F.A. Siddiqui et al. / European Journal of Medicinal Chemistry 45 (2010) 2761e2767
2767
1
Many of the functionalities of NIN and gabapentin were found
absent which confirms the formation of complex. The twin peak of
NH in gabapentin disappeared indicating that the primary amine
has been changed to tertiary. The doublet of carbonyl in NIN
The H NMR spectra of gaba-ChA complex shows that the NH
2
protons shifted to
amino group [30] and eCH protons shifted to d 2.97 ppm
2
d 6.87 ppm may be because of salt formation at
2
appearing as a broad peak.
ꢀ1
1
changed significantly into one single sharp peak at 1680 cm and
The H NMR spectra of gaba-DDQ complex show similar results
ꢀ
1
the broad band of OeH shifted to 3400 cm
.
as that of gaba-CH complex, that is, the NH
2.94 ppm while that of eCH shifted to 3.96 ppm and appeared
as a doublet showing that NH has been changed to NH.
The above results were found in accord with UV and IR spectra,
confirming the proposed structure.
2
protons shifted to
ꢀ1
CH exhibited a ketonic carbonyl stretch at 1691 cm and aryl
d
2
d
ꢀ1
chloride bends at 1141 and 1245 cm . This also corresponded with
the reported IR of CH [27]. When the infrared spectra of gaba-CH
complex was compared with that of gabapentin and CH, it was
2
2
found that the twin peaks of NH changed into a singlet, showing
that the primary amine may be converted to secondary, the CeN
stretch also shifted to the higher frequency. While the aryl chloride
bends were found absent, only one aryl chloride bend was observed
4. Conclusion
The proposed methods are simple, rapid, accurate, precise and
economical for the routine analysis of gabapentin in pharmaceu-
tical quality control laboratories. With these methods, one can do
the analysis with pace at low cost without losing accuracy. The
proposed methods have been successfully applied to the determi-
nation of gabapentin in pharmaceutical formulations as well.
Although all six reagent used gave suitable results for quantitative
analysis of gabapentin, a comparative study based on the validation
data recommended that ChA and DDQ are the reagent of first choice
as the complex form instantly with lowest LOD and LOQ values,
ninhydrin as well is a suitable reagent as it is known for derivati-
zation and gave most reliable statistical data in our experiment.
ꢀ1
lower then 1000 cm
.
ꢀ
ꢀ1
1
The IR spectra of ChA reports to give OH peak at 3243 cm , C¼O
ꢀ1
stretch at 1664 and 1632 cm and CeO stretch at 1369 cm which
also coincides with the reported IR of ChA [27,28]. The IR spectra of
gaba-ChA complex, however, shows multiple peaks in the region
ꢀ
1
þ
2
[
500e3000 cm that can be attributed to ammonium ion ( NH )
3
þ
ꢀ1
3
bending at 1550 cm as observed in amino
29] along with NH
ꢀ
þ
acids [29] Peak of CeO was missing due to ON H
3
[27].
ꢀ
1
The IR spectra of DDQ showed C¼O stretch at 1679 cm and
ꢀ
1
CeO stretch at 1173 cm as also reported [27]. The IR spectra of
gaba-DDQ complex showed that the doublet of primary amine
in gabapentin changed to a singlet indicating conversion into
secondary amine. Also in the spectra of complex, a broad stretch
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ꢀ1
appeared at 3400 cm
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[
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[
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ꢀ1
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[
(
1
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3
.8.2. Nuclear magnetic resonance spectra
The 1H NMR spectra of gabapentin showed the likely peak of
[
[
[
NH
a triplet at
the region of
By studying the H NMR spectrum of the gaba-NIN complex it
was found that the NH protons completely diminished and the
broad multiplet appearing between 7.42 and 8.163 ppm showing
4.803 ppm represents the
2
at
d
3.303 ppm as a triplet and the eCH
2.873 ppm while the cyclohexyl protons appeared in
1.365e1.585 ppm.
2 2
attached to NH gave
d
d
1
[
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d
d
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eight aromatic CH protons. A singlet at
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d
8
[
By studying the 1H NMR spectrum of the gaba-CH complex it
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was found that the NH
eCH shifted to 2.51 ppm and appeared as a doublet which shows
that NH has been changed to NH.
2
protons shifted to d 2.91 ppm while that of
[
2
d
2