapeptide 5 was envisaged
to derive from coupling of a suitably protected tetrapeptide
fragment (e.g., 8) with an activated ester deriving from 7.20 The
tetrapeptide fragment 8 would be prepared incorporating base-
cleavable protective groups for the ꢀ-amino group of the L-lysine
residue and carboxy terminal D-alanine residue. An important
consideration here, with respect to synthetic design of 7, is that
the protecting groups for the L-Ala residue and the anomeric
phosphate are orthogonal to one another as are those protective
groups (acetates) used for peripheral hydoxyl groups of the
disaccharide core. Triple orthogonality is required to ensure
selective unmasking of functional groups prior to coupling of
the tetrapeptide fragment, and installation of the undecaprenyl
side chain.
We envisaged a phosphitylation/oxidation21,22 sequence for
stereoselective introduction of the anomeric phosphate in 7.
Thus, 7 could be derived from disaccharyl monopeptide 9 where,
again, a triply orthogonal protection scheme would allow
selective unmasking of the anomeric hydroxyl group prior to
introduction of the anomeric phosphate.
To initiate our synthesis of lipid II, an efficient synthetic route
to multiple gram quantities of orthogonally protected N-
acetyl-(2-deoxy-2-aminoglucopyranosyl)-â-[1,4]-N-acetylmu-
ramyl (NAG-NAM) monopeptide 9 was desired. Access to 9
would require a reliable method for establishing the desired
â-[1,4]-glycosidic bond and a functional group activation/
protection strategy that would meet the demands of triple
orthogonality. Several synthetic approaches to protected versions
of the NAG-NAM disaccharide subunit have been recorded
previously.23 Our synthetic route, which employed a triply
orthogonal protection scheme, readily provided NAG-NAM
monopeptide 9 in multiple gram quantities.24
core of lipid II consists of a â-[1,4]-linked disaccharide con-
taining N-acetylglucosamine (NAG) and N-acetylmuramic acid
(NAM) subunits. The muramyl residue is further decorated with
a pentapeptide chain (L-Ala-D-i-Gln-L-Lys-D-Ala-D-Ala) attached
to the 3-position via a lactyl linkage, as well as a chemically
sensitive undecaprenyl-linked R-glycosyl diphosphate moiety.
Our retrosynthetic analysis for the construction of lipid II is
illustrated in Scheme 2.
First, we felt it would be optimal to introduce the undeca-
prenyl-linked diphosphate moiety at a late stage in the synthesis.
This would allow us to avoid potential solubility complications
in subsequent reactions that could arise from the enhanced
lipophilic character of the undecaprenyl-linked substrate. In
addition, late stage introduction of the lipid-linked diphosphate
would minimize the number of subsequent synthetic operations
The Total Synthesis of Lipid II
Our synthesis (Scheme 3) began with hydrogenolysis of
benzyl ether 9 to provide lactol 10 in 94% yield. The stage was
now set for introduction of the anomeric phosphate group. As
(18) Care would have to be exercised when exposing the pentapeptide to
hydroxide ion-mediated deprotection conditions since the base-catalyzed
rearrangement of iso-glutamine to glutamate in peptidoglycan-related
structures has been observed. (a) Keglevic, D.; Derome, A. E. Carbohydr.
Res. 1989, 186, 63. (b) Keglevic, D.; Kidric, J. J. Carbohydr. Res. 1992,
11, 119.
(19) Undecaprenyl monophosphate bis-ammonium salt may be purchased from
the Institute of Biochemistry and Biophysics, Polish Academy of Sciences,
ul. Pawinskiego 5A, 02-106 Warszawa, Poland.
(16) (a) VanNieuwenhze, M. S. The First Total Synthesis of Lipid II: The Final
Monomeric Intermediate in Bacterial Cell Wall Biosynthesis; Presented at
the Gordon Research Conference on Stereochemistry, Newport, RI, 2000.
(b) VanNieuwenhze, M. S.; Mauldin, S. C.; Zia-Ebrahimi, M.; Hornback,
W. J.; Saha, S. L.; Blaszczak, L. C. Abstracts of the 221st National Meeting
of the American Chemical Society, San Diego, California, April 2001;
American Chemical Society: Washington, DC, 2001; Abstract No. 470.
(c) Blaszczak, L. C.; VanNieuwenhze, M. S.; Zia-Ebrahimi, M.; Mauldin,
S. C.; Skatrud, P. L.; Alborn, W. E. PCT WO 01/79268, filed April 5,
2001.
(20) The rationale for installing the peptide side chain as a tetrapeptide versus
a pentapeptide is an artifact of the synthetic strategy used for preparation
of 6. For a more detailed discussion, please refer to ref 24.
(21) Sim, M. M.; H. Kondo, H.; Wong, C.-H. J. Am. Chem. Soc. 1993, 115,
2261.
(17) Scientists at DuPont Pharmaceuticals have recently published a synthesis
of lipid II. Schwartz, B.; Markwalder, J. A.; Wang, Y. J. Am. Chem. Soc.
2001, 123, 11638.
(22) Men, H.; Park, P.; Ge, M.; Walker, S. J. Am. Chem. Soc. 1998, 120, 2484.
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3658 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002

The First Total Synthesis of Lipid II
A R T I C L E S
Scheme 3. The Total Synthesis of Lipid IIa
Scheme 4. Preparation of Tetrapeptide 8a
a Reagents and conditions: (a) i. CH2Cl2, TFA; ii. Boc-D-iso-Gln(NHS),
iPr2NEt, THF, 66% yield; (b) EtOH/CH2Cl2, p-TsOH, 97% yield.
phosphorus electrophile. This could become problematic if the
steric constraints imposed by the additional sugar subunit
compromised the nucleophilicity of the anomeric hydroxyl
group.
We were gratified to observe that, after exposure of lactol
10 to dibenzyl-N,N-diethylphosphoramidite and 1H-tetrazole in
dichloromethane followed by oxidation of the phosphite inter-
mediate with 30% hydrogen peroxide, the desired R-phosphate
product 7 was obtained in 78% yield (3JH1H2 ) 3.0 Hz). Our
next step set the stage for elaboration of the pentapeptide side
chain. Thus, unmasking of the lactyl carboxyl group was
achieved through treatment of phenylsulfonylethyl ester 7 with
DBU. The intermediate acid was activated through conversion
to the corresponding NHS ester. Addition of a DMF solution
of tetrapeptide 8, prepared via standard peptide synthesis
protocols (Scheme 426), to a solution of the activated ester and
iPr2NEt in DMF provided disaccharyl pentapeptide 11 (46%
overall yield from 7).27
Hydrogenolytic cleavage of the phosphodiester protecting
groups, followed by evaporation of the crude product from
pyridine, provided monopyridyl salt 12 in 91% yield. The stage
was now set for the final lipid coupling/deprotection sequence
that would allow completion of our lipid II total synthesis.
For the key reaction that would establish the lipid diphosphate
linkage, we utilized the phosphoroimidazolidate method28 that
was exploited in the lipid I total synthesis. The attractive feature
of this method is that it would allow us to employ commercially
available undecaprenyl monophosphate directly in a coupling
reaction with a carbohydrate-derived phosphoroimidazolidate.
The mild reaction conditions were also advantageous for
introduction of the chemically sensitive diphosphate linkage.
In the event, electrophilic activation, achieved by in situ
conversion to the intermediate phosphoroimidazolidate, followed
by exposure to undecaprenyl monophosphate 6 (bis-NH4+ salt)
in DMF/THF over 4 days cleanly afforded the fully protected
version of lipid II 13.29 Global deprotection was achieved
through exposure of 13 to aqueous NaOH and provided lipid II
4 in 24% isolated yield (from 11) after reverse-phase HPLC
purification.30
a Reagents and conditions: (a) H2, Pd/C, MeOH/THF, 94% yield;
(b) i. dibenzyl-N,N-diethylphosphoramidite, 1H-tetrazole, CH2Cl2; ii. 30%
H2O2, THF, -78 °C to room temperature, 78% yield; (c) i. DBU, CH2Cl2;
ii. EDCI, NHS, DMF, then 8 and iPr2NEt, 46% yield; (d) H2, Pd/C, MeOH,
then pyridine, 91% yield; (e) i. CDI/DMF/THF; ii. undecaprenyl mono-
phosphate 6 (bis-NH4+ salt); (f) NaOH/H2O/1,4-dioxane, 24% overall yield
from 11.
was the case in our lipid I synthesis, the phosphate group needed
to be introduced in an R-selective fashion. Given this require-
ment, and the presence of a participating group (NHAc) at C(2),
a sequence employing a nucleophilic carbohydrate component
and an electrophilic phosophorus reagent was mandated.25 As
a result, our initial efforts focused on the phosphitylation/
oxidation sequence that was exploited during our total synthesis
of lipid I. Even with this precedent, we were still concerned
about the possible erosion of the anomeric selectivity that would
arise if in situ anomerization of the free hydroxyl group occurs
at a rate that is competitive with capture by the activated
(23) For previous approaches to the â-[1,4]-linked NAG-NAM disaccharide,
see: (a) Merser, C.; Sinay¨, P. Tetrahedron Lett. 1973, 13, 1029. (b) Durette,
P. L.; Meitzner, E. P.; Shen, T. Y. Carbohydr. Res. 1979, 77, C1. (c) Kiso,
M.; Kaneda, Y.; Shimizu, R.; Hasegawa, A. Carbohydr. Res. 1980, 83,
C8. (d) Kiso, M.; Kaneda, Y.; Shimizu, R.; Hasegawa, A. Carbohydr. Res.
1982, 104, 253. (e) Kusumoto, S.; Yamamoto, K.; Imoto, M.; Inage, M.;
Tsujimoto, M.; Kotani, S.; Shiba, T. Bull. Chem. Soc. Jpn. 1986, 59, 1411.
(f) Kusimoto, S.; Imoto, M.; Ogiku, T.; Shiba, T. Bull. Chem. Soc. Jpn.
1986, 59, 1419. (g) Farkas, J.; Ledvina, M.; Brokes, J.; Jezek, J.; Zajicek,
J.; Zaoral, M. Carbohydr. Res. 1987, 163, 63. (h) Kinzy, W.; Schmidt, R.
R. Liebigs Ann. Chem. 1987, 407. (i) Kantoci, D.; Keglevic, D.; Derome,
A. Carbohydr. Res. 1987, 162, 227. (j) Termin, A.; Schmidt, R. R. Liebigs
Ann. Chem. 1989, 789. (k) Ledvina, M.; Farkas, J.; Zajicek, J.; Jezek, J.;
Zaoral, M. Collect. Czech. Chem. Commun. 1989, 54, 2784. (l) Termin,
A.; Schmidt, R. R. Liebigs Ann. Chem. 1992, 527.
(26) Tripeptide 14 was prepared as described in ref 10.
(27) A small amount (<5%) of a second product, of identical molecular weight,
is routinely observed during the coupling reaction. This product may be a
diastereomer that could, presumably, arise from epimerization of the L-Ala
R-stereocenter during the peptide-coupling event.
(28) (a) Fang, X.; Gibbs, B. S.; Coward, J. K. Bioorg. Med. Chem. Lett. 1995,
5, 2701. (b) Danilov, L. L.; Maltsev, S. D.; Shibaev, V. N.; Kochetkov, N.
K. Carbohydr. Res. 1981, 88, 203.
(24) Saha, S. L.; VanNieuwenhze, M. S.; Hornback, W. J.; Aikins, J. A.;
Blaszczak, L. C. Org. Lett. 2001, 3, 3575.
(25) Carbohydrates bearing functional groups at C(2) capable of neighboring
group participation generally favor formation of 1,2-trans-linked glycosyl
phosphates.
(29) Undecaprenyl monophosphate was added in portions and reaction progress
was monitored, through tracking the disappearance of the intermediate
phosphoroimidazolidate, by mass spectroscopy.
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A R T I C L E S
VanNieuwenhze et al.
The structural identity of lipid II was further validated via a
modification of a known biochemical assay31 that employed
dansylated derivative 16 in place of radiolabeled lipid II of
New therapeutic agents capable of disrupting steps in bacterial
cell wall biosynthesis, yet to be exploited by existing agents,
offer one potential strategy in the continuing battle against
antimicrobial resistance. Heretofore, detailed study of resistance
mechanisms at the molecular level, despite the ready availability
of the biosynthetic enzymes, has lagged due to the limited
availability of the natural substrates. This synthesis of lipid II
provides a valuable biochemical tool that may prove useful in
uncovering novel approaches to combat emerging antimicrobial
drug resistance to cell wall active agents.
Acknowledgment. We gratefully acknowledge the important
contributions of Mr. William Alborn, Dr. Angelika Kraft, and
Dr. Melissa Clague (biochemistry). Dr. David Peake and Mr.
James Gilliam provided excellent mass spectrometry support.
We are also grateful for the NMR spectroscopy support provided
by Mr. Robert Boyer.
bacterial origin. Weppner and Neuhaus had previously demon-
strated that Park nucleotide bearing a dansyl tag on the L-lysine
residue (e.g., a dansyl-tagged version of 2) could be incorporated
into glycan strands upon incubation with a membrane fraction
prepared from Gaffkya homari.32 In the event, formation of
glycan strands via enzymatic polymerization of 16 was readily
confirmed by inspection of descending paper or thin layer (silica
gel) chromatograms upon exposure to ultraviolet light.32,33
Supporting Information Available: Complete experimental
procedures and spectral data (PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
JA017386D
(32) Weppner, W. A.; Neuhaus, F. C. J. Biol. Chem. 1977, 252(7), 2296.
(33) A similar experiment utilizing a membrane particulate fraction from E.
coli with a dansyl-tagged version of lipid I (the immediate biosynthetic
precursor to lipid II) has also been reported. See: Auger, G.; Crouvoisier,
M.; Caroff, M.; van Heijenoort, J.; Blanot, D. Lett. Pept. Sci. 1997, 4, 371.
(30) Please refer to the Supporting Information for experimental details.
(31) Suzuki H.; van Heijenoort, Y.; Tamura, T.; Mizoguchi, J.; Hirota, Y.; van
Heijenoort, J. FEBS Lett. 1980, 110(2), 245.
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3660 J. AM. CHEM. SOC. VOL. 124, NO. 14, 2002