4-Substituted anilides as selective melatonin MT2 receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2003.11.030

A series of 4-substituted anilides with human melatonergic affinity is reported. Butyramides 26, 39, 42, 52, 57, and 58 all demonstrated subnanomolar MT₂ binding affinity and MT₂ selectivity of at least 70-fold over the MT₁ receptor. Compound 26 demonstrated full agonism at the MT₂ receptor.

Full text of DOI:10.1016/j.bmcl.2003.11.030

Bioorganic & Medicinal Chemistry Letters 14 (2004) 1023–1026
4-Substituted anilides as selective melatonin MT2
receptor agonists
James R. Epperson,* Jeffrey A. Deskus, Anthony J. Gentile, Lawrence G. Iben,
Elaine Ryan and Nathan S. Sarbin
Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, CT 06492-7660, USA
Received 15 September 2003; revised 7 November 2003; accepted 14 November 2003
Abstract—A series of 4-substituted anilides with human melatonergic affinity is reported. Butyramides 26, 39, 42, 52, 57, and 58 all
demonstrated subnanomolar MT2 binding affinity and MT2 selectivity of at least 70-fold over the MT1 receptor. Compound 26
demonstrated full agonism at the MT2 receptor.
# 2003 Elsevier Ltd. All rights reserved.
Melatonin (1) is a pineal hormone involved in circadian
and photoperiodic behavior and helps regulate the
sleep/wake cycle.1 Melatonin transmits its effects, in
part, through G-protein coupled receptors.2 In humans,
the MT1 and MT2 melatonin receptors have been iden-
tified in the brain.3,4 The MT2 receptor now appears to
play a major role in mammalian circadian entrainment.5
In mice lacking the MT1 receptor,6 melatonin produced
phase shifts, and the MT2 selective antagonist 4-P-
PDOT (2) blocked this effect.7
Recently, structurally rigid N-acyl-4-indanylpiperazines
3 were reported to be MT2 selective agonists.8 In con-
trast to these indanylpiperazines, conformationally flex-
ible N-acyl benzylpiperazines 4 possessed only modest
melatonergic affinity. We now report a series of 4-sub-
stituted anilides which are potent and selective agonists
at the human melatonin MT2 receptor. These anilides
have similar conformational flexibility to benzylpiper-
idines 4 and demonstrate that structural rigidity is not an
absolute requirement for either potency or selectivity.
The synthesis of the anilides consisted of two parts: (1)
assembly of a substituted nitrobenzene intermediate by
one of five methods (Scheme 1) and (2) reduction and
acylation of that intermediate to form the anilide (Scheme
2). 4-Aryloxy- and 4-arylthio- intermediates 7 were
prepared by nucleophilic displacement of 4-fluoro-
nitrobenzene (6) with a phenol or thiophenol 5 under
basic conditions (method a). 3-Aryloxy intermediate 10
was prepared in modest yield by a modified Ullmann
procedure9 employing PhCCCu to couple 3-nitrophenol
(9) with 3-methoxybromobenzene (8) (method b). 4-
Ketoaryl intermediate 13 was prepared under Stille
conditions10 to couple 4-nitrobenzoyl chloride (12) with
3-methoxyphenyltributyl stannane (11) (method c). 4-
Benzyl intermediate 16 was prepared under Suzuki
* Corresponding author. Tel.:+1-203-677-6974; fax:+1-203-677-6900;
e-mail: james.epperson@bms.com
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.11.030

1024
J. R. Epperson et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1023–1026
system. Finally, 4-anilinyl intermediate 19 was prepared
under improved Buchwald conditions for coupling aryl
triflate 17 with aniline 18 under mild basic conditions
(method e).13 Intermediate 19 was also methylated to
afford methylamino intermediate 20.
The intermediate nitrophenyl compounds 21 were then
hydrogenated to afford penultimate anilines 22 and
subsequently acylated with acid chlorides or isocyanates
to afford anilides 23–53 (Scheme 2).14
Additionally, thioether 38 was cleanly oxidized to pro-
vide sulfone 39. Keto compounds 13 and 53, however,
could not be reduced to methylene compound 52 under
a variety of conditions (acidic, basic, and neutral pH)
either directly or through the reduced hydroxy com-
pounds. This led to the Liebeskind modified Suzuki
coupling to obtain methylene bridged analogues.
Cyclic isosteres of the 3-methoxy moiety were also pre-
pared (compounds 54–59). Thus, 2,3-dihydro-4-
hydroxybenzofuran15 and 5-hydroxybenzodioxane16
were coupled with 4-fluoronitrobenzene to form inter-
mediates analogous to 7. 2,3-Dihydro-4-hydroxy-
benzofuran was also coupled to 4-nitroaniline by
Buchwald coupling via the triflate to form intermediates
analogous to 19 and 20. These intermediates were then
converted to N-acylanilides 54–57 by the methods of
Scheme 2. The syntheses of compounds 58 and 59 were
prepared from (benzofuran-4-yl)methanol and (2,3-
dihydrobenzofuran-4-yl)methanol17 by conversion to
the benzyl sulfonium salt (allyl bromide, CDI, followed
by THT, NaClO4, 30% for two steps) and coupling with
4-formylphenylboronic acid.18 The resulting aldehyde
was oxidized to the acid (Ag2O, 87%) and converted to
the aniline by Curtius rearrangement (DPPA, TEA,
tBuOH followed by HCl, EtOH, 25% for two steps)
before acylation as in Scheme 2.
Scheme 1. Synthesis of nitrobenzene intermediates. Reagents and
conditions: (a) K2CO3, CH3CN, reflux; (b) PhCCCu, pyridine, reflux;
(c) Bn(Cl)(Ph3P)2Pd, CH2Cl2, 25 ꢀC; (d) PdCl2, dppf, K2CO3, THF,
reflux; (e) Pd(OAc)2, BINAP, Cs2CO3, toluene, 80 ꢀC; (f) MeI, solid
KOH, THF, reflux.
Compounds 23–59 were evaluated for human melatonin
MT1 and MT2 receptor binding using published
methods.3,19,20 The regiochemical optimization of
(methoxy)phenoxybutyranilides is summarized in Table
1. Compound 26 had the optimum placement of sub-
stituents for this pharamacophore.21 Compounds 23,
24, and 26 show the preferred phenoxy group orienta-
tion is para to the anilide moiety for MT2 binding and
selectivity. Compounds 25–27 demonstrate the pre-
ferred location for the methoxy substituent on the
phenoxy group is the 3-position. In these regioisomers,
compound 26 was clearly unique and possessed excellent
MT2 binding affinity of 0.75 nM and 84-fold selectivity
for the MT2 receptor.
Using compound 26 as a lead pharmacophore, a variety
of related amides were evaluated and are summarized in
Table 2 (compounds 28–37). Although butyramide 26
had the most potent MT2 binding and highest MT2
selectivity, acetamide 28, propionamide 29, crotonamide
34, and methoxyacetamide 35 were also potent MT2
ligands, albeit with less MT2 selectivity. Valeramide 30
did not possess melatonergic affinity and demonstrated
the limits for binding activity in linear alkanamides.
Scheme 2. Synthesis of anilides. Reagents and conditions: (a) H2, Pd/
C, EtOAc or EtOH; (b) RCOCl, TEA, cat. DMAP, CH2Cl2; (c)
RNCO, CH2Cl2.
conditions reported by Liebeskind11 (method d). In this
method, 4-nitrobenzyl chloride was reacted with tetra-
hydrothiophene to form the stable sulfonium salt 15.12
This salt then underwent Suzuki coupling with 3-meth-
oxyphenylboronic acid (14) employing a Pd/dppf catalyst

J. R. Epperson et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1023–1026
1025
Table 1. Melatonin receptor binding of regioisomers 23–27
compounds with electron-withdrawing groups (SO2,
CO) had attenuated melatonergic activity.
Thus, thioether 38,22 the compound which proved to be
the most selective of this study, had MT2 binding of
0.19 nM and MT2 selectivity of 150. Sulfone 39, on the
other hand, was 50-fold less active at the MT2 receptor,
but still had MT2 selectivity of 50.
Compd Methoxy Aryloxy
substitution substitution
MT1
MT2
MT1/MT2
Ki (nM) Ki (nM)
1
0.53
>500
>500
>500
63
0.32
130
26.8
108
0.75
>400
1.6
3.9
19
4.6
84
Diarylamines 40–51 were also evaluated. In this class,
butyramides were again the most potent MT2 ligands
(42 and 48). Compound 42, with a bridging NH group,
had MT2 affinity of 0.39 nM and MT2 selectivity of 81.
Conversely, compound 48, with an NMe bridge, had
good binding at both MT1 and MT2 receptors (1.1 and
0.10 nM, respectively). Consequently, the MT2 selectivity
of 48 was only 11. As a result, isobutyramide 49 had the
best selectivity (19-fold) among the NMe compounds.
23
24
25
26
27
3-MeO
3-MeO
2-MeO
3-MeO
4-MeO
2-
3-
4-
4-
4-
>500
na
Table 2. Melatonin receptor binding of compounds 28–53
Finally, carbon-bridged compounds were evaluated.
Methylene bridged butyramide 5223 demonstrated
excellent MT2 affinity and selectivity of 91. Keto
bridged compound 53 had attenuated MT2 affinity and
selectivity relative to 52 (MT2 Ki=33, MT1/MT2=15).
Compd
X
R
MT1
MT2
MT1/MT2
Ki (nM)
Ki (nM)
In all of these cases, the most potent MT2 binding resi-
ded with butyramides. When optimally bridged, these
compounds had subnanomolar affinity, and except for
one compound (48), the highest MT2 selectivity also
resided with butyramides, with a selectivity range of
81- to 150-fold over the MT1 receptor.
1
0.53
84
300
63
>500
>500
>500
99
0.32
4.1
6.8
0.75
>400
122
15
13
2.1
1.6
20
44
84
na
4
30
13
47
31
5
28
29
26
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
O
O
O
O
O
O
O
O
O
Me
Et
nPr
nBu
iPr
iBu
cPr
Compounds in which the 3-methoxy moiety was
replaced with a variety of cyclic ethers were evaluated in
four differently bridged series: O, NH, NMe, and CH2
(Table 3). Except for NH-bridged compound 56, all
compounds in this series had potent MT2 affinity (all
but 55 had subnanomolar affinity), and all possessed
some MT2 selectivity. Ether compounds 54 and 55 had
selectivity of 27 and 19. NH Compound 56 had selec-
tivity of 12 while NMe compound 57 had selectivity of
73. This situation is the reverse of the NH- and NMe-
bridged methoxy analogues, 42 and 48, where the NH
compound had selectivity of 81 and the NMe com-
pound had selectivity of 11. Methylene bridged com-
pounds 58 and 5924 also had good selectivity, 118 and
57 respectively, with 58 having the highest selectivity of
the cyclic ether series.
1-propenyl
CH2OMe
propargyl
NHEt
nPr
98
180
>500
>500
29
>500
84
61
31
>500
61
>500
0.05
1
1.1
106
12
34
10.9
>500
5.9
O
O
S
110
250
0.19
10
4.2
1.8
0.39
84
64
150
0.23
0.17
0.1
5.5
4.8
7.2
0.12
33
2
150
50
20
34
81
6
SO2
NH
NH
NH
NH
NH
NH
NMe
NMe
NMe
NMe
NMe
NMe
CH2
CO
nPr
Me
Et
nPr
iPr
cPr
OEt
Me
Et
nPr
iPr
cPr
OEt
nPr
nPr
1
3
0.22
6.1
11
19
3
5
91
15
Compound 26 was selected for functional evaluation at
the MT2 receptor and demonstrated full agonism in an
assay measuring the inhibition of forskolin-stimulated
cAMP accumulation in NIH-3T3 cells stably expressing
the MT2 receptor (EC50=1.07 nM; intrinisic activity
=1.09).8
Isovalerylamide 32 and cyclopropylcarboxamide 33 had
some MT2 binding with little MT1 binding, while iso-
butyramide 31 had poor binding at both receptors. 2-
Butynamide 36 and ethyl urea 37 were also poor ligands
at both receptors.
In summary, we have discovered a series of anilides, the
butyramides of which are often potent and selective
human MT2 ligands. In particular, butyramides 26, 39,
42, 52, 57, and 58 all demonstrated subnanomolar MT2
binding affinity and MT2 selectivity of at least 70-fold
over the MT1 receptor. Compound 26 of this series
demonstrated full agonism at the MT2 receptor.
In addition to ether compounds 23–37, a number of
analogues replacing the diaryl ether oxygen were also
evaluated (Table 2, compounds 38–53). Compounds
replacing the ether oxygen with electron-donating
groups (S, NH, and NMe) or electron-neutral groups
(CH2) were potent and selective MT2 ligands, whereas

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J. R. Epperson et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1023–1026
Table 3. Melatonin receptor binding of cyclic compounds 54–59
9. Afzali, A.; Firouzabaki, H.; Khalafi-Nejad, A. Synth.
Commun. 1983, 13, 335.
10. Labadie, J. W.; Tueting, D.; Stille, J. K. J. Org. Chem.
1983, 48, 4634.
11. Srogl, J.; Allred, G. D.; Liebeskind, L. S. J. Am. Chem.
Soc. 1997, 119, 12376.
Compd
Ar
X
MT1
Ki (nM)
0.53
MT2
Ki (nM)
0.32
MT1/MT2
12. Aggarwal, V. K.; Thompson, A.; Jones, R. V. H. Tetra-
hedron Lett. 1994, 35, 8659.
13. Ahman, J.; Buchwald, S. L. Tetrahedron Lett. 1997, 38,
6363.
14. All final compounds were characterized by LC/MS, 1H
NMR, 13C NMR, and combustion analysis.
1
1.6
27
54
O
18
92
0.68
4.7
15. Takaki, K. S.; Luo, H.; Bertenshaw, S. B. U.S. Patent
6,211,225, 2001.
16. Munk, S. A.; Harcourt, D. A.; Arasasingham, P. N.;
Burke, J. A.; Kharlamb, A. B.; Manlapaz, C. A.; Padillo,
E. U.; Roberts, D.; Runde, E.; Williams, L.; Wheeler,
L. A.; Garst, M. E. J. Med. Chem. 1997, 40, 18.
17. Catt, J. D.; Johnson, G. J.; Keavy, D. J.; Mattson, R. J.;
Parker, M. F.; Takaki, K. S.; Yevich, J. P. U.S. Patent
5,856,529 1999.
18. Suzuki coupling of the triflate of either 4-hydroxy-
benzofuran or 4-hydroxydihydrobenzofuran with 4-nitro-
phenylboronic acid was unsuccessful.
19. Takaki, K. S.; Sun, L.-Q.; Johnson, G.; Epperson, J. R.;
Bertenshaw, S. B. U.S. Patent 6,569,894, 2003.
20. Ki values were the mean of at least three determinations
run at five concentrations with the radioligand at the Kd
concentration. Standard errors were typically Æ20% of
the mean value.
55
56
57
58
59
O
19
12
NH
NMe
CH2
CH2
>500
36
39
0.49
0.78
0.71
73
92
118
57
41
21. N-[4-(3-Methoxyphenoxy)phenyl] butanamide (26). Mp
45–47 ꢀC; 1H NMR (CDCl3) d 7.76 (bs, 1H), 7.46 (d,
J=8.9 Hz, 2H), 7.15 (t, J=7.6 Hz, 1H), 6.94 (d, J=8.9
Hz, 2H), 6.60 (d, J=7.6 Hz, 1H), 6.51 (m, 2H), 3.73 (s,
3H), 2.30 (t, J=7.3 Hz, 2H), 1.72 (sex, J=7.3 Hz, 2H),
0.96 (t, J=7.3 Hz, 3H). Anal. calcd for C17H19NO3: C,
71.56; H, 6.71; N, 4.91. Found: 71.39; H, 6.62; N, 4.80.
22. N-[4-(3-Methoxyphenyl)thiophenyl] butanamide (38). Mp
48–49 ꢀC; 1H NMR (CDCl3) d 7.80 (bs, 1H), 7.50 (d,
J=8.6 Hz, 2H), 7.33 (d, J=8.6 Hz, 2H), 7.15 (t, J=7.9
Hz, 1H), 6.73 (m, 3H), 3.72 (s, 3H), 2.32 (t, J=7.3 Hz,
2H), 1.73 (sex, J=7.3 Hz, 2H), 0.96 (t, J=7.3 Hz, 3H).
Anal. calcd for C17H19SNO2: C, 67.75; H, 6.35; N, 4.65.
Found: 67.69; H, 6.30; N, 4.89.
References and notes
1. (a) Vanacek, J. Physiol. Rev. 1998, 78, 687. (b) Cassone,
V. M. Chronobiol. Int. 1998, 15, 457.
2. Li, P.-K.; Witt-Enderby, P. A. Drugs Fut. 2000, 25, 945.
3. (a) Reppert, S. M.; Weaver, D. R.; Ebisawa, T. Neuron
1994, 13, 1177. (b) Reppert, S. M.; Godson, C.; Mahle,
C. D.; Weaver, D. R.; Slaugenhaupt, S. A.; Gusella, J. F.
Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 8734.
4. IUPHAR reclassified the Mel 1a and Mel 1b receptors to
MT1 and MT2, The IUPHAR compendium of receptor
Characterization and Classification, IUPHAR media,
London, 2000, 271–277.
5. Liu, C.; Weaver, D. R.; Jin, X.; Shearman, L. P.; Pieschl,
R. L.; Gribkoff, V. K.; Reppert, S. M. Neuron 1997, 19,
91.
6. Nonno, R.; Pannacci, M.; Lucini, V.; Angeloni, D.;
Fraschini, F.; Stankov, B. Brit. J. Pharmacol. 1999, 127,
1288.
23. N-[4-(3-Methoxybenzyl)phenyl] butanamide (52). Mp 73–
75 ꢀC; H NMR (CDCl3) d 7.40 (d, J=8.4 Hz, 2H), 7.18
1
(t, J=7.7 Hz, 1H), 7.12 (d, J=8.4 Hz, 3H), 6.73 (m, 3H),
3.90 (s, 2H), 3.75 (s, 3H), 2.31 (t, J=7.3 Hz, 2H), 1.74
(sex, J=7.3 Hz, 2H), 0.99 (t, J=7.3 Hz, 3H). Anal. calcd
ꢁ
for C18H21NO2 0.425H2O: C, 71.56; H, 6.71; N, 4.91.
Found: 74.30; H, 7.99; N, 4.21.
24. N-[4-(4-Benzofuranyloxy)phenyl] butanamide. (58). Mp
110–113 ꢀC; H NMR (CDCl3) d 7.56 (d, J=2.2 Hz, 1H),
1
7.45 (m, 3H), 7.29 (m, 2H), 7.18 (d, J=11 Hz, 1H), 7.06
(d, J=7.3 Hz, 1H), 6.68 (d, J=2.2 Hz, 1H), 4.18 (s, 2H),
2.31 (t, J=7.3 Hz, 2H), 1.75 (q, J=14.9, 7.4 Hz, 2H), and
0.99 (t, J=7.4 Hz, 3H); MS: 292.3 (MÀH)À. Anal. calcd
7. Dubocovich, M. L.; Yun, K.; Al-Ghoul, W. M.; Benlowcif,
S.; Masana, M. I. FASEB J. 1998, 12, 1211.
8. Mattson, R. J.; Catt, J. D.; Keavy, D.; Sloan, C. P.;
Epperson, J.; Gao, Q.; Hodges, D. B.; Iben, L.; Mahle,
C. D.; Ryan, E.; Yocca, F. D. Bioorg. Med. Chem. Lett.
2003, 13, 1199.
ꢁ
for C19H19NO2 0.20H2O: C, 76.84; H, 6.59; N, 4.72.
Found: 76.90; H, 6.64; N, 4.70.