562 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 3
Letters
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Ta ble 2. Effect of ip Injection of Nipecotic Acid (0.75 mmol/kg)
or 6-O-Nipecotil-ascorbate (4, 0.75 mmol/kg) on
Pentylenetetrazole-Induced Convulsions in Mice
treatment
latency to convulsion (s)
control (saline + PTZ)
nipecotic acid + PTZ
4 + PTZ
621 ( 28
603 ( 53
922 ( 124a
a
p
< 0.05, significantly different from the other groups,
according to ANOVA followed by the Newman-Keuls test for
multiple comparisons.
also possible, in view of a consistent reduction of SVCT2
transporters available for the AA transport. However,
this consideration requires further investigations.
When nipecotic, kynurenic, and diclofenamic acids
were conjugated to AA, all enhanced their ability to
interact with SVCT2 transporters in a competitive
manner; this implies a potential use of this approach
to transport purposes.
In this context, it is interesting to note that diclofe-
namic acid is converted from a noncompetitive inhibitor
to a competitive inhibitor upon conjugation. Further
work is in progress to understand this intriguing
phenomenon.
To support the possibility that conjugation to AA
could be a mean to improve the entry into the brain of
drugs that do not easily penetrate the BBB, we evalu-
ated the effects of the systemic injection of the nipecotic
acid conjugate (4) on PTZ-induced convulsions in mice.
Compound 4 was selected in view of the possibility to
examine its behavior in a well-known animal model and
moreover for its better solubility in water as compared
to compound 10. In the saline group, the sc injection of
PTZ (80 mg/kg) induced tonic convulsions with a latency
of 621 ( 27 s. As shown in Table 2, the ip injection of 4
(0.75 mmol/kg) significantly increased the latency to
appearance of PTZ-induced tonic convulsions, while as
expected,23 nipecotic acid (0.75 mmol/kg) was ineffective.
In all groups, no lethality was observed.
The compound 4 and nipecotic acid-treated mice
showed no apparent abnormality in general behavior
except for a mild diarrhea, which appeared 40 min after
the injection only in animals treated with compound 4.
We can conclude that the conjugation of drugs with
AA is an important tool in studying the mechanism of
the interaction of AA to its transporters and can open
new interesting perspectives for the possibility of ob-
taining prodrugs effective for the crossing of the BBB
by means of endogenous transporters. Further studies
are currently ongoing in order to assess and extend this
possibility.
(12) Kim, Y. C.; Zhao, L. X.; Kim, T. H.; J e, S. M.; Kim, E. K.; Choi,
H.; Chae, W. G.; Park, M.; Choi, J .; J ahng, Y.; Lee, E. S. Design
and synthesis of anticonvulsive agents as gamma-vinylGABA-
based potential dual acting prodrugs and their biological activi-
ties. Bioorg. Med. Chem. Lett. 2000, 10, 609-614.
(13) Spath, E. Constitution of kynurenic acid. Monatsh. 1921, 42,
89-95.
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scavengers of active oxygen species. 1. Synthesis and biological
activity of 2-O-alkylascorbic acids. J . Med. Chem. 1988, 31, 793-
798.
(15) Manfredini, S.; Baraldi, P. G.; Bazzanini, R.; Bortolotti, F.;
Vertuani, S.; Ashida, N.; Machida, H. Enzymatic synthesis of
2′-O-acyl-prodrugs of 1-(beta-D-arabinofuranosyl)-5(E)-(2-bro-
movinyl)uracil (sorivudine, BV-araU) and of 2′-O-acyl-araU,
-araC and -araA. Antiv. Chem. Chemother. 1998, 25, 9-16.
(16) Beuckmann, C. T.; Gordon, W. C.; Kanaoka, Y.; Eguchi, N.;
Marcheselli, V. L.; Gerashchenko, D. Y.; Urade, Y.; Hayaishi,
O.; Bazan, N. G. Lipocalin-type prostaglandin D synthase (beta-
trace) is located in pigment epithelial cells of rat retina and
accumulates within interphotoreceptor matrix. J . Neurosci.
1996, 16, 6119-6124.
(17) Lambert, D. M. Rationale and applications of lipids as prodrug
carriers. Eur. J . Pharm. Sci. 2000, 2, S15-27.
(18) Hodgkins, P. S.; Schwarcz, R. Metabolic control of kynurenic acid
formation in the rat brain. Dev. Neurosci. 1998, 20, 408-416.
(19) Smith, Q. R. Transport of glutamate and other amino acids at
the blood-brain barrier. J . Nutr. 2000, 130, 1016S-1022S.
(20) Hull, M.; Lieb, K.; Fiebich, B. L. Antiinflammatory drugs: a hope
for Alzheimer’s disease? Expert Opin. Invest. Drugs 2000, 9,
671-83.
(21) Baures, P. W.; Oza, V. B.; Peterson, S. A.; Kelly, J . W. Synthesis
and evaluation of inhibitors of transthyretin amyloid formation
based on the nonsteroidal antiinflammatory drug,flufenamic
acid. Bioorg. Med. Chem. 1999, 7, 1339-1347.
(22) Patel, P. M.; Drummond, J . C.; Sano, T.; Cole, D. J .; Kalkman,
C. J .; Yaksh, T. L. Effect of ibuprofen on regional eicosanoid
production and neuronal injury after forebrain ischemia in rats.
Brain Res. 1993, 614, 315-324.
Ack n ow led gm en t. This work was supported by
University of Ferrara (S.M., A.D., A.S., C.B., and S.V.)
and National Institutes of Health Grant (HD37150,
P.P.).
(23) Frey, H. H.; Popp, C.; Loscher W. Influence of inhibitors of the
high affinity GABA uptake on seizure thresholds in mice.
Neuropharmacology 1979, 18, 581-590.
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