Substituted tetrahydroisoquinolines as selective antagonists for the orexin 1 receptor

Article abstract of DOI:10.1021/jm400720h

Increasing evidence implicates the orexin 1 (OX₁) receptor in reward processes, suggesting OX₁ antagonism could be therapeutic in drug addiction. In a program to develop an OX₁ selective antagonist, we designed and synthesized a series of substituted tetrahydroisoquinolines and determined their potency in OX₁ and OX₂ calcium mobilization assays. Structure-activity relationship (SAR) studies revealed limited steric tolerance and a preference for electron deficiency at the 7-position. Pyridylmethyl groups were shown to be optimal for activity at the acetamide position. Computational studies resulted in a pharmacophore model and confirmed the SAR results. Compound 72 significantly attenuated the development of place preference for cocaine in rats.

Full text of DOI:10.1021/jm400720h

Article
pubs.acs.org/jmc
Substituted Tetrahydroisoquinolines as Selective Antagonists for the
Orexin 1 Receptor
David A. Perrey,† Nadezhda A. German,† Brian P. Gilmour,† Jun-Xu Li,‡ Danni L. Harris,†
Brian F. Thomas,† and Yanan Zhang*,†
†Research Triangle Institute, Research Triangle Park, North Carolina 27709, United States
‡Department of Pharmacology and Toxicology, University at Buffalo, the State University of New York, Buffalo, New York 14214,
United States
S
* Supporting Information
ABSTRACT: Increasing evidence implicates the orexin 1
(OX1) receptor in reward processes, suggesting OX1
antagonism could be therapeutic in drug addiction. In a
program to develop an OX1 selective antagonist, we designed
and synthesized a series of substituted tetrahydroisoquinolines
and determined their potency in OX1 and OX2 calcium
mobilization assays. Structure−activity relationship (SAR)
studies revealed limited steric tolerance and a preference for
electron deficiency at the 7-position. Pyridylmethyl groups were shown to be optimal for activity at the acetamide position.
Computational studies resulted in a pharmacophore model and confirmed the SAR results. Compound 72 significantly
attenuated the development of place preference for cocaine in rats.
seeking in rats, and the effect is blocked by the selective OX1
antagonist SB334867 (1).16 Blockade of orexin A transmission
also decreases alcohol self-administration and cue-induced
reinstatement of extinguished alcohol and cocaine seeking,22,23
and it attenuates the stress-induced reinstatement of extin-
guished cocaine and alcohol seeking.19,24 Moreover, antago-
nism of orexin A transmission at the OX1 receptor decreases
nicotine self-administration in rats and the motivation to obtain
the drug.25
Early efforts to modulate the orexin system have been
focused on the blockade of both receptors, or OX2 selectively,
because of their well-recognized implications in the pathophysi-
ology of sleep disorders. As a result, several structural classes of
dual OX1/OX2 antagonists and OX2-selective antagonists were
developed (Figure 1).12,26−29 The dual antagonists almorexant
(2), SB-649868 (3), and suvorexant (4) entered clinical trials
for insomnia.27,28 However, relatively few OX1-selective
antagonists have been reported to date. Compound 1,
developed by GlaxoSmithKline, was the first selective OX1
antagonist described.30,31 It has a potency of ∼40 nM at OX1
and is at least 50-fold selective for OX1 over OX2. Structure−
activity relationship (SAR) studies have resulted in analogs with
improved OX1 selectivity,32 but 1 remains an important tool to
probe the pharmacology and function of OX1. Despite its wide
application, 1 has limitations including a less than desirable
pharmacokinetic profile and a recently discovered hydrolytic
instability in which the 2-methylbenzoxazole undergoes ring-
opening under acidic conditions.31,33 Other antagonists with
INTRODUCTION
■
Orexin A and B, also known as hypocretin 1 and 2, are
hypothalamic neuropeptides independently discovered by two
groups in 1998.1,2 They are the endogenous ligands for two G
protein-coupled receptors (GPCRs), orexin 1 (OX1) and orexin
2 (OX2).3,4 Orexin-expressing neurons are located predom-
inantly in a small area of the hypothalamus.2,5−7 However, the
nerve fibers of orexin neurons project throughout the central
nervous system (CNS).1,7−9 Interestingly, orexin receptors have
different patterns of expression: Some brain regions express
predominantly OX1, whereas others express predominantly
OX2,2,10,11 suggesting that these receptors might modulate
many unrelated functions, as also suggested by antagonist and
knockout mouse studies.3,4,12 The orexin system has been
shown to play a role in a variety of important biological
processes, including sleep/wake cycle,13,14 feeding,2 and energy
homeostasis.2
Recently, the orexin system, particularly the OX1 receptor,
was implicated in drug reward, reinstatement of drug seeking,
and psychomotor sensitization.15−18 This is consistent with the
findings that orexin neurons have a prominent input to the
basal ganglia and forebrain structures (central amygdala, ventral
bed nucleus of the stria terminalis, nucleus accumbens shell,
ventral pallidum, and ventral tegmental area) that underlie
motivation, reward, stress, and addiction-related behaviors.19
Orexinergic signaling seems to be involved in the rewarding
effects of natural rewards and some drugs. Mice lacking orexins
not only have reduced appetite but also show much less
addiction-like sequelae associated with exposure to morphine
and amphetamines.20,21 Chemical activation of lateral hypo-
thalamus (LH) neurons reinstates extinguished morphine
Received: May 15, 2013
© XXXX American Chemical Society
A
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Figure 1. Orexin antagonists.
a
Scheme 1. Synthesis of 6-Methoxy-7-alkoxy-N-benzylacetamidotetrahydroisoquinolines
a
Reagents and conditions: (a) HBTU, i-Pr2EtN, DMF; (b) (i) POCl3, toluene, 90 °C, (ii) NaBH4, MeOH; (c) BrCH2CONHBn, i-Pr2EtN, Bu4NI,
DMF; (d) R1-Br, K2CO3, Bu4NI, DMF; (e) R1-I, Cs2CO3, DMF, 50 °C; (f) R-SO2Cl, Et3N, CH2Cl2 (R1R-SO2).
OX1 selectivity or preference are pyrrolidine-based SB674042
and disubstituted piperidines based on the structure of 3.34,35
Two compounds of the latter series showed OX1 selectivity or
preference, although significant OX2 activity remains for
most.35 A similar approach by Rottapharm resulted in a
number of spiro-piperidines and spiro-pyrrolidines with
reasonable OX1 potency and selectivity.36 During the
preparation of this manuscript, a phenylglycine-amide-sub-
stituted tetrahydroisoquinoline derivative (ACT-335827) was
reported by Actelion that was potent and OX1 selective;
however, some OX2 activity remained (IC50 OX1 = 6 nM and
OX2 = 417 nM).37
nM and OX2 = 8100 nM).39 Initial SAR studies by the same
group identified several positions that could be modified to
improve OX1 activity. For example, replacement of the methoxy
group at the 7-position with larger groups such as ethoxy or
propoxy further increased OX1 potency, whereas little OX2
activity was observed. The present work further examines SARs
within the tetrahydroisoquinoline series with the aim to
improve their potency and selectivity over OX2 and to identify
a viable tool compound for pharmacological studies. Our
investigation looked specifically at the structural requirement at
the 7-position of the tetrahydroisoquinoline as well as the
substitution pattern at the acetamide.
Here, we report our efforts in developing OX1-selective
antagonists based on a tetrahydroisoquinoline scaffold as
present in both 2 and TCS-OX2-29 (5), a selective OX2
antagonist.38 Compound 6, identified in a high-throughput
screening campaign by Actelion that led to the discovery of 2,
showed reasonable OX1 activity and selectivity (IC50 OX1 = 119
RESULTS AND DISCUSSION
■
Chemistry. 7-Alkoxytetrahydroisoquinolines were synthe-
sized according to Scheme 1. Thus, amide coupling between
amine 7 and acid 8 using HBTU yielded 9. Bischler−
B
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a
Scheme 2. Synthesis of N-Acetamidotetrahydroisoquinolines
a
Reagents and conditions: (a) BrCH2−CO2Et, i-Pr2EtN, Bu4NI, DMF; (b) (i) 2N NaOH, EtOH, (ii) R2-NH2 (or R2-NHMe), BOP, i-Pr2EtN, DMF
or BnBr, K2CO3, Bu4NI, DMF; (c) (i) Raney nickel, NH2NH2·H2O, EtOH, (ii) R3-CO2H and BOP, i-Pr2EtN, CH2Cl2 or R3CO2O, i-Pr2EtN,
CH2Cl2 or R3NCO, toluene.
Napieralski reaction of 9 with phosphorus oxychloride in
toluene at 90 °C gave the intermediate dihydroisoquinoline,40
which was readily reduced to tetrahydroisoquinoline 10 using
sodium borohydride. N-Alkylation with α-bromo-benzylacetoa-
mide gave desired tetrahydroisoquinoline derivative 11.41,42
The 7-position could then be alkylated as desired using
potassium carbonate as base and the addition of tetrabuty-
lammonium iodide as appropriate. For trifluoroethyl analog 24,
better results were obtained using cesium carbonate at 50 °C.
Sulfonates (22, 23, 25, and 26) were prepared using the
appropriate sulfonyl chloride in dichloromethane with triethyl-
amine as base.
Scheme 3. Synthesis of Tetrahydroisoquinoline Derivatives
Varied at Both Acetamide and 7 Positions
a
To prepare compounds varying in the N-acetamide (Scheme
2), the base tetramethoxy-tetrahydroisoquinoline (31) was
made according to literature procedures and then N-alkylated
by ethyl bromoacetate to give ester 32.39 The ester could then
be hydrolyzed and the acid converted to the amide using BOP
and the corresponding amine. Further elaboration of the 4-
nitrophenyl derivative gave a series of acylated anilines, 57−59.
Benzyl ester 40 was also made by alkylation on the acid with
benzyl bromide.
a
Reagents and conditions: (a) BrCH2CO2Et, i-Pr2EtN, Bu4NI, DMF;
(b) R1-X, K2CO3 or Cs2CO3, Bu4NI (for X = Br), DMF; (c) (i) 2N
NaOH, EtOH, (ii) R2-NH2, BOP, i-Pr2EtN, DMF.
To prepare the 7-alkoxy derivatives with a greater variety in
the acetamide, a series of compounds were synthesized via
Scheme 3. Phenol 10 was alkylated with ethyl bromoacetate to
give the tetrahydroisoquinoline acetate 65 in good yield. The
phenol was then alkylated with the appropriate alkyl halide,
with either potassium or cesium carbonate as base. Hydrolysis
of ester 66−68 with aqueous sodium hydroxide in ethanol gave
the acid, which could then be coupled with the desired amine
using BOP as the coupling agent.
test compound. In these assays, the EC50 for orexin A at OX1
and OX2 is 0.13 0.02 and 4.2 0.2 nM, respectively. All of
the compounds that had OX1 Ke values <1 μM were also tested
alone at 10 μM as agonists at the OX1 receptor. None of them
showed any agonist activity. Because of the lack of
commercially available radioligands, binding studies were not
performed on these compounds.
Our studies on this series focused on two primary areas of
the molecule: the 7-position of the tetrahydroisoquinoline
moiety and the acetamide side chain. Table 1 shows the
changes at the 7-position. Unsubstituted 7-hydroxy analog 11
showed micromolar potency at both OX1 and OX2. The OX1
potency increased as the size of the alkoxy group increased (6,
12, and 13), in agreement with the literature.39 However, the
potency started to drop as the chain length further increased
(14 and 15), and the isopentyl (16) was equipotent with hexyl
(15). Finally, compound 17, with the space-demanding
cyclohexylmethyl group, had no OX1 activity up to 10 μM,
suggesting a limited bulk tolerance at this position. In an
The activity of the target compounds at the OX1 and OX2
receptors was evaluated in a calcium mobilization-based
functional assay. The apparent dissociation constant, Ke, was
calculated from the compound-mediated inhibition of orexin A
activity as previously described.32 Briefly, EC50 curves of the
agonist, orexin A, were obtained alone and together with the
test compound, respectively, and the right-shift of the agonist
curve was measured. The Ke values were then calculated using
the equation Ke = [L]/ ((EC50−/EC50+) − 1), where [L] is the
−
test compound concentration, EC50 is the EC50 of orexin A
alone, and EC50+ is the EC50 of orexin A in the presence of the
C
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(30) sulfonates both had higher potency than the benzyl
analog.
Table 1. Effect of the 7-Position Substitution on OX
Antagonism
At the acetamide position (Table 2), extending the benzyl to
a phenethyl (33) or phenylpropyl (34) lowered the potency at
OX1. Conformational restriction of the aromatic group led to
analogs such as tetrahydroisoquinoline 35, piperidines 36 and
37, and piperazine 38, but none of these compounds showed
any appreciable OX1 activity. It was posited that the NH group
might be required for potency, and, indeed, its importance was
highlighted by N-methyl 39 and benzyl ester 40, which both
had a low potency at OX1. None of these compounds showed
any activity at OX2.
Several fused aromatic or biphenyl systems were examined
where the second aromatic ring occupies a similar position as
that in the benzyl group but in a planar conformation.
Naphthalene 41 had a Ke value of 732 nM, which is around 3.6-
fold less potent than the benzyl compound. Heteroatom-
containing aromatic systems such as quinolines 42 and 43 gave
a further reduction in potency, suggesting a preference for a
nonplanar conformation for the aromatic ring. We next
examined a series of biphenyl analogs, 44−46, with each acting
as a phenyl spacer to the second aromatic ring. However, only
2-biphenyl 44 showed submicromolar OX1 potency, with some
activity at OX2. These results suggest that a nonaromatic spacer
is preferred for OX1 potency. Indeed, the tetrahydronaph-
thalene (47) gave a Ke value of 41 nM, significantly more
potent than naphthalene 41. Interestingly, tetrahydroquinoline
48 was inactive, which shows that hydrophobic interactions
might be preferred in this region of the molecule.
With the chiral center at the 1-position of the tetrahy-
droisoquinoline, substitution with a methyl at the α-position of
the benzyl group (S-α-methylbenzyl) gave two diastereomers,
which were separated by HPLC into compounds 49 and 50.
Although 50 showed good OX1 potency and selectivity, 49 was
inactive at 10 μM at both receptors. This is consistent with
previous findings that the S conformation at the 1-position of
the tetrahydroisoquinoline is required in 2 and its analogs.28,43
Substituents on the phenyl ring were generally well tolerated,
with chloride 51 and fluoride 52 being about equipotent with
the benzyl (6), suggesting that electron-withdrawing groups are
tolerated. Among the pyridylmethyl analogs, the 3-pyridyl (54)
showed a similar potency as the 2-analog (53), of which both
were more potent than the 4-analog (55). Interestingly, the
electron-rich dimethylamino (56) showed limited OX1 potency
in the micromolar range. To determine whether this activity
loss is due to electronic or steric reasons, substituents, including
amides and ureas, were introduced onto the nitrogen.
Surprisingly, the acetyl group (57) resulted in a total loss of
OX1 activity. Large amide 58 and urea 59 showed no or little
potency, suggesting limited or no tolerance for size at the 4-
position of the benzyl group.
Ke
Ke
OX2/
OX1
b
c
no.
R1
(OX1, nM)
(OX2, nM)
11
6
H
1530 530
199 47
30.0 9.0
17.3 3.1
54.7 23
315 81
326 46
>10 000
5740 96
>10 000
>10 000
>10 000
3.8
methyl
>50.3
>333
>578
34.6
12 ethyl
13 n-propyl
14 n-butyl
15 n-hexyl
16 isopentyl
1890 480
>10 000
>31.7
12.0
3920 1200
a
17 cyclohexylCH2
18 Me2N-CH2CH2
19 Me2N-(CH2)4
a
a
a
a
a
a
4740 440
5740 3600
20 N-piperidinyl-CH2CH2 8040 5400
21 benzyl
402 58
101 56
277 75
43.5 9.2
78.5 24
7.3 2.7
10.0 2.8
9.4 1.7
30.5 9.1
118 54
22 2-pyridine-CH2
23 3-pyridine-CH2
24 PhO-(CH2)4
25 CH3CH2CH2CO
26 CH3SO2
>10 000
>10 000
2170 790
>10 000
>10 000
>230
>127
297
27 CF3SO2
>1000
>1060
95.1
28 CF3CH2
29 PhSO2
2900 191
a
30 4-MePhSO2
a
b
Demonstrated <30% inhibition at 10 μM. These values are the mean
of at least three independent experiments performed in duplicate.
These values are the mean of at least two independent experiments
performed in duplicate; for compounds with Ke < 100 nM at OX1, at
c
least three independent experiments in duplicate were performed.
attempt to probe possible hydrogen-bonding effects, heter-
oatoms as H acceptors were introduced on the alkyl chain, and
this resulted in a significant decrease in potency (18, 19, and
20). Aromatic substituents were then examined. Although the
benzyl (21) was similar in potency to the hexyl (15), the two
pyridylmethyl analogs (22 and 23) showed a modest increase
in potency over benzyl 21. Interestingly, when a phenoxybutyl
group was introduced, 24 displayed equipotency to the butyl
analog. This may suggest additional aromatic-stacking inter-
action in this region, which is probably farther away from the
tetrahydroisoquinoline core.
The electronic properties at the 7-position were also
investigated. Butyryl analog 25 showed similar OX1 activity as
that of butyl compound 14, suggesting that electron-with-
drawing groups are tolerated. Interestingly, two highly electron-
withdrawing sulfonate analogs (26 and 27) showed excellent
potency, further confirming the preference of electronegativity
at this position. Trifluoroethyl (28), a group that can be
considered a bioisostere for acetyl or mesylate because of its
electron-deficient character and similar size, gave a low
nanomolar potency and an over 1000-fold selectivity over the
OX2 receptor. This also suggests that the observed high
potency is a result of the electronic properties other than
potential hydrogen-bonding interactions with the presence of
the additional oxygen atoms. Finally, the phenyl (29) and tolyl
Finally, the requirement for aromaticity was investigated at
the acetamide position. Straight-chain heptyl analog 60 showed
a modest potency at 500 nM, although it was poorly selective
over OX2. Attempts to introduce heteroatoms or polar groups
(61−64) all resulted in a dramatic loss of OX1 potency. Taken
together, these findings suggest that an aromatic group is
generally needed for OX1 potency and selectivity.
Although none of the acetamide substituents gave a
significant improvement in potency from that of parent benzyl
compound 6, pyridylmethyl analogs 54 and 55 showed the
most promise given their improved physicochemical properties
because of the possibility of salt formation. Thus, several
D
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Table 2. Effect of N-Alkylation on OX Antagonism
a
b
c
Demonstrated <30% inhibition at 10 μM. These values are the mean of at least three independent experiments performed in duplicate. These
values are the mean of at least two independent experiments performed in duplicate; for compounds with Ke < 100 nM at OX1, at least three
independent experiments in duplicate were performed.
E
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pyridylmethyl analogs were studied in conjunction with the
more potent 7-position substituents (Table 3). Such analogs
determining potency. OX1 potency increases monotonically
from 1530 to 17 nM for compounds 11 (−OH), 6 (−OCH3),
12 (−OCH2CH3), and 13 (−OCH2CH2CH3), respectively, at
which point the trend begins to reverse. This indicates that
substituents of a particular size are required for activity.
Although steric properties at the 7-position play a main role
in determining potency, the QSAR analysis also highlights the
importance of other nonobservable factors, such as LUMO
energy, on antagonist potency. Figure 2E depicts the spatial
distribution of the LUMO density on compound 6. Position 7
is on the aromatic ring most associated with LUMO electron
density. Naturally, substitutions at that position would
modulate the energy of the LUMO orbital and charge-density
transfer, a facet plausibly having a role in stabilization of the
receptor bound ligand configuration.
Figure 3 depicts a similar 3D QSAR and COMFA analysis for
substituent variation corresponding to the N-alkylation
variations summarized in Table 2. Figure 3B illustrates results
from a COMFA analysis of the training set superposition
shown in Figure 3A. Both steric and electrostatic variations in
the ligand substituents contributed relatively equally to the
underlying rationale for the Ke(OX1) variations. This was
independently verified in the 2D QSAR analysis shown in
Figure 3D, where coefficients of the B1 Verloop parameter and
the polar surface area made significant contributions along with
the energy of the HOMO and led to a model predictive of ln
Ke(OX1). Analogous to our identification of the E(LUMO)
term for position 7 variations, the atomic centers containing the
highest occupied molecular orbital were found on the ring
system directly attached to the position 2 substitutions. The
results from these studies highlight the manner in which
substitutions can be rationalized in terms of underlying physical
properties keyed to the molecular interactions and binding free
energies, and they provide a basis for a comprehensive 3D
pharmacophore.
Through the establishment of this 3D pharmacophore
model, a basic understanding of the impact that specific
substitutions have on receptor potency and selectivity has been
achieved. This information will be important to guide the
selection of scaffold modifications to favorably alter receptor
potency, subtype selectivity, or ADM. Alternatively, establishing
quantitative pharmacophore models allows us to transfer the
information from the 3D display of physiochemical properties
to new scaffolds with an understanding of those that are critical
for activity.
Conditioned Place Preference. Given the well-established
activity of OX1 antagonists in attenuating the rewarding and
reinforcing the effects of drugs, compound 72 was studied in
conditioned place preference (CPP). As shown in Figure 4, the
vehicle did not produce significant CPP. Cocaine at 10 mg/kg
induced a robust and significant CPP. Compound 72 at 20 mg/
kg did not produce CPP or place aversion but significantly
attenuated the development of place preference induced by
cocaine.
Table 3. Effect of Multiple Changes on OX Antagonism
Ke
Ke
OX2/
OX1
a
a
no.
R1
R2
(OX1, nM)
(OX2, nM)
69
70
71
72
73
74
n-propyl
n-propyl
CF3CH2
CF3CH2
ethyl
2-pyridyl
3-pyridyl
2-pyridyl
3-pyridyl
2-pyridyl
3-pyridyl
20.6 5.5
41.9 16
22.5 2.7
8.5 1.0
87.4 12
15.7 1.7
>10 000
>10 000
>10 000
>10 000
>10 000
>10 000
>485
>239
>444
>1180
>114
>637
ethyl
a
These values are the mean of at least three independent experiments
performed in duplicate.
include 2- and 3-pyridines combined with the 7-ethoxy,
propoxy, and trifluoroethoxy derivatives (69−74). All com-
pounds showed good to excellent OX1 potency (8−87 nM)
and high selectivity over OX2, with none of the compounds
showing any activity at 10 μM.
Computational Analysis. A comprehensive 3D pharma-
cophore for the orexin antagonists evaluated in this study was
developed. The pharmacophore was initiated by generating
conformational libraries for each analog in this class. This
included computation of the 3D distance metrics between four
candidate pharmacophore points (variable substituents off the
7-position, the two centroids for each of the aromatic ring
substituents, and the nitrogen on the tetrahydroisoquinoline
core) and the determination of the conformations of each
ligand giving rise to a common 3D display (Figure 2A,B).
Superposition of all ligands in the training set with these four
pharmacophore points allowed us to investigate a series of
substituent properties that proved to be important for OX1
potency. Twenty-one properties, including stereochemical
(Verloop parameters,44,45 volume, area, and globularity),
electrostatic (positions of electrostatic minima and maxima),
polar (polar surface area), electronic (E-HOMO, E-LUMO,
and polarizability), thermodynamic (vibrational and rotational
heat capacity and entropies at 300 K), and atom-based
hydrophobicity (clogP) were evaluated for ligand conforma-
tions that complied with a 3D pharmacophore overlap rule.46 In
addition, the same subset of properties was computed for
substituents (fragments) alone without the tetrahydroisoquino-
line core compliant pharmacophoric region. This dual approach
was chosen to allow the addition of substituent-independent
properties to the QSAR analysis.
Three properties were found to correlate the structural
modification at the 7-position with alterations in OX1 potency
using a three-variable QSAR analysis. The Sterimol parameters,
including the spatial extent of the substituent at position 7 and
particularly the width (Verloop B1) relative to the long axis,
logP of the substituent, and energy of the lowest unoccupied
molecular orbital (E-LUMO), demonstrated statistically
significant correlations with changes in OX1 potency (R2 =
0.69) (Figure 2C). It is apparent from the 3D QSAR model
(Figure 2D) and the functional activity data that the size of the
substituent at the 7-position plays a considerable role in
CONCLUSIONS
■
To develop OX1-selective antagonists, we synthesized and
evaluated a series of tetrahydroisoquinolines, a core structure
that is present in both dual OX1/OX2 antagonist 2 and OX2-
selective antagonist 5. SAR studies suggested a preference for
steric bulk at the 7-position; however, this tolerance is limited,
as the potency decreases with the further size increase of the
substituents. Electron-deficient groups are also well tolerated at
F
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Figure 2. (A) Ligands superimposed at 3D pharmacophore points defined by (B) the abstract pharmacophore representation computed from 21
ligands in Table 1. (C) Plot of the predicted ln Ke(OX1) vs experimental for a fragment (2D) QSAR illustrating that contributions from the width
(Verloop Sterimol “B1”), polar surface area, clogP, and lowest unoccupied (LUMO) energy of the substituent give a robust analysis (R2 = 0.7/F =
8.2 (n1 = 4, n2 = 18), p = 0.001/2.8B1 + 0.7×E(LUMO) − 0.13logP −5.5). (D) 3D COMFA/QSAR illustrating that the increased steric-bulk
contributions region of the substituent variation highlighted by green correlate with low Ke values with minor modulation because of electrostatic
contributions. (E) Depiction of the location of the LUMO density on compound 6.
this position. At the acetamide position, an aromatic system was
generally preferred, and the pyridylmethyl groups gave the best
potency. The pharmacophore model obtained through
computational analysis confirmed the steric and electronic
requirement at the 7-position. This model also suggests that
steric and electrostatic variations in the ligand substituents
contributed equally to the underlying rationale for the Ke(OX1)
variations at the acetamide position. In the CPP paradigm,
compound 72, which had excellent OX1 potency and selectivity
over OX2 in the calcium assay, significantly attenuated cocaine
CPP. In summary, several compounds with excellent potency at
and selectivity for the OX1 receptor have been identified, and
they will serve as probes to investigate further the
pharmacology and function of the OX1 receptor and the
orexin system. Modifications at other positions are ongoing and
will be reported in due course.
EXPERIMENTAL SECTION
■
Chemistry. All solvents and chemicals were reagent grade. Unless
otherwise mentioned, all solvents and chemicals were purchased from
commercial vendors and used as received. Flash column chromatog-
raphy was done with a Teledyne ISCO CombiFlash Rf system using
prepacked columns. The solvents used were hexane, ethyl acetate
(EtOAc), dichloromethane, methanol and chloroform/methanol/
ammonium hydroxide (80:18:2) (CMA-80). The purity and character-
ization of the compounds was established by a combination of high-
pressure liquid chromatography (HPLC), thin-layer chromatography
(TLC), mass spectrometry (MS), and nuclear magnetic resonance
(NMR) analysis. 1H and 13C NMR spectra were recorded on a Bruker
Avance DPX-300 (300 MHz) spectrometer and were determined in
chloroform-d or methanol-d4 with tetramethylsilane (TMS) (0.00
ppm) or solvent peaks as the internal reference. Chemical shifts are
reported in ppm relative to the reference signal, and coupling constant
(J) values are reported in Hz. TLC was done on EMD precoated silica
gel 60 F254 plates, and spots were visualized with UV light or iodine
staining. Low-resolution mass spectra were obtained using a Waters
Alliance HT/Micromass ZQ system (ESI). All test compounds were
G
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Figure 3. Depiction of COMFA steric (left) and electrostatic fields (right) about compound 6 derived from the analysis of 6, 20, 21, 23, 30, 41, 44,
47, 50, 51, 52, 55, and 60. The analysis (R2 = 0.761/F[n1 = 1, n2 = 11]) 35.108, SE = 0.61) for ln Ke(OX1) using the 3D pharmacophore quaternion
least-squares superposition of the pharmacophore points illustrated in Figure 2.
give the desired amide as a yellow oil that solidified upon standing
1
(0.72 g, 91%). H NMR (300 MHz, chloroform-d) δ 2.67 (t, J = 6.88
Hz, 2H), 3.36−3.43 (m, 2H), 3.45 (s, 2H), 3.82 (s, 3H), 3.83 (s, 3H),
3.88 (s, 3H), 6.04 (br s, 1H), 6.44−6.53 (m, 1H), 6.61 (d, J = 1.70 Hz,
1H), 6.66−6.77 (m, 3H), 6.78−6.86 (m, 1H), 7.97 (s, 1H).
General Procedure for the Bischler−Napieralski Reaction/Sodium
Borohydride Reduction. 1-[(3,4-Dimethoxyphenyl)methyl]-6-me-
thoxy-1,2,3,4-tetrahydroisoquinolin-7-ol (10). Amide 9 (0.39 g,
0.91 mmol) was suspended in anhydrous toluene (5 mL), and
phosphorus oxychloride (0.70 g, 0.4 mL, 4.56 mmol) was added
slowly. The reaction was heated at 90 °C for 2 h. The reaction was
cooled, quenched by the slow addition of the reaction mixture to
water, and stirred vigorously at room temperature for 15 min. A
sodium hydroxide solution (2N) was added until pH was 8 to 9, and
the solution was then extracted three times with dichloromethane. The
combined extracts were dried over MgSO4, and the solvent was
removed under reduced pressure.
The crude dihydroisoquinoline was dissolved in methanol (5 mL)
and cooled in an ice bath under N2. Sodium borohydride (0.17 g, 4.52
mmol) was added portionwise, and the reaction was allowed to warm
slowly to rt overnight. The reaction was quenched with water, and the
methanol was removed under reduced pressure. The aqueous solution
was extracted three times with dichloromethane, the combined
extracts were dried over MgSO4, and the solvent was removed
under reduced pressure to give desired tetrahydroisoquinoline 10 as a
frothy solid (0.26 g, 67%). 1H NMR (300 MHz, chloroform-d) δ
2.59−2.93 (m, 5H), 3.11−3.24 (m, 1H), 3.34−3.58 (m, 2H), 3.79−
3.92 (m, 9H), 4.08 (dd, J = 9.42, 3.20 Hz, 1H), 6.57 (s, 1H), 6.60−
6.71 (m, 1H), 6.72−6.88 (m, 3H).
Figure 4. Effects of compound 72 on cocaine-induced conditioned
place preference in rats (n = 8 to 9). The data are presented as the
mean SEM. * P < 0.05 as compared to vehicle-treated rats. P <
0.05 as compared to 10 mg/kg cocaine-treated rats.
$
greater than 95% pure (except where noted), as determined by HPLC
on an Agilent 1100 system using an Agilent Zorbax SB-Phenyl, 2.1 ×
150 mm2, 5 μm column with gradient elution using mobile phases (A)
H2O containing 0.1% CF3COOH and (B) MeCN, with a flow rate of
1.0 mL/min.
2-(3,4-Dimethoxyphenyl)-N-[2-(4-hydroxy-3-methoxyphenyl)-
ethyl]acetamide (9). 3,4-Dimethoxyphenylacetic acid (0.45 g, 2.29
mmol), 4-hydroxy-3-methoxyphenethylamine hydrochloride (0.47 g,
2.29 mmol), and HBTU (0.96 g, 2.52 mmol) were combined in dry
dimethylformamide (20 mL) at rt under N2. Diisopropylethylamine
(1.19 g, 1.6 mL, 9.17 mmol) was added, and the reaction was stirred at
rt overnight. The reaction was diluted with ethyl acetate, washed with
2N hydrochloric acid, sodium bicarbonate solution, and brine, dried
over MgSO4, and the solvent was removed under reduced pressure to
H
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1
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-7-hydroxy-6-me-
thoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (11). Amine 10
(3.65 g, 11.08 mmol), N-benzyl-2-bromoacetamide (3.77 g, 16.62
mmol), and tetrabutylammounium iodide (0.82 g, 2.21 mmol) were
combined in dry DMF (110 mL), and diisopropylethylamine (3.58 g,
4.8 mL, 27.70 mmol) was added. The reaction was stirred at rt
overnight under N2. The reaction was diluted with EtOAc, washed
with a NaHCO3 solution, water, and brine (×2), and dried over
MgSO4, and the solvent was removed under reduced pressure. The
crude product was purified by chromatography on silica (0−100%
EtOAc in hexane) to obtain the desired product as a frothy white solid
Prepared in 88% yield. H NMR (300 MHz, chloroform-d) δ 7.20−
7.36 (m, 3H), 7.11 (d, J = 6.97 Hz, 2H), 6.95−7.04 (m, 1H), 6.62−
6.76 (m, 3H), 6.59 (s, 1H), 6.48 (s, 1H), 4.51 (dd, J = 8.01, 14.98 Hz,
1H), 3.95 (t, J = 6.88 Hz, 2H), 3.85 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H),
3.60−3.71 (m, 2H), 3.35−3.49 (m, 1H), 3.13−3.34 (m, 2H), 2.78−
2.99 (m, 4H), 2.49 (d, J = 15.73 Hz, 1H), 1.84 (td, J = 6.62, 13.33 Hz,
1H), 1.71−1.77 (m, 2H), 0.98 (d, J = 6.50 Hz, 6H). m/z 547 (M +
H).
N-Benzyl-2-[7-(cyclohexylmethoxy)-1-[(3,4-dimethoxyphenyl)-
methyl]-6-methoxy-1,2,3,4-tetrahydroisoquinolin-2-yl]acetamide
1
(17). Prepared in 33% yield. H NMR (300 MHz, chloroform-d) δ
1
7.19−7.34 (m, 3H), 7.10 (d, J = 6.78 Hz, 2H), 7.01 (d, J = 6.97 Hz,
1H), 6.61−6.76 (m, 3H), 6.58 (s, 1H), 6.45 (s, 1H), 4.49 (dd, J = 8.01,
14.98 Hz, 1H), 3.82 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H), 3.59−3.72 (m,
4H), 3.34−3.47 (m, 1H), 3.12−3.34 (m, 2H), 2.79−2.95 (m, 4H),
2.48 (d, J = 16.01 Hz, 1H), 1.61−1.97 (m, 6H), 0.92−1.40 (m, 5H).
m/z 573 (M + H).
(2.98 g, 56%). H NMR (300 MHz, chloroform-d) δ 7.15−7.36 (m,
3H), 7.07 (d, J = 7.06 Hz, 2H), 6.89 (br s, 1H), 6.65−6.77 (m, 4H),
6.52−6.64 (m, 3H), 5.51 (s, 1H), 4.48 (dd, J = 8.24, 15.02 Hz, 1H),
3.88 (s, 3H), 3.80 (s, 3H), 3.73 (s, 3H), 3.33−3.68 (m, 3H), 3.06−
3.32 (m, 2H), 2.78−2.99 (m, 4H), 2.46 (d, J = 15.82 Hz, 1H). m/z
477 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-7-[2-
General Procedure for O-Alkylation. N-Benzyl-2-{1-[(3,4-
dimethoxyphenyl)methyl]-7-ethoxy-6-methoxy-1,2,3,4-tetrahydroi-
soquinolin-2-yl}acetamide (12). Phenol 11 (25 mg, 0.025 mmol) and
potassium carbonate (22 mg, 0.157 mmol) were combined in dry
dimethylformamide, 1-bromoethane (12 mg, 6 μL, 0.079 mmol) was
added, and the reaction was stirred at rt under N2 overnight. The
reaction mixture was diluted with ethyl acetate, washed with a sodium
bicarbonate solution and brine, and dried over MgSO4, and the solvent
was removed under reduced pressure. The compound was purified by
chromatography on silica (0−75% EtOAc in hexane) to obtain the
(dimethylamino)ethoxy]-6-methoxy-1,2,3,4-tetrahydroisoquinolin-
1
2-yl}acetamide (18). Prepared in 46% yield. H NMR (300 MHz,
chloroform-d) δ 7.19−7.34 (m, 3H), 7.07−7.14 (m, 2H), 6.95 (dd, J =
4.76, 7.77 Hz, 1H), 6.68−6.75 (m, 2H), 6.61−6.67 (m, 1H), 6.59 (s,
1H), 6.56 (s, 1H), 4.50 (dd, J = 8.19, 14.98 Hz, 1H), 4.01−4.12 (m,
2H), 3.84 (s, 3H), 3.82 (s, 3H), 3.75 (s, 3H), 3.57−3.68 (m, 2H),
3.36−3.50 (m, 1H), 3.12−3.34 (m, 2H), 2.83−2.99 (m, 4H), 2.75−
2.82 (m, 2H), 2.44−2.54 (m, 1H), 2.38 (s, 6H). m/z 548 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-7-[4-
(dimethylamino)butoxy]-6-methoxy-1,2,3,4-tetrahydroisoquinolin-
2-yl}acetamide (19). Phenol 11 (0.30 g, 0.63 mmol) and potassium
carbonate (0.35 g, 1.26 mmol) were combined in dimethylformamide
(6 mL), and 1-bromo-4-chlorobutane (0.22 g, 0.15 mL, 1.26 mmol)
was added. The reaction was heated at 50 °C overnight. The reaction
was cooled, diluted with water, and extracted twice with EtOAc. The
combined extracts were washed with brine and dried over MgSO4, and
the solvent was removed under reduced pressure. The compound was
then purified by chromatography on silica (0−80% EtOAc in hexane)
to obtain the desired chloride (0.22 g, 61%) for use in the following
1
desired product as a pale-yellow solid (19 mg, 73%). H NMR (300
MHz, chloroform-d) δ 7.19−7.34 (m, 3H), 7.07−7.14 (m, 1H), 6.94−
7.01 (m, 1H), 6.56−6.74 (m, 5H), 6.48 (s, 1H), 4.49 (dd, J = 8.05,
14.93 Hz, 1H), 4.02 (q, J = 6.97 Hz, 2H), 3.85 (s, 3H), 3.81 (s, 3H),
3.74 (s, 3H), 3.57−3.70 (m, 2H), 3.34−3.48 (m, 1H), 3.12−3.34 (m,
2H), 2.79−2.99 (m, 4H), 2.41−2.54 (m, 1H), 1.45 (t, J = 6.97 Hz,
3H). m/z 505 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6,7-dimethoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (6). Prepared in 51%
yield. 1H NMR (300 MHz, chloroform-d) δ 7.18−7.35 (m, 2H),
7.07−7.14 (m, 2H), 6.98 (dd, J = 4.94, 7.58 Hz, 1H), 6.62−6.74 (m,
3H), 6.59 (s, 1H), 6.45 (s, 1H), 4.50 (dd, J = 8.05, 14.93 Hz, 1H),
3.84−3.89 (m, 3H), 3.81 (d, J = 1.88 Hz, 6H), 3.78−3.83 (m, 6H),
3.75 (s, 3H), 3.59−3.71 (m, 2H), 3.35−3.48 (m, 1H), 3.11−3.35 (m,
2H), 2.80−3.00 (m, 4H), 2.41−2.55 (m, 1H). m/z 491 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-pro-
poxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (13). Prepared in
1
reaction. H NMR (300 MHz, chloroform-d) δ 7.20−7.35 (m, 3H),
7.11 (d, J = 7.16 Hz, 2H), 6.93−7.01 (m, 1H), 6.62−6.75 (m, 3H),
6.60 (s, 1H), 6.48 (s, 1H), 4.50 (dd, J = 14.93, 8.05 Hz, 1H), 3.97 (t, J
= 5.51 Hz, 2H), 3.85 (s, 3H), 3.80 (s, 3H), 3.75 (s, 3H), 3.58−3.70
(m, 4H), 3.36−3.55 (m, 1H), 3.12−3.34 (m, 2H), 2.79−2.98 (m, 4H),
2.42−2.56 (m, 1H), 1.94−2.03 (m, 4H).
The chloride (30 mg, 0.053 mmol), dimethylamine hydrochloride
(7 mg, 0.079 mmol), potassium carbonate (18 mg, 0.132 mmol), and
tetrabutylammonium iodide (4 mg, 0.011 mmol) were combined in
dimethylformamide (0.5 mL) and heated at 50 °C overnight. The
reaction was cooled, diluted with water, and extracted three times with
EtOAc. The combined extracts were washed with brine and dried over
MgSO4, and the solvent was removed under reduced pressure. The
compound was purified by chromatography on silica (0−50% CMA-80
1
48% yield. H NMR (300 MHz, chloroform-d) δ 7.20−7.34 (m, 3H),
7.07−7.14 (m, 2H), 6.98 (dd, J = 4.95, 7.77 Hz, 1H), 6.61−6.75 (m,
3H), 6.59 (s, 1H), 6.47 (s, 1H), 4.50 (dd, J = 8.10, 14.98 Hz, 1H), 3.89
(t, J = 6.88 Hz, 2H), 3.85 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H), 3.58−
3.70 (m, 2H), 3.34−3.48 (m, 1H), 3.11−3.34 (m, 2H), 2.79−2.99 (m,
4H), 2.49 (d, J = 15.92 Hz, 1H), 1.77−1.92 (m, 2H), 1.00−1.09 (m,
3H). m/z 519 (M + H).
1
in EtOAc) to give the desired product (6 mg, 19%). H NMR (300
N-Benzyl-2-{7-butoxy-1-[(3,4-dimethoxyphenyl)methyl]-6-me-
thoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (14). Prepared
MHz, chloroform-d) δ 7.19−7.35 (m, 3H), 7.07−7.15 (m, 2H), 6.91−
7.00 (m, 1H), 6.62−6.76 (m, 3H), 6.59 (s, 1H), 6.51 (s, 1H), 4.50
(dd, J = 8.15, 15.02 Hz, 1H), 3.98 (t, J = 6.50 Hz, 2H), 3.84 (s, 3H),
3.82 (s, 3H), 3.75 (s, 3H), 3.57−3.68 (m, 2H), 3.36−3.49 (m, 1H),
3.11−3.34 (m, 2H), 2.81−2.99 (m, 4H), 2.43−2.54 (m, 1H), 2.33−
2.42 (m, 2H), 2.27 (s, 6H), 1.79−1.92 (m, 2H), 1.62−1.76 (m, 2H).
m/z 576 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-[2-
(piperidin-1-yl)ethoxy]-1,2,3,4-tetrahydroisoquinolin-2-yl}-
acetamide (20). Prepared in 24% yield. 1H NMR (300 MHz,
chloroform-d) δ 7.20−7.35 (m, 3H), 7.10 (d, J = 7.06 Hz, 2H), 6.93
(dd, J = 4.71, 7.82 Hz, 1H), 6.68−6.76 (m, 2H), 6.61−6.66 (m, 1H),
6.59−6.61 (m, 1H), 6.58 (s, 1H), 4.49 (dd, J = 8.24, 15.02 Hz, 1H),
4.11 (t, J = 6.45 Hz, 2H), 3.85 (s, 3H), 3.81−3.84 (m, 3H), 3.74 (s,
3H), 3.55−3.65 (m, 2H), 3.36−3.51 (m, 1H), 3.11−3.33 (m, 2H),
2.75−2.98 (m, 6H), 2.41−2.61 (m, 5H), 1.56−1.71 (m, 4H), 1.48 (d, J
= 4.99 Hz, 2H). m/z 588 (M + H).
1
in 75% yield. H NMR (300 MHz, chloroform-d) δ 7.19−7.35 (m,
3H), 7.10 (d, J = 6.78 Hz, 2H), 6.93−7.02 (m, 1H), 6.61−6.75 (m,
3H), 6.58 (s, 1H), 6.47 (s, 1H), 4.50 (dd, J = 8.10, 14.98 Hz, 1H),
3.89−3.97 (m, 2H), 3.83−3.87 (m, 3H), 3.81 (s, 3H), 3.75 (s, 3H),
3.58−3.71 (m, 2H), 3.34−3.48 (m, 1H), 3.11−3.34 (m, 2H), 2.80−
2.98 (m, 4H), 2.42−2.54 (m, 1H), 1.75−1.88 (m, 2H), 1.42−1.55 (m,
2H), 0.98 (t, J = 7.30 Hz, 3H). m/z 533 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-7-(hexyloxy)-6-me-
thoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (15). Prepared
1
in 64% yield. H NMR (300 MHz, chloroform-d) δ 7.18−7.35 (m,
3H), 7.10 (d, J = 6.69 Hz, 2H), 6.97 (dd, J = 4.99, 7.44 Hz, 1H), 6.61−
6.76 (m, 3H), 6.58 (s, 1H), 6.48 (s, 1H), 4.50 (dd, J = 8.10, 14.98 Hz,
1H), 3.92 (t, J = 6.83 Hz, 2H), 3.82−3.87 (m, 3H), 3.81 (s, 3H), 3.74
(s, 3H), 3.58−3.69 (m, 2H), 3.34−3.49 (m, 1H), 3.11−3.34 (m, 2H),
2.80−2.99 (m, 4H), 2.41−2.54 (m, 1H), 1.75−1.89 (m, 2H), 1.30−
1.53 (m, 6H), 0.91 (t, J = 6.90 Hz, 3H). m/z 561 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-(3-
methylbutoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (16).
N-Benzyl-2-[7-(benzyloxy)-1-[(3,4-dimethoxyphenyl)methyl]-6-
methoxy-1,2,3,4-tetrahydroisoquinolin-2-yl]acetamide (21). Pre-
I
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pared in 78% yield. 1H NMR (300 MHz, chloroform-d) δ 7.39 (td, J =
7.11, 15.16 Hz, 3H), 7.19−7.33 (m, 4H), 7.10 (d, J = 6.69 Hz, 2H),
6.91−7.01 (m, 1H), 6.57−6.70 (m, 5H), 6.49 (s, 1H), 5.06 (s, 2H),
4.48 (dd, J = 8.05, 14.93 Hz, 1H), 3.87 (s, 3H), 3.79 (s, 3H), 3.74 (s,
3H), 3.52−3.70 (m, 2H), 3.32−3.45 (m, 1H), 3.10−3.32 (m, 2H),
2.79−2.98 (m, 3H), 2.67−2.78 (m, 1H), 2.41−2.53 (m, 1H). m/z 567
(M + H).
Hz, 1H), 3.90 (s, 3H), 3.80 (s, 3H), 3.74 (s, 3H), 3.60−3.73 (m, 2H),
3.33−3.45 (m, 1H), 3.11−3.33 (m, 2H), 2.77−3.04 (m, 4H), 2.56 (d, J
= 18.46 Hz, 1H). 19F NMR (282 MHz, chloroform-d) δ −73.7. m/z
609 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-
(2,2,2-trifluoroethoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide
(28). Phenol 11 (100 mg, 0.24 mmol) and cesium carbonate (235 mg,
0.72 mmol) were combined in dry dimethylformamide (1.5 mL), and
2,2,2-trifluoroiodoethane (101 mg, 47 μL, 0.48 mmol) was added. The
reaction was heated at 50 °C overnight until TLC (4:1 EtOAc/
hexane) showed that all starting material was gone. The reaction was
cooled, diluted with ethyl acetate, and washed with a sodium
bicarbonate solution and brine. The solution was dried over MgSO4,
and the solvent was removed under reduced pressure. The compound
was purified by chromatography on silica (0−50% EtOAc in hexane)
to obtain the desired product as a pale-yellow solid (86 mg, 72%). 1H
NMR (300 MHz, chloroform-d) δ 7.19−7.34 (m, 3H), 7.09 (d, J =
6.69 Hz, 2H), 6.94 (d, J = 5.09 Hz, 1H), 6.59−6.75 (m, 5H), 4.48 (dd,
J = 8.15, 15.02 Hz, 1H), 4.23−4.41 (m, 2H), 3.87 (s, 3H), 3.81 (s,
3H), 3.74 (s, 3H), 3.57−3.68 (m, 2H), 3.34−3.50 (m, 1H), 3.09−3.34
(m, 2H), 2.76−3.00 (m, 4H), 2.44−2.57 (m, 1H). m/z 559 (M + H).
2-[(Benzylcarbamoyl)methyl]-1-[(3,4-dimethoxyphenyl)methyl]-
6-methoxy-1,2,3,4-tetrahydroisoquinolin-7-yl Benzenesulfonate
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-(pyri-
din-2-ylmethoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide
1
(22). Prepared in 61% yield. H NMR (300 MHz, chloroform-d) δ
8.60 (d, J = 4.71 Hz, 1H), 7.68−7.77 (m, 1H), 7.58 (d, J = 7.82 Hz,
1H), 7.17−7.35 (m, 5H), 7.08 (d, J = 7.06 Hz, 2H), 6.89 (br s, 1H),
6.56−6.75 (m, 4H), 5.27 (s, 2H), 4.48 (dd, J = 8.19, 14.98 Hz, 1H),
3.90 (s, 3H), 3.82 (s, 3H), 3.74 (s, 3H), 3.50−3.62 (m, 2H), 3.33−
3.48 (m, 1H), 3.08−3.31 (m, 2H), 2.68−3.00 (m, 4H), 2.48 (d, J =
15.64 Hz, 1H). m/z 568 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-(pyri-
din-3-ylmethoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide
1
(23). Prepared in 47% yield. H NMR (300 MHz, chloroform-d) δ
8.68 (s, 1H), 8.58 (d, J = 4.71 Hz, 1H), 7.79 (d, J = 7.82 Hz, 1H),
7.18−7.37 (m, 4H), 7.11 (d, J = 7.06 Hz, 2H), 6.98 (br s, 1H), 6.57−
6.73 (m, 4H), 6.50 (s, 1H), 5.05 (s, 2H), 4.49 (dd, J = 8.01, 14.98 Hz,
1H), 3.87 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H), 3.54−3.71 (m, 2H),
3.34−3.48 (m, 1H), 3.10−3.33 (m, 2H), 2.72−3.01 (m, 4H), 2.43−
2.57 (m, 1H). m/z 568 (M + H).
1
(29). Prepared in 64% yield. H NMR (300 MHz, chloroform-d) δ
7.87−7.94 (m, 2H), 7.62−7.71 (m, 1H), 7.48−7.58 (m, 2H), 7.19−
7.35 (m, 3H), 7.09 (d, J = 6.88 Hz, 2H), 6.96 (s, 1H), 6.83 (d, J = 2.83
Hz, 1H), 6.58−6.73 (m, 3H), 6.55 (s, 1H), 4.48 (dd, J = 8.24, 15.02
Hz, 1H), 3.82 (s, 3H), 3.74 (s, 3H), 3.54−3.67 (m, 2H), 3.51 (s, 3H),
3.32−3.47 (m, 1H), 3.07−3.31 (m, 2H), 2.73−2.99 (m, 4H), 2.41−
2.56 (m, 1H). m/z 617 (M + H).
2-[(Benzylcarbamoyl)methyl]-1-[(3,4-dimethoxyphenyl)methyl]-
6-methoxy-1,2,3,4-tetrahydroisoquinolin-7-yl 4-Methylbenzene-1-
sulfonate (30). Prepared in 63% yield. 1H NMR (300 MHz,
chloroform-d) δ 7.78 (d, J = 8.19 Hz, 2H), 7.19−7.37 (m, 5H),
7.08 (d, J = 6.97 Hz, 2H), 6.94 (s, 1H), 6.79−6.86 (m, 1H), 6.59−6.72
(m, 3H), 6.56 (s, 1H), 4.49 (dd, J = 8.19, 14.98 Hz, 1H), 3.82 (s, 3H),
3.74 (s, 3H), 3.58−3.67 (m, 2H), 3.54 (s, 3H), 3.32−3.45 (m, 1H),
3.07−3.31 (m, 2H), 2.73−2.98 (m, 4H), 2.47−2.54 (m, 1H), 2.45 (s,
3H). m/z 631 (M + H).
General Procedure for N-alkylation with Acetate: 2-{1-[(3,4-
Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoqui-
nolin-2-yl}acetate (32). Tetrahydroisoquinoline 31 (0.26 g, 0.63
mmol), ethyl bromoacetate (0.16 g, 0.11 mL, 0.95 mmol), and
tetrabutylammonium iodide (47 mg, 0.13 mmol) were combined in
anhydrous dimethylformamide (6 mL), and diisopropylethylamine
(0.20 g, 0.28 mL, 1.58 mmol) was added. The reaction was stirred at rt
under N2 overnight. The reaction was diluted with ethyl acetate,
washed with a sodium bicarbonate solution and brine, and dried over
MgSO4, and solvent was removed under reduced pressure. The
compound was purified by chromatography on silica (0−50% EtOAc/
hexane) to give the desired product as a frothy solid (0.17 g, 55%). 1H
NMR (300 MHz, chloroform-d) δ 6.73−6.79 (m, 1H), 6.60−6.68 (m,
2H), 6.55 (s, 1H), 6.01 (s, 1H), 4.11−4.22 (m, 2H), 3.93 (dd, J = 7.39,
5.23 Hz, 1H), 3.85 (s, 3H), 3.83 (s, 3H), 3.80 (s, 3H), 3.57 (s, 3H),
3.39−3.55 (m, 2H), 3.28 (ddd, J = 12.88, 9.68, 5.04 Hz, 1H), 3.14 (dd,
J = 13.37, 4.99 Hz, 1H), 2.98 (dt, J = 12.60, 4.77 Hz, 1H), 2.73−2.87
(m, 2H), 2.45−2.59 (m, 1H), 1.26 (t, J = 7.11 Hz, 3H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6-methoxy-7-(4-
phenoxybutoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (24).
1
Prepared in 82% yield. H NMR (300 MHz, chloroform-d) δ 7.20−
7.36 (m, 5H), 7.11 (d, J = 6.78 Hz, 2H), 6.87−7.01 (m, 4H), 6.62−
6.76 (m, 3H), 6.60 (s, 1H), 6.51 (s, 1H), 4.51 (dd, J = 8.05, 14.93 Hz,
1H), 3.98−4.11 (m, 4H), 3.84 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H),
3.58−3.70 (m, 2H), 3.35−3.51 (m, 1H), 3.11−3.34 (m, 2H), 2.81−
3.02 (m, 4H), 2.42−2.56 (m, 1H), 1.94−2.11 (m, 4H). m/z 624 (M +
H).
2-[(Benzylcarbamoyl)methyl]-1-[(3,4-dimethoxyphenyl)methyl]-
6-methoxy-1,2,3,4-tetrahydroisoquinolin-7-yl butanoate (25). Phe-
nol 11 (50 mg, 0.105 mmol), butyric acid (9 mg, 0.105 mmol), and
BOP (46 mg, 0.105 mmol) were combined in dichloromethane (1
mL). Diisopropylethylamine (34 mg, 46 μL, 0.262 mmol) was added,
and the reaction was stirred at rt under N2 overnight. The reaction was
diluted with EtOAc, washed with 2 M HCl, an NaHCO3 solution, and
brine and dried over MgSO4, and the solvent was removed under
reduced pressure. The crude product was purified by chromatography
on silica (0−75% EtOAc in hexane) to give the desired product as a
pale-yellow solid (54 mg, 95%). 1H NMR (300 MHz, chloroform-d) δ
7.18−7.34 (m, 4H), 7.10 (d, J = 6.69 Hz, 2H), 6.92 (d, J = 6.97 Hz,
1H), 6.74 (s, 1H), 6.56−6.71 (m, 4H), 4.47 (dd, J = 8.01, 15.07 Hz,
1H), 3.80 (s, 3H), 3.79 (s, 3H), 3.74 (s, 3H), 3.59−3.70 (m, 2H),
3.11−3.44 (m, 3H), 2.77−3.01 (m, 4H), 2.55 (t, J = 7.00 Hz, 2H),
2.49 (d, J = 2.64 Hz, 1H), 1.72−1.87 (m, 2H), 1.05 (t, J = 7.39 Hz,
3H). m/z 547 (M + H).
General Procedure for Sulfonate Formation: 2-
[(Benzylcarbamoyl)methyl]-1-[(3,4-dimethoxyphenyl)methyl]-6-
methoxy-1,2,3,4-tetrahydroisoquinolin-7-yl Methanesulfonate (26).
To a solution of phenol 11 (30 mg, 0.063 mmol) in dichloromethane
(0.5 mL) cooled in ice under N2 was added triethylamine (16 mg, 22
μL, 0.157 mmol) and methanesulfonyl chloride (14 mg, 10 μL, 0.126
mmol). The reaction was allowed to warm slowly to rt overnight. The
solvent was removed under reduced pressure, and the crude product
was purified by chromatography on silica (0−100% EtOAc in hexane)
to give the desired product (35 mg, 54%). 1H NMR (300 MHz,
chloroform-d) δ 7.20−7.36 (m, 3H), 7.03−7.12 (m, 3H), 6.86 (br s,
1H), 6.67−6.76 (m, 3H), 6.60−6.65 (m, 1H), 4.48 (dd, J = 8.10, 14.98
Hz, 1H), 3.89 (s, 3H), 3.82 (s, 3H), 3.74 (s, 3H), 3.54−3.72 (m, 2H),
3.24−3.48 (m, 2H), 3.19 (s, 3H), 3.10−3.17 (m, 1H), 2.82−3.05 (m,
4H), 2.48−2.61 (m, 1H). m/z 555 (M + H).
General Procedure for Ester Hydrolysis: 2-{1-[(3,4-
Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoqui-
nolin-2-yl}acetic acid. Ester (80 mg, 0.16 mmol) was dissolved in
ethanol (2 mL), and an aqueous sodium hydroxide solution (2N, 0.3
mL, 0.64 mmol) was added. The reaction was stirred at rt for 2 h. The
pH of the solution was adjusted to between 8 and 9 with 2N HCl, and
all solvents were removed under reduced pressure. The crude solid was
redissolved as much as possible in methanol, the remaining solids were
removed by filtration, and the filtrate was concentrated. The desired
1
acid was obtained as a white solid (75 mg, 100%). H NMR (300
2-[(Benzylcarbamoyl)methyl]-1-[(3,4-dimethoxyphenyl)methyl]-
6-methoxy-1,2,3,4-tetrahydroisoquinolin-7-yl Trifluoromethanesul-
fonate (27). Prepared in 18% yield. 1H NMR (300 MHz, chloroform-
d) δ 7.21−7.36 (m, 4H), 7.10 (d, J = 8.01 Hz, 2H), 6.90 (s, 1H), 6.87
(br s, 1H), 6.75 (s, 1H), 6.59−6.72 (m, 2H), 4.49 (dd, J = 8.05, 15.02
MHz, methanol-d4) δ 6.92 (d, J = 8.10 Hz, 1H), 6.82 (s, 1H), 6.68−
6.78 (m, 2H), 5.96 (s, 1H), 4.67 (dd, J = 9.04, 5.09 Hz, 1H), 3.81−
3.82 (m, 3H), 3.76 (s, 3H), 3.71−3.85 (m, 6H), 3.46 (s, 3H), 3.38−
3.66 (m, 2H), 2.95−3.18 (m, 3H).
J
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Journal of Medicinal Chemistry
Article
General Procedure for Final Coupling: 2-{1-[(3,4-
Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoqui-
nolin-2-yl}-N-(2-phenylethyl)acetamide (33). Acid (30 mg, 0.075
mmol), phenethylamine (9 mg, 9 μL, 0.075 mmol), and BOP (33 mg,
0.075 mmol) were combined in anhydrous dimethylformamide (1
mL), and diisopropylethylamine (24 mg, 33 μL, 0.187 mmol) was
added. The reaction was stirred at rt under N2 overnight. The reaction
was diluted with ethyl acetate, washed with a sodium bicarbonate
solution and brine, and dried over MgSO4, and the solvent was
removed under reduced pressure. The compound was purified by
chromatography on silica (0−75% EtOAc/hexane) to give the desired
3H), 3.45−3.65 (m, 5H), 3.22−3.36 (m, 1H), 3.09−3.20 (m, 1H),
2.94−3.08 (m, 1H), 2.71−2.90 (m, 2H), 2.53 (d, J = 16.39 Hz, 1H).
m/z 492 (M + H). HPLC purity 91.0%.
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(naphthalen-1-yl)acetamide (41). Pre-
1
pared in 64% yield. H NMR (300 MHz, chloroform-d) δ 9.25 (s,
1H), 7.84 (d, J = 7.63 Hz, 2H), 7.66 (d, J = 8.10 Hz, 1H), 7.33−7.54
(m, 4H), 6.63−6.72 (m, 2H), 6.59 (s, 1H), 6.46 (s, 1H), 6.30 (d, J =
8.10 Hz, 1H), 3.87−3.92 (m, 3H), 3.90 (s, 1H), 3.80 (s, 3H), 3.65 (s,
3H), 3.36−3.61 (m, 3H), 3.27 (s, 3H), 2.92−3.15 (m, 4H), 2.64 (d, J
= 15.82 Hz, 1H). m/z 527 (M + H).
1
product as a pale-yellow solid (10 mg, 26%). H NMR (300 MHz,
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
chloroform-d) δ 7.18−7.33 (m, 3H), 7.11−7.18 (m, 2H), 6.66−6.83
(m, 4H), 6.58 (s, 1H), 6.41 (s, 1H), 3.87 (s, 6H), 3.85 (s, 3H), 3.80 (s,
3H), 3.59 (dd, J = 5.56, 9.23 Hz, 1H), 3.28−3.47 (m, 2H), 3.03−3.28
(m, 2H), 2.73−2.99 (m, 5H), 2.39−2.67 (m, 3H). m/z 505 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(3-phenylpropyl)acetamide (34). Prepared
hydroisoquinolin-2-yl}-N-(8-fluoroquinolin-4-yl)acetamide (42).
1
Prepared in 27% yield. H NMR (300 MHz, chloroform-d) δ 8.88
(d, J = 4.99 Hz, 1H), 8.31 (d, J = 4.99 Hz, 1H), 7.54 (dd, J = 1.60, 8.10
Hz, 1H), 7.28−7.46 (m, 2H), 6.87 (d, J = 8.38 Hz, 1H), 6.61−6.71
(m, 2H), 6.53 (d, J = 1.79 Hz, 1H), 6.43 (s, 1H), 6.37 (d, J = 8.10 Hz,
1H), 4.01 (t, J = 6.73 Hz, 1H), 3.90 (s, 3H), 3.75−3.81 (m, 3H), 3.68
(s, 3H), 3.39−3.55 (m, 6H), 2.89−3.20 (m, 4H), 2.62−2.76 (m, 1H).
m/z 546 (M + H). HPLC purity 93.0%.
1
in 64% yield. H NMR (300 MHz, chloroform-d) δ 7.23−7.33 (m,
2H), 7.11−7.22 (m, 3H), 6.69−6.85 (m, 3H), 6.61−6.68 (m, 1H),
6.59 (s, 1H), 6.42 (s, 1H), 3.86 (s, 3H), 3.85 (s, 3H), 3.81 (s, 3H),
3.80 (s, 3H), 3.60 (dd, J = 5.37, 9.23 Hz, 1H), 3.01−3.50 (m, 4H),
2.78−3.00 (m, 4H), 2.60−2.78 (m, 1H), 2.42−2.57 (m, 3H), 1.45−
1.69 (m, 2H). m/z 519 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(2-methylquinolin-4-yl)acetamide (43).
1
Prepared in 28% yield. H NMR (300 MHz, chloroform-d) δ 9.89
(s, 1H), 8.13 (s, 1H), 8.00 (d, J = 8.48 Hz, 1H), 7.66 (t, J = 7.30 Hz,
1H), 7.33 (t, J = 7.35 Hz, 1H), 7.11 (d, J = 8.38 Hz, 1H), 6.61−6.69
(m, 2H), 6.47−6.54 (m, 1H), 6.40 (s, 1H), 6.36 (d, J = 8.19 Hz, 1H),
3.99 (t, J = 6.64 Hz, 1H), 3.90 (s, 3H), 3.79−3.87 (m, 2H), 3.76 (s,
3H), 3.62−3.69 (m, 3H), 3.43−3.54 (m, 2H), 3.39 (s, 3H), 2.87−3.21
(m, 4H), 2.73 (s, 3H). m/z 542 (M + H). HPLC purity 93.0%.
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(2-phenylphenyl)acetamide (44). Prepared
in 40% yield. 1H NMR (300 MHz, chloroform-d) δ 9.41 (s, 1H), 8.35
(d, J = 8.29 Hz, 1H), 7.35−7.45 (m, 1H), 7.15−7.32 (m, 8H), 6.63 (d,
J = 8.29 Hz, 1H), 6.51 (s, 1H), 6.36−6.45 (m, 2H), 5.85 (s, 1H), 3.87
(s, 3H), 3.73 (d, J = 11.68 Hz, 6H), 3.57−3.66 (m, 1H), 3.54 (s, 3H),
3.30−3.45 (m, 1H), 3.17−3.29 (m, 1H), 2.93−3.08 (m, 1H), 2.60 (d, J
= 8.29 Hz, 4H), 2.27−2.39 (m, 1H). m/z 553 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(3-phenylphenyl)acetamide (45). Prepared
in 27% yield. 1H NMR (300 MHz, chloroform-d) δ 8.68 (s, 1H), 7.57
(d, J = 7.91 Hz, 2H), 7.39−7.53 (m, 3H), 7.29−7.37 (m, 1H), 7.23 (d,
J = 8.29 Hz, 3H), 6.71 (d, J = 1.51 Hz, 3H), 6.63 (s, 1H), 6.48 (s, 1H),
3.89 (s, 3H), 3.81 (d, J = 6.40 Hz, 6H), 3.76 (s, 3H), 3.45−3.57 (m,
1H), 3.24−3.45 (m, 2H), 2.89−3.09 (m, 4H), 2.52−2.64 (m, 1H). m/
z 553 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-1-(1,2,3,4-tetrahydroisoquinolin-2-yl)ethan-
1
1-one (35). Prepared in 32% yield. H NMR (300 MHz, chloroform-
d) δ 7.01−7.24 (m, 3H), 6.53−6.90 (m, 5H), 6.27 (d, J = 11.87 Hz,
1H), 4.24−4.89 (m, 2H), 3.65−4.01 (m, 12H), 3.22−3.64 (m, 5H),
2.73−3.10 (m, 6H), 2.35−2.72 (m, 2H). m/z 517.4 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-1-(3-phenylpiperidin-1-yl)ethan-1-one (36).
1
Prepared in 42% yield. H NMR (300 MHz, chloroform-d) δ 7.13−
7.41 (m, 6H), 6.88−7.10 (m, 1H), 6.52−6.83 (m, 3H), 4.64 (d, J =
7.72 Hz, 1H), 3.76−3.95 (m, 12H), 3.53−3.75 (m, 4H), 3.20−3.52
(m, 4H), 2.71−3.15 (m, 5H), 2.30−2.66 (m, 4H). m/z 545 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-1-(4-phenylpiperidin-1-yl)ethan-1-one (37).
1
Prepared in 52% yield. H NMR (300 MHz, chloroform-d) δ 7.02−
7.40 (m, 5H), 6.63−6.83 (m, 3H), 6.59 (s, 1H), 6.31 (s, 1H), 4.53−
4.85 (m, 1H), 3.77−3.91 (m, 9H), 3.72 (s, 3H), 3.62 (s, 1H), 3.21−
3.55 (m, 4H), 2.75−3.18 (m, 5H), 2.36−2.72 (m, 4H), 1.86 (br s,
1H), 1.33−1.59 (m, 2H). m/z 545 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-1-(4-phenylpiperazin-1-yl)ethan-1-one (38).
1
Prepared in 42% yield. H NMR (300 MHz, chloroform-d) δ 7.18−
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
7.39 (m, 3H), 6.89 (s, 2H), 6.71 (s, 3H), 6.59 (s, 1H), 6.33 (s, 1H),
3.77−3.94 (m, 9H), 3.73 (s, 3H), 3.47 (d, J = 12.81 Hz, 3H), 3.34 (d, J
= 12.81 Hz, 5H), 2.70−3.07 (m, 8H), 2.47 (dd, J = 3.86, 16.48 Hz,
1H). m/z 546 (M + H).
hydroisoquinolin-2-yl}-N-(4-phenylphenyl)acetamide (46). Prepared
1
in 16% yield. H NMR (300 MHz, chloroform-d) δ 8.74 (br s, 1H),
7.59 (d, J = 6.78 Hz, 3H), 7.28−7.51 (m, 4H), 7.06 (br s, 1H), 6.58−
6.92 (m, 4H), 6.45 (s, 1H), 4.12 (q, J = 7.16 Hz, 1H), 3.77−3.97 (m,
6H), 3.56−3.76 (m, 6H), 3.23−3.54 (m, 4H), 2.85−3.13 (m, 3H),
2.58 (d, J = 15.82 Hz, 1H). m/z 553 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-
acetamide (47). Prepared in 63% yield. 1H NMR (300 MHz,
chloroform-d) δ 7.06−7.22 (m, 4H), 6.53−6.63 (m, 2H), 6.18−6.49
(m, 3H), 5.00−5.21 (m, 1H), 3.79−3.88 (m, 3H), 3.74 (d, J = 6.03
Hz, 6H), 3.67 (s, 3H), 3.11−3.49 (m, 3H), 2.62−3.05 (m, 7H), 2.42−
2.56 (m, 1H), 1.66−2.02 (m, 4H). m/z 531 (M + H).
N-Benzyl-2-{1-[(3,4-dimethoxyphenyl)methyl]-6,7-dimethoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}-N-methylacetamide (39). Pre-
pared in 47% yield. 1H NMR (300 MHz, chloroform-d) δ 7.17−
7.37 (m, 4H), 7.01 (d, J = 7.16 Hz, 1H), 6.64−6.80 (m, 3H), 6.58 (d, J
= 4.90 Hz, 1H), 6.18−6.34 (m, 1H), 4.40−4.74 (m, 1H), 3.89−4.33
(m, 2H), 3.78−3.88 (m, 9H), 3.65−3.76 (m, 3H), 3.28−3.58 (m, 3H),
2.83−3.15 (m, 4H), 2.70−2.82 (m, 3H), 2.39−2.60 (m, 1H). m/z 505
(M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}acetate (40). Acid (30 mg, 0.075 mmol),
potassium carbonate (26 mg, 0.187 mmol), and tetrabutylammonium
iodide (6 mg, 0.015 mmol) were combined in dimethylformamide (1
mL), and benzyl bromide (19 mg, 13 μL, 0.112 mmol) was added.
The reaction was heated at 50 °C under N2 overnight. The reaction
was cooled and diluted with EtOAc. The reaction was washed with an
NaHCO3 solution and brine and dried over MgSO4, and the solvent
was removed under reduced pressure. The material was purified by
chromatography on silica (0−50% EtOAc in hexane) to give the
desired ester (9 mg, 24%). 1H NMR (300 MHz, chloroform-d) δ 7.35
(s, 5H), 6.73 (d, J = 8.01 Hz, 1H), 6.57−6.66 (m, 2H), 6.55 (s, 1H),
6.00 (s, 1H), 5.16 (s, 2H), 3.90−4.03 (m, 1H), 3.84 (s, 6H), 3.78 (s,
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(2-methyl-1,2,3,4-tetrahydroquinolin-4-
yl)acetamide (48). Quinoline 43 (20 mg, 0.037 mmol) and 10%
palladium on carbon (20 mg) were combined in ethanol (5 mL) and
chloroform (1 mL) and hydrogenated at 50 psi of H2 in a Parr shaker
for 3 days. The reaction was filtered through Celite, and the solvent
was removed under reduced pressure. The crude product was purified
by chromatography on silica (0−20% MMA-80 in EtOAc) to give the
1
tetrahydroisoquinoline derivative (3 mg, 15%). H NMR (300 MHz,
chloroform-d) δ 9.09 (s, 1H), 7.78 (s, 1H), 7.26 (s, 3H), 6.57−6.67
(m, 3H), 6.51 (s, 1H), 6.28 (s, 1H), 3.82−3.99 (m, 5H), 3.59−3.81
K
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(m, 10H), 3.27−3.54 (m, 4H), 3.04−3.19 (m, 1H), 2.79−3.03 (m,
5H), 2.58−2.70 (m, 1H), 2.48 (s, 3H). m/z 546 (M + H).
2-Bromo-N-[(4-nitrophenyl)methyl]acetamide. To a solution of 4-
nitrobenzylamine hydrochloride (1.89 g, 10 mmol) and triethylamine
(1.01 g, 1.39 mL, 10 mmol) in dichloromethane (10 mL) cooled in an
ice bath was added dropwise bromoacetyl bromide (1.01 g, 0.44 mL, 5
mmol). A precipitate formed immediately. The ice bath was removed,
and the reaction was stirred at rt for 2 h. The precipitate was removed
by filtration, and the solution was washed twice with 2N HCl and
dried over MgSO4, and the solvent was removed under reduced
pressure to give the bromide as a white solid (1.4 g, 100%). 1H NMR
(300 MHz, chloroform-d) δ 8.22 (d, J = 8.67 Hz, 2H), 7.47 (d, J =
8.48 Hz, 2H), 4.57−4.64 (m, 2H), 4.15 (s, 2H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-[(4-nitrophenyl)methyl]acetamide. Pre-
pared as per the general alkylation procedure using 2-bromo-N-[(4-
nitrophenyl)methyl]acetamide in 63% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.15 (d, J = 8.76 Hz, 2H), 7.23 (d, J = 8.67 Hz, 2H),
6.90−7.00 (m, 1H), 6.65−6.81 (m, 3H), 6.61 (s, 1H), 6.53 (s, 1H),
4.47 (dd, J = 8.01, 15.54 Hz, 1H), 3.87 (s, 3H), 3.87 (s, 3H), 3.83 (s,
3H), 3.70−3.75 (m, 3H), 3.42−3.71 (m, 3H), 3.11−3.35 (m, 2H),
2.83−3.03 (m, 4H), 2.45−2.57 (m, 1H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-[(1S)-1-phenylethyl]acetamide (49 and
50). Prepared from tetrahydroisoquinoline 11 and 2-bromo-N-[(1S)-
1-phenylethyl]acetamide as above as a mixture of diastereomers in
54% yield. Diastereomers were separated by reverse-phase HPLC. The
1
first to elute was 49 and the second, 50. 49: H NMR (300 MHz,
chloroform-d) δ 8.24 (br s, 1H), 7.20−7.37 (m, 5H), 6.74 (d, J = 8.10
Hz, 1H), 6.62 (s, 1H), 6.58 (s, 1H), 6.49 (d, J = 8.19 Hz, 1H), 5.86 (br
s, 1H), 4.97−5.09 (m, 1H), 4.60−4.70 (m, 1H), 3.88−4.03 (m, 2H),
3.86 (s, 3H), 3.83−3.85 (m, 3H), 3.75 (s, 3H), 3.61 (dd, J = 11.73,
6.64 Hz, 2H), 3.53 (s, 3H), 3.45−3.50 (m, 1H), 3.19 (d, J = 10.83 Hz,
1H), 2.83−3.04 (m, 2H), 1.48 (d, J = 6.97 Hz, 3H). m/z 505 (M +
1
H). 50: H NMR (300 MHz, chloroform-d) δ 8.49 (d, J = 7.63 Hz,
1H), 7.21−7.39 (m, 5H), 6.73 (d, J = 8.19 Hz, 1H), 6.62 (s, 1H), 6.54
(d, J = 1.70 Hz, 1H), 6.43 (d, J = 8.10 Hz, 1H), 5.78 (s, 1H), 5.05 (s,
1H), 4.52 (d, J = 6.31 Hz, 1H), 3.86 (s, 3H), 3.84 (s, 3H), 3.78−3.95
(m, 2H), 3.75 (s, 3H), 3.56−3.69 (m, 2H), 3.51−3.54 (m, 1H), 3.49
(s, 3H), 3.10−3.33 (m, 1H), 2.83−3.04 (m, 2H), 1.50 (d, J = 6.97 Hz,
3H). m/z 505 (M + H).
N-[(4-Aminophenyl)methyl]-2-{1-[(3,4-dimethoxyphenyl)methyl]-
6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide. To a
solution of nitrophenyl (197 mg, 0.37 mmol) and hydrazine
monohydrate (0.15 mL) in ethanol (5 mL) warmed to 50 °C was
added Raney nickel (2800, as a slurry in water, 25 mg), and the
reaction was heated at 50 °C for 1 h. The reaction was cooled and
filtered through Celite, and the solvent removed under reduced
N-[(4-Chlorophenyl)methyl]-2-{1-[(3,4-dimethoxyphenyl)-
methyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}-
acetamide (51). Prepared in 60% yield. 1H NMR (300 MHz,
chloroform-d) δ 7.21−7.29 (m, 2H), 7.03 (d, J = 8.38 Hz, 2H), 6.91 (t,
J = 6.31 Hz, 1H), 6.63−6.78 (m, 3H), 6.59 (s, 1H), 6.48 (s, 1H), 4.41
(dd, J = 8.05, 15.02 Hz, 1H), 3.87 (s, 3H), 3.84 (s, 3H), 3.82 (s, 3H),
3.77 (s, 3H), 3.52−3.65 (m, 2H), 3.36−3.51 (m, 1H), 3.09−3.34 (m,
2H), 2.80−3.01 (m, 4H), 2.42−2.55 (m, 1H). m/z 527, 525 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-[(4-fluorophenyl)methyl]acetamide (52).
1
pressure to give the aniline (155 mg, 83%). H NMR (300 MHz,
chloroform-d) δ 6.92 (d, J = 8.29 Hz, 2H), 6.70 (s, 2H), 6.56−6.68
(m, 4H), 6.40 (s, 1H), 4.39 (dd, J = 7.91, 14.51 Hz, 1H), 3.86 (s, 3H),
3.82 (s, 6H), 3.79 (s, 3H), 3.51−3.67 (m, 3H), 3.32−3.44 (m, 1H),
3.10−3.31 (m, 2H), 2.78−2.98 (m, 4H), 2.42−2.53 (m, 1H).
1
Prepared in 64% yield. H NMR (300 MHz, chloroform-d) δ 7.02−
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-[(4-acetamidophenyl)methyl]acetamide
(57). To the aniline (30 mg, 0.059 mmol) in dichloromethane (1 mL)
was added acetic anhydride (12 mg, 11 μL, 0.119 mmol) and
diisopropylethylamine (19 mg, 26 μL, 0.148 mmol), and the reaction
was stirred at rt overnight. The reaction was diluted with EtOAc and
washed with an NaHCO3 solution. The aqueous phase was extracted
once with EtOAc, and the combined organic phases were washed with
brine and dried over MgSO4, and the solvent was removed under
reduced pressure. The compound was purified by chromatography on
silica (0−100% EtOAc in hexane) to give the amide (34 mg, 100%).
1H NMR (300 MHz, chloroform-d) δ 7.41 (d, J = 8.38 Hz, 2H), 7.23
(s, 1H), 7.05 (d, J = 8.38 Hz, 2H), 6.89−6.99 (m, 1H), 6.64−6.79 (m,
3H), 6.59 (s, 1H), 6.46 (s, 1H), 4.41 (dd, J = 7.91, 15.07 Hz, 1H), 3.87
(s, 3H), 3.81−3.84 (m, 6H), 3.78 (s, 3H), 3.54−3.67 (m, 2H), 3.35−
3.50 (m, 1H), 3.09−3.33 (m, 2H), 2.78−2.99 (m, 4H), 2.42−2.56 (m,
1H), 2.17 (s, 3H). m/z 548 (M + H).
N-{4-[(2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}acetamido)methyl]phenyl}-
hexanamide (58). Aniline (23 mg, 0.046 mmol), hexanoic acid (5 mg,
0.046 mmol), and BOP (20 mg, 0.046 mmol) were combined in
dichloromethane (1 mL), and diisopropylethylamine (12 mg, 16 μL,
0.091 mmol) was added. The reaction was stirred at rt overnight and
diluted with EtOAc. The reaction was washed with an NaHCO3
solution and brine and dried over MgSO4, and the solvent was
removed under reduced pressure. The compound was purified by
chromatography on silica (0−100% EtOAc in hexane) to give the
amide (30 mg, 100%). 1H NMR (300 MHz, chloroform-d) δ 7.43 (d, J
= 8.29 Hz, 2H), 7.21−7.28 (m, 1H), 7.04 (d, J = 8.38 Hz, 2H), 6.94
(dd, J = 5.09, 7.72 Hz, 1H), 6.65−6.75 (m, 3H), 6.59 (s, 1H), 6.46 (s,
1H), 4.41 (dd, J = 8.05, 14.83 Hz, 1H), 3.86 (s, 3H), 3.81−3.84 (m, J
= 0.80 Hz, 6H), 3.78 (s, 3H), 3.54−3.66 (m, 2H), 3.35−3.53 (m, 1H),
3.09−3.33 (m, 2H), 2.79−2.99 (m, 4H), 2.43−2.56 (m, 1H), 2.34 (t, J
= 7.54 Hz, 2H), 1.64−1.79 (m, 2H), 1.31−1.39 (m, 4H), 0.87−0.95
(m, 3H). m/z 604 (M + H).
7.11 (m, 2H), 6.87−7.02 (m, 3H), 6.64−6.78 (m, 3H), 6.59 (s, 1H),
6.47 (s, 1H), 4.42 (dd, J = 8.10, 14.79 Hz, 1H), 3.87 (s, 3H), 3.83 (s,
3H), 3.82 (s, 3H), 3.78 (s, 3H), 3.52−3.66 (m, 2H), 3.36−3.51 (m,
1H), 3.09−3.34 (m, 2H), 2.80−3.00 (m, 4H), 2.42−2.56 (m, 1H). m/
z 509 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(pyridin-2-ylmethyl)acetamide (53). Pre-
pared in 57% yield. 1H NMR (300 MHz, chloroform-d) δ 8.52 (d, J =
4.52 Hz, 1H), 7.53−7.69 (m, 2H), 7.16 (dd, J = 5.18, 7.16 Hz, 1H),
7.09 (d, J = 7.82 Hz, 1H), 6.62−6.72 (m, 3H), 6.60 (s, 1H), 6.29 (s,
1H), 4.53 (dd, J = 6.55, 16.25 Hz, 1H), 4.17 (dd, J = 5.32, 16.25 Hz,
1H), 3.86 (s, 3H), 3.77 (s, 3H), 3.67−3.75 (m, 7H), 3.17−3.51 (m,
3H), 2.82−3.11 (m, 4H), 2.45−2.60 (m, 1H). m/z 492 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(pyridin-3-ylmethyl)acetamide (54). Pre-
pared in 49% yield. 1H NMR (300 MHz, chloroform-d) δ 8.50 (dd, J =
1.37, 4.76 Hz, 1H), 8.33 (d, J = 1.70 Hz, 1H), 7.43 (d, J = 7.82 Hz,
1H), 7.22 (dd, J = 4.80, 7.72 Hz, 1H), 6.89−6.98 (m, 1H), 6.64−6.79
(m, 3H), 6.60 (s, 1H), 6.51 (s, 1H), 4.41 (dd, J = 8.01, 15.26 Hz, 1H),
3.87 (s, 3H), 3.85 (s, 3H), 3.84 (s, 3H), 3.77 (s, 3H), 3.56−3.70 (m,
2H), 3.38−3.54 (m, 1H), 3.09−3.34 (m, 2H), 2.82−3.02 (m, 4H),
2.43−2.57 (m, 1H). m/z 492 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-(pyridin-4-ylmethyl)acetamide (55). Pre-
1
pared in 89% yield. H NMR (300 MHz, chloroform-d) δ 8.48−8.56
(m, 2H), 6.96−7.02 (m, 2H), 6.92 (dd, J = 5.13, 7.68 Hz, 1H), 6.71−
6.80 (m, 2H), 6.58−6.68 (m, 2H), 6.53 (s, 1H), 4.40 (dd, J = 8.10,
15.92 Hz, 1H), 3.88 (s, 3H), 3.86 (s, 3H), 3.83 (s, 3H), 3.69 (s, 3H),
3.55−3.66 (m, 2H), 3.41−3.54 (m, 1H), 3.10−3.37 (m, 2H), 2.82−
3.04 (m, 4H), 2.53 (d, J = 16.29 Hz, 1H). m/z 492 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-{[4-(dimethylamino)phenyl]methyl}-
acetamide (56). Prepared in 7% yield. 1H NMR (300 MHz,
chloroform-d) δ 7.03 (d, J = 8.57 Hz, 2H), 6.92−6.99 (m, 1H),
6.62−6.73 (m, 5H), 6.58 (s, 1H), 6.38 (s, 1H), 4.38−4.49 (m, 1H),
3.86 (s, 3H), 3.83 (s, 3H), 3.82 (s, 3H), 3.78 (s, 3H), 3.52−3.69 (m,
2H), 3.31−3.45 (m, 1H), 3.21 (q, J = 16.80 Hz, 2H), 2.90−2.96 (m,
6H), 2.77−2.90 (m, 4H), 2.41−2.53 (m, 1H). m/z 534 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-({4-[(hexylcarbamoyl)amino]phenyl}-
methyl)acetamide (59). To the aniline (40 mg, 0.079 mmol) in
toluene (1 mL) was added n-hexyl isocyanate (11 mg, 13 μL, 0.087
L
dx.doi.org/10.1021/jm400720h | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
mmol), and the mixture was heated at 75 °C for 2 h. The reaction was
cooled, the solvent was removed under reduced pressure, and the
crude was purified by chromatography on silica (0−100% EtOAc in
hexane) to give the urea (38 mg, 76%). 1H NMR (300 MHz,
chloroform-d) δ 7.12 (d, J = 8.48 Hz, 2H), 7.00 (dd, J = 5.27, 7.72 Hz,
1H), 6.93 (d, J = 8.48 Hz, 2H), 6.87 (s, 1H), 6.66−6.77 (m, 3H), 6.60
(s, 1H), 6.49 (s, 1H), 5.29 (t, J = 5.56 Hz, 1H), 4.33 (dd, J = 7.82,
14.98 Hz, 1H), 3.87 (s, 3H), 3.84 (s, 3H), 3.82 (s, 3H), 3.75 (s, 3H),
3.54−3.66 (m, 2H), 3.36−3.51 (m, 1H), 3.07−3.32 (m, 4H), 2.79−
3.01 (m, 4H), 2.43−2.56 (m, 1H), 1.39−1.54 (m, 2H), 1.21−1.36 (m,
6H), 0.82−0.90 (m, 3H). m/z 633 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-heptylacetamide (60). Prepared in 63%
yield. 1H NMR (300 MHz, chloroform-d) δ 6.67−6.91 (m, 3H), 6.59
(m, 2H), 6.42 (m, 1H), 3.74−3.96 (m, 12H), 3.62 (m, 1H), 3.33−3.49
(m, 1H), 3.03−3.30 (m, 3H), 2.78−3.02 (m, 4H), 2.62 (m, 1H), 2.51
(d, J = 16.29 Hz, 1H), 1.08−1.38 (m, 10H), 0.89 (m, 3H). m/z 499
(M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6-methoxy-7-propoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-2-ylmethyl)-
acetamide (69). Prepared in 52% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.52 (d, J = 4.80 Hz, 1H), 7.52−7.69 (m, 2H), 7.13−
7.21 (m, 1H), 7.08 (d, J = 7.82 Hz, 1H), 6.62−6.74 (m, 3H), 6.59 (s,
1H), 6.33 (s, 1H), 4.53 (dd, J = 6.69, 16.20 Hz, 1H), 4.16 (dd, J =
5.27, 16.20 Hz, 1H), 3.85 (s, 3H), 3.77 (s, 3H), 3.72 (s, 3H), 3.66−
3.83 (m, 3H), 3.17−3.51 (m, 3H), 2.81−3.09 (m, 4H), 2.46−2.59 (m,
1H), 1.73−1.88 (m, 2H), 1.01 (t, J = 7.39 Hz, 3H). m/z 520 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6-methoxy-7-propoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-3-ylmethyl)-
acetamide (70). Prepared in 43% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.45−8.52 (m, 1H), 8.33 (s, 1H), 7.43 (d, J = 7.82
Hz, 1H), 7.22 (dd, J = 4.85, 7.77 Hz, 1H), 6.89−6.99 (m, 1H), 6.63−
6.78 (m, 3H), 6.59 (s, 1H), 6.53 (s, 1H), 4.40 (dd, J = 8.01, 15.26 Hz,
1H), 3.93 (t, J = 6.88 Hz, 2H), 3.85 (s, 3H), 3.83 (s, 3H), 3.76 (s, 3H),
3.54−3.70 (m, 2H), 3.37−3.54 (m, 1H), 3.09−3.33 (m, 2H), 2.80−
2.99 (m, 4H), 2.42−2.55 (m, 1H), 1.79−1.93 (m, 2H), 1.05 (t, J =
7.44 Hz, 3H). m/z 520 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6-methoxy-7-(2,2,2-trifluor-
oethoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-2-ylmethyl)-
acetamide (71). Prepared in 31% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.52 (d, J = 3.96 Hz, 1H), 7.63 (t, J = 7.63 Hz, 1H),
7.51 (br s, 1H), 7.13−7.22 (m, 1H), 7.07 (d, J = 7.63 Hz, 1H), 6.55−
6.73 (m, 4H), 6.50 (s, 1H), 4.50 (dd, J = 6.55, 15.97 Hz, 1H), 4.08−
4.35 (m, 3H), 3.86 (s, 3H), 3.77 (s, 3H), 3.72 (s, 3H), 3.66−3.75 (m,
1H), 3.14−3.49 (m, 3H), 2.78−3.09 (m, 4H), 2.47−2.62 (m, 1H). m/
z 560 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6-methoxy-7-(2,2,2-trifluor-
oethoxy)-1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-3-ylmethyl)-
acetamide (72). Prepared in 29% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.49 (d, J = 4.71 Hz, 1H), 8.32 (s, 1H), 7.42 (d, J =
7.82 Hz, 1H), 7.22 (dd, J = 4.85, 7.68 Hz, 1H), 6.81−6.92 (m, 1H),
6.62−6.77 (m, 5H), 4.24−4.49 (m, 3H), 3.86 (s, 3H), 3.84 (s, 3H),
3.76 (s, 3H), 3.54−3.66 (m, 2H), 3.38−3.53 (m, 1H), 3.07−3.34 (m,
2H), 2.77−3.02 (m, 4H), 2.45−2.61 (m, 1H). m/z 560 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-7-ethoxy-6-methoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-2-ylmethyl)-
acetamide (73). Prepared in 36% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.49−8.55 (m, 1H), 7.63 (dt, J = 1.84, 7.70 Hz, 1H),
7.55 (t, J = 5.79 Hz, 1H), 7.16 (dd, J = 5.32, 7.02 Hz, 1H), 7.08 (d, J =
7.82 Hz, 1H), 6.61−6.72 (m, 3H), 6.59 (s, 1H), 6.34 (s, 1H), 4.53 (dd,
J = 6.69, 16.20 Hz, 1H), 4.14 (dd, J = 5.27, 16.20 Hz, 1H), 3.88−4.00
(m, 2H), 3.85 (s, 3H), 3.77 (s, 3H), 3.72 (s, 3H), 3.65−3.70 (m, 1H),
3.17−3.48 (m, 3H), 2.81−3.08 (m, 4H), 2.46−2.57 (m, 1H), 1.41 (t, J
= 6.97 Hz, 2H). m/z 506 (M + H).
2-{1-[(3,4-Dimethoxyphenyl)methyl]-7-ethoxy-6-methoxy-
1,2,3,4-tetrahydroisoquinolin-2-yl}-N-(pyridin-3-ylmethyl)-
acetamide (74). Prepared in 41% yield. 1H NMR (300 MHz,
chloroform-d) δ 8.49 (dd, J = 1.55, 4.76 Hz, 1H), 8.33 (d, J = 1.70 Hz,
1H), 7.43 (td, J = 1.93, 7.82 Hz, 1H), 7.18−7.25 (m, 1H), 6.93 (dd, J
= 5.23, 7.58 Hz, 1H), 6.71−6.78 (m, 2H), 6.64−6.70 (m, 1H), 6.60 (s,
1H), 6.54 (s, 1H), 4.40 (dd, J = 8.01, 15.26 Hz, 1H), 4.06 (q, J = 7.00
Hz, 2H), 3.86 (s, 3H), 3.83 (s, 3H), 3.76 (s, 3H), 3.55−3.68 (m, 2H),
3.38−3.54 (m, 1H), 3.10−3.33 (m, 2H), 2.77−3.01 (m, 4H), 2.43−
2.56 (m, 1H), 1.47 (t, J = 6.97 Hz, 3H). m/z 506 (M + H).
Functional Determinations. The activity of the target com-
pounds at the OX1 and OX2 receptors was assayed using RD-HGA16
cells (Molecular Devices), a CHO cell line stably overexpressing the
promiscuous Gq-protein Ga16. Two individual cell lines were used
that stably express either OX1 or OX2 receptors. Cells were cultured
overnight in black, clear bottom, 96-well tissue culture plates at 25 000
cells per well in 100 μL/well of Ham’s F12 medium supplemented
with 10% FBS, 1× pen/strep, 0.1 μg/mL of normocin, 400 μg/mL of
geneticin, and 200 μg/mL of hygromycin. The medium was then
removed, and the cells were loaded with 200 μL/well of a calcium-
sensitive fluorescent dye (calcium 5, Molecular Devices) in assay buffer
(1× HBSS, 20 μM HEPES plus 2.7 mM probenecid) as per the
manufacturer’s instructions for 45 min at 37 °C. Cells were then
pretreated by the addition of 25 μL/well of 10% DMSO (for intrinsic
activity measurements) or 25 μL of 10% DMSO including a 10× final
2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-tetra-
hydroisoquinolin-2-yl}-N-[3-(dimethylamino)propyl]acetamide
1
(61). Prepared in 57% yield. H NMR (300 MHz, chloroform-d) δ
6.86 (d, J = 8.10 Hz, 2H), 6.72−6.79 (m, 1H), 6.70 (d, J = 1.79 Hz,
1H), 6.59 (s, 1H), 6.35 (s, 1H), 3.89 (s, 3H), 3.87 (s, 3H), 3.86 (s,
3H), 3.77 (s, 3H), 3.58−3.65 (m, 1H), 3.32−3.46 (m, 1H), 3.05−3.31
(m, 3H), 2.78−3.03 (m, 4H), 2.59−2.74 (m, 1H), 2.44−2.58 (m, 1H),
2.12−2.22 (m, 6H), 2.10−2.24 (m, 2H), 1.35−1.53 (m, 2H). m/z 486
(M + H).
2-(2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl}acetamido)acetate (62). Prepared in
1
55% yield. H NMR (300 MHz, chloroform-d) δ 7.27 (d, J = 2.35
Hz, 1H), 6.94 (br s, 1H), 6.73−6.86 (m, 2H), 6.59 (d, J = 2.17 Hz,
1H), 6.41 (d, J = 2.07 Hz, 1H), 4.06 (s, 1H), 3.84−3.91 (m, 8H),
3.75−3.83 (m, 5H), 3.68−3.75 (m, 3H), 3.38−3.57 (m, 2H), 3.11−
3.33 (m, 2H), 2.82−3.00 (m, 4H), 2.46−2.59 (m, 1H). m/z 473 (M +
H).
2-(2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl}acetamido)acetic acid. Ester (60 mg,
0.127 mmol) was dissolved in methanol (5 mL), and a 2N sodium
hydroxide solution (0.25 mL, 0.508 mmol) was added. The reaction
was stirred at rt overnight. The pH was adjusted to 7 to 8 with 2N
HCl, and all solvent was removed under reduced pressure. The solids
were redissolved as much as possible in methanol, the solids were
removed by decantation, and the solvents were removed under
1
reduced pressure to give the acid as a white solid (93 mg, 100%). H
NMR (300 MHz, methanol-d4) δ 6.78−6.96 (m, 3H), 6.69 (s, 1H),
6.51 (s, 1H), 3.77−3.86 (m, 9H), 3.63−3.77 (m, 6H), 3.46 (d, J = 5.18
Hz, 1H), 3.17−3.28 (m, 2H), 2.83−3.04 (m, 4H), 2.47−2.61 (m, 1H).
2-(2-{1-[(3,4-Dimethoxyphenyl)methyl]-6,7-dimethoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl}acetamido)-N-methylacetamide (63).
The acid (30 mg, 0.065 mmol), methylamine hydrochloride (9 mg,
0.131 mmol), and BOP (38 mg, 0.085 mmol) were combined in dry
DMF (1 mL), and diisopropylethylamine (42 mg, 57 μL, 0.327 mmol)
was added. The reaction was stirred at rt overnight and then diluted
with EtOAc. The reaction was washed with an NaHCO3 solution and
brine and dried over MgSO4, and the solvents were removed under
reduced pressure. The crude product was purified by chromatography
on silica (0−50% CMA-80 in EtOAc) to give the desired amide (13
1
mg, 42%). H NMR (300 MHz, methanol-d4) δ 6.80−6.96 (m, 3H),
6.69 (s, 1H), 6.62 (s, 1H), 3.78−3.85 (m, 10H), 3.75 (s, 3H), 3.60−
3.73 (m, 3H), 3.42−3.59 (m, 1H), 3.01−3.09 (m, 1H), 2.84−2.99 (m,
6H), 2.72 (s, 3H), 2.53 (dd, J = 5.09, 15.73 Hz, 1H). m/z 472 (M +
H).
N-(Carbamoylmethyl)-2-{1-[(3,4-dimethoxyphenyl)methyl]-6,7-
dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl}acetamide (64). Pre-
1
pared from acid using ammonium chloride in 23% yield. H NMR
(300 MHz, methanol-d4) δ 6.79−6.95 (m, 3H), 6.69 (s, 1H), 6.57−
6.61 (m, 1H), 3.83 (s, 3H), 3.82 (s, 3H), 3.80 (s, 3H), 3.73 (s, 3H),
3.65−3.76 (m, 2H), 3.43−3.57 (m, 1H), 3.26−3.37 (m, 2H), 3.01−
3.11 (m, 1H), 2.84−3.00 (m, 4H), 2.53 (dd, J = 5.04, 15.49 Hz, 1H).
m/z 458 (M + H).
M
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concentration of the test compound (for antagonist assays) for 15 min
at 37 °C. Activity was then assayed on a FlexStation II at 37 °C.
Baseline fluorescence was measured every 1.52 s for 19 s at which time
25 μL of 100 μM test compound (for intrinsic activity) or an 8-point
half-log concentration curve of Orexin A (for antagonist activity) was
added by the FlexStation II. Fluorescence was measured every 1.52 s
for another 41 s. Activity was measured as the change in fluorescence
intensity by setting the average baseline value of each well to 0 and
measuring the peak fluorescence intensity following compound
addition. EC50 values were calculated for orexin A (EC50−) and orexin
A + test compound (EC50+), and these values were used to calculate
the Ke value of the test compound. The concentration/response data
were fit to a three-parameter logistic equation using GraphPad Prism
(v5 for Windows; GraphPad Software, San Diego, CA) to calculate the
EC50 values. For OX1, at least two different concentrations of test
compound were used for these experiments, and these were chosen
such that they caused a 4-fold or greater rightward shift in the orexin A
EC50. For OX2, test compounds were run at 10 μM because of the low
potency of these compounds at OX2. The Ke value was calculated from
the formula Ke = [L]/ ((EC50−/EC50+) − 1), where [L] equals the test
Animal maintenance and experiments were done in accordance with
the Institutional Animal Care and Use Committee, University at
Buffalo, and the 2010 Guide for the Care and Use of Laboratory
Animals (Institute of Laboratory Animal Resources on Life Sciences,
National Research Council, National Academy of Sciences, Wash-
ington, DC).
Apparatus. The standard experimental chamber for the automated
assessment of CPP (LE890, Harvard Apparatus, Holliston, MA)
consisted of two Perspex compartments of the same size (30 × 30 ×
34 cm3) interconnected by a central corridor (8 × 10 × 34 cm3). Both
side compartments were equipped with a gray Perspex guillotine door
that separated the end compartment from the central gray corridor.
Each compartment had distinct, yet neutral, visual and tactile cues:
One had black walls and a white rough floor, the other had white walls
and a black smooth floor. The corridor had gray walls and a gray floor.
The time spent in each compartment was monitored by a video
camera located on the ceiling that was controlled by video-tracking
software (Smart Junior, Harvard Apparatus, Holliston, MA).
Procedure. Details were described previously.50 Briefly, the
experiment started with a 30 min pretest session during which rats
had free access to both compartments to verify the absence of
preference for either. Only the first 15 min (900 s) of the pretest
session was recorded and analyzed. Rats spending more than 75%
(>675 s) or less than 25% (<225 s) of the total time in a compartment
were eliminated from further testing (only 1 rat was excluded from the
studies). Although this was an unbiased set up, individual rats
somewhat preferred one side over the other. On average, individual
rats spent 58% of the total pretest time in one chamber and 38% in the
other chamber, with the remaining 4% being spent in the central
corridor. Following the pretest phase, the rats underwent place
conditioning across 8 days, with alternating treatment-compartment
pairings. The rats received a vehicle-compartment pairing on odd days
and drug (cocaine, compound 72, or cocaine + compound 72)-
compartment pairing on even days. For a conditioning session, vehicle
or drug was administered, and the rat was placed immediately in the
paired compartment with no access to the other compartment for 30
min. This conditioning time was chosen because it was used in other
studies and was established in our laboratory.50 The drug and
compartment pairing were counterbalanced. On the test day (24 h
after last conditioning session), the rats were randomly placed into one
compartment without treatment and had access to both compartments
during the 15 min observation period, and the time spent in each
compartment was recorded. For the combination group, compound 72
was administered 10 min before cocaine. This pretreatment time was
chosen because initial studies found that 10 min was adequate for
compound 72 to be behaviorally active in a drug discrimination assay
(data not shown).
Data Analyses. The magnitude of place preference was presented
as the preference score, which was defined as the time spent in the
drug-associated compartment on the test day minus the time spent in
the drug-associated compartment on pretest day. The data were
subjected to one-way analysis of variance with treatment (four groups)
as the factor followed by Bonferroni’s posthoc test. An effect was
considered significant if P < 0.05.
Drugs. Cocaine hydrochloride (Research Technology Branch,
National Institute on Drug Abuse, Rockville, MD) and compound
72 were dissolved in 0.9% physiological saline and administered i.p.
The dose was expressed as milligrams of the form indicated above per
kilogram of body weight (mg/kg). The injection volume was 1 mL/kg.
−
compound concentration, EC50 equals the EC50 of orexin A alone,
+
and EC50 equals the EC50 of orexin A in the presence of the test
compound. The data represent the mean from at least three
independent experiments.
Conformational Libraries and 3D Pharmacophores. The
initial 3D geometries of the ligands were generated from SMILES
strings using CORINA (Molecular Networks, Erlangen, Germany).
Conformational libraries were generated using 12 genetic algorithm
(GA) and energy minimization runs, each was based on a distinct
random number seed, employing BALLOON as the GA engine.47 An
initial population size of 200 was employed for every GA run, each
consisting of 200 generations. The energy (fitness) function was
evaluated using the full MMFF94 force field and a continuum
dielectric of 80 for dielectric response screening electrostatics. The GA
runs for each ligand were then pooled and unique conformers retained.
For the purposes of this study, a unique conformer was defined as any
structure differing by less than 30 degrees for any torsion (excluding
those terminating in hydrogens).
Three-dimensional pharmacophores were developed using MOL-
MOD.48,49 This code takes as input (1) pharmacophore hypotheses,
(2) conformational libraries for each of the ligands, (3) distance and
tolerance criteria for each set of pharmacophore points defining
pharmacophore metric compliance, and (4) an energy window for the
consideration of conformations from each library. Given the relative
homogeneity of the present study chemotype, the objective of the
pharmacophore analysis was primarily the development of an overlap
rule for those structural commonalities in the scaffold common to all
ligands, enabling property evaluation and multivariate statistical
analysis (2D and 3D QSAR) of the pharmacophore compliant
conformations. Should one or more pharmacophores be found,
MOLMOD outputs both distance metrics and a quaternion least-
squares superposition of conformations of each of the ligands
complying with the pharmacophore.
Property Evaluation: Properties of both whole ligand and fragments
(substituents) were evaluated for each of the conformations complying
with the pharmacophore(s) using semiempirical QM (MOPAC)
models. Postcomputation analysis of the results was done with
GRAPHA, a utility that extracts QM-energetic, electrostatic, hydro-
phobic, frontier-orbital energetic, Sterimol, shape, polar−nonpolar
surface area, volume, and thermodynamic descriptors.47
Fragment/2D/3D QSAR: Properties compiled were analyzed to
develop quantitative structure relationships in an effort to ascertain the
key physiochemical properties modulating orexin Ke values as a
function of substitution. Multivariate least-squares approaches
embodied in the R PROJECT software for Statistical Computing
(http://www.r-project.org/) and Tripos Sybyl were employed.
Conditioned Place Preference. Subjects. Adult Sprague−
Dawley rats (Harlan, Indianapolis, IN) were housed individually on
a 12/12 h light/dark cycle with free access to water and food except
during experimental sessions. Testing occurred during the light period.
ASSOCIATED CONTENT
* Supporting Information
HPLC analysis of target compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: yzhang@rti.org; Tel: 919-541-1235; Fax: 919-541-
6499.
■
N
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(9) Sutcliffe, J. G.; de Lecea, L. The hypocretins: Setting the arousal
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Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
(11) Trivedi, P.; Yu, H.; MacNeil, D. J.; Van der Ploeg, L. H.; Guan,
X. M. Distribution of orexin receptor mRNA in the rat brain. FEBS
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ACKNOWLEDGMENTS
■
(12) Scammell, T. E.; Winrow, C. J. Orexin receptors: pharmacology
and therapeutic opportunities. Annu. Rev. Pharmacol. Toxicol. 2011, 51,
243−266.
We are grateful to the National Institute of Health/National
Institute on Drug Abuse (grant nos. DA032837 and DA026582
to Y.Z. and DA034806 to J.X.L.) for financial support of this
research. We thank Tiffany Langston, Keith Warner, Allyson
Smith, Dr. Angela Giddings, and Dr. Ann Decker for their
valuable technical assistance. We also thank Dr. Scott Runyon
and Dr. Gerald Pollard for their critical reading and editing of
the manuscript.
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ABBREVIATIONS USED
■
(16) Harris, G. C.; Wimmer, M.; Aston-Jones, G. A role for lateral
hypothalamic orexin neurons in reward seeking. Nature 2005, 437,
556−559.
ADME, absorption distribution metabolism excretion; BOP,
(benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexa-
fluorophosphate; COMFA, comparative molecular field anal-
ysis; CPP, conditioned place preference; HBTU, O-benzo-
triazole-N,N,N′,N′-tetramethyl-uronium-hexafluoro-phosphate;
HOMO, highest occupied molecular orbital; HPLC, high-
performance liquid chromatography; LUMO, lowest unoccu-
pied molecular orbital; OX1, orexin 1 receptor; OX2, orexin 2
receptor; QSAR, quantitative structure−activity relationship;
SAR, structure−activity relationship; TLC, thin layer chroma-
tography
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Acad. Sci. U.S.A. 2005, 102, 19168−19173.
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