Synthesis of 2-amido-2,3-dihydro-1H-phenalene derivatives as new conformationally restricted ligands for melatonin receptors

Article abstract of DOI:10.1021/jm960219h

Tetrahydroanthracene, tetrahydrophenanthrene, and tetrahydrophenalene moieties were used to design novel constrained melatoninergic agents. Compounds 1 and 2 were synthesized from the cyclization of the aryl succinic acids 6a,b followed by catalytic reduction, Curtius degradation to the amino derivatives, and acetylation. The phenalene derivatives 3 were prepared by cyclization of the aza lactones of the corresponding α-N-acetyl amino acids. The ketone derivatives were reduced directly by catalytic hydrogenation to produce the compounds 3. The different compounds were evaluated in vitro in binding assays using 2-[¹²⁵I]iodomelatonin and chicken brain membranes. Melatonin and 2-acetamido-8-methoxytetralin were used as the reference compounds. The results showed the superiority of the dihydrophenalene framework 3 over those of tetrahydroanthracene and tetrahydrophenanthrene. 3a had relatively good affinity for melatonin receptors (K(i) = 28.7 nM). Introduction of an additional methoxy group gave a derivative (3c) with nanomolar affinity (K(i) = 0.7 nM), confirming the existence of a secondary binding site in the receptor which has been described previously. An increase in the affinity was also observed with the propionamido derivative 3e (K(i) = 6.0 nM). The potential agonist properties of the compound 3e were evaluated on the dermal melanocytes of Xenopus laevis tadpoles. At the concentration of 2.3 nM (5 x K(i)), melatonin gave a melanophore index value of 1. Similarly to melatonin, 3e was shown to be a potent agonist of the melanosome aggregation.

Full text of DOI:10.1021/jm960219h

J . Med. Chem. 1996, 39, 3089-3095
3089
Syn th esis of 2-Am id o-2,3-d ih yd r o-1H-p h en a len e Der iva tives a s New
Con for m a tion a lly Restr icted Liga n d s for Mela ton in Recep tor s
Monique Mathe´-Allainmat,† Florence Gaudy,† Sames Sicsic,† Anne-Laure Dangy-Caye,† Shuren Shen,†
Be´atrice Bre´mont,† Zohra Benatalah,† Michel Langlois,*,† Pierre Renard,‡ and Philippe Delagrange§
CNRS-BIOCIS, URA 1843, Faculte´ de Pharmacie, 5 rue J . B. Cle´ment, 92296 Chaˆtenay-Malabry, France, ADIR,
1 rue C. He´bert, 92415 Courbevoie, France, and Institut de Recherche Internationale Servier, Place des Ple´iades,
92415 Courbevoie, France
Received March 18, 1996X
Tetrahydroanthracene, tetrahydrophenanthrene, and tetrahydrophenalene moieties were used
to design novel constrained melatoninergic agents. Compounds 1 and 2 were synthesized from
the cyclization of the aryl succinic acids 6a ,b followed by catalytic reduction, Curtius degradation
to the amino derivatives, and acetylation. The phenalene derivatives 3 were prepared by
cyclization of the aza lactones of the corresponding R-N-acetyl amino acids. The ketone
derivatives were reduced directly by catalytic hydrogenation to produce the compounds 3. The
different compounds were evaluated in vitro in binding assays using 2-[125I]iodomelatonin and
chicken brain membranes. Melatonin and 2-acetamido-8-methoxytetralin were used as the
reference compounds. The results showed the superiority of the dihydrophenalene framework
3 over those of tetrahydroanthracene and tetrahydrophenanthrene. 3a had relatively good
affinity for melatonin receptors (Ki ) 28.7 nM). Introduction of an additional methoxy group
gave a derivative (3c) with nanomolar affinity (Ki ) 0.7 nM), confirming the existence of a
secondary binding site in the receptor which has been described previously. An increase in
the affinity was also observed with the propionamido derivative 3e (Ki ) 6.0 nM). The potential
agonist properties of the compound 3e were evaluated on the dermal melanocytes of Xenopus
laevis tadpoles. At the concentration of 2.3 nM (5 × Ki), melatonin gave a melanophore index
value of 1. Similarly to melatonin, 3e was shown to be a potent agonist of the melanosome
aggregation.
In tr od u ction
structure-activity relationships have demonstrated the
favorable role of 2-halogeno substitution in increasing
the affinity for melatonin receptors. 5-Methoxy substi-
tution seems to be implicated in agonist activity because
N-acetyltryptamine has been described as a partial
agonist12a and, more recently, antagonist activity at
melatonin receptors has been demonstrated with 2-aryl-
substituted derivatives.13 Several recent reports have
described the melatoninergic agonist properties of bioi-
sosteric naphthalene derivatives,14 and, in particular,
we emphasized the important role played by the sub-
stituent located on the ortho position14c of the ethyla-
mido chain on the affinity of such compounds for high-
affinity 2-[125I]iodomelatonin binding sites.
Melatonin is a pineal hormone which regulates a
variety of endocrinological, neurophysiological, and
behavioral functions in vertebrates.1 It plays a role in
the regulation of circadian rhythms2 and has been
implicated in several disorders such as delayed sleep
phase syndrome, anxiety, and seasonal depression.3
More recently, some important new properties of mel-
atonin have been described such as antitumoral activity,
regulation of immune responsiveness,4 and scavenging
of hydroxy radicals.5 Its effects are mediated through
membrane receptors located in different structures of
the brain, in particular in the suprachiasmatic nucleus
(SCN)6 and pars tuberalis7 where it regulates reproduc-
tive function in photoperiodic species. Receptors are
also present in peripheral tissues such as the intestine.8
Recently, several melatonin receptors have been
cloned;9a-d they are members of the G protein-coupled
receptor family and appear to inhibit the synthesis of
cyclic AMP.9e These receptors have been characterized
by the high-affinity specific binding of 2-[125I]iodomel-
atonin.10 Moreover, melatonin has also been character-
ized as the natural ligand of some nuclear receptors.11
Recently, considerable interest has evolved in the search
for new molecules capable of mimicking or antagonizing
responses to melatonin. Such compounds constitute
important tools for the elucidation of the physiological
roles of melatonin. Several indolic analogues12a,b of
melatonin have been found to act as agonists, and
The determination of structural parameters impli-
cated in molecular recognition by the receptor is impor-
tant for the description of the melatoninergic pharma-
cophore. Conformational analysis15 of melatonin demon-
strated, as expected for such a molecule, a large number
of permissible conformers and the impossibility of
assigning the active conformation. The development of
high-affinity, conformationally locked compounds is
essential for this purpose. Several rigid analogues of
melatonin have been reported by Garratt13b who dem-
onstrated, in a series of tricyclic indoles, the superiority
of the cis partially constrained conformer over the trans
as an agonist in the pigment aggregation model. Cop-
inga16 also reported that 2-acetamido-8-methoxytetralin
could be a useful framework for the design of new
melatoninergic agents.
† CNRS-BIOCIS.
‡ ADIR.
We present, herein, our approach to the design of new
constrained melatoninergic agents using the 2-acet-
§ Institut de Recherche Internationale Servier.
X Abstract published in Advance ACS Abstracts, J uly 1, 1996.
S0022-2623(96)00219-1 CCC: $12.00 © 1996 American Chemical Society

3090 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16
Mathe´-Allainmat et al.
Sch em e 1a
a
(a) (Ac)2O, reflux, 2 h; (b) AlCl3, nitrobenzene, 0 °C, 5 min; (c) H2, Pd/C (10%), AcOH, 70 °C or Pd/C (5%), MeOH, HCl, 50 °C, 19 h;
(d) diphenyl phosphorazidate, Et3N, t-BuOH, reflux, 18 h; (e) 4 N HCl, AcOEt, rt, 3 h; (f) AcCl, CH2Cl2, Et3N.
Sch em e 2a
a
(a) Ac-NHCH(COOEt)2, NaH/DMF or Na/EtOH, NaOH, EtOH, reflux; (b) (Ac)2O, reflux; (c) AlCl3, CHCl2-CHCl2 or CH2Cl2; (d) H2,
Pd/C (10%), AcOH; (e) 3b, HCl (20%), reflux; (f) EtCOCl, Et3N, CH2Cl2.
amido-8-methoxytetralin moiety as the main element
of the pharmacophore and a naphthalene ring for its
ability to increase the affinity. Consequently, com-
pounds 1-3 were synthesized and evaluated in binding
assays and compared to the tetralin derivative 4. These
derivatives should provide important structural infor-
mation on the relative positions of the aromatic ring and
the acetamido group of the active form of melatonin in
the receptor site.
in nitrobenzene with AlCl3. The ketone function was
reduced by hydrogen in either acetic acid or methanol
in the presence of 10% or 5% Pd/C, respectively, to
provide the carboxylic acids 8a ,b which were reacted
with diphenyl phosphorazidate (DPPA) in tert-butyl
alcohol under reflux to give the corresponding carbam-
ates. They were hydrolyzed directly by anhydrous HCl
in EtOAc to the amino hydrochlorides 9a ,b and trans-
formed to the acetamido derivatives 1 and 2 according
to the process recently reported by us.14c 4 was syn-
thesized by a previously described pathway.17
With the purpose of comparing the affinities of the
phenalene derivatives 3 and the previously described
naphthalene derivatives14c for melatonin receptors, the
unsubstituted, monomethoxy, and dimethoxy deriva-
tives 3a -c, respectively, were synthesized. They were
prepared via a pathway shown in Scheme 2 using
cyclization of the R-N-acetyl amino acid derivatives 11.
Compounds 11a -c were prepared from a condensation
reaction between the diethyl N-acetamidomalonate and
the corresponding arylmethyl chlorides 10a -c followed
by decarboxylation in a NaOH ethanolic solution.
1-Naphthylmethyl chloride (10a ) was condensed easily
with diethyl N-acetamidomalonate in ethanol under
reflux in the presence of NaOEt to yield the correspond-
ing derivative 11a , while the 2-methoxy and 2,7-
dimethoxy derivatives only reacted in DMF under reflux
in the presence of NaH. The amino acids 11a -c were
transformed to the aza lactone derivatives 12 by reac-
tion with acetic anhydride, and they were then cyclized
to the tricyclic ketones 13a -c in 1,1′,2,2′-tetrachloro-
ethane in the presence of AlCl3.17 It was observed that
the reaction could be run in methylene chloride instead
of 1,1′,2,2′-tetrachloroethane. However, the yield from
the reaction was poor (10-25%) in both cases. In the
course of the cyclization reaction, demethylation of the
Ch em istr y
Compounds 1 and 2, derived from tetrahydroan-
thracene and tetrahydrophenanthrene moieties, respec-
tively, were prepared by the synthetic route shown in
Scheme 1 according to the method reported by us for
the synthesis of 8-OH-DPAT.17 Briefly, (arylmethyl)-
succinic acids 6a ,b were prepared by the condensation
of diethylacetylsuccinate with 1-methoxy-2-(chlorometh-
yl)naphthalene (5a ) and 2-methoxy-3-(chloromethyl)-
naphthalene (5b), respectively. These were then trans-
formed to their corresponding anhydrides to be cyclized
to the keto acids 7a ,b under Friedel-Craft conditions

Phenalenes as New Ligands for Melatonin Receptors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16 3091
Ta ble 1. Affinities of the Tricyclic Derivatives 1-3 for
for these receptors. These results indicate that the
relative position of the aromatic ring with regard to the
acetamido group is an important structural parameter
of the melatoninergic pharmacophore. The influence of
the methoxy group on the affinity for the receptor was
emphasized by these results as a marked decrease in
affinity was observed with the unsubstituted compound
3a (Ki ) 195 nM), while the introduction of an additional
methoxy group (compound 3c) gave a derivative with
nanomolar affinity (Ki ) 0.7 nM), equipotent to mela-
tonin (Ki ) 0.46 nM). These data confirmed the results
reported recently by us14c on the existence of a secondary
binding site capable of productive interactions in the
ortho position of the ethylamido chain of melatonin
which is different from the binding site for the methoxy
group mimicking that of melatonin. The unfavorable
influence of the hydroxy group was noted with com-
pound 3d (Ki ) 22.8 nM) compared to 3c. However, its
effect was less marked than in N-acetyl-5-hydroxy-
tryptamine which was clearly less active (Ki ) 1640 nM)
than melatonin. The favorable role of the 10 π-electron
system on the efficency of binding to the receptor was
also confirmed by comparing the affinity of 3b (Ki ) 28.7
nM) with that of 2-acetamido-8-methoxytetralin (Ki )
161 nM). Moreover, the derivative 3e was prepared for
comparison with the propionamide naphthalene deriva-
tive previously reported by us13c to be a full melatonin-
ergic agonist. A clear increase in affinity was observed
with compound 3e which was 5-fold more potent (Ki )
6 nM) than compound 3b. These data again indicate
that the structure-activity relationship for the dihy-
drophenalene derivatives seems to be similar to that
observed with the naphthalene derivatives and, conse-
quently, that the binding site could be similar for both
series of compounds. Thus, dihydrophenalene deriva-
tives provide essential information on the structural
parameters implicated in recognition by melatonin
receptors, particularly on the relative locations of the
aromatic ring and the amido group of melatonin in the
receptor site.
Melatonin Receptorsa
However, it was also important to examine the
stereochemistry of the amido group with regard to the
ring in compounds 3 to provide definitive confirmation
of the pharmacophore structure. Analysis of the 1H
NMR spectra of compounds 3a -c showed clearly that
the pseudoaxial or pseudoequatorial stereochemistry of
the amido group depended upon the solvent. In CDCl3,
the coupling values (Hz) of the hydrogen in the R
positions of the amido function (J 1-2 ) 5.9, J 1′-2 ) 3.9
for 3a , J 1-2 ) 5.0, J 1′-2 ) 4.3 for 3b, and J 1-2 ) 5.9,
J 1′-2 ) 4.4 for 3c) indicated an axial position of the
amido group, while in DMSO-d6 they were in favor of
the equatorial position (J 1-2 ) 10.1, J 1′-2 ) 4.2 for 3a ,
a
Ki values were obtained in vitro by binding assays using
2-[125I]iodomelatonin (0.05 nM) and chicken brain membranes (25
°C, 60 min). Seven concentrations of the compound under test
were used, and each assay was performed in triplicate. Ki values
are expressed in nM ( the standard error of the mean (SEM) and
were calculated using the Cheng-Prussof equation from the IC50
values obtained from competition curves; the data are the results
of one or two separate determinations.
b
dimethoxy compound 13c was observed to provide
compound 13d . The reduction of the different ketones
13a -d took place in acetic acid in the presence of 10%
Pd/C to give compounds 3a -d .
J 1-2 ) 10.4, J 1′-2 ) 3.4 for 3b, and J 1-2 ) 10.5, J 1′-2
)
Biologica l Eva lu a tion a n d Discu ssion
4.4 for 3c). Conformational analysis of 3b was per-
formed with the Random Search program (Sybyl 6.03)
and showed that the absolute minimum energy con-
former had axial stereochemistry. However, an energy
difference of only 0.6 kcal/mol was calculated for the
corresponding equatorial stereoisomer, confirming the
NMR data and indicating that either conformer could
be considered as the biologically active form.
The affinities of the compounds for melatonin binding
sites were evaluated in vitro in binding assays using
2-[125I]iodomelatonin and chicken brain membranes
according to the previously described method14c and are
reported in Table 1.
Examination of the results showed the superiority of
the dihydrophenalene framework over those of the
tetrahydroanthracene and tetrahydrophenanthrene moi-
eties for recognition by melatonin receptors. Com-
pounds 1 and 2 had low activity compared to compound
3b which had relatively good affinity (Ki ) 28.7 nM)
Comparison of the biological activity of compounds
3b,c with the corresponding naphthalene derivatives14c
showed a decrease of 1 order of magnitude in their
potency for melatonin receptors. It is possible that the

3092 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16
Mathe´-Allainmat et al.
2-Meth oxy-3-(ch lor om eth yl)n a p h th a len e (5b). It was
synthesized from 2-methoxy-3-(hydroxymethyl)naphthalene
(13.49 g, 71.8 mmol) according to the general procedure. It
was obtained as a pale yellow powder (14.57 g, 98.3%) and
loss of flexibility due to the phenalene framework
decreased the fit with the receptor and might also have
changed the pharmacological profile of these molecules.
The potential agonist properties of the compound 3e,
the rigid analogue of the previously described14c naph-
thalene derivative, were evaluated on dermal melano-
cytes of Xenopus laevis tadpoles. It was previously
demonstrated that melatonin brought about a contrac-
tion of the melanophores and, consequently, produced
significant lightening of the skin.19 The degree of the
melanosome dispersion on the head and the dorsal
surface of the tadpoles was examined under the micro-
scope and evaluated using the melanophore index
ranging from 1 to 5.20 At a concentration of 30 nM (5
× Ki value for chicken brain receptors), the phenalene
derivative 3e gave a clear melanosome aggregation with
a melanophore index value of 1. Melatonin used at a
concentration of 2.3 nM (5 × Ki value for chicken brain
receptors) gave a similar effect.
1
used without further purification: mp 134 °C; H NMR (200
MHz, CDCl3) δ 7.7 (m, 1H), 7.6 (m, 2H), 7.25-7.35 (m, 2H),
7.0 (s, 1H), 4.7 (s, 2H), 3.8 (s, 3H); 13C NMR (200 MHz, CDCl3)
δ 155.2, 134.4, 129.7, 128.1, 127.5, 127.1, 126.6, 126.2, 123.8,
105.3, 55.3, 41.9.
2-Meth oxy-1-(ch lor om eth yl)n aph th alen e (10b). 2-Meth-
oxy-1-(chloromethyl)naphthalene was synthesized from 2-meth-
oxy-1-(hydroxymethyl)naphthalene (7.4 g, 39.31 mmol) accord-
ing to the general procedure. The pale yellow powder obtained
was pure 2-methoxy-1-(chloromethyl)naphthalene (7.2 g, 88%)
and used without further purification: 1H NMR (200 MHz,
CDCl3) δ 8.05 (d, 1H), 7.84 (2d, 2H), 7.57 (t, 1H), 7.39 (t, 1H),
7.28 (d, 1H), 4.19 (s, 2H), 4.01 (s, 3H).
2,7-Dim eth oxy-1-(ch lor om eth yl)n aph th alen e (10c). 2,7-
Dimethoxy-1-(chloromethyl)naphthalene was synthesized from
2,7-dimethoxy-1-(hydroxymethyl)naphthalene (4.0 g, 18 mmol)
according to the general procedure; 4.08 g (94%) of the pure
2,7-dimethoxy-1-(chloromethyl)naphthalene was obtained and
used without further purification: 1H NMR (200 MHz, CDCl3)
δ 7.77 (d, J ) 9 Hz, 1H), 7.70 (d, J ) 9 Hz, 1H), 7.28 (d, J )
3 Hz, 1H), 7.11 (d, J ) 9 Hz, 1H), 7.05 (dd, J ) 9, 3 Hz, 1H),
5.16 (s, 2H), 3.99 (s, 3H), 3.97 (s, 3H).
P r ep a r a tion of th e (Ar ylm eth yl)su ccin ic Acid s 6a ,b:
Gen er a l P r oced u r e. Sodium (265 mmol) was added in small
pieces to a solution of diethyl acetylsuccinate (278 mmol) in
200 mL of dry toluene and heated at 80 °C. Arylmethyl
chloride (316 mmol) was added slowly, and the reaction
mixture was refluxed for 18 h. The cooled solution was
acidified with acetic acid to pH 7 and evaporated. Water was
added, and the solution was extracted with ether. The
combined organic layers were dried over MgSO4, and the
solvent was removed to give a residue which was hydrolyzed
by boiling with 1400 mL of 2 N NaOH for 18 h. The cold
alkaline solution was washed with ether, and acidification with
concentrated HCl produced the (arylmethyl)succinic acid as
an oil which was extracted with ethyl acetate. The organic
layer was dried (MgSO4) and the solvent evaporated.
Phenalene derivatives would therefore appear to be
promising tools to improve the understanding of the
structural parameters implicated in molecular recogni-
tion by the receptor. Moreover they constitute a new
class of melatonin receptor agonists. Further studies
are in progress to evaluate their pharmacological po-
tential.
Exp er im en ta l Section
Melting points were determined on a METTLER FP 61
apparatus and are uncorrected. 1H and 13C NMR spectra were
recorded on a BRUKER AC 200 or an AM 300 spectrometer
with tetramethylsilane as the internal standard. Chemical
shifts are reported in parts per million (ppm) in δ units. 1H
NMR multiplicity data are denoted by s (singlet), d (doublet),
dd (doublet of doublets), t (triplet), q (quadriplet), m (multip-
let), and br (broad). Coupling constants are in hertz. Elemen-
tal analyses were performed at the CNRS analysis service in
Vernaison (France) or at the Microanalysis Service in Chaˆt-
enay-Malabry Faculty (France). Each compound gave an
elemental analysis within (0.45% of the theoretical values.
Diethyl acetylsuccinate, 2-methoxybenzyl alcohol, 1-methyl-
naphthyl chloride (10a ), and the naphthoic acids were pur-
chased from Aldrich-Chimie (Strasbourg).
Methyl 2-methoxy-3-naphthoate, methyl 1-methoxy-2-naph-
thoate, and methyl 2-methoxy-1-naphthoate were synthesized
by esterification of the corresponding acids.21 2-Methoxy-3-
(hydroxymethyl)naphthalene, 1-methoxy-2-(hydroxymethyl)-
naphthalene, and 2-methoxy-1-(hydroxymethyl)naphthalene
were prepared by the reduction of the above esters with
AlLiH4.14c 2,7-Dimethoxy-1-(hydroxymethyl)naphthalene was
prepared by the reduction of 2,7-dimethoxy-1-naphthaldehyde.14c
2-Amino-8-methoxytetralin was synthesized according to the
process already described.17
P r ep a r a t ion of Ch lor id es 5a ,b a n d 10b ,c: Gen er a l
P r oced u r e. A solution of thionyl chloride (1.5 equiv) and
pyridine (1 equiv) in anhydrous toluene (360 mL) was cooled
to 0 °C in an ice bath. Alcohol (360 mmol, 1 equiv) was added
slowly while stirring vigorously. The reaction mixture was
stirred at room temperature overnight and then poured into
ice. The solution was stirred for 1 h. The organic layer was
separated and washed twice with water and then with a
saturated aqueous solution of NaHCO3 and brine. After drying
over MgSO4, the solvent was evaporated to give the crude
chloride.
1-Meth oxy-2-(ch lor om eth yl)n a p h th a len e (5a ). It was
synthesized from 1-methoxy-2-(hydroxymethyl)naphthalene
(26 g, 138.3 mmol) according to the general procedure. It was
obtained as a pale yellow powder (27.95 g, 98%) and used
without further purification: mp 134 °C; 1H NMR (200 MHz,
CDCl3) δ 8.0 (m, 1H), 7.7 (m, 1H), 7.3-7.5 (m, 4H), 4.75 (s,
2H), 3.9 (s, 3H); 13C NMR (200 MHz, CDCl3) δ 155.0, 134.9,
128.0, 127.6, 127.4, 126.6, 126.15, 125.9, 124.5, 122.3, 62.9,
40.9.
[(1-Meth oxy-2-n a p h th yl)m eth yl]su ccin ic Acid (6a ). It
was obtained from compound 5a (27.95 g, 135.4 mmol)
according to the general procedure. The crude product was
recrystallized (acetone/toluene) to provide 6.51 g of the pure
1
compound (17%): mp 161 °C; H NMR (200 MHz, CD3OD) δ
7.85 (d, J ) 7.3 Hz, 1H), 7.6 (d, J ) 7.3 Hz, 1H), 7.35 (d, J )
8.5 Hz, 1H), 7.2-7.3 (m, 2H), 7.1 (d, J ) 8.5 Hz, 1H), 3.7 (s,
3H), 2.8-3.1 (m, 3H), 2.2-2.6 (m, 2H); 13C NMR (200 MHz,
CD3OD) δ 178.2, 175.6, 155.3, 135.6, 129.2, 129.1, 129.0, 128.0,
126.9, 126.7, 125.1, 122.9, 62.3, 43.4, 35.0, 32.8. Anal.
(C16H16O5) C, H.
[(2-Meth oxy-3-n a p h th yl)m eth yl]su ccin ic Acid (6b). It
was synthesized from compound 5b (19.43 g, 94.1 mmol)
according to the general procedure. The crude product was
recrystallized (acetone/toluene) to provide 4.3 g of the pure
1
compound (16%): mp 159 °C; H NMR (200 MHz, CD3OD) δ
7.75-7.8 (m, 2H), 7.6 (s, 1H), 7.3-7.5 (m, 2H), 7.3 (s, 1H), 4.0
(s, 3H), 3.2-3.4 (m, 2H), 3.0 (m, 1H), 2.4-2.75 (m, 2H); 13C
NMR (200 MHz, CD3OD) δ 178.6, 175.9, 157.8, 135.6, 130.9,
130.2, 129.9, 128.3, 127.6, 127.1, 124.8, 106.3, 55.9, 42.9, 36.4,
34.2. Anal. (C16H16O5‚0.25H2O) C, H.
P r ep a r a t ion of t h e Ca r b oxyt et r a lon e Der iva t ives
7a ,b: Gen er a l P r oced u r e. The (arylmethyl)succinic acids
(33.6 mmol) were converted to their corresponding anhydrides
by refluxing for 2 h with acetic anhydride (80 g). The solvent
was removed in vacuo to give a brown oil which was the crude
anhydride used without further purification. It (25.5 mmol)
was dissolved in 60 mL of nitrobenzene and added slowly to a
cooled solution (0 °C) of AlCl3 (75.5 mmol) in 60 mL of
nitrobenzene. The reaction mixture was stirred for 5 min, and
a solution of 40 g of ice with 40 mL of concentrated HCl was
added. After standing overnight, the nitrobenzene was re-
moved by steam distillation. The cooled solution was extracted
with ethyl acetate, the organic layer was dried over MgSO4,
and the solvent was evaporated. The crude product was

Phenalenes as New Ligands for Melatonin Receptors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16 3093
purified by flash chromatography (silica gel, CH2Cl2-MeOH,
95:5) to give the pure carboxytetralone.
4.38-4.17 (m, 4H), 4.07 (s, 2H), 3.94 (s, 3H), 3.82 (s, 3H), 1.65
(s, 3H), 1.29 (t, 6H).
10-Meth oxy-3-ca r boxy-1,2,3,4-tetr a h yd r oa n th r a cen -1-
on e (7a ). It was prepared from the 1-succinic acid derivative
6a (7.79 g, 27 mmol) according to the general procedure to give
It (4.01 g, 10 mmol) was converted into 11c by hydrolysis
according to the general procedure to give 2.3 g (76%) of the
pure product: 1H NMR (200 MHz, CD3OD) δ 7.68 (d, 1H), 7.63
(d, 1H), 7.32 (d, 1H), 7.13 (d, 1H), 6.84-6.78 (dd, 1H), 4.67 (t,
1H), 3.90 (s, 6H), 3.67-3.40 (m, 2H), 1.83 (s, 3H). Anal.
(C17H19NO5) C, H, N.
1
3.38 g of the pure tetralone 7a (46.3%): mp 202 °C; H NMR
(200 MHz, CD3OD) δ 8.3 (s, 1H), 8.0 (d, J ) 8.4 Hz, 1H), 7.95
(d, J ) 8.2 Hz, 1H), 7.5 (td, J ) 8.2, 6.9 Hz, 1H), 7.4 (td, J )
8.4, 6.91 Hz, 1H), 3.9 (s, 3H), 2.8-3.5 (m, 5H); 13C NMR (200
MHz, CD3OD) δ 197.0, 170.0, 153.7, 136.3, 130.2, 128.7-
127.2-126.4-124.6-121.7 (7C), 62.0, 40.8, 39.3, 25.3. Anal.
(C16H14O4‚0.3H2O) C, H.
P r ep a r a tion of th e 2,3-Dih yd r o-1H-p h en a len -1-on e
Der iva tives 13a -c: Gen er a l P r oced u r e. 2-Acetamidopro-
panoic acid derivatives 11a -c (13.92 mmol) were converted
into their corresponding azalactones 12a -c by refluxing for
40 min in acetic acid (14 mL). The solvent was removed in
vacuo to give a brown-yellow product as an oil which was used
without purification in the next step. It was dissolved in dry
1,1′,2,2′-tetrachloroethane (90 mL) or CH2Cl2 and added
dropwise to a suspension of AlCl3 (3 equiv) in the same solvent
(50 mL). The reaction mixture was heated to 60 °C for 2 h,
poured into a mixture of ice (17 g) and concentrated HCl (1.1
mL), and stirred vigorously for 1 h. The organic layer was
separated and the aqueous phase extracted twice with dichlo-
romethane. The combined organic layers were dried over
MgSO4 and removed in vacuo. The residue was chromato-
graphed (silica gel, CH2Cl2-MeOH, 99:1) to give the pure
product.
10-Meth oxy-2-ca r boxy-1,2,3,4-tetr a h yd r oph en a n th r en -
4-on e (7b). It was synthesized from the succinic acid deriva-
tive 6b (5.09 g, 17.7 mmol) according to the general procedure
1
to give 2.77 g of the pure tetralone 7b (58%): mp 196 °C; H
NMR (200 MHz, CD3OD) δ 9.1 (m, 1H), 7.6 (m, 1H), 7.35 (m,
2H), 7.2 (s, 1H), 3.8 (s, 3H), 2.8-3.4 (m, 5H); 13C NMR (200
MHz, CD3OD) δ 200.6, 177.0, 155.7, 138.8, 135.2, 129.4, 128.9,
128.4, 127.7, 127.5, 127.2, 112.7, 56.4, 43.4, 40.2, 27.7. Anal.
(C16H14O4) C, H.
P r ep a r a tion of th e 2-Aceta m id op r op a n oic Acid De-
r iva tives 11a -c: Gen er a l P r oced u r e. A suspension of 60%
sodium hydride in oil (1.2 equiv) was added in small portions
to a solution of diethyl acetamidomalonate (1.2 equiv) in 80
mL of dry DMF under an inert atmosphere. The solution was
stirred until no more gaseous emissions were observed. The
(chloromethyl)naphthalene derivative (50.57 mmol, 1.0 equiv),
dissolved in 40 mL of dry DMF, was added dropwise, and the
reaction mixture was refluxed with stirring for 20 h. The
solvent was removed in vacuo and the residue taken up in CH2-
Cl2 and washed with water. The organic layer was dried over
MgSO4 and evaporated to give the acetamidomalonate deriva-
tive which was used without further purification. It (1.0 equiv)
was dissolved in 44 mL of ethanol. A solution of 2 N aqueous
sodium hydroxide (3 equiv) was added, and the reaction
mixture was refluxed for 6 h and then concentrated. After an
initial extraction with diethyl ether, the aqueous solution was
2-Aceta m id o-2,3-d ih yd r o-1H-p h en a len -1-on e (13a ). It
was synthesized from the corresponding acetamido acid 11a
(6 g, 23 mmol) according to the general procedure in 1,1′,2,2′-
tetrachloroethane to give 1.47 g (26%) of the desired product
13a : mp 180 °C; 1H NMR (200 MHz, CDCl3) δ 8.17-8.09 (m,
2H), 7.86-7.79 (m, 1H), 7.64-7.49 (m, 3H), 6.89 (br s, 1H),
5.09-4.96 (m, 1H), 4.13-4.02 (dd, J ) 15, 6.5 Hz, 1H), 3.21-
3.08 (dd, J ) 15, 13 Hz, 1H), 2.15 (s, 3H). Anal. (C15H13
NO2‚0.25 H2O) C, H, N.
-
4-Met h oxy-2-a cet a m id o-2,3-d ih yd r o-1H -p h en a len -1-
on e (13b). It was synthesized from the corresponding aceta-
mido acid 11b (4 g, 13.92 mmol) according to the general
procedure in 1,1′,2,2′-tetrachloroethane to give 0.93 g (25%)
of the pure compound 13b: 1H NMR (200 MHz, CDCl3) δ 7.83
(d, 1H), 7.72 (2d, 2H), 4.72 (t, 1H), 7.18-7.3 (m, 2H), 4.41-
4.51 (q, 1H), 3.88 (s, 3H), 3.55-3.60 (m, 2H), 2.1 (s, 3H). Anal.
(C16H15NO3‚0.25H2O) C, H, N.
4,9-Dim eth oxy- an d 4-Meth oxy-9-h ydr oxy-2-acetam ido-
2,3-d ih yd r o-1H-p h en a len -1-on e (13c,d ). They were syn-
thesized from the corresponding acetamido acid 11c (4 g, 13.92
mmol) according to the general procedure in dichloromethane.
The compounds were obtained as solids. 13c (0.19 g, 10%):
1H NMR (200 MHz, CDCl3) δ 7.96 (d, J ) 9 Hz, 1H), 7.71 (d,
J ) 9 Hz, 1H), 7.18-7.12 (q, 2H), 6.97 (br s, 1H), 4.88 (m,
1H), 4.39-4.19 (dd, J ) 16, 7 Hz, 1H), 4.04 (s, 3H), 3.94 (s,
3H), 2.74-2.59 (m, 1H), 2.11 (s, 3H). Anal. (C17H17NO4) C,
H, N. 13d (0.2 g, 12%): 1H NMR (200 MHz, CDCl3) δ 12.35
(s, 1H), 7.90 (d, J ) 9 Hz, 1H), 7.67 (d, J ) 9 Hz, 1H), 7.12 (d,
J ) 9 Hz, 1H), 6.97 (d, J ) 9 Hz, 1H), 6.52 (br s, 1H), 4.97-
4.94 (m, 1H), 4.22-4.17 (dd, J ) 16, 8 Hz, 1H), 3.94 (s, 3H),
2.74-2.67 (m, 1H), 2.15 (s, 3H).
P r ep a r a tion of th e 2-Ca r boxytetr a lin Der iva tives 8a ,b
a n d 2-Aceta m id o-2,3-d ih yd r o-1H-p h en a len e Der iva tives
3a -d : Gen er a l P r oced u r e. The ketone derivative (11.1
mmol) was reduced with H2 under atmospheric pressure using
palladium on activated carbon as the catalyst. For the tetralin
derivatives 7a ,b, the mixture was stirred overnight with a 10%
weight of Pd/C (10%) in AcOH or with Pd/C (5%) with a few
drops of concentrated HCl in MeOH. For the phenalene
derivatives 13a -d , a 50% weight of Pd/C (10%) was used at
room temperature for 28 h. The catalyst was filtered, and the
solution was concentrated under reduced pressure. The
residue was purified by chromatography on silica gel to give
the pure compound.
9-Meth oxy-2-car boxy-1,2,3,4-tetr ah ydr oan th r acen e (8a).
It was synthesized from 7a (2.81 g, 9.8 mmol) according to
the general procedure in MeOH at 50 °C. After filtration the
oil was hydrolyzed by boiling with 2 N NaOH for 30 min and
acidified with concentrated HCl to pH 1 (1.53 g, 61%): mp
192 °C; 1H NMR (200 MHz, CDCl3) δ 7.9 (m, 1H), 7.6 (m, 1H),
7.3 (s, 1H), 7.3-7.2 (m, 2H), 3.8 (s, 3H), 3.3 (m, 1H), 3.0-2.5
(m, 5H), 2.1 (m, 1H), 1.8 (m, 1H); 13C NMR (200 MHz, CDCl3)
acidified to pH 1 with
a solution of 1 N KHSO4. The
suspension obtained was extracted with ethyl acetate. The
organic layer was dried over MgSO4 and evaporated under
reduced pressure to give the pure acetamido acid derivative.
2-Aceta m id o-3-(1-n a p h th yl)p r op a n oic Acid (11a ). It
was prepared from 1-methylnaphthyl chloride (10a ) (13.5 mL,
91 mmol) according to the general procedure to give diethyl
(1-methylnaphthyl)acetamidomalonate (24.5 g, 95%) as a pure
product: mp 107 °C; 1H NMR (200 MHz, CDCl3) δ 7.93-7.88
(m, 1H), 7.75-7.43 (m, 2H), 7.38-7.24 (m, 3H), 7.09 (d, 1H),
6.36 (s, 1H), 4.18-4.12 (m, 4H), 4.07 (s, 2H), 1.82 (s, 3H), 1.26
(t, 6H).
It was converted into 11a according to the general proce-
dure. The product was recrystallized (acetone/petroleum
ether) to give 11.26 g (61%) of a white powder: mp 169 °C; 1H
NMR (200 MHz, CD3OD) δ 7.98 (d, 1H), 7.68 (dd, 1H), 7.58 (t,
1H), 7.38-7.19 (m, 4H), 4.65-4.60 (m, 1H), 3.63-3.53 (dd, 1H),
3.19-3.08 (dd, 1H), 1.68 (s, 3H). Anal. (C15H15NO3‚0.25H2O)
C, H, N.
2-Acet a m id o-3-(2-m et h oxyn a p h t h yl)p r op a n oic Acid
(11b). It was prepared from the chloride derivative 10b (10.45
g, 50.57 mmol) according to the general procedure to give the
diethyl acetamidomalonate derivative (12.63 g, 64.5%) as a
1
pure product: mp 110 °C; H NMR (200 MHz, CDCl3) δ 7.89
(d, 1H), 7.71 (d, 1H), 7.68 (d, 1H), 7.36 (t, 1H), 7.24 (t, 1H),
7.16 (d, 1H), 6.19 (s, 1H), 4.16 (q, 4H), 4.05 (s, 2H), 3.78 (s,
3H), 1.63 (s, 3H), 1.22 (t, 6H).
It (8.1 g, 21.38 mmol) was converted into 11b (5.34 g, 87%)
by hydrolysis according to the general procedure: mp 201 °C;
1H NMR (200 MHz, CD3OD) δ 8.12 (d, 1H), 7.87 (2d, 2H), 7.56
(t, 1H), 7.45-7.36 (m, 2H), 4.78-4.74 (q, 1H), 4.04 (s, 3H),
3.77-3.52 (m, 2H), 1.88 (s, 3H). Anal. (C16H17NO4) C, H, N.
2-Acetam ido-3-(2,7-dim eth oxyn aph th yl)pr opan oic Acid
(11c). It was prepared from the chloride derivative 10c (4.08
g, 17 mmol) according to the general procedure to give the
diethyl acetamidomalonate derivative as a pure compound
(4.01 g, 55%): 1H NMR (200 MHz, CDCl3) δ 7.69 (d, J ) 9 Hz,
1H), 7.63 (d, J ) 9 Hz, 1H), 7.27 (d, J ) 2.3 Hz, 1H), 7.04 (d,
J ) 9 Hz, 1H), 6.96 (dd, J ) 9, 2.3 Hz, 1H), 6.27 (br s, 1H),

3094 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16
Mathe´-Allainmat et al.
δ 178.4, 153.1, 135.3, 133.1, 127.1, 125.4, 124.9, 122.6, 121.4
(11C), 61.1, 39.5, 28.8, 25.9, 25.6. Anal. (C16H16O3‚0.25H2O)
C, H.
1H), 3.0 (m, 2H), 2.8 (m, 1H), 2.5 (m, 1H), 2.1 (m, 1H), 1.8 (m,
1H); 13C NMR (200 MHz, CD3OD) δ 154.8, 135.15, 135.1, 128.6,
127.6, 127.1, 126.4, 124.0, 123.5, 122.6, 61.6, 49.0, 29.3, 28.2,
26.3. Anal. (C15H18ClNO) C, H, N.
10-Me t h o x y -2-c a r b o x y -1,2,3,4-t e t r a h y d r o p h e n a n -
th r en e (8b). It was synthesized from 7b (2.5 g, 9.3 mmol)
according to the general procedure in AcOH at 70 °C to give
10-M e t h o x y -2-a m i n o -1,2,3,4-t e t r a h y d r o p h e n a n -
th r en e Hyd r och lor id e (9b). It was obtained from the
corresponding acid 8b (1.18 g, 4.5 mmol) according to the
general procedure (77%): mp 272 °C; 1H NMR (200 MHz, CD3-
OD) δ 7.6 (d, J ) 7.3 Hz, 1H), 7.5 (d, J ) 8.7 Hz, 1H), 7.2-7.1
(m, 2H), 6.9 (s, 1H), 3.7 (s, 3H), 3.3 (m, 1H), 3.2-3.0 (m, 2H),
3.0-2.8 (m, 1H), 2.5 (m, 1H), 2.15 (m, 1H), 1.8-1.7 (m, 1H);
13C NMR (200 MHz, CD3OD) δ 156.5, 134.7, 132.3, 128.5,
128.2, 126.8, 124.8, 123.6, 123.5, 104.4, 55.7, 48.9, 29.3, 27.7,
25.0. Anal. (C15H18ClNO‚0.5H2O) C, H, N, Cl.
P r ep a r a tion of th e 2-Aceta m id o Der iva tives 1, 2, a n d
4. The free amine (1 equiv) was dissolved in dry dichlo-
romethane in the presence of triethylamine (1.2 equiv). Acetyl
chloride (1.2 equiv) was added at 0 °C, and the reaction mix-
ture was stirred for 1 h at room temperature. The organic
solution was washed with water, dried over MgSO4, and evap-
orated. The crude residue was purified by chromatography
(silica gel, CH2Cl2-MeOH, 98:5) to give the expected acet-
amide.
8-Meth oxy-2-a ceta m id otetr a lin (4). Compound 4 was
synthesized from the corresponding amine (0.35 g, 2 mmol)
according to the general procedure to give 0.24 g (56%) of the
pure product: 1H NMR (200 MHz, CDCl3) δ 7.0 (t, J ) 7.87
Hz, 1H), 6.61 (d, J ) 7.66 Hz, 1H), 6.55 (d, J ) 8.14 Hz, 1H),
6.05 (d, 1H), 4.16-4.08 (m, 1H), 3.68 (s, 3H), 3.03-2.92 (q, J
) 17.26, 5.5 Hz, 1H), 2.74-2.72 (m, 2H), 2.40-2.27 (q, J )
17.24, 8.4 Hz, 1H), 1.99-1.7 (m, 1H), 1.87 (s, 3H), 1.67-1.56
(m, 1H). Anal. (C13H17NO2‚0.25H2O) C, H, N.
1
the pure compound (1.96 g, 83%): mp 235 °C; H NMR (200
MHz, CDCl3) δ 7.8 (dd, J ) 7.3, 2.2 Hz, 1H), 7.6 (dd, J ) 7.2,
2 Hz, 1H), 7.3 (m, 2H), 6.9 (s, 1H), 3.8 (s, 3H), 2.5-3.3 (m,
5H), 2.25 (m, 1H), 1.8 (m, 1H); 13C NMR (200 MHz, CDCl3) δ
178.4, 155.6, 132.8, 132.0, 127.4, 126.9, 125.3, 125.2, 123.3,
122.5, 102.5, 54.9, 39.0, 26.2, 25.2, 25.1; low-resolution CIMS
m/ z 257 (M + 1)+.
2-Acet a m id o-2,3-d ih yd r o-1H -p h en a len e (3a ). Com-
pound 3a was synthesized from the corresponding phenalen-
1-one derivative 13a (1.47 g, 6 mmol) according to the general
procedure and purified by chromatography (silica gel, CH2-
Cl2-MeOH, 98:2) to give 0.96 g (70%) of the desired product:
1
mp 186 °C; H NMR (200 MHz, CDCl3) δ 7.72 (d, J ) 8 Hz,
2H), 7.41 (t, J ) 8 Hz, 2H), 7.25 (d, J ) 7 Hz, 2H), 5.54 (br s,
1H), 4.7-4.69 (m, 1H), 3.4-3.35 (dd, J ) 16, 4 Hz, 2H), 3.15-
3.09 (dd, J ) 16, 6 Hz, 2H), 1.86 (s, 3H); 13C NMR (400 MHz,
CDCl3) δ 169.87, 133.52, 132.63 (2C), 129.47, 126.6 (2C), 125.9
(2C), 125.5 (2C), 44.18, 36.54 (2C), 23.49. Anal. (C15H15
-
NO‚0.25H2O) C, H, N.
4-Meth oxy-2-acetam ido-2,3-dih ydr o-1H-ph en alen e (3b).
Compound 3b was synthesized from the corresponding phe-
nalen-1-one derivative 13b (1.0 g, 3.71 mmol) according to the
general procedure and purified by chromatography (silica gel,
CH2Cl2-MeOH, 98:1) to give the pure product (76%): mp 196-
1
197 °C; H NMR (200 MHz, CDCl3) δ 7.73 (d, J ) 9 Hz, 1H),
7.65 (dd, J ) 7 Hz, 1H), 7.3-7.19 (m, 3H), 5.5 (br s, 1H), 4.71-
4.62 (m, 1H), 3.93 (s, 3H), 3.34-3.01 (m, 4H), 1.86 (s, 3H).
Anal. (C16H17NO2) C, H, N.
9-Me t h oxy-2-a c e t a m id o-1,2,3,4-t e t r a h yd r oa n t h r a -
cen e (1). Compound 1 was synthesized from the correspond-
ing amine 9a (0.18 g, 0.79 mmol) to give 0.18 g (85%) of pure
4,9-Dim et h oxy-2-a cet a m id o-2,3-d ih yd r o-1H -p h en a l-
en e (3c). Compound 3c was synthesized from the correspond-
ing phenalen-1-one derivative 13c (0.17 g, 0.6 mmol) according
to the general procedure and purified by chromatography
(silica gel, CH2Cl2-MeOH, 98:2) to give 0.07 g of the pure
1
product: mp 161-162 °C; H NMR (200 MHz, CDCl3) δ 8.0
(m, 1H), 7.74 (m, 1H), 7.44-7.40 (m, 3H), 5.55 (d, 1H), 4.38
(m, 1H), 3.90 (s, 3H), 3.38-3.27 (q, 1H), 3.10-3.03 (t, 2H),
2.86-2.73 (q, 1H), 2.17-2.10 (m, 1H), 1.99 (s, 3H), 1.97-1.74
(m, 1H). Anal. (C17H19NO2) C, H, N.
1
product (43%): mp 254 °C; H NMR (200 MHz, DMSO-d6) δ
7.99 (d, 1H), 7.71 (dd, 2H), 7.22 (d, 2H), 3.95-3.89 (m, 1H),
3.86 (s, 6H), 3.28-3.23 (dd, J ) 16, 4 Hz, 2H), 2.6-2.53 (dd,
J ) 16, 10 Hz, 2H), 1.83 (s, 3H); 13C NMR (400 MHz, CDCl3)
δ 169.83, 153.07, 130.7, 127.05, 123.7, 116.74, 11.12, 55.98,
43.64, 29.02, 22.77. Anal. (C17H19NO3‚0.25H2O) C, H, N.
4-Meth oxy-9-h ydr oxy-2-acetam ido-2,3-dih ydr o-1H-ph e-
n a len e (3d ). Compound 3d was synthesized from the corre-
sponding phenalen-1-one derivative 13d (0.17 g, 0.6 mmol)
according to the general procedure and purified by chroma-
tography (silica gel, CH2Cl2-MeOH, 98:2) to give 0.07 g of the
pure product (37%): mp 245°C, 1H NMR (200 MHz, CD3-
COCD3) δ 7.62 (d, J ) 9 Hz, 1H), 7.50 (d, J ) 9 Hz, 1H), 7.25
(br s, 1H), 7.12 (d, J ) 9 Hz, 1H), 7.01 (d, J ) 9 Hz, 1H), 4.32-
4.18 (m, 1H), 3.89 (s, 3H), 3.41-3.33 (dd, 1H), 2.99 (br s, 1H),
2.79-2.67 (q, 2H), 1.86 (s, 3H).
P r ep a r a tion of th e 2-Am in otetr a lin Hyd r och lor id es
9a ,b. A solution of 2-carboxytetralin 8a ,b (7.5 mmol), diphenyl
phosphorazidate (1 equiv), and triethylamine (1.1 equiv) in 35
mL of tert-butyl alcohol was refluxed for 18 h. The reaction
mixture was evaporated, 220 mL of toluene was added, and
this solution was successively washed with a 5% citric acid
solution (20 mL), water (20 mL), a saturated aqueous NaHCO3
solution (40 mL), and brine (20 mL). The solvent was removed
in vacuo to provide the carbamate which was used without
further purification.
To a solution of the carbamate (1.1 mmol) in 10 mL of ethyl
acetate was added 10 mL of a 4 N HCl solution in dry ethyl
acetate. The reaction mixture was stirred for 3 h and then
evaporated to give the crude hydrochloride which was purified
by dissolution in ethanol and precipitation by the addition of
diethyl ether. The precipitate was filtered and dried to give
the pure amino hydrochloride.
9-Meth oxy-2-a m in o-1,2,3,4-tetr a h yd r oa n th r a cen e Hy-
d r och lor id e (9a ). It was synthesized from the corresponding
acid 8a (1.45 g, 5.7 mmol) according to the general procedure
(45%): mp 285 °C; 1H NMR (200 MHz, CD3OD) δ 7.8 (m, 1H),
7.6 (m, 1H), 7.3 (s, 1H), 7.2-7.3 (m, 2H), 3.8 (s, 3H), 3.4 (m,
10-Met h oxy-2-a cet a m id o-1,2,3,4-t et r a h yd r op h en a n -
th r en e (2). Compound 2 was synthesized from the corre-
sponding amine 9b (0.11 g, 0.5 mmol) according to the general
procedure to give 0.24 g (56%) of the pure product: 1H NMR
(200 MHz, CDCl3) δ 7.81 (d, 1H), 7.64 (d, 1H), 7.38-7.26 (m,
2H), 6.9 (s, 1H), 5.34 (d, 1H), 4.33-4.2 (m, 1H), 3.83 (s, 3H),
3.1-3.04 (m, 2H), 2.67-2.44 (m, 2H), 2.11-2.01 (m, 1H), 1.90
(s, 3H), 183-1.69 (m, 1H). Anal. (C17H19NO2‚0.25H2O) C, H,
N.
4-Met h oxy-2-p r op ion a m id o-2,3-d ih yd r o-1H -p h en a l-
en e (3e). To a solution of compound 3b (1.52 g, 5.95 mmol)
in ethanol (20 mL) was added 54 mL of a 10% aqueous HCl
solution. The reaction mixture was stirred for 20 h at 90 °C
and then cooled and made basic using 10% NaOH. The
aqueous solution was extracted with dichloromethane. The
organic layer was dried over MgSO4 and removed in vacuo to
afford the free amine which was used without further purifica-
tion.
The free amine (0.120 g, 0.56 mmol) was dissolved in dry
dichloromethane (5 mL) with triethylamine (0.118 mL, 0.84
mmol). Propionyl chloride (0.05 g, 0.56 mmol) was added at
0 °C, and the reaction mixture was stirred for 40 min at room
temperature. It was washed with water and dried over MgSO4
and the solvent removed. The crude propionamido derivative
was purified by column chromatography (silica gel, CH2Cl2-
MeOH, 95:5) to give the pure compound 3e (66%): mp 184-
1
186 °C; H NMR (200 MHz, CDCl3) δ 7.73 (d, J ) 9 Hz, 1H),
7.65 (d, J ) 7.5 Hz, 1H), 7.29-7.18 (m, 3H), 5.45 (d, 1H), 4.68-
4.65 (m, 1H), 3.93 (s, 3H), 3.35-3.03 (m, 4H), 2.03 (q, J ) 7.6
Hz, 2H), 1.07 (t, J ) 7.6 Hz, 3H); 13C NMR (200 MHz, CDCl3)
δ 177.22, 153.78, 131.52, 130.20, 128.44, 127.28, 126.26,
125.72, 123.44, 117.24, 112.91, 56.16, 43.28, 36.12, 29.74,
29.66, 9.79. Anal. (C17H19NO2) C, H, N.
Mela ton in Recep tor Bin d in g Assa y. Chickens (Red
Brook, 4 months, 3-4 kg; Cellubio, France) were decapitated
at 12 a.m. The brains were quickly removed and stored at
-80 °C. They were homogenized (Polytron) in 10 vol of ice-

Phenalenes as New Ligands for Melatonin Receptors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 16 3095
Mahle, C. D.; Weaver, D. R.; Slaugenhaupt, S. A.; Gusella, J . F.
cold Tris-HCl buffer (50 mM, pH 7.4) and washed twice by
centrifugation (44000g, 25 min, 4 °C). The resulting pellet was
resuspended in 10 vol of the same buffer to a final concentra-
tion of 5 or 6 mg of protein/mL as determined by the method
of Lowry et al. (1951). The membrane aliquots were stored at
-80 °C until subsequent use. Membrane aliquots (30 µL) were
incubated in a total volume of 0.25 mL of Tris-HCl buffer (50
mM, pH 7.4) with 0.05 nM 2-[125I]iodomelatonin and seven
concentrations of the compound under test. Each binding
assay was performed in triplicate. The incubation (25 °C, 60
min) was stopped by the addition of 3 mL of ice-cold buffer
and immediate vacuum filtration through glass fiber filters
(GF/B Whatman strips) presoaked in 0.1% poly(ethylenimine)
using a Brandel cell harvester. The filters were washed (3 ×
4 mL) with buffer, dried, and counted in a γ-counter (Crystal-
Packard). Nonspecific binding was defined with 10 µM 2-io-
domelatonin and represented 10% of the total binding.
Mela n op h or e Con tr a ction in X. la evis Ta d p oles. The
X. laevis larvae (stage 41) used in this study were obtained
from the Laboratoire de Biologie Cellulaire et Reproduction,
CNRS (Rennes, France). They were maintained in an aquarium
at 22 °C in the laboratory under natural illumination for 8
days and fed daily with powdered fish food. Prior to the
bioassay, tadpoles of uniform stage, size, and color were
selected, removed from the aquarium, and placed in groups of
5 in 100 mL beakers 18 h before the experiments which were
performed at midday. The compound under test was dissolved
in DMF and water mixture in a final volume of 5 mL and
added to the liquid in the beaker (45 mL) to a final concentra-
tion of 5 × Ki, the Ki value having been determined in binding
assays on chicken brain membranes. After 15 min, the
experiment was terminated by the addition to the test beaker
of an equal volume of 30% formaldehyde solution. The degree
of the melanophore response in each tadpole was determined
by examination of the melanosome configuration on the head
and dorsal surface under a microscope (magnification ×4) and
evaluated according to the melanophore index scale (1-5) of
Hogben and Slome.19 The data are the result of the mean of
individual determinations of the melanophore index and of two
consecutive assays. In the control assays, the value of the
melanophore index was 4.
Molecular characterisation of
a second melatonin receptor
expressed in human retina and brain: the Mel1b melatonin
receptor. Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 8734-8738. (d)
Reppert, S. M.; Weaver, D. R.; Cassone, V. M.; Godson, C.;
Kolakowski, L. F., J r. Melatonin receptors are for the birds:
molecular analysis of two receptor subtypes differentially ex-
pressed in chick brain. Neuron 1995, 15, 1003-1015. (e) Morgan,
P. J .; Lawson, W.; Davidson, G.; Howell, H. E. Guanine nucle-
otides regulate the affinity of melatonin receptors on the ovine
pars tuberalis. Neuroendocrinology 1989, 50, 359-362.
(10) Yuan, H.; Pang, S. F. 2-[125I]iodomelatonin-binding sites in the
pigeon brain: binding characteristics, regional distribution and
diurnal variation. J . Endocrinol. 1991, 128, 475-482.
(11) (a) Steinhilber, D.; Brungs, M.; Werz, O.; Wiensenberg, I.;
Danielsson, C.; Kahlen, J .-P.; Nayeri, S.; Schra¨der, M.; Carlberg,
C. The nuclear receptor for melatonin represses 5-lipoxygenase
gene expression in human B lymphocytes. J . Biol. Chem. 1995,
270, 7037-7040. (b) Carlberg, C.; Wiesenberg, I. The orphan
receptor family RZR/ROR, melatonin and 5-lipoxygenase: an
unexpected relationship. J . Pineal Res. 1995, 18, 171-178.
(12) (a) Heward, C. B.; Hadley, M. E. Structure activity-relationships
of melatonin and related indoleamines. Life Sci. 1975, 17, 1167-
1178. (b) Spadoni, G.; Stankov, B.; Duranti, A.; Biella, G.; Lucini,
V.; Salvatori, A.; Fraschini, F. 2-substituted 5-methoxy N-acyl-
tryptamines: synthesis, binding affinity for the melatonin
receptor, and evaluation of the biological activity. J . Med. Chem.
1993, 36, 4069-4074. (c) Garratt, P. J .; J ones, R.; Rowe, S. J .;
Sugden, D. Mapping the melatonin receptor. 1. The 5-methoxyl
group of melatonin is not an essential requirement for biological
activity. BioMed. Chem. Lett. 1994, 4, 1555-1558.
(13) (a) Garratt, P. J .; J ones, R.; Tocher, D. A.; Sugden, D. Mapping
the melatonin receptor. 3. Design and synthesis of melatonin
agonists and antagonists derived from 2-phenyltryptamines. J .
Med. Chem. 1995, 38, 1132-1139. (b) Garratt, P. J .; Vonhoff,
S.; Rowe, S. J .; Sugden, D. Mapping the melatonin receptor. 2.
Synthesis and biological activity of indole-derived melatonin
analogues with restricted conformations of the C-3 amidoethane
side chain. BioMed. Chem. Lett. 1994, 4, 1559-1564.
(14) (a) Yous, S.; Andrieux, J .; Howell, H. E.; Morgan, P. J .; Renard,
P.; Pfeiffer, B.; Lesieur, D.; Guardiola-Lemaitre, B. Novel
naphthalenic ligands with high affinity for the melatonin
receptor. J . Med. Chem. 1992, 35, 1484-1486. (b) Depreux, P.;
Lesieur, D.; Mansour, H. A.; Morgan, P.; Howell, F.; Renard,
P.; Caignard, D.-H.; Pfeiffer, B.; Delagrange, P.; Guardiola, B.;
Yous, S.; Demarque, A.; Adam, G.; Andrieux, J . Synthesis and
structure-activity relationships of novel naphthalenic and bioi-
sosteric related amidic derivatives as melatonin receptor ligands.
J . Med. Chem. 1994, 37, 3231-3239. (c) Langlois, M.; Bre´mont,
B.; Shen, S.; Poncet, A.; Andrieux, J .; Sicsic, S.; Serraz, I.; Mathe´-
Allainmat, M.; Renard, P.; Delagrange, Ph. Design and synthesis
of new naphthalenic derivatives as ligands for 2-[125I]iodomela-
tonin binding sites. J . Med. Chem. 1995, 38, 2050-2060.
(15) J ansen, J . M.; Karle´n, A.; Grol, C. J .; Hacksell, U. Conforma-
tional properties of melatonin and two conformationally re-
stricted agonists: a molecular mechanic and NMR spectroscopy
study. Drug Design and Discovery; Harwood Academic Publish-
ers GmbH: New York, 1993; Vol. 10, pp 115-133.
(16) Copinga, S.; Tepper, P. G.; Grol, C. J .; Horn, A. S.; Dubocovich,
M. L. 2-Amido-8-methoxytetralins: A series of nonindolic me-
latonin-like agents. J . Med. Chem. 1993, 36, 2891-2898.
(17) Langlois, M.; Gaudy, F. A new synthesis of 8-hydroxy-2-di-n-
propylamino-tetralin (8-OH-DPAT). Synth. Commun. 1992, 22,
1723-1734.
(18) (a) Violland, R.; Gaige, R.; Pacheco, H. Determination a` l’aide
de la RMN de la configuration d’R-amino-alcools cyclaniques
apparente´s a` l’adre´naline. Bull. Soc. Chim. 1967, 2105-2106.
(b) Violland, R.; Violland-Duperret, N.; Pacheco, H. Psychotropes
potentiels. IV. Synthe`se de nouveaux R-amino-alcools cycla-
niques apparente´s a` l’e´phe´drine et a` la mescaline. De´termination
de leur configuration a` l’aide de la RMN. Chim. Ther. 1969, 2,
95-102. (c) Varie, D. L. Preparation of 1-benzoyl-4(amino)-1,2,-
2a,3,4,5,-hexahydrobenzo[cd]indoles from L-tryptophan. Tetra-
hedron Lett. 1990, 31, 7583-7586.
(19) Quay, W. B.; Bagnara, J . T. Relative potencies of indolic and
related compounds in the body-lightening reaction of larval
xenopus. Arch. Int. Pharmacodyn. 1964, 150, 137-143.
(20) Hogben, L.; Slome, D. The pigmentary effector sytem: VI. The
dual character of endocrine co-ordinationin amphibian colour
chang. Proc. R. Soc. (London), Ser. B 1931, 108, 10-53.
(21) Murphy, R. A.; Kung, H. F.; Kung, M.-P.; Billing, J . Synthesis
and characterization if iodobenzamide analogues: potential D-2
dopamine receptor imaging agents. J . Med. Chem. 1990, 33,
171-178.
Refer en ces
(1) Reiter, R. J . Pineal melatonin: Cell biology of its synthesis and
its physiological interactions. Endocrinol. Rev. 1991, 12, 151-
180.
(2) Pierpaoi, W. The pineal gland: a circadian or seasonal aging
clock. Aging 1991, 3, 99-101.
(3) (a) Waldhauser, F.; Ehrhart; B.; Fo¨rster, E. Clinical aspects of
the melatonin action: impact of development, aging, and pu-
berty, involvement of melatonin in psychiatric disease and
importance of neuroimmunoendocrine interactions. Experientia
1993, 49, 671-681. (b) Blehar, M. C.; Lewy, A. J . Seasonal mood
disorders: consensus and controversy. Psychopharmacol. Bull.
1990, 4, 465-482.
(4) Maestroni, G. J . M. The immunoneuroendocrine role of mela-
tonin. J . Pineal Res. 1993, 14, 1-10.
(5) Poeggeler, B.; Reiter, R. J .; Tan, D.-X.; Chen, L.-D.; Manchester,
L. C. Melatonin, hydroxy radical-mediated oxidative damage,
and aging: a hypothesis. J . Pineal Res. 1993, 14, 151-158.
(6) Williams, L. M.; Morgan, P. J .; Hasting, M. H.; Lawson, W.;
Davidson, G.; Howell, H. E. Melatonin receptor sites in the
Syrian hamster brain and pituitary: localization and charac-
terisation using 2-[125I]iodomelatonin. J . Neuroendocrinol. 1989,
1, 315-320.
(7) Kennaway, D. J .; Rowe, S. A. Melatonin binding sites and their
role in seasonal reproduction. J . Reprod. Fertil. Suppl. 1995, 49,
423-435.
(8) Pontoire, C.; Bernard, M.; Silvain, C.; Collin, J . P.; Voisin, P.
Characterisation of melatonin binding sites in chicken and
human intestines. Eur. J . Pharmacol. 1993, 247, 111-118.
(9) (a) Ebisawa, T.; Karne, S.; Lerner, M. R.; Reppert, S. M.
Expression cloning of a high-affinity melatonin receptor from
Xenopus dermal melanophores. Proc. Natl. Acad. Sci. U.S.A.
1994, 91, 6133-6137. (b) Reppert, S. M.; Weaver, D. R.; Ebisawa,
T. Cloning and characterisation of a mammalian melatonin
receptor that mediates reproductive and circadian responses.
Neuron 1994, 13, 1177-1185. (c) Reppert, S. M.; Godson, C.;
J M960219H