Physiol. Res. 53: 35-43, 2004 Pergolide, Terguride and N,N'-spacer-linked Oligomers of Both Interact with 5-HT2A Receptors of Rat Tail Artery V. KŘEN, E. EICH1, H. H. PERTZ1 Institute of Microbiology, Laboratory of Biotransformation, Academy of Sciences of the Czech Republic, Prague, Czech Republic, 1Institut für Pharmazie, Freie Universität Berlin, Germany Received November 5, 2002 Accepted February 27, 2003 Summary Pergolide, terguride and N,N'-spacer-linked oligomers of both have been tested for their ability to interact with 5-hydroxytryptamine(HT)2A receptors of rat tail artery. Pergolide was a potent partial agonist (pEC50 7.5, Emax 55 %) and antagonized 5-HT-induced contractions (pKP 7.2). Pergolide dimer 3 with a p-xylene spacer between the indole nitrogens (N-1) displayed somewhat lower agonist potency than pergolide (pEC50 7.0, Emax 55 %, pKP 6.6). The contractile responses to pergolide and dimer 3 were antagonized by the 5-HT2A receptor antagonist ketanserin (pA2 9.4, 9.1). In contrast to pergolide dimer 3, pergolide dimers 5 and 9 with an alkyl and an aralkyl spacer between the piperidine nitrogens (N-6) lacked agonism and displayed low affinity at 5-HT2A receptors (pA2 < 5.5). Terguride behaved as an insurmountable antagonist of 5-HT (pA2 8.4). Oligomers of terguride showed 5 to 50-fold lower affinity. It is concluded that pergolide and terguride show a high affinity for 5-HT2A receptors, but dimerization (oligomerization) of both drugs fails to increase affinity. Key words Pergolide • Terguride • Oligomers of pergolide and terguride • 5-HT2A receptors • Contraction • Rat tail artery Introduction tryptamine (5-HT) receptors and α-adrenoceptors (for review see Pertz and Eich 1999). Due to their agonist activity at dopamine The aim of the present study was to characterize receptors pergolide (compound 1) and terguride the interaction of pergolide and terguride and their dimers (compound 2) (Fig. 1) are currently available for the with 5-HT2A receptors in the isolated rat tail artery. We treatment of Parkinson's disease (Rinne 1987). While used the so-called bivalent ligand approach that pergolide is a potent agonist of the D1 and D2 class of represents a strategy for medicinal chemists to design dopamine receptors (Fuller and Clemens 1991), terguride potent and selective receptor ligands by combining two or (dihydrolisuride) shows partial agonist activity at the D2 more pharmacophores in a single molecule (Portoghese class of dopamine receptors (Stephens et al. 1990). Just as 1989, 1992, Halazy et al. 1996) (Figs 2 and 3). Previous the well established drug bromocriptine, pergolide and studies on 5-HT1B/1D receptors have demonstrated that terguride are ergoline derivatives of which the spectrum dimerization of 5-HT receptor ligands resulted in higher of adverse effects is similar due to the powerful affinities for this subtype (Perez et al. 1998). We now interaction with nearly all subtypes of 5-hydroxy- report the preparation of oligomers of pergolide and PHYSIOLOGICAL RESEARCH ISSN 0862-8408 2004 Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic Fax +420 241 062 164 E-mail: [email protected] http://www.biomed.cas.cz/physiolres 36 Křen et al. Vol. 53 terguride, respectively, in order to find out whether these Methods compounds show activity at vascular 5-HT2A receptors of the rat. Materials Chemicals used for synthesis were reagent-grade mostly from Sigma-Aldrich; solvents were dried and distilled prior to use. Drugs were obtained from the N following sources: cocaine-HCl (Merck, Darmstadt, S O H3C NH Germany), 5-hydroxytryptamine creatinine sulphate (Janssen, Beerse, Belgium), ketanserin tartrate (Janssen), 8 7 H H prazosin-HCl (RBI, Natick, MA, USA). 10 6N CH N 3 H 13 11 5 H 16 Chemistry 4 NMR spectra were measured on a Varian 12 HN HN INOVA-400 spectrometer (399.90 and 100.56 MHz for 1 13 1 (pergolide) 2 (terguride) H and C, respectively) in CDCl3 or d6-DMSO at 30 ºC. Chemical shifts were referenced to the residual solvent Fig. 1. Chemical structures of pergolide and terguride signal (δH 7.265, δC 77.0; δH 2.50, δC 39.6. 2D NMR) experiments (gCOSY, TOCSY, HMQC, HMBC) were run using the default parameters in the available Varian S S software. The pulse sequence for 1D-TOCSY was CH H C 3 3 obtained from the Varian User Library. Positive ion MALDI mass spectra were H H N N measured on a Bruker BIFLEX reflectron time-of-flight H H mass spectrometer (Bruker-Franzen, Bremen, Germany) equipped with a multiprobe sample inlet, a griddles N N delayed extraction ion source and a nitrogen laser S N α O (337 nm). A saturated solution of -cyano-4- H3C 3 NH hydroxycinnamic acid in aqueous 50 % acetonitrile/0.1 % H TFA was used as a MALDI matrix. Spectra were N H + N CH3 calibrated externally using the monoisotopic [M+H] ion H H of α-cyano-4-hydroxycinnamic acid and a peptide N standard (angiotensin II, Aldrich). N 4 Preparation of compounds 3, 4, 5, 6a-e, 7 and 8 S Compounds 3, 4, 5, 6a-e, 7 and 8 were prepared H3C S CH3 as described previously (Křen et al. 2001, 2002). H N H N β H 1,4 -Di[8 ’- (methylthiomethyl) ergoline - 6’- yl - methyl] H benzene (compound 9) HN The title compound was prepared as described NH 5 for compound 5 (Křen et al. 2001) in 67 % yield as a + yellowish amorphous powder. MS MALDI [M + H] S S CH 1 H3C 3 (found 647.5, required 647.32 for C40H47N4S2). H NMR (DMSO) δ: 1.01 (ddd, J = 12.4, 12.2, 12.2, 2H), 1.77 (dd, H H N N J = 11.2, 11.2, 2H), 1.92 (m, 2H), 2.00 (s, 6H), 2.34 (m, H H 4H), 2.44 (dd, J = 13.1, 6.4, 2H), 2.62 (ddd, J = 14.9, 10.9, 1.4, 2H), 2.71 (m, 2H), 2.89 (m, 2H), 3.03 (m, 2H), HN NH 9 3.38 (d, J = 13.8, 2H), 3.51 (dd, J = 14.9, 4.0, 2H), 4.22 (d, J = 13.8, 2H), 6.77 (ddd, J = 7.2, 1.2, 0.6, 2H), 6.99 Fig. 2. Chemical structures of ergot alkaloid dimers (dd, J = 2.1, 1.4, 2H), 7.02 (dd, J = 8.2, 7.2, 2H), 7.12 2004 Pergolide and Terguride Oligomer Interaction with 5-HT2A Receptors 37 (ddd, J = 8.2, 0.8, 0.6, 2H), 7.30 (s, 4H), 10.60 (d, J = d, 110.32 s, 111.97 d, 118.50 d, 122.08 d, 126.09 s, 2.1, 2H). 13C NMR (DMSO) δ: 15.46 q, 27.15 t, 33.96 t, 128.54 d (2 C), 132.92 s, 133.21 s, 137.89 s. 34.63 d, 38.20 t, 40.60 d, 56.54 t, 58.43 t, 65.12 d, 108.69 6a X = -CH - N N 2 O O 6b X = -(CH ) - HN NH 2 6 H H H C N N CH 6c X = H CCH 3 3 2 2 H H CH2 6d X = N N (X) CH2 CH2 6e X = CH2 N O NH N N N O O O HN H N CH3 HN NH H H H H H3C N NCH H3CN 3 H N H H N N N N N N H H H NCH3 H3C N N CH H H H 3 NH HN NH O O O 7 N N N 8 Fig. 3. Chemical structures of terguride dimers and oligomers 1,6-Di[8β‘-(methylthiomethyl)ergoline-1’-yl-]hexane within 3 h as indicated by TLC: silica gel F254 plates (compound 10) (Merck), CHCl3-MeOH-NH3 94.5 : 5.5 : 0.1 (v/v). The Finely powdered KOH (370 mg, 6.6 mmol) was spots were visualised by UV light and charred with 10 % mixed with DMSO (2 ml) and stirred for 10 min. H2SO4 in ethanol where N-1-unsubstituted ergolines gave Depropylpergolide (compound 1a) (135 mg, 0.5 mmol) blue spots and substituted compounds (dimers) gave grey was added and the stirring was continued for further spots. The product had quite similar Rf like compound 1a. 30 min. The mixture turns green indicating deprotonation The reaction mixture was poured into water (40 ml), the of N-1. After cooling to 10 ºC, 1,6-dibromohexane precipitate was filtered off, washed with water till neutral (54 mg, 0.22 mmol, dissolved in 2 ml of DMSO) was pH and dried affording 130 mg of the crude product. slowly added in portions. The reaction was completed Flash chromatography (silica gel, CHCl3-MeOH-NH3 38 Křen et al. Vol. 53 97 : 3 : 0.1 (v/v)) afforded pure compound 10 as the artery to rub off the endothelium. Up to 12 cylindrical amorphous yellow foam (52 mg, 33 %). MS MALDI [M segments (3-4 mm long) were horizontally suspended + + H] (found 627.2, required 627.35 for C38H51N4S2). between two L-shaped stainless steel hooks (diameter 1 H NMR (CDCl3, 30 ºC) δ: 1.28 (ddd, J = 13.3, 12.1, 0.15 mm) and mounted in a 20-ml organ bath filled with 11.9, 2H), 1.33 (m, 4H), 1.79 (m, 4H), 2.08 (m, 2H), 2.16 modified Krebs-Henseleit solution of the following (s, 6H), 2.47 (dd, J = 11.9, 11.7, 2H), 2.48 (dd, J = 13.2, composition (mM): NaCl 118, KCl 4.7, CaCl2 2.5, 7.3, 2H), 2.54 (dd, J = 13.2, 6.6, 2H), 2.77 - 2.90 (m, 8H), MgSO4 1.2, KH2PO4 1.2, NaHCO3 25, and D-glucose 10.