SYNTHESIS AND 5-HT
1A/5-HT
2ARECEPTOR ACTIVITY OF NEW N-[3-(4-PHENYLPIPERAZIN-1-YL)-PROPYL]
DERIVATIVES OF 3-SPIRO-CYCLOHEXANEPYRROLIDI- NE-2,5-DIONE AND 3-SPIRO- b-TETRALONEPYRRO- LIDINE-2,5-DIONE
Jolanta Obniska
1, Maciej Paw³owski
1, Marcin Ko³aczkowski
1, Anna Czopek
1, Beata Duszyñska
2, Aleksandra K³odziñska
2, Ewa Tatarczyñska
2, Ewa Chojnacka-Wójcik
2,#Department of Medicinal Chemistry, Jagiellonian University Medical College, Medyczna 9, PL 30-688 Kraków, Institute of Pharmacology, Polish Academy of Sciences, Smêtna 12, PL 31-343 Kraków, Poland
Synthesis and 5-HT )/5-HT )receptor activity of new N-[3-(4-phenylpipe- razin-1-yl)-propyl] derivatives of 3-spiro-cyclohexanepyrrolidine-2,5-dione and 3-spiro-b-tetralonepyrrolidine-2,5-dione. J. OBNISKA, M. PAW£OW- SKI, M. KO£ACZKOWSKI, A. CZOPEK, B. DUSZYÑSKA, A. K£ODZIÑ- SKA, E. TATARCZYÑSKA, E. CHOJNACKA-WÓJCIK. Pol. J. Pharma- col., 2003, 55, 553–557.
Novel N-[3-(4-phenylpiperazin-1-yl)-propyl] derivatives of 3-spiro-cyclo- hexanepyrrolidine-2,5-dione (5–7) and 3-spiro-b-tetralonepyrrolidine-2,5- dione (8–10) were synthesized and their 5-HT )and 5-HT )receptor affini- ties were determined. All tested compounds exhibited moderate to low 5-HT ) receptor affinity, whereas compounds 5–7 demonstrated high 5-HT )receptor affinity (KE= 27, 46 and 15 nM, respectively) and features of 5-HT )receptor antagonists. Introduction of ab-tetralone fragment in the 3-position of pyrrolidine-2,5-dione ring (8–10) did not affect 5-HT )but de- creased 5-HT )receptor affinity.
Key words: 3-spiro-cyclohexanepyrrolidine-2,5-dione, 3-spiro-b-tetralone- pyrrolidine-2,5-dione, spirosuccinimides, arylpiperazines, 5-HT )and 5-HT ) receptor affinity, structure-activity relationship
ISSN 1230-6002
INTRODUCTION
Long chain arylpiperazines (LCAPs) are one of the largest and most diverse classes of compounds exerting actions on the central nervous system.
Their general chemical structure consists of the arylpiperazine moiety connected by an alkyl chain with the terminal amide or imide fragment. Mole- cules based on arylpiperazine core were classified as ligands of serotonin (5-HT),a-adrenergic or do- pamine receptors and some of them became clini- cally useful drugs in the treatment of anxiety, de- pression and psychosis as well as other psychiatric disorders. Although the role of the respective ele- ments of LCAPs was a subject of earlier studies [7–9], new modifications still result in obtaining compounds presenting interesting pharmacological properties.
In our previous studies [2, 3] we obtained a group of complex arylpiperazines in which the role of ter- minal amide was played by cyclohexanespiro- or b-tetralonespiro-derivatives of imidazolidine-2,4- dione. Some of the obtained compounds (1–3) shown in Figure 1 displayed high 5-HT2Aand low to moderate 5-HT1A receptor affinities [2, 3]. We also synthesized a series of 3-arylpyrrolidine-2,5-di-
one derivatives [10] which showed weak 5-HT1A/ 5-HT2Areceptor activity (4) (Fig. 1).
In the present study, for comparison with previ- ously obtained compounds, we have synthesized and tested two groups of LCAPs with 3-spiro- substituted pyrrolidine-2,5-dione as a terminal imide (Tab. 1). In 3-position of pyrrolidine-2,5-dione ring the first group contains spirocyclohexyl (5–7) and the second one spiro-b-tetralone moiety (8–10). All compounds were tested for their 5-HT1A/5-HT2A receptor affinity and for the most potent ones func- tional profile towards 5-HT2A receptor was deter- mined.
MATERIALS and METHODS
CHEMISTRY
The synthesis of compounds 5–10 is presented in Figure 2. The starting 1-carboxy-1-cyclohexa- ne-acetic acid was prepared according to the de- scribed procedure [11]. 3,4-Dihydro-1(2H)naphtha- lene-1-carboxy-1-acetic acid was obtained by the method described by Faust et al. [6]. The appropri- ately substituted 1-(3-aminopropyl)-4-phenylpipe-
1. Ki [nM]*: 5-HT1A= 17 ± 6, 5-HT2A= 133 ± 11 2. R=H Ki [nM]*: 5-HT1A= 70 ± 1, 5-HT2A= 34 ± 2 3. R=3-Cl Ki [nM]**: 5-HT1A= 96 ± 1, 5-HT2A= 17 ± 2 4. Ki [nM]#: 5-HT1A= 1069 ± 50, 5-HT2A= 268 ± 4
(CH2)3 N
N (CH2)3 N
N NH
N O O N R
H N
O O
(CH2)3 N N N
O O comp. 1
comp. 2, 3
comp. 4
Fig. 1. Chemical structure of compounds 1–4, *[2], **[3],[10]
razines were synthesized according to the previ- ously described method [1]. The compounds 5–10 were obtained by cyclization of the acids with 1-(3-aminopropyl)-4-phenylpiperazine derivatives by heating at temperature 180–200°C for 2 h. All the compounds 5–10 were isolated as the hydro- chloride salts and crystallized from ethanol.
General procedure for the preparation of the compounds 5–10
A total of 0.02 mol of the appropriately substi- tuted 1-(3-aminopropyl)-4-phenylpiperazine was dissolved in 25 ml of water, and 0.02 mol of the
1-carboxy-1-acetic acid or 3,4-dihydro-1(2H)naph- thalene-1-carboxy-1-acetic acid was gradually added.
The mixture was heated in an oil bath with simulta- neous distillation of water. After complete removal of water, the temperature of the reaction mixture was raised up to 180°C and maintained for 1.5 h.
The crude products were recrystallized from etha- nol. Free bases were converted into hydrochloride salts in anhydrous ethanol saturated with HCl gas.
The obtained precipitates were crystallized from ethanol.
The structure of the final compounds was con- firmed by1H NMR spectra and by elemental C, H,
A – cyclohexane or -tetraloneb O
O OH
OH + NH2 (CH2)3 N
N
R A
180-200°C
- H2O 5–10
Fig. 2. Synthesis of the new compounds 5–10
Table 1. Physicochemical data of new compounds 5–10
Comp. System A R M.p. (°C) Yield (%)
Cryst. solvent
Molecular formula*
Molecular weight
RB
5 6 7 8 9 10
cyclohexane
cyclohexane
cyclohexane b-tetralone b-tetralone b-tetralone
H
2-F
3-Cl
H
2-F
3-Cl
185–187
220–222
214–216
212–215
202–204
230–233
45 ethanol
63 ethanol
60 ethanol
52 ethanol
48 ethanol
50 ethanol
C H! ON!× HCl 405.97 C H! ON!F × HCl
423.96 C H! ON!Cl × HCl
440.41 C $H! ON!× HCl
454.01 C $H! ON!F × HCl
472.00 C $H! ON!Cl × HCl
488.47
0.89 S 0.36 S 0.87 S 0.42 S 0.89 S 0.43 S 0.86 S 0.73 S! 0.87 S 0.68 S! 0.92 S 0.79 S!
Solvent system: S chloroform : isopropanol: 25% ammonia (9:11:2), S benzene : ethyl acetate : acetone (10:5:1), S!n-butanol : ace- tic acid : water (5:4:1); * calculated from elemental analysis
O N O
(CH2)3 N N R A
× HCl
N analysis (see: supplementary materials). The pu- rity of the obtained compounds were checked by TLC on silica gel plates (Merck), and the spots were visualized in the UV light. Physicochemical data of compounds 5–10 are given in Table 1.
PHARMACOLOGY Binding experiments
Radioligand binding studies were carried out in a rat brain using hippocampus (5-HT1A receptors) and cortex (5-HT2A receptors) according to pub- lished procedures [1]. The used radioligands were [3H]-8-OH-DPAT (190 Ci/mmol, Amersham) and [3H]-ketanserin (60 Ci/mmol, NEN Chemicals) for 5-HT1Aand 5-HT2Areceptors, respectively. KEval- ues were determined on the basis of at least three competition binding experiments in which the tested compounds were used at concentrations between 1010– 103M, run in triplicate. KEvalues were cal- culated using the Cheng and Prusoff [4] equation.
In vivo experiments
The experiments were carried out on male Al- bino Swiss mice (25–30 g). The animals were kept at a room temperature of 20 ± 1°C and were housed under standard laboratory conditions with free ac- cess to food (standard laboratory pellets, LSM) and tap water before the experiment. All experiments were conducted in the light phase, on a natural light-dark cycle (from December to March) be- tween 9 a.m. and 2 p.m. All the experimental pro- cedures were approved by the Animal Care and Use Committee at the Institute of Pharmacology, Polish Academy of Sciences in Kraków. (±)-1-(2,5- Dimethoxy-4-iodophenyl)-2-aminopropane ((±)-DOI, Research Biochemicals, Inc.) and ketanserin (To- cris Cookson Ltd.) were dissolved in saline. The in- vestigated salts of the tested compounds were used in the form of freshly prepared suspensions in a 1%
Tween 80. (±)-DOI, ketanserin and the tested com- pounds were administered intraperitoneally (ip) in a volume of 10 ml/kg. Each group consisted of 9 animals. The obtained data were analyzed by Dunnett’s test.
Head twitches in mice
In order to habituate the mice to the experimen- tal environment, each animal was randomly trans- ferred to a 12 cm (diameter) × 20 cm (height) glass
cage, lined with sawdust, 30 min prior to treatment.
Head twitches in mice were induced by (±)-DOI (2.5 mg/kg). Immediately after the treatment the number of head twitches was counted for 30 min [5]. The tested compounds or saline were adminis- tered 60 min before (±)-DOI. The doses inhibiting the effect of (±)-DOI were expressed as ED50and were calculated from three doses using a standard method.
RESULTS and DISCUSSION As seen in Table 2, the tested compounds 5–10 showed moderate to low 5-HT1A receptor affinity (Ki from 106 to 535 nM) but some of them (5–7) exhibited a high 5-HT2A receptor affinity (Ki = 15–46 nM). The results of radioligand binding studies indicate that introduction of spirocyclo- hexyl moiety in 3 position of pyrrolidine-2,5-dione ring (5–7) increased receptor affinity, especially to- wards 5-HT2Areceptor subtype in comparison with previously obtained 3-phenyl derivatives [10]. Ad- ditionally, it seems that introduction of a supple- mentary aromatic ring to the spirocyclohexyl moi- ety (8–10) did not change 5-HT1A but decreased 5-HT2A receptor affinity. This suggests that the 3-spirocyclohexane ring in pyrrolidine-2,5-dione (5–7) is tolerated better than b-tetralone (8–10) fragment at 5-HT2Abinding sites.
Table 2. The 5-HT )and 5-HT )receptor affinities of the in- vestigated compounds 5–10
Compound KE± SEM (nM)
5-HT ) 5-HT )
5 535 ± 30 27 ± 3
6 368 ± 75 46 ± 12
7 106 ± 12 15 ± 2
8 480 ± 13 132 ± 18
9 424 ± 20 506 ± 12
10 251 ± 18 264 ± 43
Ketanserin* 1933 ± 219 1.5 ± 0.2
* [12]
The next step of our investigation was concen- trated on the in vivo functional effects induced by some selected compounds. As already mentioned derivatives 5–7 demonstrated a high affinity for 5-HT2Areceptors. For that reason the ability of 5–7
and ketanserin, a well-known 5-HT2Areceptor an- tagonist, to reduce head twitches in mice, observed after administration of (±)-DOI, a 5-HT2Areceptor agonist [5] was used to evaluate 5-HT2A receptor antagonistic properties. Results presented in Tab- le 3 indicate that compounds 5–7, as well as the ref- erence drug ketanserin effectively inhibited the (±)-DOI-induced head twitches in mice with ED50 values of derivatives 5–7 ranging between 4.5–9.7 mg/kg, hence they may be classified as 5-HT2Are- ceptor antagonists. However, the tested novel de- rivatives were significantly less potent than ketan- serin in inhibition of (±)-DOI-induced effect in mice.
and ketanserin, a well-known 5-HT2Areceptor an- tagonist, to reduce head twitches in mice, observed after administration of (±)-DOI, a 5-HT2Areceptor agonist [5] was used to evaluate 5-HT2A receptor antagonistic properties. Results presented in Tab- le 3 indicate that compounds 5–7, as well as the ref- erence drug ketanserin effectively inhibited the (±)-DOI-induced head twitches in mice with ED50 values of derivatives 5–7 ranging between 4.5–9.7 mg/kg, hence they may be classified as 5-HT2Are- ceptor antagonists. However, the tested novel de- rivatives were significantly less potent than ketan- serin in inhibition of (±)-DOI-induced effect in mice.
Table 3. The effects of the investigated compounds on the (±)-DOI-induced head-twitch response in mice
Compound ED# =(mg/kg, ip) 5
6 7 Ketanserin
9.7 (6.9–13.7)>
4.8 (3.3–7.0) 4.5 (3.3–6.1) 0.14 (0.07–0.02)
=ED# – the dose inhibiting the head twitches in mice by 50%.
>Confidence limits (90%) given in parenthesis. The investi- gated compounds were administered ip 60 min before (±)-DOI (2.5 mg/kg, ip)
In conclusion, the present results showed that introduction of spirocyclohexane moiety in posi- tion 3 of pyrrolidine-2,5-dione leads to the ligands with higher 5-HT2Areceptor affinity, also in com- parison to 3-phenyl-derivative (4) obtained earlier [10]. It has been found thatb-tetralone ring in 3-po- sition (8–10) does not change 5-HT1Areceptor af- finity in comparison to their 3-phenyl analogues although significantly decreases 5-HT2A receptor affinity.
Acknowledgment. This study was supported by the State Committee for Scientific Research, grant no. 4PO5FO3517, Warszawa, Poland.
REFERENCES
1. Bojarski A.J., Ceg³a M.T., Charakchieva-Minol S., Mokrosz M.J., Maækowiak M., Misztal S., Mokrosz J.L.: Structure-activity relationship studies of CNS agents. Part 9. 5-HT )and 5-HT )receptor affinity of
some 2- and 3-substituted 1,2,3,4-tetrahydro-b-carbo- lines. Pharmazie, 1993, 48, 289–294.
2. Byrtus H., Paw³owski M., Charakchieva-Minol S., Duszyñska B., Mokrosz M.J., Mokrosz J.L., Zejc A.:
3-(w-Aminoalkyl)-5,5-dialkyl (or spirocycloalkyl-1’,5-) hydantoins as new 5-HT ) and 5-HT ) receptor li- gands. Arch. Pharm. Pharm. Med. Chem., 1996, 329, 283–290.
3. Byrtus H., Paw³owski M., Duszyñska B., Weso³owska A., Chojnacka-Wójcik E., Bojarski A.J.: Arylopipera- zine derivatives of 3-propyl-b-tetralonohydantoin as new 5-HT )and 5-HT )receptor ligands. Pol. J. Phar- macol., 2001, 53, 395–401.
4. Cheng Y., Prusoff W.H.: Relationships between the in- hibition constant (Ki) and the concentration of inhibi- tor which causes 50 percent inhibition (I# ) of an enzy- matic reaction. Biochem. Pharmacol., 1973, 22, 3099–
3108.
5. Darmani N.A., Martin B.R., Pandey V., Glennon R.A.:
Do functional relationships exist between 5-HT )and 5-HT )receptors? Pharmacol. Biochem. Behav., 1990, 36, 901–906.
6. Faust J.A., Jules L.H., Yee L., Sahyun M.: Anticon- vulsants: spirohydantoines and derivatives of tetrahy- dronaphthalene. J. Amer. Pharmacol. Assoc., 1957, 46, 118–124.
7. Glennon R.A., Dukat M.: Serotonin receptors and ligands. In: Psychopharmacology: The Fourth Genera- tion of Progress; Eds. Bloom F.E., Kupfer D.J., Raven Press, New York, 1999, CD-ROM edn.
8. López-Rodriguez M.L., Morcillo M.J., Rovat T.K., Fernandez E., Vicente B., Sanz A.M., Hernandez M., Orensanz L.: Synthesis and structure-activity relation- ships of a new model of arylpiperazine. 4. 1-[Omega- (4-arylpiperazin-1-yl)-alkyl]-3-(diphenylmethylene)- 2,5-pyrrolidinediones and 3-(9H-fluoren-9-ylidene)- 2,5-pyrrolidinediones: study of the steric requirements of the terminal amide fragment on 5-HT )affinity/se- lectivity. J. Med. Chem., 1999, 42, 36–49.
9. Oh S.J., Chi D.Y., Lee H.K.: Serotonin receptor and transporter ligands – current status. Curr. Med. Chem., 2001, 8, 999–1034.
10. Paw³owski M., Ch³oñ G., Obniska J., Zejc A., Charak- chieva-Minol S., Mokrosz M.J.: Synthesis, 5-HT ) and 5-HT )receptor affinity of new 1-phenylpiperazi- nylpropyl derivatives of purine-2,6- and pyrrolidine- 2,5-diones. Farmaco, 2000, 55, 461–468.
11. Scott K.R., Moore J.A., Zalucky T.B., Nicholson J.M.:
Spiro[4.5] and spiro[4.6]carboxylic acids: cyclic analo- gues of valproic acid. J. Med. Chem., 1985, 28, 413–417.
12. Titeler M., Lyon R.A., Davis K.H., Glennon R.A.: Se- lectivity of serotonergic drugs for multiple brain sero- tonin receptors, role of [!H]-4-bromo-2,5-dimethoxy- phenylisopropylamine ([!H]DOB), a 5-HT agonist ra- dioligand. Biochem. Pharmacol., 1987, 36, 3265–3271.
Received: April 29, 2003; in revised form: June 25, 2003.
