Synthesis and Evaluation of Oxazaborolidines for Antibacterial Activity against Streptococcus mutans

Article abstract of DOI:10.1021/jm049899b

Several representative oxazaborolidines have been synthesized and evaluated against S. mutans for antibacterial activity. This is the first reported antibacterial activity of this class of compounds. The minimal inhibitory concentration values ranged from

Full text of DOI:10.1021/jm049899b

J . Med. Chem. 2004, 47, 2409-2410
2409
bacteria accumulate on the surface of the tooth (dental
plaque biofilm) and initiate demineralization of tooth
enamel, resulting in cavitation. Mutans streptococci
such as Streptococcus mutans (S. mutans) are among
the cariogenic bacteria highly associated with the
prevalence and pathogenicity of tooth decay.12 Elimina-
tion of these bacteria is a fundamental step in prevent-
ing and treating dental caries. Several antibacterial
drugs are being used for prevention or treatment of
tooth decay.13 Irrespective of the ongoing debate as to
which is the drug of choice for eliminating cariogenic
bacteria, new drugs are still being sought.
Syn th esis a n d Eva lu a tion of
Oxa za bor olid in es for An tiba cter ia l
Activity a ga in st Str eptococcu s m u ta n s
Adel J abbour,† Doron Steinberg,‡
Valery M. Dembitsky,† Arieh Moussaieff,†
Batia Zaks,‡ and Morris Srebnik*,†
Department of Medicinal Chemistry and Natural Products,
School of Pharmacy, and Faculty of Dentistry,
Institute of Dental Sciences, Hebrew University,
J erusalem 91120, Israel
The purpose of this investigation was to synthesize
and assess the antimicrobial activity of several deriva-
tives of oxazaborolidines against S. mutans as a step
in studying potential antibacterial activity of these
chemical compounds. Our initial results have been more
than satisfying and are the subject of this communica-
tion.
Received February 4, 2004
Abstr a ct: Several representative oxazaborolidines have been
synthesized and evaluated against S. mutans for antibacterial
activity. This is the first reported antibacterial activity of this
class of compounds. The minimal inhibitory concentration
values ranged from 0.53 to 6.75 mM.
The oxazaborolidines were synthesized by the reaction
of an amino alcohol, using (-)-ephedrine and (-)-
norpseudoephedrine or a diol amine and a boronic acid,
with the azeotropic removal of water 1-6:
Although boron is an essential element for higher
plants1 and the biological role of boron has been the
subject of a number of biological studies,2 the potential
of boron-containing compounds in medicine lags behind
other elements. Some success in the use of boron-
containing compounds has been achieved in boron
neutron capture therapy (BNCT).3 Very recently an
R-amido boronic acid, Velcade, a proteosome inhibitor,
has been approved as an antineoplastic agent.4 Never-
theless, taking into account the vast possibilities of
structures incorporating boron, the use of boron-
containing compounds in medicine has barely been
scratched.5
Compounds containing B-N bonds have been shown
to possess biological activity. Carboxyboranes have
shown anticancer, hypolipidemic, and antifungal activ-
ity.6 Diazaborines have been shown to be active against
malaria.7 Oxazaborolidines also possess a B-N bond
and are readily obtained from an amino alcohol and a
boronic acid. On the basis of the biological activity
displayed by other boron systems with B-N bonds,
oxazaborolidines should be interesting candidates for
biological screening. Nevertheless, despite their ubiquity
in organic synthesis,8 the biological activity of ox-
azaborolidines has to date never been reported. This
omission prompted us to undertake an evaluation of this
group of compounds.
After removal of toluene, 1-3 and 5 were isolated by
distillation in high yields (Figure 1). Compounds 4 and
6 were more difficult to purify. However, 4 could be
obtained in high purity by recrystallization. Attempted
recrystallization of 6 gave product accompanied by some
starting materials (<5% by NMR). Compounds 7 and
814 were isolated by filtration and purified by crystal-
lization in lower yields (Figure 1). For 1 and 4-6 the
(-)-norpseudoephedrine derivatives were used.
The minimal inhibitory concentrations (MIC)15 for
antibacterial activity of the tested oxazaborolidines was
Naturally occurring borate complexes are used as
topical antibiotics.9 Recently, a borate complex, auto-
inducer 2 (AI-2), has been identified as a universal
signaling molecule in bacteria.10 We reasoned that
oxazaborolidines resemble AI-2 in ring size and the
ability to form hydrogen bonds and thus may possess
some biological activity.
Tooth decay (caries) is a worldwide oral disease
affecting all ages, ethnic groups, and both sexes. Caries
are characterized as localized pathological disease be-
cause of the presence of cariogenic bacteria.11 These
* To whom correspondence should be addressed. Phone: 972 2 675
7301. Fax: 972 2 675 8201. E-mail: msrebni@md.huji.ac.il.
† School of Pharmacy.
F igu r e 1. Structures of oxazaborolidines derivatives (isolated
yields).
‡ Institute of Dental Sciences.
10.1021/jm049899b CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/07/2004

2410 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 10
Letters
(2) (a) Boron in Soils and Plants: Review; Dell, B., Brown, P. H., R.
W. Bell, R. W., Eds.; Kluwer Academic Publishers: Dordrecht,
The Netherlands, 1997; p 219. (b) Physiology and Biochemistry
of Boron in Plants. In Boron and Its Role in Crop Production;
Shelp, B. J ., Gupta, U. C., Eds.; CRC Press: Boca Raton, FL,
1993; pp 53-85. (c) Shkolnik, M. Y. Trace Elements in Plants;
Elsevier: New York, 1984. (d) Dugger, W. M. Boron in Plant
Metabolism. In Encyclopedia of Plant Physiology; Lauchli, A.,
Bieleski, R. L., Eds.; Springer-Verlag: Berlin, 1973; Vol. 15B,
pp 626-650. (e) Blevins, D. G.; Lukaszewski, K. M. Boron in
Plant Structure and Function. Annu. Rev. Plant Physiol. 1998,
49, 481-500.
Ta ble 1. Minimal Inhibitory Concentration (MIC) of
Oxazaborolidine Derivatives (1-8) against S. mutans
oxazaborolidine derivatives
MIC (mM)
1
2
3
4
5
6
7
8
1.55
6.00
3.38
1.33
0.53
2.83
6.75
6.75
(3) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth,
R. F.; Codogni, I. M.; Wilson, G. The Chemistry of Neutron
Capture Therapy. Chem. Rev. 1998, 98, 1515-1562.
determined as follows: Sterile microculture dishes con-
taining multiple wells were used to determine the MIC
of eight derivatives of oxazaborolidines. Each well
contained 120 µL of brain-heart infusion medium, 15
µL of an overnight suspension of S. mutans ATCC 27351
adjusted to 1 OD540nm, and 15 µL of the tested com-
pound. Each compound was tested at five different
concentrations between 0 and 50 mM. Each experiment
was repeated twice. These cultures were incubated at
37 °C in an atmosphere enriched in 5% CO2 for 24 h.
Bacteria growth was determined as the turbidity of the
overnight growth and by a computerized ELISA reader
(Thermomax microplate reader, Molecular Devices) at
650 nm. Control cultures of bacteria with no oxazaboro-
lidines added and media broth with the oxazaborolidines
added but with no bacteria were conducted. MIC was
determined as the lowest concentration of the tested
agent in which bacteria did not grow.
MIC values were used to determine the antibacterial
efficacy of oxazaborolidines 1-8 against S. mutans,
which is the one of the predominant bacteria in the
etiology of dental caries. Since the use of oxazaboro-
lidines described herein is novel, the mechanism of
antibacterial action is not known at present. The most
active compound in the series is 5, which contains both
an N-Me group and B-Bu group. Consequently, 1-4 and
6, which do not contain either an N-Me or a B-Bu group,
are less active. Compounds 7 and 8, which are formally
charged, showed the weakest activity. However, the
formal charge in itself may only be one of several
unknown factors responsible for decreased activity.
While boronic acids demonstrate no classic MIC at
their maximal solubility in water (10 mM), all the tested
oxzaborolidines demonstrated antibacterial activity at
much lower concentrations (Table 1).
(4) Velcade is
a trademark of Millenium Pharmaceuticals. (a)
Palombella, V. J .; Conner, E. M.; Fuseler, J . W.; Destree, A.;
Davis, J . M.; Larous, F. S.; Wolf, R. E.; Huang, J .; Brand, S.;
Elliott, P. J .; Lazarus, D.; McCormack, T.; Parent, L.; Stein, R.;
Adams, J .; Grisham, M. B. Role of Proteosome and NF-kappaB
in Streptococcal Cell Wall-Induced Polyarthritis. Proc. Natl.
Acad. Sci. U.S.A. 1998, 95, 15671-15676. (b) Adams, J .; Pal-
ombella, V. J .; Sausville, E. A.; J ohnson, J .; Destree, A.; Lazarus,
D. D.; Maas, J .; Pien, C. S.; Prakash, S.; Elliott, P. J . Proteasome
Inhibitors: A Novel Class of Potent and Effective Antitumor
Agents. Cancer Res. 1999, 59, 2615-2622. (c) Teicher, B. A.; Ara,
G.; Herbst, R.; Palombella, V. J .; Adams, J . The Proteasome
Inhibitor PS-341 in Cancer Therapy. Clin. Cancer Res. 1999, 5,
2638-2645. (d) Frankel, A.; Man, S.; Elliott, P.; Adams, J .;
Kerbel, R. S. Lack of Multicellular Drug Resistance Observed
in Human Ovarian and Prostate Carcinoma Treated with the
Proteasome Inhibitor PS-341. Clin. Cancer Res. 2000, 6, 3719-
3728. (e) Cusack, J . C.; Liu, R.; Houston, M.; Abendroth, K.;
Elliott, P. J .; Adams, J .; Baldwin, A. S. Enhanced Chemosensi-
tivity to CPT-11 with Proteasome Inhibitor PS-341: Implications
for Systemic Nuclear Factor-kB Inhibition. Cancer Res. 2001,
61, 3535-3540. (f) Sunwoo, J . B.; Chen, Z.; Dong, G.; Yeh, N.;
Bancroft, C. C.; Sausville, E.; Adams, J .; Elliott, P.; Waes, C. V.
Novel Proteasome Inhibitor PS-341 Inhibits Activation of Nuclear
Factor-kB, Cell Survival, Tumor Growth, and Angiogenesis in
Squamous Cell Carcinoma. Clin. Cancer Res. 2001, 7, 1419-
1428. (g) Luo, H.; Wu, Y.; Qi, S.; Wan, X.; Chen, H.; Wu, J . A
Proteasome Inhibitor Effectively Prevents Mouse Heart Allograft
Rejection. Transplantation 2001, 72, 196-202. (h) Wu, S.;
Waugh, W.; Stella, V. J . Degradation Pathways of a Peptide
Boronic Acid Derivative, 2-Pyz-(CO)-Phe-Leu-B(OH)2. J . Pharm.
Sci. 2000, 89, 758-765.
(5) Morin, C. The Chemistry of Boron Analogues of Biomolecules.
Tetrahedron 1994, 50, 12521-12569.
(6) Dembitsky, V. M.; Srebnik, M. Synthesis and Biological Activity
of R-Aminoboronic Acids. Amine-Carboxyboranes and Their
Derivatives. Tetrahedron 2003, 59, 579-593.
(7) (a) Surolia, N.; RamachandraRao, S. P.; Surolia, A. Paradigm
Shifts in Malaria Parasite Biochemistry and Anti-Malarial
Chemotherapy. BioEssays 2002, 24, 192-196. (b) Baldock, C.;
de Boer, G.-J .; Rafferty, J . B.; Stuitje, A. R.; Rice, D. W.
Mechanism of Action of Diazaborines. Biochem. Pharmacol.
1998, 55, 1541-1549.
(8) (a) Corey, E. J .; Helal, C. Reduction of Carbonyl Compounds with
Chiral Oxazaborolidine Catalysts: A New Paradigm for Enan-
tioselective Catalysis and a Powerful New Synthetic Method.
Angew. Chem., Int. Ed. 1988, 37, 1986-2012. (b) Srebnik M.;
Deloux, L. Asymmetric Boron-Catalyzed Reactions. Chem. Rev.
1993, 93, 763-784.
The eradication of cariogenic bacteria in the oral
cavity is a long-term goal that has not been successfully
accomplished. Thus, applying a novel class of antibacte-
rial agents opens another potential avenue for combat-
ing this disease that affects most of mankind.
(9) Dembitsky, V. M.; Smoum, R.; Al-Quntar, A. A.; Abu Ali, H.;
Pergament, I.; Srebnik, M. Natural Occurrence of Boron-
Containing Compounds in Plants, Algae and Microorganisms.
Plant Sci. 2002, 163, 931-942.
We have described a novel use of readily available and
stable oxazaborolidines. These initial results are very
encouraging. Structure-activity relationship studies of
oxazaborolidines against S. mutans are continuing.
(10) Chen, X.; Schauder, S.; Potier, N.; van Dorsselaer, A.; Pelczer,
I.; Bassler, B. L.; Hughson, F. M. Structural Identification of a
Bacterial Quorum-Sensing Signal Containing Boron. Nature
2002, 415, 545-549.
(11) Liljemark, W. F.; Bloomquist, C. Human Oral Microbial Ecology
and Dental Caries and Periodontal Diseases. Crit. Rev. Oral Biol.
Med. 1996, 7, 180-198.
(12) Bowden, G. H.; Hamilton, I. R. Survival of Oral Bacteria. Crit.
Rev. Oral Biol. Med. 1998, 9, 54-85.
Ack n ow led gm en t. We thank the Israeli Science
Foundation for support of this project.
(13) Steinberg, D.; Friedman, M. Dental Drug Delivery Devices:
Local and Sustained Release Applications. Crit. Rev. Ther. Drug
Carrier Syst. 1999, 16, 425-459.
Su p p or tin g In for m a tion Ava ila ble: Synthesis and char-
acterization by 1H NMR, 13C NMR, and MS for 1-8. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(14) Formally, 7 and 8 are tetrahydro-[1,3,2]oxazaborolo[2,3-b][1,3,2]-
oxazaboroles.
(15) Eisenberg, A. D.; Young, D. A.; Fan-Hsu, J .; Spitz, L. M.
Interactions of Sanguinarine and Zinc on Oral Streptococci and
Actinomyces Species. Caries Res. 1991, 25, 185-190.
Refer en ces
(1) Warington, K. The Effect of Boric Acid and Borax on the Broad
Bean and Certain Other Plants. Ann. Bot. 1923, 37, 629-672.
J M049899B