Synthesis and biological evaluation of a siderophore-virginiamycin conjugate

Article abstract of DOI:10.1055/s-1999-3655

Condensation of Virginiamycin S₁ (1) with aminooxyacetic acid afforded oxime 9. EDC/HOAt-mediated coupling of 9 to the N-terminus of the tripeptide of N⁵-hydroxy-N⁵-acetyl-L-ornithine, the common iron chelator in most hydr

Full text of DOI:10.1055/s-1999-3655

1510
PAPER
Synthesis and Biological Evaluation of a Siderophore-Virginiamycin
Conjugate
Yun-Ming Lin, Paul Helquist, Marvin J. Miller*
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
Fax +1(219)6316652
Received 4 April 1999
and increased rate of weight gain in swine and poultry4 as
well as in clinical treatment for humans. Synercid, a semi-
synthetic streptogramin, and pristinamycin have recently
been used for clinical treatment of vancomycin-resistant
Abstract: Condensation of Virginiamycin S1 (1) with aminooxy-
acetic acid afforded oxime 9. EDC/HOAt-mediated coupling of 9 to
the N-terminus of the tripeptide of N5-hydroxy-N5-acetyl-L-orni-
thine, the common iron chelator in most hydroxamate-derived sid-
erophores, provided the desired siderophore-drug conjugate 5. Enterococcus faecium and methicillin-resistant Staphylo-
coccus aureus.5 Virginiamycin resistant strains of bacteria
Preliminary biological evaluation of 5 against E. coli X580 under
both iron sufficient and deficient conditions suggested uptake of si-
derophore-drug conjugate (5) by active iron transport systems.
have been detected in Enterococcus faecium from pigs
and chickens.6 Streptogramin resistant bacterial strains
Key words: oximes, drug delivery, iron
have also been identified and isolated from hospitals
where pristinamycin was extensively used.7 In connection
with interests in siderophore-mediated drug delivery sys-
tems in the Miller group and synthesis of VS1 derivatives
in the Helquist group, we decided to incorporate VS1 into
a siderophore component via a novel oxime linkage. This
could be achieved by incorporating an aminooxyacetic
acid spacer at the N-terminus of the tripeptide of N5-hy-
droxy-N5-acetyl-L-ornithine, the common iron chelator in
most hydroxamate-derived siderophores.
Virginiamycin S1 (1, Figure 1) belongs to a family of Type
B streptogramin antibiotics remarkable for their antibac-
terial activity and their unique mode of action. This cyclic
macrolactone hexapeptide is usually coadministered with
Type A streptogramins, such as Virginiamycin M (VM, 2,
Figure 1).1 Streptogramins bind to the peptidyltransferase
domain of bacterial ribosome and inhibit bacterial growth
by disrupting the translation of mRNA into protein. VS1
stimulates the dissociation of the peptidyl-tRNA complex
and causes the premature release of polypeptides chains.
The combination of Type A and Type B antibiotics great-
ly enhances their antibacterial potency. This synergistic
effect results from an increased binding affinity of VS1 for
the ribosome due to a conformational change induced by
VM.2 Streptogramin antibiotics are much more effective
towards Gram positive than Gram negative bacteria, pre-
sumably due to membrane permeability problems associ-
ated with Gram negative bacteria.3
Siderophores are secreted by microbes as microbial iron
transport agents to sequester iron(III) under iron deficient
conditions.8 The siderophore–iron complex is recognized
by outer membrane receptors regulated by the Fur protein,
expressed under iron stressed conditions, and actively
transported inside the cell.9 Because iron is a limiting nu-
trient with the onset of infection, siderophores are essen-
tial for microbial pathogenicity.10 Siderophore-drug
conjugates (3, Figure 2) are composed of iron chelators,
chemical linkers and biologically active components
(“drug”). These siderophore-drug conjugates (3) could be
recognized by microbes and transported inside the cell by
the iron uptake system. Once inside the cell, the drug
The streptogramin antibiotics have been extensively em-
ployed as feed additives to elicit improved feed efficiency
O
N
N
O
N
O
O
O
O
N
N
HN
H
O
O
O
N
O
O
O
O
H
N
O
NH
N
OH
O
HO
1
2
Virginiamycin M
Virginiamycin S1
Figure 1 Type A and Type B Streptogramin Antibiotics
Synthesis 1999, No. SI, 1510–1514 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Biological Evaluation of a Siderophore-Virginiamycin Conjugate
1511
could be released to induce an effective dosage to the mi- Our initial attempt in making an oxime linkage for a sid-
crobes ("The Trojan Horse strategy").11 Albomycins (4, erophore-drug conjugate started from siderophore compo-
Figure 2), antibiotics produced by Streptomyces griseus nent 6 (Scheme 1), readily available through the practical
and Streptomyces substropicus, are naturally occurring synthesis of the corresponding tripeptide trihydroxy-
examples of siderophore-drug conjugates.12
lamine by an indirect oxidation method.13 Treatment of
fully unprotected siderophore component 6 with the N-hy-
droxysuccinimide (NHS) active ester of Boc-protected
aminooxyacetic acid afforded 7 in 72% yield. As a model
study, the Boc group was cleaved and the resulting hy-
droxylamine was treated with an excess of acetone and
pyridine to provide oxime 8 as its pyridinium salt in quan-
titative yield. Conceptually, this approach would provide
a general synthetic route in condensing various oxo-con-
taining drug components directly with the hydroxylamine
moiety of the siderophore component to provide the de-
sired oxime-linked conjugate at the last step of the synthe-
sis. However, reaction of this hydroxylamine with a
stoichiometric amount of VS1 did not provide the desired
conjugate, presumbly due to the instability of the hydrox-
ylamine indicated by changes in its NMR spectra upon
storage.
O
O
O
Fe
O
O
N
N
N
O
Drug
O
H
N
N
N
H
O
NH
O
R
O
O
3
Siderophore-Drug Conjugate
O
Fe
O
O
O
N
N
N
OH
O
O
HO
H
O
HO
O
N
N
H
N
O
S
H
N
We then decided to preform an oxime by reaction of Vir-
giniamycin S1 (1) with aminooxyacetic acid followed by
coupling to the N-terminus of a siderophore component
(Scheme 2). Treatment of aminooxyacetic acid with 1 in
the presence of pyridine provided the desired oxime 9 in
96% yield as a 1:1 mixture of E, Z isomers.14
N
H
Y
N
H
COOH
NH2
O
O
HO
4
Albomycins, Y = O, NH, or NCONH2
The C-terminus of the siderophore component was pro-
tected by coupling 10 with the methyl ester of 6-aminoca-
proic acid to afford 11. The 6-aminocaproic acid spacer
not only served as a protecting group, but also provided
the carboxy group for potential coupling to other drug
components in future studies. Deprotection of the Cbz
group followed by a EDC/HOAt-mediated coupling reac-
tion with oxime 9 provided the desired conjugate 5 in
good overall yield as an inseparable 1:1 mixture of E and
Z isomers.
Figure 2 Siderophore-Drug Conjugate and Albomycins
Thus, VS1 is an ideal drug component in testing the scope
of this “Trojan Horse” active drug delivery strategy due to
its structural features and unique mode of action. We
therefore decided to use an oxime linkage which can take
advantage of the oxo group found on the 4-oxopipecolic
acid domain present in 1 for constructing the desired sid-
erophore-drug conjugate (5, Figure 3). Once transported
inside the cell, hydrolysis of the oxime linkage of the con-
jugate was anticipated to regenerate VS1 and allow it to
exert its lethal effect on the bacterial ribosome.
Biological evaluation of this conjugate mixture was then
carried out at 10 mM and 20 mM using kinetic growth as-
says in Luria broth under both iron sufficient and deficient
conditions against E. coli X580, a Gram-negative bacteria
(Figure 4).
Herein, we report our synthesis of a novel virginiamycin
oxime siderophore conjugate (5) and its preliminary bio-
logical evaluation against a strain of E. coli.
O
O
O
Fe
O
O
O
N
N
N
N
N
O
O
O
O
N
HN
H
O
N
H
N
N
O
O
O
O
O
N
H
O
NH
N
N
H
O
HN
O
HO
MeO2C
5
4
Figure 3 Virginiamycin-Siderophore Conjugate
Synthesis 1999, No. SI, 1510–1514 ISSN 0039-7881 © Thieme Stuttgart · New York

1512
Y.-M. Lin et al.
PAPER
N
HO
OH
N
HO
N
OH
N
N
BocNHOCH2CONHS
72%
O
H
N
O
H
N
O
N
H
N
H
BocHNO
NH
O
O
COOH
H2N
•
COOH Pr2NEt
O
7
6
O
O
N
HO
OH
HO
N
N
1). HCl/EtOAc, AcOH
O
H
N
2). Acetone, pyridine
quant.
O
N
H
O
•
NH
O
COOH
N
N
8
Scheme 1
Scheme 1
Under iron sufficient conditions, VS1 siderophore conju- conjugate (5) at 10 mM and 20 mM. These results suggest-
gate (5), VS1 itself (1), and VS1 oxime (9) displayed no ed receptor-mediated active transport of the drug conju-
significant antibacterial activity while combination of VS1 gate since outer membrane receptors are expressed under
and VM displayed potent synergistic activity, as expected. iron stressed conditions. Interestingly, VS1 also showed
However, under iron deficient conditions, significant an- significant antibacterial activity under iron deficient con-
tibacterial activity was observed with siderophore drug ditions. It is noteworthy that oxime 9 did not display any
O
N
N
O
O
O
N
HN
H2NO
CO2H
H
N
1
N
O
O
O
O
O
Pyridine
96%
O
NH
N
OH
HO
9
O
O
O
O
O
N
HO
OH
O
HO
N
N
N
HO
OH
HO
HOAt, EDC
CO2Me
N
N
O
H2N
H
N
4
O
H
N
N
H
37%
N
H
CbzHN
O
O
NH
CbzHN
O
COOH iPr2NEt
MeO2C
11
10
4
1) H2, Pd/C
90%
5
2) HOAt, EDC
9, DMF
52%
Scheme 2
Synthesis 1999, No. SI, 1510–1514 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Biological Evaluation of a Siderophore-Virginiamycin Conjugate
1513
earlier.15 Biological evaluation procedures have been described be-
fore.16
Protected Siderophore Component 7
To a solution of Boc-aminooxyacetic acid (46 mg, 0.24 mmol),
NHS (30 mg, 0.26 mmol), in THF (2.0 mL) at 0 °C, was added DCC
(52 mg, 0.25 mmol). The mixture was then stirred at r.t. for 15 h.
The mixture was used as the active ester solution in the following
reaction.
Bioassay of VS-Siderophore conj. against E. Coli
X 580 under iron sufficient conditions
0.5
0.45
0.4
Control
Conj. 0.02mM
Conj. 0.01mM
VS1 0.01mM
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
To a solution of 6 (100 mg, 0.15 mmol), and NaHCO3 (150 mg, 1.78
mmol) in THF/H2O (5 mL/5 mL) at r.t., was added the above active
ester solution. The mixture was stirred at r.t. for 20 h. The volatiles
were removed and the residue was partitioned between H2O (20
mL) and EtOAc (20 mL). The pH of the mixture was adjusted to 2
by adding 0.2 M HCl. The layers were separated and the aqueous
layer was extracted with EtOAc (2 x 10 mL). The combined ex-
tracts were dried (Na2SO4), filtered, concentrated and purified by
reverse phase column chromatography (C18, 4:1 H2O/CH3OH to 2:1
H2O/CH3OH) to give 42 mg (72%) of 7 as a white foam. Unreacted
6 (26 mg) was recovered as its free acid.
VS1 Oxime
0.01 mM
VS+VM 0.01 mM
each
1H NMR (300 MHz, CD3OD): d = 1.47 (s, 9H) 1.69–1.88 (m, 12H),
2.10 (s, 9H), 3.61–3.69 (m, 6H), 4.29 (AB, J = 15.9 Hz, 2H), 4.36–
4.47 (m, 3H).
13C NMR (75 MHz, CD3OD): d = 20.7, 20.8, 24.5, 24.6, 24.8, 29.0,
30.3, 30.58, 30.6, 48.9, 54.0, 54.4, 54.6, 76.9, 83.6, 160.3, 172.2,
174.2, 174.3, 174.5, 175.6.
IR (neat): n = 1543, 1636, 1641, 1650, 1724, 3244 cm-1.
FABMS: calcd. for C28H49O14N7Na (M+Na)+:730.3235,
found:730.3209.
Bioassay of VS-Siderophore conj. against E. Coli
X 580 under iron deficient conditions
0.4
0.35
0.3
Control
VS-conj. 0.02mM
VS-conj. 0.01mM
VS 0.01mM
0.25
0.2
0.15
0.1
VS Oxime
0.02 mM
0.05
0
VS+VM 0.01 mM
each
Oxime 8
To a solution of 7 (23 mg, 0.032 mmol) in HOAc (6 mL) at r.t., was
added HCl/EtOAc (2 mL, saturated at 0 °C). The mixture was
stirred at r.t. for 1 min and the volatiles were removed in vacuo to
give 21 mg (quant.) of hydroxylamine as a slightly pink oil.
Figure 4 Growth Curves of E. Coli X580 in Luria Broth Culture
To a sample of the above hydroxylamine (3 mg, 0.0047 mmol) at
r.t., was added acetone (2 mL) and H2O (0.5 mL). Pyridine (0.5 mL,
6.19 mmol) was then added and the solution was stirred at r.t. for 6
h. The volatiles were removed to afford 4 mg (quant.) of 8 as a white
foam. 1H NMR (600 MHz,CD3OD): d = 1.68–1.82 (m, 12H), 1.86
(s, 3H), 1.95 (s, 3H), 2.10 (s, 9H), 3.55–3.72 (m, 6H), 4.37–4.50 (m,
5H), 8.11 (m, 2H), 8.66 (t, J = 7.8 Hz, 1H), 8.88 (d, J = 5.4 Hz, 2H).
13C NMR (150 MHz, CDOD): d = 16.3, 20.8, 22.1, 24.4, 24.6, 24.8,
30.2, 30.6, 31.1, 48.6, 48.7, 48.8, 53.9, 54.1, 54.6, 73.4, 129.2,
143.7, 148.5, 159.8, 173.2, 174.3, 174.5, 175.4.
activity under iron deficient conditions. This suggested
that the siderophore-drug conjugate was transported in-
side the cell and either the intact conjugate was active or
intracellular cleavage of the oxime linkage release of the
drug occurred by hydrolysis of the oxime.
In summary, we have described the synthesis and antibac-
terial activity of a novel siderophore drug conjugate
through an oxime linkage. The biological testing results
suggested that the conjugate was taken up by E. coli
through the receptor-mediated active transport pathway. It
would be interesting to test if a VM-siderophore conjugate
will display a synergistic effect with the VS1-conjugate.
The synthesis of a virginiamycin M siderophore conjugate
and its biological study are currently underway. This
modification of VS1 also shows that Type B streptogamin
antibiotics can be derivatized to target Gram negative bac-
teria. A broad spectrum assay of VS1 conjugate (5) is also
underway.
IR (neat) n = 1540, 1637, 1729, 3250, 3400 cm-1.
FABMS:
calcd.
for
C26H46O12N7 (M+H)+:648.3204,
found:648.3215.
Siderophore Component (11)
To a mixture of 10 (88 mg, 0.11 mmol), methyl 6-aminocaproate
hydrochloride (30 mg, 0.16 mmol), HOAt (18 mg, 0.13 mmol),
DMAP (27 mg, 0.22 mmol), Et3N (0.05 mL, 0.39 mmol) in DMF (2
mL) at 0 °C, was added EDC (25 mg, 0.13 mmol). The yellow mix-
ture was stirred to r.t. for 38 h. H2O (10 mL) was added and the
aqueous solution was washed with CH2Cl2 (2 x 10 mL), concentrat-
ed and purified by reverse phase column chromatography (C18, 2:1
H2O/CH3OH to 1:1 H2O/CH3OH) to give 28 mg (37%) of 11 as a
white foam. Unreacted 10 (10 mg) was recovered as a free acid.
1H NMR (500 MHz, CD3OD): d = 1.33 (m, 2H), 1.52 (m, 2H),
1.62–1.67 (m, 14H), 2.08 (s, 3H), 2.09 (s, 3H), 2.10 (s, 3H), 2.31 (t,
J = 7.5 Hz, 2H), 3.12 (m, 2H), 3.64 (s, 3H), 3.58–3.68 (m, 6H), 4.12
General. All reactions were carried out under N2 unless otherwise
stated. Instruments and general methods used have been described
Synthesis 1999, No. SI, 1510–1514 ISSN 0039-7881 © Thieme Stuttgart · New York

1514
Y.-M. Lin et al.
PAPER
(m, 1H), 4.27 (m, 1H), 4.33 (m, 1H), 5.09 (AB, J = 12.5 Hz, 2H),
7.33 (m, 5H).
13C NMR (125 MHz, CD3OD): d = 20.8, 24.7, 24.8, 26.1, 27.8,
30.2, 30.4, 30.4, 30.6, 30.7, 35.2, 40.7, 48.7, 48.8, 52.5, 55.0, 55.2,
56.8, 68.3, 129.3, 129.6, 130.0, 138.6, 159.2, 174.2, 174.28, 174.3,
174.5, 175.7, 176.3.
IR (neat) n = 1536, 1640, 1713, 3285 cm-1.
FABMS: calcd. for C36H58N7O13 (MH)+:796.4093, found:796.4059.
(2) Cocito, C.; Digiambattista, M.; Nyssen, E.; Vannuffel, P. J.
Antimicrob. Chemother. 1997, 39 (Suppl. A):7.
(3) Barriere, J. C.; Berthaud, N.; Beyer, D.; Dutka-Malen, S.;
Paris, J. M.; Desnottes, J. F. Current Pharmaceutical Design
1998, 4, 155.
(4) Burg, R. W. In Agricultural Uses of Antibiotics, Moats, W. A.,
Ed. ACS Symposium Series 320; American Chemical
Society: Washington, D. C. 1986 p 61.
(5) Dever, L. L.; Smith, S. M.; Dejesus, D.; Masurekar, M.; Patel,
D.; Kaminiski, Z. C.; Johanson, J. W. G. Microb. Drug Resist.
1996, 2, 407.
VS1-siderophore Conjugate (5)
Sahgal, V. S.; Urban, C.; Mariano, N.; Weinbaum, F.; Turner,
J.; Rahal, J. J. Microb. Drug Resist. 1995, 1, 24.
Torralba, M. D.; Frey, S. E.; Lagging, L. M. Clin. Infect. Dis.
1995, 21, 460.
A solution of 11 (16 mg, 0.02 mmol) in CH3OH (3 mL) was stirred
with Pd/C (10%, 3 mg) under H2 (1 atm) at r.t. for 1 h. The catalyst
was filtered off and rinsed with CH3OH. The filtrate was concen-
trated to give 12 mg (90%) of unprotected siderophore component
as a colorless oil.
(6) Hammerum, A. M.; Jensen, L. B.; Aarestrup, F. M. FEMS
Microbiol. Lett. 1998, 168, 145.
A solution of oxime 9 (25 mg, 0.028 mmol), unprotected sidero-
phore component (16 mg, 0.024 mmol), EDC (7 mg, 0.037 mmol),
HOAt (5 mg, 0.037 mmol), and DMAP (6 mg, 0.049 mmol) in DMF
(0.5 mL) was stirred at r.t. for 17 h. H2O (10 mL) and CHCl3 (20
mL) were added and the layers were separated. The aqueous layer
was extracted with CHCl3 (2 x 10 mL). The combined organic lay-
ers were washed with brine (2 x 10 mL), dried (Na2SO4), filtered,
concentrated and purified by reverse phase column chromatography
(C18, 1:1 H2O/CH3OH to 1:2 H2O/CH3OH) to give 19.5 mg (52%)
of 5 as a white foam.
1H NMR (600 MHz, CD3OD): d = 0.86–0.90 (m, 3H), 1.04–1.08
(m, 1H), 1.25–1.96 (m, 26H), 2.03–2.08 (m, 11H), 2.24–2.32 (m,
2H), 2.41–2.60 (m, 2H), 3.07–3.37 (m, 8H), 3.49–3.63 (m, 10H),
4.22–4.70 (m, 8H), 4.79–4.81 (m, 1H), 4.96–4.98 (m, 1H), 5.16–
5.38 (m, 2H), 5.55–5.63 (m, 1H), 5.78 (m, 1H), 7.12–7.58 (m, 12H),
7.86–7.90 (m, 1H).
13C NMR (150 MHz, CD3OD): d = 10.8, 16.9, 17.2, 17.3, 17.6,
20.79, 20.8, 24.5, 24.7, 24.8, 25.1, 25.2, 25.7, 26.06, 26.1, 26.3,
26.4, 27.4, 27.7, 27.8, 29.2, 29.9, 30.1, 30.4, 30.6, 30.7, 30.8, 31.6,
32.0, 32.3, 32.7, 35.2, 37.6, 37.8, 38.4, 38.6, 39.9, 40.0, 40.4, 40.7,
48.7, 48.8, 52.5, 53.5, 54.7, 54.9, 55.0, 55.2, 55.6, 57.4, 57.5, 57.6,
57.9, 58.2, 59.0, 59.6, 71.4, 71.5, 73.6, 73.8, 73.9, 108.4, 128.4,
129.4, 129.5, 129.7, 129.8, 129.9, 130.1, 130.49, 130.5, 130.79,
130.8, 131.0, 131.1, 131.2, 131.3, 131.5, 132.5, 132.7, 137.9, 138.1,
138.2, 147.4, 156.7, 157.2, 158.1, 170.2, 170.8, 170.9, 171.1, 171.5,
172.19, 172.2, 172.3, 172.8, 173.2, 173.6, 173.9, 174.0, 174.1,
174.2, 174.3, 174.4, 174.68, 174.7, 176.3.
(7) El Solh, N.; Allighnet, J. Drug Resistance Updates 1998, 1,
169.
(8) Neilands, J. B. J. Biol. Chem. 1995, 270, 26723.
Miller, M. J. Chem. Rev. 1989, 89, 1563.
Koster, W.; Braun, V. J. Biol. Chem. 1990, 265, 21407.
(9) Moeck, G. S.; Coulton, J. W. Mol. Microbiol. 1998, 28, 675.
Ferguson, A. D.; Breed, J.; Diederichs, D.; Welte, W.;
Coulton, J. W. Protein Science 1998, 7, 1636.
van der Helm, D. In Metal Ions in Biological System, Iron
Transport and Storage In Microorganisms, Plants, and
Animals Ed. Sigel, A.; Sigel, H. Marcel Dekker, Inc. New
York, 1998, 35. p 355.
(10) Wooldridge, K., G., Williams, P. H. FEMS Microbiol. Rev.
1993, 12, 325.
Neilands, J. B. Biochem. Biophys. 1993, 302, 1.
(11) Miller, M. J.; Malouin, F. Acc. Chem. Res. 1993, 26, 241.
Dolence, E. K.; Lin, C.-E.; Miller, M. J. J. Med. Chem. 1991,
34, 956.
Miller, M. J.; Malouin, F. In The Development of Iron
Chelators for Clinical Use, Bergeron, R. J.; Brittenham, G.
M., Eds., CRC Press, Boca Raton, FL, 1994, Chap 13.
Poras, H.; Kunesch, G.; Barriere, J.-C.; Andremont, A. J.
Antibiotics. 1998, 51, 786.
Tilbrook, G. S.; Hider, R. C. In Metal Ions in Biological
System, Iron Transport and Storage In Microorganisms,
Plants, and Animals Ed. Sigel, A.; Sigel, H. Marcel Dekker,
Inc. New York, 1998, 38, p 691.
Ghosh, M.; Miller, M. J. Bioorganic & Medicinal Chemistry
1996, 4, 43.
IR (neat): n = 1247, 1448, 1523, 1628, 1645, 1653, 1678, 1737,
3275, 3367 cm-1.
(12) Benz, G. Liebigs Ann. Chem. 1984, 1399.
Benz, G.; Schmidt, D. Liebigs Ann. Chem. 1984, 1434.
Benz, G.; Born, L.; Brieden, M.; Grosser, R.; Kurz, J.;
Paulsen, H.; Sinnwell, V.; Weber, B. Liebigs Ann. Chem.
1984, 1408.
FABMS: calcd: for C73H101N15O22 (M+):1540, found:1540.
Acknowledgment
Paulsen, H.; Brieden, M.; Benz, G. Liebigs Ann. Chem. 1987,
565.
We gratefully acknowledge financial support from the National In-
stitutes of Health (GM 25845-19). We appreciate the use of the
NMR facilities of the Lizzadro Magnetic Resonance Research Cen-
ter at Notre Dame. We also thank Dr. Bill Boggess and Nonka Se-
vova of the University of Notre Dame for conducting our mass
spectroscopy experiments. We thank Mr. Jason DiFusco for initial
VS derivatives and Mr. Ryan Wirtz for providing a sample of VM.
(13) Naegeli, H.-U.; Keller-Schierlein, W. Helv. Chim. Acta. 1978,
61, 2088.
Lin, Y.-M.; Miller, M. J. Paper 703, 216th American Chemical
Society National Meeting 1998, Boston.
(14) Anteunis, M. J. O.; Callens, R.; Sharma, N. K. Bull. Soc.
Chim. Belg. 1988, 97, 209.
Giambattista, M. D.; Nyssen, E.; Pecher, A.; Cocito, C.
Biochem. 1990, 29, 9203.
(15) Hu, J.; Miller, M. J. J. Am. Chem. Soc. 1997, 119, 3462.
(16) Minnick, A. A.; McKee, J. A.; Dolence, K.; Miller, M. J.
Antimicrob. Agents and Chemother. 1992, 36, 840.
References
(1) (a) Cocito, C. Microbiol. Rev. 1979, 43, 145.
(b) Paris, J. M.; Barriere, J. C.; Smith, C.; Bost, P. E. In Recent
Progress in the Chemical Synthesis of Antibiotics; Lucass, G.;
Ohno, M., Eds.; Springer: Berlin, 1990, p 183.
Article Identifier:
1437-210X,E;1999,0,SI,1510,1514,ftx,en;C02199SS.pdf
Synthesis 1999, No. SI, 1510–1514 ISSN 0039-7881 © Thieme Stuttgart · New York