J . Med. Chem. 1994,37, 3231-3239
3231
Synthesis and Structure-Activity Relationships of Novel Naphthalenic and Bioisosteric Related Amidic Derivatives as Melatonin Receptor Ligands Patrick Depreux,+Daniel Lesieur,+Hamid At Mansour,? Peter Morgan,l H. Edward Howel1,l Pierre Renard,*,$ Daniel-Henri Caignard,$ Bruno Pfeiffer,$Philippe Delagrange,$ BBatrice Guardiola,* Said YOUS,? Anne Demarque,? GBrard Adam,* and Jean A n d r i e d Institut de Chimie Pharmaceutique, Lille, France, Znstitut de Recherches Internationales Servier, 1 rue Carle Hkbert, 92415 Courbevoie Cedex, France, Facult6 de Pharmacie, Chatenay Malabry, France, and Rowett Research Institute, Aberdeen, Scotland, U.K. Received April 13, 1994@
A series of N-naphthylethyl amide derivatives were synthesized and evaluated as melatonin receptor ligands. The affinity of each compound for the melatonin receptor was determined by binding studies using [2-12511iodomelatoninon ovine pars tuberalis membrane homogenates. Structure-activity relationships led to the conclusion that naphthalene is a bioisostere of the indole moiety of melatonin. Moreover it appears that the affinity is strongly affected by the size of the substituent of the nitrogen of the amidic function. Many of these ligands give biphasic dose-response curves which suggests that there may be two melatonin receptor subtypes within the ovine pars tuberalis cells. The replacement of naphthalene by benzofuran or benzothiophene did not strongly alter the affinity for the melatonin receptor. In contrast, the benzimidazole analogue was a poor ligand. Compound 7, the naphthalenic analogue of melatonin, a selective ligand of the melatonin receptor and a n agonist derivative, has been selected for clinical development.
Introduction
age12 and the administration of melatonin has been suggested to prolong the life span of mice.13 FurtherMelatonin (1) (N-acetyl-5-methoxytryptamine) is a more antioxidant properties of melatonin have recently neurohormone. Its role as a mediator of photoperiod been proposed.14 Despite its potential involvement in in the regulation of seasonal reproduction is well the regulation in many possible physiological processes, known,l whereas in man its exact functions are not fully two problems limit its use therapeutically at the present elucidated. However, it appears that it may have a role time. The first is its very short biological half-life15(15as a chronobiotic. Recent work has suggested its 30 min), due to its rapid catabolism to 6-hydroxymelapotential usefulness to a number of therapeutic areas tonin and N-acetylkynurenamines. The second problem such as those related to the desynchronization of is the lack of selectivity of melatonin a t its target sites. biological rhythms, such as jet-lag, disturbed sleepThe development of novel analogues provides a strategic wake cycle^,^,^ seasonal disorder^,^ and depre~sion.~ approach to overcome both of these limitations. It is Melatonin may also play a role in the cardiovascular hoped to design new compounds which are not only system. This is supported by recent findings which metabolically more stable but which will also provide sites are localshow that [2-12511iodomelatonin-binding basic pharmacological tools with which to define melaized in both the caudal and cerebral arteries of the raL516 tonin receptor subtype pharmacology and thereby imA functional role has been demonstrated since melatoprove our knowledge of the functions, sites, and mechanin is able to constrict the caudal artery of juvenile rats' nisms of action of these compounds. With this double and modulate the activity of norepinephrine.6 From purpose in mind, the synthesis of analogues was carried these preliminary data, it has been suggested that out in which the indole ring, one of the main targets of melatonin could play a role in the regulation of core body the metabolic degradation, was replaced by various temperature or blood pressure and therefore be imporbioisosteric modifications. The recent development of tant to human conditions, such as migraine. In addia radioligand-binding assay for melatonin receptors tion, melatonin binding has been reported at many other using ovine pars tuberalis membranes of the pituitary sites including the retina8 (probably related to a resynhas enabled the rapid screening of melatonin analogues chronization role) and peripheral tissues such as the for their receptor-binding aEnity.16 A preliminary spleeng (related to a role in the immune system), the communication disclosed bioequivalency between naphgastrointestinal tract, blood platelets,1° and the Hardthalene and indole and the excellent affinity of some erian gland.ll These binding data have been shown in naphthalene derivatives for the ovine par t~bera1is.l~ several animal species, but their presence and funcIn the original communication, the binding affinities of tional role have yet t o be demonstrated in humans. all compounds were reported after analysis using a Perhaps more contentiously, it has been proposed that melatonin could have a role in degenerative processes, single-site binding model; although for some compounds, as the synthesis of melatonin is known to diminish with it was noted that this did not provide the best mathematical fit of the data. Thus in this study, the binding data of these compounds together with some new + Institut de Chimie Pharmaceutique. * Institut de Recherches Internationales Servier. compounds have been reanalyzed by 4-parameter logis* Facult6 de Pharmacie. tic regression and/or a 5-parameter regression18 model Rowett Research Institute. which describes biphasic inhibition. Abstract published in Advance ACS Abstracts, September 1,1994. ~
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0022-2623/94/1837-3231$04.50/0
0 1994 American Chemical Society
Deprewc et al.
3232 Journal of Medicinal Chemistry, 1994, Vol. 37, No. 20
Scheme la
H3c0d CH2COOH
CH2CONH2
CH2CN
C
8,b
__c
\
3
2
4
7-19 ; 22-29 a Reagents: (a) SOC12, CHCl3; (b) NH40H, ether; (c) (CF~CO)ZO, THF; (d) Hz,Ni; (e) HC1, ether; (0 RCOC1, KzCO3, HzO, CHCl3; (g) HCOOH; (h) CHsSOzCl, Kzc03, HzO, CHC13.
In this paper, we report the synthesis of 60 derivatives among which were 38 naphthalenic bioisosteres, most of them including variations on the N-acylamino group (6-43). This group was first selected for chemical modification as it has been reported that the N-acetyl substituent of melatonin has a primary importance for the efficacy of binding,lg whereas modifications of the methoxy group are thought to be of primary importance to biological activity.lg Moreover, we introduced several variations on the ethylene group of the side chain and replaced the naphthalenic moiety by other bicyclic systems such as benzofuran, benzothiophene, and benzimidazole. Finally some indolic compounds with the most representative substituents introduced in the naphthalenic family were studied to check the equivalence for the melatonin receptor between these two systems. For these families of bicyclic compounds, the synthesis, the binding data for the melatonin receptor, and the potency of the agonistic character are reported.
-
Scheme 2"
a
Ar CH2 CH2 NH CO CH2 Br
I\r CH2 CHZ NH CO CHZ I
19
20
47
H 3 c 0 y J\ -7y6
I
H
H3c0yJ-$* \
a
19
Reagents: (a) NaI, acetone.
Chemistry and in the presence of EtONa afforded the pyrrolidinone 32 (Scheme 4) with a moderate yield (32%). The 2-(7-Methoxy-l-naphthyl)ethylamine (SA)was pretrifluoroacetamido compounds (21, 39, 48) were obpared from (7-methoxy-l-naphthy1)aceticacid (2) actained cording to the procedures previously d e ~ c r i b e d lfor ~ , ~ ~ ~ ~ ~ by treatment of the corresponding amines (5A, 5C, 5F) with trifluoroacetic anhydride29 in pyridine the corresponding amine. Formamide 6 was conve(Scheme 5). N-Alkylation30of 21 with methyl iodide in niently obtained by reaction of 5A with formic acid. The DMF and in the presence of K2CO3 gave 33 which was N-acylated derivatives (7- 19,22-29) and the sulfonahydrolyzed by %COS in a methanol-water mixture to mide 43 were prepared from 5A (Scheme 1)by treatafford the secondary amine SB. The N-acylated derivament with the appropriate acid chloride in the presence tives of 5B were obtained according to the procedure of K2CO3 as base and a biphasic medium (according to described for amide 7. Treatment of amide 7 with HBr a variant of the Schotten-Baumann procedure22). In gave (Scheme 6), contrary to a previous report,31 the a similar manner, amides 36-38, 41, 42, 44, 45, 49hydrobromide salt of the amino phenol 5D, which was 58, and 60 from the previously described corresponding acylated at 25 "C in a water-ethyl acetate mixture to were obtained. Reaction of the above afford the phenolic analogue of 7 (40). obtained 19 and 58 or the previously described2s bromoacetyl compound (46) with sodium iodide in acetone Results and Discussion afforded (Scheme 2) the corresponding iodo derivatives (20,47,59) with good yields (7547%). Tertiary amines For all compounds, the chemical structures and their 30 and 31 were prepared from 19 by treatment with binding characteristics to melatonin receptors, as well the appropriate amine in acetone and in the presence as the biological activity expressed as a CAMPindex, of triethylamine (Scheme 3). Cyclization of 22 in DMF obtained by studying the melatonin-mediated inhibition
Naphthalenic Derivatives as Melatonin Receptor Ligands
Scheme 6"
Scheme 3"
19
R
-
CH C
R
a
HZ
H"O&
R
3 0 -N,
a
n
=
-NWo
R R
?1 aReagenls : (a) HN , (C2Hg)3N, acetone Rl
Scheme 4" Q
32
Reagents: (a) Na, ethanol; (b) DMF,heat.
Scheme 5" Ar CH2 CH2 NH2
Ar CH2 CH2 NH CO CF3
21
39
F
J
-
-
-
Q 0
c
48
3 H
I
H
21
b
? a _
,
\
,Her
5D
R
ArCH2CH2yCOCF3
3P
3
%
NH COCH3
NH2
NHCOCH2N,
30. 31
a
Journal of Medicinal Chemistry, 1994, Vol. 37, No. 20 3233
MCHg*NHCb,HCi
10
Reagents: (a)(CFsC0)20, pyridine; (b) CHd, KzCOs, DMF; (c) HzO, CH30H, KzC03; (d) HC1, ethanol. a
of forskolin-stimulated CAMPproduction are shown in Table 1. Binding data are presented in two forms. Firstly after primary analysis using a single-site binding model as described previously:17 these results are expressed as KD values. Secondly after analysis of binding data by nonlinear monophasic and biphasic regression models which permitted distinction of the
\
/ 40
Reagents: (a)HBr; (b)CH3COC1, KzC03, HzO, ethyl acetate.
compounds into two categories: (1)compounds that give monophasic inhibition for which IC50 values are reported in Table 1and (2) compounds that give biphasic inhibition for which Table 1 reports loglo KH (high affinity) and loglo KL (low affinity). If biphasic curves provide the best fits to the data, then the simplest prediction is that either two melatonin receptor subtypes exist in the ovine pars tuberalis cells or the same receptor has been measured in two different affinity states. As it has been shown in recent studies that melatonin receptors are coupled through two independent and distinct G-proteins, both of which mediate the inhibition of cyclic AMP in pars tuberalis cells,32the former of these two possibilities seems the more likely to pertain. Furthermore the large differences in magnitude of the affinities would seem more compatible with distinct sites than with a single receptor in different affinity states. While it is possible for there to be only a single population of receptors which can interact with different G-proteins, it seems more probable that distinct receptors couple to distinct Gproteins. Nevertheless, in either case, the nature of the receptor-G-protein coupling is an important determinant of the efficacy of a ligand as a full or partial agonist.33 Therefore in this study, the efficacy of a biphasic agonist will represent the combined effects of the drug acting as either a partial or full agonist through each receptor-G-protein-coupled pathway. This would explain why CAMPindices ranging from 0.2 to 1 were obtained. However, to dissect the specific differences in efficacy which are occurring will require full dose-response curves to be made rather than the singledose bioassays used in this study. It appears from examination of the data in Table 1 that there is little correlation between the structure of a compound and its property as a biphasic ligand for the melatonin receptor, as both poor ligands (such as 11) as well as compounds having affinity for the melatonin receptor (such as 15) can give biphasic fits. This is also not dependent on the steric bulk of the substituents since the formamide naphthalenic analogue of melatonin (61, the least bulky compound of Table 1, and the bulky n-pentyl derivative 11 give biphasic fits. From study of the structure-affinity relationships, the first important point to note is that the indole nucleus in compound 1 can be substituted by naphthalene without loss of binding potency. However structural variations of the acylamino group of the naphthalene family causes major changes in the affinity for the melatonin receptor. Increasing the chain length of the linear acyl substituent (ethyl ( 8 ) , n-propyl (91,n-butyl (10))results in a corresponding increase in binding affinity. Similarly substitution of the lower alkyl C1 or CS groups by one (19,20,22) or several (21)halogen atoms slightly increases the affinity for the melatonin receptor. However further homologation as seen with 11 (n-pentyl) or 12 (n-hexyl) results in lowered affinity. When cycloalkyl substituents were used, the best af-
3234 Journal of Medicinal Chemistry, 1994, Vol. 37, No. 20
Deprewc et al.
Table 1. Binding and Agonistic Properties of Analogues of Melatonin" 0
II
43
6.42
compd 1
R1 OCHs
Rz H
n
R3 NH H
R4
orx 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
CHn
H H
n-CiHii iGH7
H H
CF3n-CxH&l
1 1
1 1 1 1 1 1
1
40 41 42
1 1 1 1 1 1 1 1 1
H COOCH3 1 COOCH3 1
54 56 57
H H H H H H H H H H H H
NH NH NH NH NH NH O O O S S S
H H H H H H H F F H H H H H H
59
H
S
H
43 44
45 47 48 49 50
51 52 53
CHzI CFn
H H TMZ: 1-(2',3',4'-trimethoxybenzy1)piperazine.
60
60
biphasic monophasic loglo KH log10 KL CAMPf SEM, KD,mean i SD IC50 f SD (M) i SD i SD activity index (9.15 i 3.98) E-11 (1.57 f 0.22) E-10 1.00 (4.05 f 1.93) E-11 -13.14 f 0.61 -8.11 i 0.52 0.98 i 0.32 (1.00 f 0.35) E-10 (7.61 i 3.13)E-11 1.01 f 0.22 -11.54 i 0.05 -8.71 i 0.07 1.02 i 0.22 (2.19 i 0.90) E-11 (6.15 f 0.18) E-12 (3.45 i 2.43) E-12 1.02 i 0.35 -11.22 i 0.26 -7.03 i 0.27 1.03 i 0.23 (3.43 i 2.43) E-12 (2.80 f 0.20) E-07 -9.09 f 0.22 -5.69 f 0.09 0.58 f 0.07 (2.60 i 1.05) E-06 >E-05 0.18 f 0.03 (2.29 i 0.75) E-09 -12.20 & 0.18 -7.90 i 0.11 1.01 f 0.19 -14.49 i 0.03 -7.15 f 0.03 1.00 f 0.19 (8.70 f 0.34) E-09 (4.18 f 0.87) E-13 -13.17 i 0.07 10.36 f 0.23 1.02 i 0.18 (2.42 i 0.54) E-08 -12.38 f 0.23 -6.91 i 0.17 0.52 f 0.11 (1.90 f 1.16)E-07 (3.07 i 1.04) E-07 0.48 i 0.12 (1.59 i 0.79) E-07 (4.38 f 0.47) E-07 0.39 i- 0.10 (8.00 f 0.74) E-13 (1.18 f 1.72) E-12 1.05 f 0.30 (1.55 i 1.03)E-11 -12.56 i 0.04 -8.93 i 0.15 1.00 i 0.33 (2.70 i 0.76) E-13
