140 Posters / European Journal of Pharmaceutical Sciences 2 (1994) 117-194

P85 HIGHLY POTENT AND SELECTIVE HISTAMINE H3-RECEPTOR ANTAGONISTS K. Purand 1, H. Stark1, X. Ligneau2, M. Garbarg2, J.-C. Schwartz2, W. Schunaekf 1 Institut for Pharmazie, Frsie UniversitAt Berlin, 14195 Bedin, Germany 2 Unitti de Neurobiologie et Pharrnscologis, Centre Paul Broca de I'INSERM, 75014 Paris, France

A new subtype of histamine receptors, named H3-receptor, was found 1983 in the rat brain cortex by Arrang et al. [1]. Lateron this receptor was also identified in the pedphery in different species and tissues. This presynaptically located receptor regulates the synthesis and the release of histamine. Furthermore it acts as a heteroreceptor on serotoninergic, cholinergic, dopaminergic, adrenergic and peptidergic nerve endings. For the characterization of this receptor and its role in physiological function it is necessary to have highly potent and selective ligands. Additionally it seems to be an interesting field for the development of new drugs for treatment of several diseases like migraine, psychatnc disorders or epilepsia. We prepared new H3-receptor antagonists different to thioperamide [2], which is a potent and selective antagonist with a -log K i value of 8.4 and a EDso of 1 .O mg/kg (p.o., mice). The disadvantage of thioperamide is its liver toxicity which may depend on the thiourea moiety. Therefore we replaced this thiourea group by a carbamate moiety.

S

H H

Thioperamide Carbaunates

The synthesis stads from atkyl- or substituted and unsubstituted ary[isocyanates treated with 3-(1H-imidazol-4-yl)propanol [3]. The isocyanates were yielded by the reaction of the corresponding amines with diphosgene (tnchloromethyl ch[oroformate), which is a liquid substitute for gaseous phosgene. We received antagonists, which are highly potent in vitro with -log Ki values between 7 and 8 and with low affinity to Hi- and H2-receptors. Some of these compounds are still more potent in vivo than thioperamide, In conclusion, the urethanes are a new class of histamine H3-receptor antagonists, which are highly potent and selective.

[1] J.-M. Arrang. M. GarbaffJ and J.-C. Schwartz, Nature (London) 1983, 302, 832-837. [21 J.-M. Arran9, M. Garbacg, J.-C. Lar~elot, J.-M. Lecomta, H. Polt~rd, M. Robba, W. Schur,.ack and J :C.

Schwartz, Nature (London) 1987, .527,117-123. [3] J.-C. Schwartz, J.-M. Arrang, M. Garbarg, J.-M. Lecomta, R.C. Ganelfin, A. Fkyerat, W. Tertiuk, W.

Schunack, R. Lipp, H. Stark and K. Purand, Fr. Pat. Appt. FR 2 686 084 (10.1.1992).

Supported by the Biomedical and Health Research Pmgrarnme EEC BMHT1 CT92-1087

P86 NOVEL HISTAMINE H3-RECEPTOR ANTAGONISTS: AFRNITIES IN AN H3-RECEPTOR BINDING ASSAY AND POTENCIES IN TWO FUNCTIONAL H3-RECEPTOR MODELS M. Kathmannl, E. Schlicker 1, S. Reidemeistar2, H. Stark2, W. Schunsck2 1 tnstitut flit Pharmakologie und Toxikologie, Universit~l Bonn, 53113 Bonn, Germany 2 Institut flit Pharmazie, Freie Universit&t Berlin, 14195 Berlin, Germany

We studied the effects of ten compounds in which the side chain of histamine (1) is . NO n replaced by a propyl or butyl chain linked t 2 NH2 - - - -

H 0 to a polar group (annde, thioanude, ester, OH=)~-n ~-NH-CH= guanidine, guanidine ester or urea), 2 3 .H- which, in turn, is connected to a ring 3 3 ~-eo-(e~=)2~ ] containing alkyl residue. For comparison, the standard H 3 receptor antagonist thioperamide (which differentiates between the H3A and H3B receptors, postulated by West ¢t al. 1990) was used. The affinities were determined in rat brain cortex homogenates, in whic.Ja the displacement of the specific [3H]-Na-methylhistamine binding by the test drugs was examined. The potencies were determined in superfusod mouse brain cortex slices (preineubated with [3H]- noradrenalinc) and in guinea-pig ileum strips. We examined the antagonism of the test drugs and of tluopcramide against the inhibitory effect of histatmnc on the electrically evoked tritium overflow (mouse brain cortex; H3A receptor model) and of the H 3 receptor agonist R-(-)-a-methylhistamine on the electrically induced contractions (guinea-pig ileum). The novel compounds displaced [3HJ-Na-mcthylhistamine binding monophasicaUy at pK i values ranging from 7.56 to 8.68, whereas thioperamide produced a biphasic displacement. In the functional models, all compounds proved to be antagonists, exhibiting pA 2 values ranging from 7.07 to 9.20 (mouse brain) and from 6.64 to 8.81 (guinea-pig ileum). The pA 2 values in the two functional models were significantly correlated. The pA 2 values in either functional model were significantly correlated to their pK i values in the binding assay if the pK i of thioperamide for H3A binding sites (8.31) was considered but not when its pK i for H3B sites (7.19) was used instead. Compound 2 proved to be the most potent one in each of the three models. If the basic capacity of the guanidino moiety was attenuated by substitution with a t-butoxy-carbonyl group, a compound with lower affinity and potency was obtained. The amide 3 exhibited a pK i of 7.63 and pA 2 values of 7.18 (mouse brain) and 7.21 (guinea-pig ileum). Similar values were obtained (i) for the corresponding thioamide, and (ii) when the cyclopentyl residue was replaced by a norbomyl ring. In conclusion, potent H 3 receptor antagonists are obtained if the histamine molecule is modified in the aforementioned way. The H 3 receptor in the guinea-pig ileum (like that in the mouse brain) may belong to the H3A subclass.

P87 2-(3-TRIFLUOROMETHYLPHENYL)HISTAMINE AND 2-(3-BROMOPHENYL)HISTAMINE AS THE MOST POTENT HISTAMINE H1 AGONISTS C. Leschke, S. EIz, W. Schunack Institute of Pharmacy, Free University of Berlin, 14195 Bedin, Germany

P88 RECEPTOR-INDEPENDENT G-PROTEIN ACTIVATION BY 2-SUBSTITUTED HISTAMINES H. Detert I , A. Hagel0ken 2, C. Leschke 1 , B. NiJmberg 2, R. Seifert 2, W. Schuneck 1 1 Institut for Pharmazie, Freie Universit~t Bedin, 14195 Bedin, Germany 2 Institut f0r Pharmakologie, Freie Universit~t Berlin, 14195 Berlin, Germany

The study of the histamine H1 receptor mediated effects is limited by the lack of potent and selective

H 1 agonists [1,2]. Some years ago ZINGEL showed, that the met&position of 2-phenylhistamine is

important for Ht agonistic activity. /n vitro 2-(3-fluoro- and chlorophenyl)histamine contracted the

segments of guinea-pig ileum with the relaWe activity of 87 % or 81%, respectively [31.

Outgoing from these results many 2-hateroaromatic, 2-benzyl- and 2.phenylhistamine derivatives were

synthesized and screened in the standard assay on the isolated guinea-pig ileum and guinea-pig aorla

[41. The most potent Ht agonists were 2-(3-trifluoromethy~phenyt)histeroine (128 % rek act. on the ileum)

and 2-(3-bmmophenyl)histaroine (112 % rel. act. on the ileum). There was a good correlation between

PD2-vatues on the ileum and the pECso-values on the aorta assay. In the ileum assay both compounds

were full agoniats compared with histamine, but partial agonists in the aorta assay.

3 1 < ) NJI H H

2-(3-bro ,mophenyl)histamine 2-(3-trifluoromethyiphenyl)histamioe

The H1 receptor mediated nature of the response in both test systems was verified by experiments with

the H1 antagonist mepyramine (pKB range 8.9 - g.2). The affinites to the H1 receptor were more than

2000 times higher than to the H2 receptor (guinse-pig atrium} and over 50 times higher than to the H3

receptor (guinea-pig ileum).

[1] I. Sakuma, S. S. Gross and R. Levi, J. Pharmaco/. Exp. "/'her. 1988, 247, 466. [2] N. Toda, Circ. Res. 1987, 10, 129. [3] V. ZingeI, S. Elz and W. Schunack, Eur. J. Med. Chem. 1990, 25, 673. [4] C. Leschks, S. EIz, W. Schunack, XXllnd Annual Meeting of the European Histamine Research

Society, Cologne (Germany), May 19-22, 1993.

At this time, pharmacologically important possibilities to manipulate the G-protein-mediated signal

transduction cascade are mainly activation of receptors by selective agonists and blocking of receptors by

antagonists. Current investigations of various research groups open a new pathway: certain cationic-

amphiphilio compounds activate G-protains directly, i. e, independently ot receptor activation. Recently,

we have shown that 2-(3-halogenpheny~)histamines activate perlussis toxin-sensitive G-prcteins of the

Gi-subfamily in HL-60 cells by a mechanism which is independent of known histamine receptor subtypes

(Seifert et al., Me/. Pharmaco/. 45, 578, 1994). These results prompted us to study the structure-activity

relationships of 2-substitutad histamines concerning G-protein activation. The relatiye potency of

2-phenylhistamines on GTP-hydrolysis in HL-60 membranes increases with increasing volume of the

halogene and with the length of the alkyl chain connecting phenyl and imidazole ring.

[ i " = 00,0 J Hydrogenation of phenyl to cyclohexyl changes Hi.receptor activity from agonistic to antagonistic

behaviour; with respect to G-protein stimulation, activity is enhanced. 2-Substituted histam~es also

activate reconstituted bovine brain G-proteins. Our data show that 2-substituted histamines activate

G-proteins by a receptor-independent mechanism and that lipophilicity of these compounds is important

for their G-protein-activating prope~es. 2-(4-Cy~lohexytbutyl)histamine is presentty the most potent

G-protain activator in the class of the 2-substitutad histamines.

Supported by Deutsche Forschungsgerneinscheft (SFB 366)