Synthesis, physicochemical and anticonvulsant properties of N-benzyl and N-aminophenyl derivatives of 2-azaspiro[4.4]nonane and [4.5]decane-1,3-dione. Part I

Article abstract of DOI:10.1016/j.farmac.2005.05.006

To continue our systematic SAR studies, two series of N-benzyl- (X = CH₂) and N-aminophenyl- (X = NH) derivatives of 2-azaspiro[4.4]nonane (1a-1j) and 2-azaspiro[4.5]decane-1,3-dione (2a-2j) were synthesized, and evaluated in maximum electroshock seizure (MES), subcutaneous pentylenetetrazole (sc.MET) and rotorod (TOX) tests for their anticonvulsant activity. Among those derivatives, the most potent N-aminophenyl-2-azaspiro[4.4]nonane-1,3-dione 1j had ED₅₀ = 76.27 mg kg^-1. X-ray structures for two pairs of derivatives with a different linker were solved. Then 3-D data for the active 1j versus less active 2j, both having an imine linker (X = NH), and the respective parent of compounds with a methylene linker (X = CH₂) (1a and 2a) were discussed.

Full text of DOI:10.1016/j.farmac.2005.05.006

Il Farmaco 60 (2005) 529–539
http://france.elsevier.com/direct/FARMAC/
Synthesis, physicochemical and anticonvulsant properties of N-benzyl
and N-aminophenyl derivatives of 2-azaspiro[4.4]nonane
and [4.5]decane-1,3-dione. Part I
Jolanta Obniska a,*, Agnieszka Dzierzawska-Majewska b, Agnieszka Zagorska a,
Pawel Zajdel a, Janina Karolak-Wojciechowska b
a Department of Pharmaceutical Chemistry, Jagiellonian University Medical College, Medyczna 9, 30-688 Krakow, Poland
b Institute of General and Ecological Chemistry, Technical University, Zwirki 36, 90-924 Lodz, Poland
Received 20 July 2004; received in revised form 5 March 2005; accepted 10 May 2005
Available online 13 June 2005
Abstract
To continue our systematic SAR studies, two series of N-benzyl- (X = CH2) and N-aminophenyl- (X = NH) derivatives of
2-azaspiro[4.4]nonane (1a–1j) and 2-azaspiro[4.5]decane-1,3-dione (2a–2j) were synthesized, and evaluated in maximum electroshock sei-
zure (MES), subcutaneous pentylenetetrazole (sc.MET) and rotorod (TOX) tests for their anticonvulsant activity.Among those derivatives, the
most potent N-aminophenyl-2-azaspiro[4.4]nonane-1,3-dione 1j had ED50 = 76.27 mg kg–1. X-ray structures for two pairs of derivatives with
a different linker were solved. Then 3-D data for the active 1j versus less active 2j, both having an imine linker (X = NH), and the respective
parent of compounds with a methylene linker (X = CH2) (1a and 2a) were discussed.
© 2005 Elsevier SAS. All rights reserved.
Keywords: 2-Azaspiro[4.4]nonane-1,3-dione; 2-Azaspiro[4.5]decane-1,3-dione; Spirosuccinimides; Pyrrolidine-2,5-diones; Anticonvulsant activity; X-ray
structures
1. Introduction
aryl moiety by changing the methylene group into an oxym-
ethylene one. The resulting N-benzyloxy-2-azaspiro[4.4]-
nonane-1,3-dione was classified as a potent anticonvulsant
compound (ED50 = 111 mg kg–1).
Anticonvulsant activity was found in compounds having a
spirocycloalkyl fragment connected with the heterocyclic ring
in many types of derivatives, e.g. spirohydantoins [1,2],
spirobarbiturates [3], and spirosuccinimides [4–7]. Structure
activity relationship studies conducted with a group of spiro-
succinimides showed a pivotal role of the cycloalkyl system
attached to the C3 spiro carbon atom, as well as the signifi-
cance of the kind of substituents in the aromatic ring in the
aspect of influence of that type of compounds on anticonvul-
sant activity.Also the influence of a linker joining the endocy-
clic nitrogen atom and the aromatic ring was investigated
[8,9]. A research conducted by Edafiogho et al. [10] led to
the synthesis of N-benzyl-2-azaspiro[4.4]nonane-1,3-dione
1a, which was devoid of anticonvulsant activity, later those
authors modified the linker between the imide ring and the
Our earlier SAR studies with a group of N-pirydyl-3-aryl
succinimide derivatives indicated that their anticonvulsant
activity was closely connected with the conformational and
electronic properties of those molecules. An analysis of the
molecular electrostatic potential (MEP) distribution showed
that the differences in MEP minima depth in the proximity of
both carbonyl oxygen atoms of the imide ring were different
for active and inactive compounds [11–14]. On a basis of those
facts and our earlier chemical and pharmacological investi-
gations with a group of differently 1,3-substituted pyrrolidine-
2,5-diones [15–20], in the present study we designed two
series of 2-azaspiro[4.4]nonane- and 2-azaspiro[4.5]decane-
1.3-diones with different linkers (methylene, imine) between
the imide moiety and the aromatic center. Furthermore, we
examined the impact of the aromatic ring substitution mode
on anticonvulsant activity. The synthesis and the results of
* Corresponding author.
E-mail address: mfobnisk@cyf-kr.edu.pl (J. Obniska).
0014-827X/$ - see front matter © 2005 Elsevier SAS. All rights reserved.
doi:10.1016/j.farmac.2005.05.006

530
J. Obniska et al. / Il Farmaco 60 (2005) 529–539
pharmacological investigation are presented below. For two
pairs of compounds with the methylene (1a, 2a) or the imine
(1j, 2j) linker, crystallographic studies were carried out to
correlate the conformation and the electronic properties of
those compounds with their anticonvulsant activity.
2. Chemistry
Compounds 1a1–j and 2a–j were synthesized according
to Scheme 1. The starting dicarboxylic acids were prepared
as reported previously [7] using a two-step procedure. First,
in a reaction of cyclopentanone or cyclohexanone with ethyl
cyanoacetate in the presence of acetic acid and ammonium
acetate, the corresponding cycloalkylidene cyjanoethyl esters
were obtained. Treatment of the intermediate products with
potassium cyanide, followed by a hydrolysis, furnished the
respective acids. The final N-substituted spirosuccinimides
(1a–j and 2a–j) were obtained in a one-pot cyclization reac-
tion of the prepared acids and appropriately substituted ben-
zylamines or phenylhydrazines by heating them at ca. 190–
200 °C for 1.5–2 h (Scheme 1).
Scheme 1. Synthesis and structures of 2-azaspiro[4.4]nonane- (1a–1j) and
Compounds 1j, 2a and 2j had been previously described
by El-Telbany et al. [21,22] (no 1H-NMR data are available),
but none of them were tested for their anticonvulsant activity.
Products 1b–i and 2b–i are the new ones.
2-azaspiro[4.5]decane-1,3-dione (2a–2j) derivatives.
and 0.02 mol of cyclopentane-1-carboxy-1-acetic acid or
cyclohexane-1-carboxy-1-acetic acid was gradually added.
The mixture was heated in an oil bath with the simultaneous
distillation of water.After the water was completely removed,
the temperature of the reaction mixture was raised up to 190–
200 °C and maintained for 1.5 h. Crude products were recrys-
tallized from a 96% ethanol.
3. Experimental
3.1. Chemistry
The chemical structures of the obtained compounds were
confirmed by elemental and spectral analyses (1H-NMR, IR).
1H-NMR spectra were determined on a Varian Mercury
300 MHz spectrometer, in CDCl3 with TMS as an internal
standard.All chemical shifts are given in d values. Signal mul-
tiplicities are represented by the following abbreviations: s
(singlets), m (multiplets). IR spectra were recorded with a
Fourier transform spectrometer FT/IR-410 (Jasco Corp.,
Japan) using KBr discs. Elemental analyses (C, H, N) were
within 0.4% of the theoretical values.
The purity of all the synthesized compounds was checked
by a thin-layer chromatography performed on Merck Silica
gel GF254 aluminum plates, using the following systems: A.
chloroform/acetone (9:1), B. ethyl acetate/n-hexane (3:7).
After developing chromatograms, the plates were inspected
under UV light (k = 254 nm), and spots were additionally
visualized with 0.05 mol I2 in a 10% HCl solution. Melting
points (°C) are uncorrected.
3.1.1.1. N-benzyl-2-azaspiro[4.4]nonane-1,3-dione (1a)2.
(Yield: 65%); m.p. 58–60 °C3; Rf = 0.79A, Rf = 0.45B,
1H-NMR (CDCl3) d (ppm) 1.58–2.13 (m, 8H, cyclopentane),
2.58 (s, 2H, imide), 4.65 (s, 2H, CH2), 7.23–7.36 (m, 4H,
arom.); IR m (cm–1) 1773, 16914 (C=O), Anal. C15H16O2N1
(C, H, N).
3.1.1.2. N-(2-chlorobenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1b). (Yield: 55%); m.p. 72–74 °C; Rf = 0.86A,
1
Rf = 0.43B, H-NMR (CDCl3) d (ppm) 1.58–2.20 (m, 8H,
cyclopentane), 2.65 (s, 2H, imide), 4.79 (s, 2H, CH2), 7.08–
7.37 (m, 4H, arom.); IR m (cm–1) 1772, 1698 (C=O), Anal.
C15H16O2N1Cl1 (C, H, N).
3.1.1.3. N-(2,4-dichlorobenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1c). (Yield: 59%); m.p. 79–81 °C; Rf = 0.91A,
1
Rf = 0.49B, H-NMR (CDCl3) d (ppm) 1.59–2.21 (m, 8H,
cyclopentane), 2.68 (s, 2H, imide), 4.78 (s, 2H, CH2), 7.18–
7.42 (m, 3H, arom.); IR m (cm–1) 1773, 1709 (C=O), Anal.
C15H15O2N1Cl2 (C, H, N).
3.1.1. General procedure for the preparation of N-benzyl-
or N-aminophenyl-2-azaspiro[4.4]nonane- (1a–j)
and 2-aza-spiro[4.5]decane-1,3-dione (2a–j) derivatives
A total of 0.02 mol of the appropriately substituted benzy-
lamine or phenylhydrazine was dissolved in 25 ml of water,
2 Reference [10].
3 63.5 °C.
1 Compound 1a was earlier described in ref. [10].
4 1780 (C=O), 1715 (C=O).

J. Obniska et al. / Il Farmaco 60 (2005) 529–539
531
3.1.1.4. N-(3-chlorobenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1d). (Yield: 65%); m.p. 97–99 °C; Rf = 0.88A,
Rf = 0.38B, H-NMR (CDCl3) d (ppm) 1.61–2.20 (m, 8H,
3.1.1.12. N-(2-chlorobenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2b). (Yield: 62%); m.p. 100–102 °C; Rf = 0.86A,
Rf = 0.50B, H-NMR (CDCl3) d (ppm) 1.32–1.88 (m, 10H,
1
1
cyclohexane), 2.62 (s, 2H, imide), 4.77 (s, 2H, CH2), 7.06–
7.36 (m, 4H, arom.); IR m (cm–1) 1777, 1707 (C=O), Anal.
C16H18O2N1Cl1 (C, H, N).
cyclopentane), 2.53 (s, 2H, imide), 4.65 (s, 2H, CH2), 7.27–
7.37 (m, 4H, arom.); IR m (cm–1) 1772, 1700 (C=O), Anal.
C15H16O2N1Cl1 (C, H, N).
3.1.1.13. N-(2,4-dichlorobenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2c). (Yield: 63%), m.p. 88–90 °C; Rf = 0.85A,
Rf = 0.47B H-NMR (CDCl3) d (ppm) 1.28–1.88 (m, 10H,
cyclohexane), 2.60 (s, 2H, imide), 4.72 (s, 2H, CH2), 7.06–
7.37 (m, 3H, aromat); IR m (cm–1) 1775, 1693 (C=O), Anal.
C16H17O2N1Cl2 (C, H, N).
3.1.1.5. N-(4-chlorobenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1e). (Yield: 65%); m.p. 92–94 °C; Rf = 0.84A,
Rf = 0.41B, H-NMR (CDCl3) d (ppm) 1.57–2.12 (m, 8H,
cyclopentane), 2.57 (s, 2H, imide), 4.60 (s, 2H, CH2), 7.27–
7.32 (m, 4H, arom.); IR m (cm–1) 1772, 1701 (C=O), Anal.
C15H16O2N1Cl1 (C, H, N).
1
1
3.1.1.14. N-(3-chlorobenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2d). (Yield: 69%), m.p. 108–109 °C; Rf = 0.89A,
Rf = 0.59B, H-NMR (CDCl3) d (ppm) 1.25–2.20 (m, 10H,
cyclohexane), 2.60 (s, 2H, imide), 4.63 (s, 2H, CH2), 7.23–
7.35 (m, 4H, arom.); IR m (cm–1) 1772, 1702 (C=O), Anal.
C16H18O2N1Cl1 (C, H, N).
3.1.1.6. N-(2-methylbenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1f). (Yield: 68%); m.p. 76–78 °C; Rf = 0.88A,
Rf = 0.55B, H-NMR (CDCl3) d (ppm) 1.59–2.19 (m, 8H,
cyclopentane), 2.46 (s, 3H, CH3), 2.66 (s, 2H, imide), 4.71
(s, 2H, CH2), 7.16–7.20 (m, 4H, arom.); IR m 1773, 1698
(C=O), Anal. C16H19O2N1 (C, H, N).
1
1
3.1.1.15. N-(4-chlorobenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2e). (Yield: 67%); m.p. 112–114 °C; Rf = 0.84A,
Rf = 0.38B, H-NMR (CDCl3) d (ppm) 1.24–1.83 (m, 10H,
cyclohexane), 2.53 (s, 2H, imide), 4.58 (s, 2H, CH2), 7.23–
7.30 (m, 4H, arom.); IR m (cm–1) 1773, 1689 (C=O), Anal.
C16H18O2N1Cl1 (C, H, N).
3.1.1.7. N-(4-methylbenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1g). (Yield: 58%); m.p. 78–80 °C; Rf = 0.90A,
Rf = 0.54B, H-NMR (CDCl3) d (ppm) 1.57–2.13 (m, 8H,
cyclopentane), 2.30 (s, 3H, CH3), 2.56 (s, 2H, imide), 4.60
(s, 2H, CH2), 7.09–7.11 (d, 2H, aromat, J = 7.98 Hz), 7.23–
7.26 (d, 2H arom. J = 7.70 Hz); IR m (cm–1) 1772, 1701 (C=O),
Anal. C15H19O2N1 (C, H, N).
1
1
3.1.1.16. N-(2-methylbenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2f). (Yield: 62%); m.p. 94–96 °C; Rf = 0.90A,
3.1.1.8. 2-(2-Methoxybenzyl)-2-azaspiro[4.4]nonane-1,3-
1
Rf = 0.55B, H-NMR (CDCl3) d (ppm) 1.32–1.92 (m, 10H,
dione (1h). (Yield: 62%); m.p. 58–60 °C; Rf = 0.85A,
cyclohexane), 2.44 (s, 3H, CH3) 2.62 (s, 2H, imide), 4.69 (s,
2H, CH2), 7.13–7.29 (m, 4H, arom.), IR m (cm–1) 1771, 1696
(C=O), Anal. C17H21O2N1 (C, H, N).
1
Rf = 0.47B, H-NMR (CDCl3) d (ppm) 1.62–2.15 (m, 8H,
cyclopentane), 2.60 (s, 2H, imide), 3.82 (s, 3H, OCH3), 4.71
(s, 2H, CH2), 6.83–7.22 (m, 4H, arom.); IR m (cm–1) 1772,
1690 (C=O), Anal. C15H19O3N1 (C, H, N).
3.1.1.17. N-(4-methylbenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2g). (Yield: 69%); m.p. 72–74 °C; Rf = 0.91A,
3.1.1.9. N-(4-methoxybenzyl)-2-azaspiro[4.4]nonane-1,3-
dione (1i). (Yield: 56%); m.p. 69–71 °C; Rf = 0.81A,
1
Rf = 0.54B, H-NMR (CDCl3) d (ppm) 1.28–1.84 (m, 10H,
cyclohexane), 2.30 (s, 3H, CH3) 2.53 (s, 2H, imide), 4.58 (s,
2H, CH2), 7.08–7.23 (m, 4H, arom.); IR m (cm–1) 1773, 1703
(C=O), Anal. C17H21O2N1 (C, H, N).
1
Rf = 0.40B, H-NMR (CDCl3) d (ppm) 1.56–2.12 (m, 8H,
cyclopentane), 2.55 (s, 2H, imide), 3.77 (s, 3H, OCH3), 4.58
(s, 2H, CH2), 6.79–7.32 (m, 4H, arom.); IR m (cm–1) 1769,
1706 (C=O), Anal. C15H19O3N1 (C, H, N).
3.1.1.18. 2-(2-Methoxybenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2h). (Yield: 65%); m.p. 120–122 °C; Rf = 0.84A,
Rf = 0.38B H-NMR (CDCl3) d (ppm) 1.27–1.88 (m, 10H,
1
3.1.1.10. N-aminophenyl-2-azaspiro[4.4]nonane-1,3-dione
(1j). (Yield: 68%); m.p. 124–126 °C; Rf = 0.61A, Rf = 0.19B,
1H-NMR (CDCl3) d (ppm) 1.71–2.23 (m, 8H, cyclopentane),
2.69 (s, 2H, imide), 6.25 (s, 1H, NH), 6.73–7.27 (m, 5H,
arom.); IR m (cm–1) 1791, 1715 (C=O), Anal. C14H16O2N2
(C, H, N).
cyclohexane), 2.57 (s, 2H, imide), 3.81 (s, 3H, OCH3), 4.68
(s, 2H, CH2), 6.82–6.89 (dd, 2H, arom. J = 7.80 Hz), 7.01–
7.04 (d, 1H, arom. J = 7.42 Hz), 7.19-7.24 (t, 1H, arom.
J = 7.0 Hz); IR m (cm–1) 1773, 1710 (C=O), Anal. C17H21O3N1
(C, H, N).
3.1.1.11. N-benzyl-2-azaspiro[4.5]decane-1,3-dione (2a).
(Yield: 52%), m.p. 49–51 °C, Rf = 0.86A, Rf = 0.53B, H-
NMR (CDCl3) d (ppm) 1.21–1.85 (m, 10H, cyclohexane),
2.54 (s, 2H, imide), 4.63 (s, 2H, CH2), 7.23–7.33 (m, 5H,
arom.); IR m (cm–1) 1773, 1697 (C=O), Anal. C16H19O2N1
(C, H, N).
3.1.1.19. N-(4-methoxybenzyl)-2-azaspiro[4.5]decane-1,3-
dione (2i). (Yield: 53%); m.p. 88–90 °C; Rf = 0.80A,
Rf = 0.44B; 1H-NMR (CDCl3) d (ppm) 1.23–1.82 (m, 10H,
cyclohexane), 2.51 (s, 2H, imide), 3.76 (s, 3H, OCH3), 4.55
(s, 2H, CH2), 6.79–7.29 (m, 4H, arom.); IR m (cm–1) 1773,
1689 (C=O), Anal. C17H21O3N1 (C, H, N).
1

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J. Obniska et al. / Il Farmaco 60 (2005) 529–539
3.1.1.20. N-aminophenyl-2-azaspiro[4.5]decane-1,3-dione
(2j). (Yield: 60%); m.p. 114–116 °C; Rf = 0.65A, Rf = 0.23B;
1H-NMR (CDCl3) d (ppm) 1.33–1.94 (m, 10H, cyclohex-
ane), 2.64 (s, 2H, imide), 6.290 (s, 1H, NH), 6.71–7.23 (m,
5H, arom.); IR m (cm–1) 1793, 1715 (C=O), Anal. C15H18O2N2
(C, H, N).
100 mg kg–1 (class 2), inactive at 300 mg kg–1 (class 3). The
results of preliminary screening are presented in Tables 1 and
2.
Promising compounds from phase I underwent phaseVIa.
The compounds were administrated orally into rats using four
animals at a fixed dose of 30 mg kg–1 for both the MES and
the rotorod toxicity tests. Rats were tested at five times period
ranging from one quarter to 4 h post drug administration. The
rats classification are as follows: 4/4 of the animals protected
(class 4), 3/4 of the animals protected (class 3), 2/4 of the
animals protected (class 2), 1/4 of the animals protected (class
1). The results are shown in Table 3.
Compound 1j, which was active in mice and rats, was quan-
titatively evaluated in phase II of theADD program. The quan-
titative determination of the median effective (ED50) and toxic
doses (TD50) were conducted at previously calculated time
of peak effect using oral route in rats. Groups of eight rats
received various doses of the compound until at least two
points were established between the limits of 100% protec-
tion or toxicity and 0% protection or minimal toxicity. The
dose of the compounds required to produce the desired end-
point (abolition of hindlimb tonic extensor) in 50% of the
animals in each test, and 95% confidence interval were cal-
culated by computer program based on the method described
previously [25]. The results of quantitative pharmacological
studies are presented in Table 4.
3.2. Pharmacology
Compounds 1a–j and 2a–j were pharmacologically pre-
evaluated within the antiepileptic drug development (ADD)
program (Epilepsy Branch, Neurological Disorders Pro-
gram, National Institute of the Neurological and Communi-
cative Disorders and Stroke (NINCDS), Bethesda,) using pro-
cedures described elsewhere [23,24].
Phase I studies of the investigated compounds involved
three tests: maximum electroshock seizure (MES), subcuta-
neous pentylenetetrazole (sc.MET) and a rotorod test for neu-
rological toxicity (TOX). Male albino mice (CF#1 strain,
weighing 18–25 g) and male albino rats (Sprague–Dawley,
weighing 100–150 g) were used as experimental animals.
In the MES test, an electrical stimulus of 0.2 s in duration
(50 mA) was delivered via corneal electrodes primed with an
electrolyte solution containing an anesthetic agent. Mice were
tested using the following doses 30, 100 and 300 mg kg–1 of
investigated compounds. The compounds were injected intra-
peritoneally as a suspension in a 0.5% methylcellulose/water
mixture, in a volume of 0.01 ml g–1 body weight for mice and
0.04 ml g–1 body weight for rats. In the MES seizure test one
animal was used at 30 and 300 mg kg–1 and three animals at
100 mg kg–1. Abolition of the hindlimb tonic extensor com-
ponent indicates the test compound’s ability to inhibit MES-
induced seizure spread.
The sc.MET test utilizes of pentylenetetrazole (85 mg kg–1
in mice and 70 mg kg–1 in rats). This produce clonic seizures
lasting for a period of at least five seconds in 97% (CD97) of
animals tested. At the anticipated time of testing the pentyle-
netetrazole was administrated subcutaneously. The tested
compounds were dissolved in 0.9% saline and injected intra-
peritoneally at a volume of 0.01 ml g–1 body weight in mice
and 0.04 ml g–1 in rats. Animals were observed over a 30 min
period. Absence of clonic seizure in the observed time of
period indicated an ability of compounds to abolish the effect
of pentylenetetrazole on seizure threshold.
3.3. X-ray structure analysis
An X-ray structure analysis was carried out for the selected
compounds 1a, 1j, 2a and 2j. It is noteworthy that the struc-
ture of 1a had been described earlier [28]. In the present paper,
that structure was determined a new for the structural unifi-
cation of results.
All the monocrystals were obtained by slowly evaporating
the ethanol solution. The measurements of crystals were per-
formed on a Kuma4CCD j-axis diffractometer with graphite-
monochromated MoKa radiation (k = 0.71073 Å) [26] at a
room temperature. All the crystallographic data and experi-
mental details are presented in Table 5. The structures were
solved by a direct method using the SHELXTS [27] program
and refined with SHELXTL [28].
An E-map provided positions for all non-H-atoms. The
full-matrix least-squares refinement was carried out on F2′s
using anisotropic temperature factors for all non-H-atoms.
The H-atoms were located geometrically then the positions
of H-atoms were refined in a riding model with isotropic ther-
mal parameters taken as 1.5 times the temperature factors for
their parent-atoms. Atomic coordinates are shown in
Table 6a,6b.
A neurological toxicity test (TOX) induced by a com-
pound was detected in mice using standardized rotorod test.
Untreated control mice, when placed on a 6 rpm rotation rod,
can maintain their equilibrium for a prolonged period of time.
Neurological impairment can be demonstrated by the inabil-
ity of mice to maintain equilibrium for 1 min in each of three
successive trials. For these experiments four animals were
used at 30 and 300 mg kg–1 and eight at 100 mg kg–1.
According to theADD program activity of the compounds
was classed with the following categories: active at doses of
100 mg kg–1 or less (class 1), active at doses greater than
3.4. Computational procedures
The geometry of molecules of 1a, 2a, 1j and 2j (starting
with the crystallographically obtained geometry) was opti-
mized with the Gaussian98 using rhf/6-311 ++ (d,p) [29].

J. Obniska et al. / Il Farmaco 60 (2005) 529–539
533
Table 1
Anticonvulsant screening project (ASP) phase I in mice (1a–j)
Compound
Dose
MES a
sc.MET b
TOX c
4 h
ASP d class
3
(mg kg–1
)
0.5 h
0/1
0/3
0/1
0/1
0/3
1/1
0/1
0/3
1/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
1/1
0/1
0/3
0/1
0/1
0/3
1/1
0/1
0/3
0/1
0/1
1/3
1/1
4 h
0.5 h
0/1
0/1
0/1
0/1
0/1
2/5
0/1
0/1
2/5
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
5/5
0/1
0/1
0/1
0/1
0/1
1/1
4 h
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
1/5
0/1
0/1
0.5 h
0/4
0/8
0/4
0/4
0/8
2/4
0/4
0/8
2/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
4/414
0/4
0/8
1/4
0/4
0/8
4/414
1a e
30
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
100
300
30
1b
1c
1d
1e
1f
2
2
3
3
2
3
2
3
1
100
300
30
100
300
30
100
300
30
100
300
30
100
300
30
1g
1h
1i
100
300
30
100
300
30
100
300
30
1j
100
300
Response comments 14 unable to grasp rotorod.
a Maximal electroshock test (number of animals protected/number of animals tested).
b Subcutaneous pentylenetetrazole test (number of animals protected/number of animal tested.
c Rotorod toxicity (number of animals exhibiting toxicity/number of animals tested).
d The classification as follows: 1 – anticonvulsant activity at doses 100 mg kg–1 or less; 2 – anticonvulsant activity at doses greater than 100 mg kg–1; 3 –
compound inactive at 300 mg kg–1
e Data from Ref. [10].
.
4. Results and discussion
vulsant activity, probably due to an unfavorable steric inter-
action.
The synthesized derivatives of N-benzyl and N-amino-
phenyl 2-azaspiro[4.4]nonane (1a–j) and [4.5]decane-1,3-
dione (2a–j) showed diversified anticonvulsant properties.
In the first part of our study we investigated the substitu-
tion mode in the aryl ring of the 2-azaspiro[4.4]nonane-1,3-
dione set as compared to that of the model compound 1a.
Considering our earlier experiments, introduction of a sub-
stituent into position-2 should enhance activity. Such an effect
was observed for 2-Cl (1b), 2-CH3 (1f) and 2-OCH3 (1h)
derivatives, which demonstrated activity at a dose of
300 mg kg–1 (1/1 of the animals protected at 0.5 h) in the
MES test and were more active than the unsubstituted analog
1a. Additionally, compounds 1b and 1h were active at dose
of 300 mg kg–1 (5/5 of the animals protected at 0.5 h) in the
sc.MET test. Derivatives that contained 3-Cl (1d), 4-Cl (1e),
4-CH3 (1g) and 4-OCH3 (1i) groups were devoid of anticon-
Next, to have an insight into the physicochemical influ-
ence of the size of a spirocycloalkyl unit, we designed a set
of 2-azaspiro[4.5]decane analogues with the same substitu-
ents in the aryl ring. The unsubstituted compound 2a and its
2-Cl derivative 2b were active at doses of 100 mg kg–1 (2/3 of
the animals protected at 0.5 h) and 300 mg kg–1 (1/1 of the
animals protected at 4 h) in the MES test. Moreover, com-
pound 2a exhibited anti-sc.MET activity at doses of 100 and
300 mg kg–1 (1/5 and 1/1 of the animals protected at 0.5 h,
respectively), and 2b at a dose of 300 mg kg–1 (1/1 of the
animals protected at 0.5 and 4 h). The 2,4-dichloro derivative
2c was effective in the MES procedure at doses of 100 and
300 mg kg–1 (3/3 and 1/1 of the animals protected at 4 h).
Thus, the introduction of a spirocyclohexane moiety had a
positive effect on anticonvulsant activity in the case of unsub-
stituted (2a), 2-Cl substituted (2b) and 2,4-dichloro deriva-

534
J. Obniska et al. / Il Farmaco 60 (2005) 529–539
Table 2
ASP phase I in mice (2a–j)
Compound Dose (mg kg–1
)
MES a
4 h
sc.MET b
TOX c
4 h
ASP d class
1
0.5 h
0/1
2/3
1/1
0/1
2/3
1/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0.5 h
0/1
1/5
1/1
0/1
0/1
1/125
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
4/5
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
4/525
4 h
0/1
0/1
0/1
0/1
0/1
1/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0/1
0.5 h
0/4
3/8
4/4
0/4
4/8
4/4
0/4
2/8
2/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
0/4
0/4
0/8
3/4
2a
2b
2c
2d
2e
2f
30
0/1
0/3
1/1
0/1
0/3
1/1
0/1
3/3
1/1
0/1
0/3
0/1
0/1
0/3
1/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/1
0/3
0/1
0/2
0/4
0/2
0/2
0/4
1/2
0/2
0/4
1/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
0/2
0/4
0/2
100
300
30
1
1
3
2
3
3
3
3
2
100
300
30
100
300
30
100
300
30
100
300
30
100
300
30
2g
2h
2i
100
300
30
100
300
30
100
300
30
2j
100
300
Response comments 25myoclonic yerks.
a Maximal electroshock test (number of animals protected/number of animals tested).
b Subcutaneous pentylenetetrazole test (number of animals protected/number of animals tested).
c Rotorod toxicity (number of animals exhibiting toxicity/number of animals tested).
d The classification as follows: 1 – anticonvulsant activity at doses 100 mg kg–1 or less; 2 – anticonvulsant activity at doses greater than 100 mg kg–1; 3 –
compound inactive at 300 mg kg–1
.
Table 3
ASP phase VIa. Test results in rats (p.o. administration at a dose of 30 mg kg–1
)
Compound
MES a
TOX b
1 h
0.25 h
1/4
0.5 h
1/4
0/4
1/4
0/4
0/4
0/4
1/4
1 h
2 h
1/4
0/4
3/4
0/4
1/4
0/4
0/4
4 h
1/4
0/4
3/4
1/4
0/4
0/4
2/4
0.25 h
0/4
0.5 h
0/4
0/4
0/4
0/4
0/4
0/4
0/4
2 h
0/4
0/4
0/4
0/4
0/4
0/4
0/4
4 h
0/4
0/4
0/4
0/4
0/4
0/4
0/4
1b
1f
1j
2a
2b
2c
2e
1/4
0/4
1/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
4/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
a Maximal electroshock test, number of animals protected/number of animals tested.
b Rotorod test for neurological toxicity, number of animals exhibiting toxicity/number of animals tested.
tives (ASP class 1). In contrast, the activity of 2-CH3 (2f) and
2-OCH3 (2h) derivatives was decreased in comparison with
their cyclopentane analogues. Surprisingly, increased anti-
convulsant activity was observed in the case of the 4-Cl deriva-
tive (2e), which was potent at a dose of 300 mg kg–1 (1/1 of
the animals protected at 0.5 h) in the MES test, and at the
same dose in the sc.MET tests (4/5 of the animals protected
at 4 h). As was expected, the 4-substituted compounds 2g
and 2i were inactive.
Finally, we chose model unsubstituted compounds (1a and
2a) and altered the linker between the imide moiety and the
aromatic ring. The introduction of an imine group (NH)
instead of a methylene joining arm yielded N-aminophenyl-
2-azaspiro[4.4]nonane-1,3-dione (1j). The latter compound

J. Obniska et al. / Il Farmaco 60 (2005) 529–539
535
Table 4
Quantitative anticonvulsant data in rats dosed orally a (phase II ASP)
Compound
1j
Phenytoin e
ED50 b MES (mg kg–1
72.61 (47.86–100.27)
29.8 (21.9–38.9)
)
ED50 b sc.MET (mg kg–1
)
TD50 c (mg kg–1
> 250
)
PI d MES (TD50/ED50
)
TPE e MES (h)
< 250
3.44
0.25
4
> 800
> 3000
> 100
a Pharmacological values given in this Table are follows.
b The ED50 dose of drug required to assure anticonvulsant protection in 50% animals.
c The TD50 dose eliciting minimal neurological toxicity in 50% animals.
d The PI, protection index. e) The TPE, time to peak effect.
e Data on phenytoin are from Ref. H.S. White, J.H. Woodhead, M.R. Franklin, General principles: experimental selection, quantification and evaluation of
anticonvulsant drugs, in: R. Levy, Mattson, B.S. Meldrum (Eds.), Antiepileptic Drugs, fourth ed., Raven Press, New York, 1995, pp. 99–110.
Table 5
Crystal data and structure refinement details for 1a, 1j, and 2a, 2j
1a
1j
2a
2j
Empirical formula
C15H17NO2
C14H16N2O2
C16H19NO2
C15H18N2O2
Formula weight
243.30
244.29
Monoclinic
P21/c
257.32
Monoclinic
P21/n
258.31
Monoclinic
C2/c
Crystal system
Monoclinic
P21/n
Space group
a (Å)
13.377(3)
6.599(1)
14.976(3)
90.00
11.161(2)
6.389(1)
17.32 (3)
90.00
14.040(3)
6.760(10)
15.280 (3)
90.00
24.530(5)
6.152(1)
18.071(4)
90.00
b (Å)
c (Å)
␣ (°)
b (°)
101.00(3)
90.00
96.20(3)
90.00
102.72(3)
90.00
91.90(3)
90.00
c (°)
Volume (Å)3
z
1297.5(4)
4
1226.4(4)
4
1414.6(5)
4
2725.6(9)
8
Calculated density (g m–3
Wavelength (Å)
Absorption coefficient (mm–1
F(000)
)
1.245
1.329
1.208
1.259
MoKa 0.07093
0.083
)
0.090
0.079
0.085
520
520
552
1104
Reflections cool./unique
Data/parameters
5881/1198
1198/164
3.10 ÷ 20.00
–12 < h < 12
–6 < k < 6
–13 < l < 14
1.085
5454/2147
2147/164
3.41 ÷ 24.99
–13 < h < 11
–7 < k < 7
–20 < l < 20
0.963
14,330/2481
2481/173
2.97 ÷ 25.00
–16 < h < 16
–7 < k < 8
–18 < l < 18
1.059
3582/1719
1791/173
3.41 ÷ 25.50
–26 < h < 26
0 < k < 6
0 < l < 19
0.967
Theta range data (°)
Index ranges
S
R1
R1 = 0.059
wR2 = 0.1389
0.010(2)
0.118; –0.138
R1 =0.054
wR2 = 0.095
0.013(2)
R1 = 0.058
wR2 = 0.1055
0.026(3)
R1 = 0.077
wR2 = 0.130
0.00
wR2
Extinction
Largest difference in peak and hole (eÅ–3
)
0.168; –0.151
0.117; –0.139
0.212; –0.193
was active at doses of 30 mg kg–1 (1/5 of the animals pro-
tected at 4 h) and 300 mg kg–1 (1/1 of the animals protected
at 0.5 h) in the sc.MET test, and also was active at doses of
100 and 300 mg kg–1 in the MES test (1/3 and 1/1 of the
animals protected at 0.5 h, respectively). Compound 2j was
effective at a dose of 300 mg kg–1 (4/5 of the animals pro-
tected at 0.5 h), in the sc.MET test, but at the same dose it
produced myoclonic jerks. Therefore, the simple modifica-
tion led to an increase in activity in the case of the 5-membered
spirocyclopentane ring (1j), but the same procedure did not
significantly influence the activity of the respective spirocy-
clohexane analogue (2j).
1,3-diones, compounds 2a–c showed neurotoxicity at a dose
of 100 mg kg–1 at 0.5 h.
Further pharmacological investigation was concerned with
an oral evaluation of the anti-MES and the neurotoxic activ-
ity (phase VIa) of the selected compounds 1b, 1f, 1j, 2a–c
and 2e in rats. Those compounds were administered per os at
a dose of 30 mg kg–1, and their effects were studied after
0.25, 0.5, 1, 2, and 4 h. Compound 1b protected 25% of the
animals at all time period, 2e also inhibited seizure in 25% of
animals at 0.5 and 1 h, and in 50% of animals at 4 h. Com-
pounds 1f, 2a and 2b exhibited only marginal activity in this
test. The 2,4-dichloro substituted derivative 2c, which was
active in mice (class 1 ASP) turned out to be inactive in rats.
The most active, in this series, compound 1j protected 100%
(4/4) of the animals at 0.25 h, and 75% (3/4) of the animals
tested at 2 h and 4 h. When given orally, none of the tested
compounds was neurotoxic.
In a neurological toxicity screening test compounds 1b,
1c and 1h–j showed neurotoxicity at the higher dose
(300 mg kg–1) after 0.5 h. The mice were unable to grasp the
rotorod after administration of 1h and 1j at a dose of
300 mg kg–1 at 0.5 h. In a series of 2-aza-spiro[4.5]decane-

536
J. Obniska et al. / Il Farmaco 60 (2005) 529–539
Table 6a
Atomic coordinates (×104) and equivalent isotropic displacement parameters (Å2 × 103) for 1a and 2a. U(eq) is defined as one third of the trace of the
orthogonalized Uij tensor
Compound 1a
z
Compound 2a
x
y
U(eq)
41(1)
48(1)
62(1)
65(1)
43(1)
41(1)
53(1)
48(1)
61(1)
88(2)
71(2)
54(1)
40(1)
49(1)
65(2)
79(2)
79(2)
61(1)
x
y
z
U(eq)
45(1)
54(1)
64(1)
68(1)
45(1)
43(1)
59(1)
50(1)
60(1)
70(1)
83(1)
82(1)
61(1)
50(1)
60(1)
83(1)
103(2)
104(2)
78(1)
N(1)
1461(3)
1009(3)
2976(2)
182(2)
2230(5)
3640(6)
1723(4)
2347(4)
1359(7)
–123(6)
406(7)
1723(6)
–77(7)
5902(2)
6462(3)
6878(2)
4647(2)
6162(3)
5443(3)
4640(3)
5016(3)
5230(3)
N(1)
3574(2)
006(2)
2350(3)
3736(4)
1972(3)
2299(3)
1554(4)
109(4)
–916(2)
–451(2)
–875(1)
305(1)
C(20)
O(1)
C(20)
O(1)
2082(1)
4858(2)
2646(2)
2477(2)
3402(2)
4049(2)
1542(2)
1297(2)
1158(3)
2094(3)
2375(2)
4726(2)
4595(2)
5263(3)
6066(3)
6206(3)
5530(3)
O(2)
O(2)
C(2)
2410(3)
2582(3)
1728(3)
1013(4)
3652(3)
3798(4)
3044(4)
2490(3)
263(3)
C(2)
–178(2)
–468(2)
287(2)
C(3)
C(3)
C(4)
C(4)
324(5)
C(5)
C(5)
1735(4)
653(5)
–67(2)
C(11)
C(12)
C(13)
C(14)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(11)
C(12)
C(13)
C(14)
C(15)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
–155(2)
472(2)
–2151(8)
–3554(7)
–2290(6)
2701(7)
756(7)
4812(4)
5152(3)
5767(3)
6969(3)
7318(3)
7821(3)
7988(3)
7642(4)
7136(3)
–924(6)
–2939(6)
–3528(5)
–1961(4)
2768(5)
869(5)
13(3)
–286(2)
–903(2)
–910(2)
–254(2)
–697(2)
–787(3)
–454(3)
–009(2)
394(3)
–284(4)
–1090(4)
–1215(4)
–39(4)
–42(8)
1122(10)
3076(9)
3864(7)
33(6)
1110(10)
3003(9)
3853(6)
Table 6b
Atomic coordinates (× 104) and equivalent isotropic displacement parameters (Å2 × 103) for 1j and 2j. U(eq) is defined as one third of the trace of the
orthogonalized Uij tensor
Compound 1j
z
Compound 2j
x
y
U(eq)
43(1)
64(1)
56(1)
72(1)
39(1)
33(1)
44(1)
45(1)
48(1)
81(1)
63(1)
44(1)
39(1)
48(1)
57(1)
66(1)
65(1)
50(1)
x
y
z
U(eq)
38(1)
59(2)
53(1)
67(2)
44(2)
40(2)
51(2)
38(2)
58(2)
92(3)
91(3)
72(2)
59(2)
49(2)
61(2)
84(3)
77(2)
67(2)
41(2)
N(1)
4672(2)
5636(2)
4117(2)
4663(2)
3978(3)
3051(3)
3138(3)
4230(3)
1791(3)
1168(3)
2126(3)
3325(3)
6807(3)
7086(3)
8273(3)
9167(3)
8878(3)
7702(3)
2888(4)
4127(4)
1830(4)
3772(4)
1778(5)
545(5)
1126(2)
973(2)
N(1)
2356(2)
1806(2)
2645(2)
2284(2)
2750(2)
3276(2)
3155(2)
2562(3)
3723(3)
4292(3)
4443(3)
4044(3)
3463(3)
1456(3)
919(3)
3004(7)
3205(9)
1807(7)
4847(7)
2326(10)
2467(10)
3780(10)
3977(10)
3575(11)
3416(16)
1128(17)
–14(11)
107(11)
1722(12)
2333(12)
962(16)
–999(15)
–602(12)
–221(10)
1457(3
1621(3)
2589(3)
352(2)
N(2)
N(2)
O(1)
–121(1)
2409(2)
560(2)
O(1)
O(2)
O(2)
C(2)
C(2)
1970(4)
1588(3)
908(3)
C(3)
940(2)
C(3)
C(4)
1441(5)
2822(5)
659(5)
1767(2)
1848(2)
493(2)
C(4)
C(5)
C(5)
842(4)
C(11)
C(12)
C(13)
C(14)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(11)
C(12)
C(13)
C(14)
C(15)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
2125(3)
1828(4)
1657(4)
1115(4)
1415(3)
1256(3)
1223(4)
918(4)
–330(6)
–861(6)
–817(5)
3536(5)
1581(5)
1103(6)
2560(7)
4519(7)
5026(5)
701(3)
999(2)
927(2)
1261(2)
1552(2)
1814(2)
1784(2)
1493(2)
1233(2)
527(3)
687(4)
615(4)
1222(3)
1601(2)
644(4)
956(3)
Compound 1j was chosen for phase II evaluation to quan-
tify its anticonvulsant activity and neurotoxicity. In the
sc.MET test 1j was active at a dose greater than 250 mg kg–1.
In the MES test, a median effective dose (ED50
= 72.6 mg kg–1) was recorded. The tested compound had its
TD50 value higher than 250 mg kg–1, and showed a protec-
tive index (PI) value of 3.44. The time to peak effect (TPE)
was 0.25 h.
which had a different type of the linker (X = imine or meth-
ylene) and the size of a spirocycloalkyl moiety were selected
for an X-ray analysis. First of all, the most active compound
1j and its spirocyclohexane analogue 2j were chosen. Then,
the respective analogues 1a and 2a with a methylene linker
were selected for crystallographic and molecular structure
studies.
The molecules of 1a, 1j, 2a and 2j, together with the
observed sequences of H-bonds in the crystal, are shown in
Fig. 1. In the structures of those compounds, the undulated
five-member succinimide ring was the crucial fragment.After
In view of structure and activity studies (SAR), it was of
special interest to study the 3-D structures of the representa-
tive derivatives. To cover the structural diversity, compounds

J. Obniska et al. / Il Farmaco 60 (2005) 529–539
537
Fig. 1
.
The molecules of 1a (a), 2a (b), 1j (c) and 2j (d) together with observed sequences of H-bonds in the crystal.
Table 7
Selected geometrical and electronic data from 1a, 2a, 1j and 2j molecules
Compound
a) Succinimide ring description
Bond lengths (Å)
Parameter d a (°)
X–C21
R angles at N1 (°)
MEP (eV mol–1
)
N1–X
O1
O2
X = CH2
1a
2a
356.9
360.0
1.458 (5)
1.461 (2)
1.498 (5)
1.502 (4)
0.031 (4)
–22.353
–22.355
–22.353
–22.351
0.013 (3)
X = NH
1j
2j
359.7
358.1
1.384 (3);
1.396 (3)
1.399 (4)
1.403 (7)
0.047 (3)
0.111 (6)
–22.353
–22.349
–22.347
–22.355
b) H-bonds in the crystal
H··A (Å)
D–H A (sym. code)
D–H (Å)
D··A (Å)
D–H··A (°)
Strong H-bonds
1j
2j
N2–H2···O1 [–x + 1, –y + 1, –z]
0.90
0.90
2.14
2.999(4)
2.938(7)
159.6
116.2
N2–H2···O1 [–x + 1/2, y + 1/2, –z + 1/2]
2.43
Weak H-bond
2.41
1a
2a
C20–H20B···O2 [–x, 1 – y, 1 – z]
C20–H20B···O2 [1 – x, 1 – y, –z]
0.96
1.00
3.362(5)
3.402(4)
170.2
163.7
2.43
a For definition see Fig. 2.
a careful analysis, it was found that all the important differ-
ences in this ring were connected with the X-linker variation.
That was easily visualized by two subsequent descriptors: the
N1–X bonds length (Table 7) and the value of the d param-
eter describing the out-of-plane deviation of N1 (Table 7 and
Fig. 2). In N-aminophenyl-derivatives (1j, 2j), the linking

538
J. Obniska et al. / Il Farmaco 60 (2005) 529–539
Subsequent studies will be published shortly.
Acknowledgements
The authors wish to thank Dr. James Stables for providing
them with pharmacological data within theAntiepileptic Drug
Development Program (Epilepsy Branch, National Institute
of Neurological Disorders and Stroke National Institute of
Health Bethesda, MD, USA).
This study was supported by the KBN grand No. 3P05F
024.
Fig. 2. Parameter d defining out-of-plane deviation for N1; X = NH, CH2.
atom N2 adopted planar configuration, and the free electron
pair from the N1 atom in the molecule of 1j had slightly stron-
ger contribution to the N1–N2 bond conjugation, than that in
2j. In the case of the N-benzyl analogues 1a, 2a (X = CH2),
only a typical bond length in the linker was found.
In both crystals of the N-aminophenyl derivatives (1j, 2j),
the main H-bond motive was always based on N2–
H2···O1 strong interactions (Table 7). However, the crystal
nets were different. In the crystal of 1j, dimer formation
(Fig. 1c) was a direct result of those interactions, while in the
crystal of 2j molecules were arranged in one chain (Fig. 1d).
For details see Table 7. In the crystals of N-benzyl derivatives
(X = CH2), the main motive has created dimers with weak H-
bonds of C20–H20B···O2 (Table 7 and Fig. 1a, b).
Subsequently, an electrostatic potential (MEP) at the
respective oxygen atoms (Table 7) was calculated for all crys-
tallographically studied compounds (ab initio calculations)
[29]. It was established that, in the molecule of 1j, the MEP
minimum at O1 was deeper than that at O2. However, in mol-
ecule 2j, the respective minima depths were in inverse rela-
tion: the minimum at O2 was deeper than that at O1 (Table 7).
In the case of compounds 1a and 2a, the electrostatic poten-
tial MEP-values at two oxygen atoms O1 and O2 were almost
identical in either molecule (Table 7).
Supplementary material
Crystallographic data (excluding structural factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Center and allocated the
deposition numbers: CCDC 235191-235194 for compounds
1a, 1j, 2a and 2j. Copies of the data can be obtained free of
charge on application to the CCDC, 12 Union Road, Cam-
bridge CB2 1EW, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk).
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