239
J . Med. Chem. 1987,30, 239-249 Table I. Opioid Antagonist Activity of Bimorphinans in the GPI and MVD agonist ICKnratio' f SEU antagonist morphineb ethylketazocine* DADLE' la 1.6 i 0.4 50.4 f 9.9 2.0 f 0.1 lb 5.4 i 1.3 128.1 f 16.6 4.5 i 0.7 2 (naltrexone) 17.3 2.9 nThe IC5ovalue of agonist in presence of antagonist (20 nM) divided by the control IC6ovalue (no antagonist) in the same preparation ( N = 6 for la and lb). *Determined in the GPI preparation. cDetermined in the MVD preparation.
Registry No. la, 105618-26-6; l b , 105618-27-7; 2.HC1, 16676-29-2;NH2NH2,302-01-2; NH2NHMe, 60-34-4. f
Department of Medicinal Chemistry.
* Department of Pharmacology.
P. S. Portoghese,*t A. W. Lipkowski; A. E.Takemorif Department of Medicinal Chemistry College of Pharmacy Department of Pharmacology Medical School University of Minnesota Minneapolis, Minnesota 55455
for his advice a n d assistance. W e also t h a n k Dr. I a n J a r d i n e for determining the FAB-MS of la.
Received September 5, 1986
Articles Synthesis and Structure-Activity Relationships of a Series of Aminopyridazine Derivatives of y-Aminobutyric Acid Acting as Selective GABA-A Antagonists Camille-Georges Wermuth,*t Jean-Jacques Bourguignon,? Gilbert Schlewer,+ Jean-Pierre Gies,? AngGle Schoenfelder,? Anita Melikian,? Marie-Jeanne Bouchet,? Dominique Chantreux,f Jean-Charles Molimard,t Michel Heaulme,$ Jean-Pierre Chambon,t a n d Kathleen Bizierez Dgpartement de Pharmacochimie Molgculaire, Centre de Neurochimie d u CNRS, UniversitZ Louis Pasteur, 67084 Strasbourg CZdex, France, and Centre de Recherches CLIN-MIDY, Groupe Sanofi, 34082 Montpellier Cgdex, France. Received May 12, 1986
We have recently shown that an arylaminopyridazine derivative of GABA, SR 95103 [2-(3-carboxypropyl)-3amino-4-methyl-6-phenylpyridaziniumchloride], is a selective and competitive GABA-A receptor antagonist. In order to further explore the structural requirements for GABA receptor affinity, we synthesized a series of 38 compounds by attaching various pyridazinic structures to GABA or GABA-like side chains. Most of the compounds displaced [3H]GABAfrom rat brain membranes. All the active compounds antagonized the GABA-elicited enhancement of [3H]diazepambinding, strongly suggesting that all these compounds are GABA-A receptor antagonists. None of the compounds that displaced [3H]GABAfrom rat brain membranes interacted with other GABA recognition sites (GABA-B receptor, GABA uptake binding site, glutamate decarboxylase,GABA-transaminase). They did not interact with the C1- ionophore associated with the GABA-A receptor and did not interact with the benzodiazepine, strychnine, and glutamate binding sites. Thus, these compounds appear to be specific GABA-A receptor antagonists. In terms of structure-activity, it can be concluded that a GABA moiety bearing a positive charge is necessary for optimal GABA-A receptor recognition. Additional binding sites are tolerated only if they are part of a charge-delocalized amidinic or guanidinic system. If this delocalization is achieved by linking a butyric acid moiety to the N(2) nitrogen of a 3-aminopyridazine, GABA-antagonisticcharacter is produced. The highest potency (-250 times bicuculline) was observed when an aromatic ?r system, bearing electron-donating substituents, was present on the 6-position of the pyridazine ring.
It is well-known that N-alkylation of t h e central neurotransmitter y-aminobutyric acid (GABA) leads t o a n almost complete loss of affinity for the GABA receptor site. T h i s has been observed with monosubstituted derivatives such as N-methyl-GABAl a n d N-butyl- or N-phenethylGABA,2 disubstituted derivatives such a s N,N-dipropylGABA or 4-pyrrolidinobutyric acid (Table I), a n d quaternary ammonium salts such as N,N,N-trimethyl-GABA.2 A similar detrimental effect has been described for muscimo1.l However, if a secondary amino function is present in a cyclic structure as in piperidine-4-carboxylic acid, some affinity (IC,o = 15 pM') for t h e GABA-A receptor is recovered. O t h e r cyclic secondary amines derived from flexible GABA agonists such as isoguvacine, piperidine4-sulfonic acid, a n d THIP (4,5,6,7-tetrahydroisoxazolot
DBpartement de Pharmacochimie MolBculaire. Centre de Recherches CLIN-MIDY, Groupe Sanofi.
[5,4-c]pyridin-3-01) even possess high a f f i n i t i e ~ . For ~ these cyclic analogues, again, N-methylation strongly weakens t h e p ~ t e n c y .These ~ observations suggest that ligands for t h e GABA receptors are sensitive t o steric hindrance at t h e proximity of t h e cationic moiety of t h e molecule a n d t h a t the primary or secondary structure of the amino group is of minor importance. N-Acylation of GABA also led t o poorly active compounds in t e r m s of receptor binding a5 shown for N-lauroyl-GABA4 or for N-t-BOC-GABA a n d
(1) Krogsgaard-Larsen, P.; Johnston, G. A. R. J. Neurochem. 1978, 30, 1377. (2) Breckenridge,R. J.; Nicholson, S. H.; Nicol, A. J.; Suckling, C. J.; Leigh, B.; Iversen, L. J. Neurochem. 1981, 37, 837. (3) Falch, E.; Krogsgaard-Larsen, P.; Jacobsen, P.; Engesgaard, A.; Braestrup, C.; Curtis, D. R. Eur. J. Med. Chem.-Chim. Ther. 1985, 20, 447.
0022-2623/87/1830-0239$01.50/00 1987 American Chemical Society
240 Journal of Medicinal Chemistry, 1987, Vol. 30, No. 2
Wermuth et al.
Table 1. Chemical Data and GABA Receptor Affinities of Compound SR 95103 (lo),Analogues with Modified Side Chains, and Reference Compounds
%; \
"2
*o
Rl
starting pyridazone compd lit. ref R R1 crystn solvent mp, "C formula (anal.) 10 11,60 (CHz)3C02H CHB AcOH-Et20 238 C15H18N302Cl (C, H, N) 11 11, 60 (CHZ)3COzEt CH3 EtOH >260 Cl7HzZN3O2Br (C, H, N) 12 11, 60 (CHz)3CONHz CH3 i-PrOH 119 C1~H1~N,O*HzO (C, H, N) 13 11, 60 (CHZ)sC=N CH3 i-PrOH a C15H17N4Br (C, H, N) 14 11, 60 CHZCOzH CH3 AcOH-Et20 240' CI3Hl4N3O2 (C, H, N) 15 11,60 CH3 AcOH (CH2)ZCOzH >210' C14H16N302Br (C, H, N) 16 11, 60 i-PrOH CH3 (CHz)4COzH C16HzoN,OzCl (C, H, N, C1) 214 17 11, 60 (CH2)5COzH CH, i-PrOH 197 Cl7HzZN3O2Br (C, H, N) 18 11,60 i-PrOH-HzO (CH2)&H(CH3)COZH CH, 175 CI6Hz0N3O2Br (C, H, N) 19 11, 60 i-PrOH-HzO CH(CH3)(CHz)zC02H CH3 180 CI6HzON3OzBr (C,' H, N) (CHz)&=N 20 60 H i-PrOH a C14H15N4Br (C, H, N) 21 61, 62 C6H5 i-PrOH (CH2)JkN a C20H,,N,Br (C, H, N) N-di-n-propyl-GABA i-PrOH-EtzO 125 CloHz2NOZCl (C, H, N) 4-pyrrolidinobutyric acid i-PrOH 127d c~H16NOzC1 (C, H, N) 4-ureidobutyric acid N-t-BOC-GABA bicuculline methiodide iso-THAZ R 5135 Hygroscopic. 'Decomposition. cC: calcd, 52.68; found, 53.40. dLiterature: 127 0C.67
"\> N/H HzN (CH,),-COOH \
K,, & I 2.3 >lo0
91 20 62 7 10 12.7 7 9 91 91 >lo0 >lo0
--
100
100 38 50
0.047
"*S HzN
H Nr>(CH2). /
LCOOH
g
S
\\
'COOH
H
/
dNHi H N-COOH
-9
N3
Figure 1. Amidinic and guanidinic GABA-mimetic compounds. IC5ovalues for the inhibition of [3H]GABA binding (pM): a = 2.1;2 b = 1.84or 26.6: c = 29.Q2d = 18.Q6e = 0.g4or 0 ~ 5f;= ~ 2w2g = 68.Q2 i = 9.0s~' (Kivalue). Ki value for the sodium-dependent synaptosomal uptake (pM):i = 8.' K, value for the inhibition of GABA-transaminase (pM): h = 91.' ureidobutyric acid (Table I). However, N-benzoyl- a n d N-pivaloyl-GABA exhibit some anticonvulsant activity in animals5 presumably because they act as prodrugs of GABA. Unexpectedly, t h e incorporation of t h e amino group of GABA in a n amidinic system such as t h a t found in
guanidinoacetic acid (a)6 and guanidinopropionic acid (b)4 a n d N-(thio(Figure 1) or in S-thioureylacetic acid ( c ) ~ carbamoy1)glycine (d)' or even in cyclic amidines like imidazoleacetic (e) a n d imidazolepropionic (f) or (2aminothiazol-4-y1)acetic acid (g)2restores the affinity for t h e GABA-A receptor site, a n d reasonable ICso values, in
(4) Olsen, R. W.; Ticku, M. K.; Greenlee, D.; Van Ness, P. In GABA-Neurotransmitters, Pharmacochemical, Biochemical and Pharmacological Aspects; Krogsgaard-Larsen, P., Scheel-Kriiger, J., Kofold, H., Eds.; Munksgaard Copenhagen, 1979; p 168. (5) Galzigna, L.; Garbin, L.; Bianchi, M.; Marzotto, A. Arch. Int. Pharmacodyn. Ther. 1978,235, 73.
(6) Iversen, L. L.; Bird, E,; Spokes, E.; Nicholson, S. H.; Suckling, C. J. In GABA-Neurotransmitters, Pharmacochemical, Biochemical and Pharmacological Aspects; Krogsgaard-Larsen, P., Scheel-Kruger, J., Kofold, H., Eds.; Munksgaard: Copenhagen, 1979; p 180. (7) Tunnicliff, G.; Welborn, K. L.; Ngo, T. T. Gen. Pharmacol. 1985, 16, 25.
Journal of Medicinal Chemistry, 1987, Vol. 30, No. 2 241
Aminopyridazine Derivatives of y-Aminobutyric Acid
'
,HCI
H
Figure 2. Structure of minaprine (left) and of SR 95103 (right).
-Ld
%
B
I
Bicuculline
\
CH,, N CH,'aC
iso-THAZ
H,
, 2c1-
Tubocurarine
0 I
OH
Socurinin.
R 5135
Pitrrropino
Figure 3. GABA antagonists at the GABA-A receptor site. Scheme I"
"2
I NH-NH,
NH,
CI'
R1 II
Ivb
vb
HzNNHz, BuOH, reflux. b: Hz-Raney Ni-MeOH. c: ",OH, 28%; NH4C1;autoclave. d: Br(CHz),COzEt, DMF, 60 "C. e: HBr (48%)-AcOH, 100 "C. f KZCO8-H20. g: HCl (36%)- AcOH, 100 "C. h: (1)2 N NaOH; (2) HCl, 36%. "a:
the micromolar range, have been observed for these compounds. Two other amidinic compounds, phenylthiohydantoic acid (h)8and 4-[(4-azidobenzoimidyl)amino]butanoic acid (i),gJOhave also been shown to possess notable affinity for GABA recognition sites such as GABAa-ketoglutarate transaminase (GABA-T) or the GABA uptake system, respectively. Finally, the potent (but not selective) synthetic GABA antagonist R 5135 contains an
endo-exocyclic amidinic system carried by a steroid skeleton (Figure 3).11 Taken together, these observations suggest that N-substitution, even by bulky substituents, is tolerated if it is part of a charge-delocalized amidinic or guanidinic system. Previous studies from our group on minaprine (Figure 2), an antidepressant containing a 3-aminopyridazinic s t r u ~ t u r e , had ~ ~ -demonstrated ~~ that this compound and
(8) Tunnicliff, G. 14th Annual Meeting of the Society of Neuroscience, Anaheim, CA, October 10-15, 1984; Abstracts, Vol. 10, Part 2, 286.10, p 974. (9) Tunnicliff, G.; Smith, J. A. Neurochem. Int. 1981, 3, 371. (10) Tunnicliff, G.; Ngo, T. T. J. Neurochem. 1982, 39, 998.
(11) Hunt, P.; Clements-Jewery, S. Neuropharmacology 1981,20,
357. (12) Wermuth, C. G.; Exinger, A. Agressologie 1972, I 3 ( 5 ) , 285. (13) Biziere, K.; Kan, J. P.; Souilhac, J.; Muyard, J. P.; Roncucci, R. ArtneimA'orsch. (Drug Res.) 1982, 3211, 8, 824.
242 Journal of Medicinal Chemistry, 1987, Vol. 30, No, 2
Wermuth et al.
Scheme 11. Pyridazinone Syntheses
-1
2-
"
3-
OH
H
.To 7a 7_b - RR :: ci-Bu -C~H,,
-J
+
O
yo 7
its analogues also presented an endo-exo amidinic charge delocalization16and prompted us to link the butyric chain of GABA to a 6-phenyl-4-methyl-3-aminopyridazine. The resulting GABA derivative, SR 95103 (Figure 2, compound 10, Table I), displaced [3H]GABAfrom rat brain membranes with an apparent Ki of 2.2 yM and was shown, on the basis of biochemical, electrophysiological, and pharmacological results, to be a selective and competitive antagonist of GABA at the GABA-A receptor site.16 The object of the present study is to describe the synthesis and to examine the structure-activity relationships of a series of compounds structurally related to SR 95103. Chemistry Direct alkylation of the exo-endo amidinic system of the 3-aminopyridazines I11 with ethyl 4-bromobutyrate or its homologues followed by hydrolysis in acidic medium yielded the endo-substituted isomers V (Scheme I). The acetic acid derivative 14 (Table I) was obtained by reacting the triethylammonium salt of bromoacetic acid in acetone with 3-amino-4-methyl-6-phenylpyridazine. The same reaction performed with 4-bromobutyronitrile yielded the cyano analogues 13,20, and 21 (Table I) and, after partial hydrolysis, the primary amide 12. The starting 3-aminopyridazines I11 were obtained from the corresponding 3chloropyridazines I either by direct substitution with ammonia or by catalytic hydrogenolysis of the 3-hydrazinopyridazines II.17 Quaternizations of 3-aminopyridazines have been examined by Lund and Lunde, with use of 'H NMR.I8 Alkylation generally led to a mixture of N(1)(14) Wermuth, C. G. Actual. Chim. Ther. 1985,12,3. (15) Michel, A.;Gustin, R.; Evrard, G.; Durant, F. Bull. SOC.Chim. Belg. 1982,91,49. (16) Chambon, J. P.; Feltz, P.; Heaulme, M.; Restle, S.; Schlichter, R.; Biziere, K.; Wermuth, C. G. h o c . Natl. Acad. Sci. U.S.A. 1986,82,1832. (17) Murakami, H.; Castle, R. N. J. Heterocycl. Chem. 1967,4,555.
and N(2)-alkyl derivatives in a ratio of 1:1, and no alkylation on the exo amino group was observed. However, when a phenyl group was present at the 6-position (111,R1 = R2 = H, R3 = C6H5),tpe amount of the N(1)-alkylated derivative was considerablydecreased (
