Synthesis and Evaluation of Orexin-1 Receptor Antagonists with Improved Solubility and CNS Permeability

Article abstract of DOI:10.1021/acschemneuro.7b00402

Orexins are hypothalamic neuropeptides playing important roles in many functions including the motivation of addictive behaviors. Blockade of the orexin-1 receptor has been suggested as a potential strategy for the treatment of drug addiction. We have previously reported OX₁ receptor antagonists based on the tetrahydroisoquinoline scaffold with excellent OX₁ potency and selectivity; however, these compounds had high lipophilicity (clogP > 5) and low to moderate solubility. In an effort to improve their properties, we have designed and synthesized a series of analogues where the 7-position substituents known to favor OX₁ potency and selectivity were retained, and groups of different nature were introduced at the 1-position where substitution was generally tolerated as demonstrated in previous studies. Compound 44 with lower lipophilicity (clogP = 3.07) displayed excellent OX₁ potency (K_e = 5.7 nM) and selectivity (>1,760-fold over OX₂) in calcium mobilization assays. In preliminary ADME studies, 44 showed excellent kinetic solubility (>200 μM), good CNS permeability (P_app = 14.7 × 10^-6 cm/sec in MDCK assay), and low drug efflux (efflux ratio = 3.3).

Full text of DOI:10.1021/acschemneuro.7b00402

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Article
Synthesis and Evaluation of Orexin-1 Receptor
Antagonists with Improved Solubility and CNS Permeability
David A Perrey, Ann M. Decker, and Yanan Zhang
ACS Chem. Neurosci., Just Accepted Manuscript • DOI: 10.1021/acschemneuro.7b00402 • Publication Date (Web): 11 Nov 2017
Downloaded from http://pubs.acs.org on November 15, 2017
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Synthesis and Evaluation of Orexinꢀ1 Receptor
Antagonists with Improved Solubility and CNS
Permeability
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†
†
†,*
David A. Perrey, Ann M. Decker, and Yanan Zhang,
†
Research Triangle Institute, Research Triangle Park, North Carolina 27709, United
States
KEYWORDS: orexin, antagonist, selective, tetrahydroisoquinoline, ADME
ABSTRACT: Orexins are hypothalamic neuropeptides playing important roles in many
functions including the motivation of addictive behaviors. Blockade of the orexinꢀ1
receptor has been suggested as a potential strategy for the treatment of drug addiction.
We have previously reported OX1 receptor antagonists based on the
tetrahydroisoquinoline scaffold with excellent OX potency and selectivity; however,
1
these compounds had high lipophilicity (clogP > 5) and low to moderate solubility. In an
effort to improve their properties, we have designed and synthesized a series of analogs
where the 7ꢀposition substituents known to favor OX potency and selectivity were
1
retained, and groups of different nature were introduced at the 1ꢀposition where
substitution was generally tolerated as demonstrated in previous studies. Compound 44
with lower lipophilicity (clogP = 3.07) displayed excellent OX potency (K = 5.7 nM)
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and selectivity (> 1,760ꢀfold over OX ) in calcium mobilization assays. In preliminary
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ADME studies, 44 showed excellent kinetic solubility (> 200 ꢀM), good CNS
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permeability (Papp = 14.7 x 10 cm/sec in MDCK assay), and low drug efflux (efflux
ratio = 3.3).
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Introduction
OrexinꢀA and ꢀB, also known as hypocretinꢀ1 and ꢀ2, are two neuropeptides
synthesized by neurons in the lateral hypothalamic areas, that activate two G proteinꢀ
coupled receptors (GPCRs), the orexinꢀ1 (OX ) and ꢀ2 (OX ) receptors. Orexins, the
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orexin receptors and the hypocretin genes were first discovered in 1998 by two research
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, 2
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groups, and the system has been widely studied since. Initially, orexins were named
for their appetiteꢀenhancing effects as they were found to play a role in feeding behavior
and energy expenditure. The orexin system was later shown to also be a key regulator of
arousal and sleep/wake cycles. Hence, the orexin system is a promising target in the
development of medications for the treatment of sleep disorders. A number of dual orexin
receptor antagonists (DORAs) have been developed for this purpose, such as almorexant
5-9
(
1) and suvorexant (2) (Figure 1). In particular, 2 developed by Merck & Co became
the first orexin antagonist approved by the FDA for the treatment of insomnia in 2014
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and is currently marketed under the brand name Belsomra.
More recently, the orexins have been implicated in a range of motivation and reward
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processes, including drug addiction.
Accumulating evidence has confirmed the
involvement of the orexin system, particularly the OX receptor, in different stages of the
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5, 16
addiction process to several drugs of abuse.
In conditioned place preference (CPP)
experiments, the widely used animal model measuring drug rewarding effects, the orexin
16, 17
system showed a role in acquisition, expression and reinstatement of morphine CPP.
Blockade of the OX receptor by systemically or intraꢀVTA (ventral tegmental area)
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administrated SB334867 (3, Fig. 1), an OX antagonist, attenuated motivated drug
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seeking behaviors of cocaine.
Administration of 3 also attenuated cueꢀ and stressꢀ
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induced reinstatement of extinguished cocaine seeking in animals. In addition, ethanol
and nicotine selfꢀadministration and reinstatement can also be decreased by
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administration of 3.
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Compound 3 was the first reported OX selective antagonist and is still widely used in
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the orexin research community. However, 3 suffers from several limitations, including
moderate selectivity over OX (~50x), offꢀtarget interactions with several receptors
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(serotonin, adenosine), and instability of the hydrochloride salt.
Several other OX1
selective antagonists have been since described (e.g. ACTꢀ335827, 4, Fig. 1), but most of
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them still have certain OX activities.
While blockade of both orexin receptors has
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been shown to be effective in some addiction models in a limited number of studies,
selective OX antagonists provide the benefit of minimized sedation arising from OX
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antagonism.
In addition, the majority of in vivo studies so far for OX1ꢀspecific
pathways were done with 3. OX antagonists with improved selectivity will help to
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further elucidate and validate the in vivo role and biology of the OX receptors.
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Figure 1. Representative Orexin antagonists
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Our group has previously reported a series of OX selective antagonists based on the
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tetrahydroisoquinoline (THIQ) scaffold.
In these studies, we explored the structureꢀ
activity relationships (SARs) at several locations, and have identified structural features
that enhanced the potency and selectivity of OX over OX . As a result, several highly
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potent and selective OX antagonists have been identified, including RTIOXꢀ276 (5) and
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RTIOXꢀ251 (6). These compounds attenuated the development of conditioned place
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preference for cocaine, or blocked development of locomotor sensitization to cocaine in
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rats. In addition, at doses that attenuated the motivation for cocaine, 5 reduced
spontaneous dopamine transient amplitude and cueꢀevoked dopamine release, and also
attenuated cocaineꢀinduced dopamine uptake inhibition at the level of dopamine
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terminals, confirming its in vivo efficacy.
These THIQꢀbased OX antagonists, despite the excellent potency and selectivity, have
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high lipophilicity (clogP > 5). The logP value of a compound is a wellꢀestablished
measure of a compound's lipophilicity; high lipophilicity, or low hydrophilicity, causes
lower solubility and poor absorption, thus affecting amount of drug reaching its site of
action. In general, substituents with increased polarity and/or ionizability (e.g. protonable
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7
amino groups) at physiological pH lead to lower lipophilcity. Therefore, we aimed to
introduce substituents at several positions of the THIQ scaffold that would retain OX1
potency while leading to improved pharmacokinetic properties. Since the 7ꢀposition has
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been demonstrated as a key factor in determining the OX potency and selectivity, and
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substituents such as propoxy, trifluoroethoxy, methylsulfonate and dimethylamino groups
led to excellent OX potency and selectivity, these favorable 7ꢀposition substituents were
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retained (R , Fig. 2). In addition, the 1ꢀposition has been shown to tolerate a variety of
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substituents, and therefore groups of different nature were introduced at the 1ꢀposition
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trifluoroethoxy, methylsulfonate) or ionizable (e.g. dimethylamino), and are expected to
have reduced lipophilicity and increased solubitility. In addition, replacing the benzyl
group at the acetamide position with groups such as pyridyl may also reduce lipophilicity.
We herein describe the design, synthesis, and evaluation of the OX potency and
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selectivity, as well as preliminary ADME properties, including aqueous solubility and
CNS permeability, for these new analogs.
Figure 2. Structural modifications at the 7ꢀ, 1ꢀ, and acetamide positions
Results and Discussion
Chemistry. The general approach to this series of THIQ derivatives is shown in
Scheme 1, starting from phenylacetic acids 8a-f. Most of these phenylacetic acids were
commercially available, except for 8f which was synthesized by Oꢀalkylation of 4ꢀ
hydroxyꢀ3ꢀmethoxyphenylacetic acid methyl ester (7) and hydrolysis under basic
conditions. Acids 8a-f were first coupled with 4ꢀhydroxyꢀ3ꢀmethoxyphenylethylamine to
give the amides 9a-f, which were then cyclized via a BischlerꢀNapieralski reaction using
phosphorus oxychloride in toluene to form the dihydroisoquinolines, followed by
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reduction to tetrahydroisoquinolines 10a-f using sodium borohydride. NꢀAlkylation was
achieved using Nꢀbenzyl bromoacetamide in the presence of base to give intermediates
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1a-f. Finally, the phenol was alkylated using 1ꢀiodopropane in the presence of
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potassium carbonate to afford the target compounds 12a-e,g. The 3ꢀdimethylamino
derivative 12f was obtained from the 3ꢀnitro analog 12e via reduction to the aniline using
Raney nickel, then reductive amination with formaldehyde and sodium
triacetoxyborohydride. An alternate approach was attempted for both 12d and 12g,
where Oꢀalkylation was performed at the amide stage (9) prior to BischlerꢀNapieralski
reaction. While this approach generally gave better yields in the following steps, it
limited diversification in the later synthesis and was thus not further pursued.
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Scheme 1. Synthesis of 7ꢀpropoxyꢀ6ꢀmethoxy THIQ derivatives 12a-g.
a
Reagents and Conditions: (a) 2ꢀ(bromomethyl)pyridine hydrobromide, K CO , Bu NI,
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DMF, rt, 16 h; (b) 2N NaOH (aq), EtOH, rt, 16 h; (c) 4ꢀHydroxyꢀ3ꢀ
methoxyphenylethylamine, HBTU, iPr EtN, DMF, rt, 16 h; (d) (i) POCl , toluene, 90 °C,
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(f) 1ꢀiodopropane, K CO , DMF, rt, 16 h; (g) Raney Ni, NH NH .H O, EtOH, 50 °C, 1 h;
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ꢀTrifluoroethoxy derivatives 15a-b were made via a similar approach (Scheme 2). The
tetrahydroisoquinolines 10a-b were Nꢀalkylated with ethyl bromoacetate to give ester
3a-b. Ester hydrolysis gave the acid, followed by amide coupling with 3ꢀ
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aminomethylpyridine to give 14a-b. OꢀAlkylation using 1ꢀiodoꢀ2,2,2ꢀtrifluoroethane and
cesium carbonate gave the desired analogs 15a-b. 1ꢀPyridylmethyl derivatives 19a-c
were synthesized in analogous fashion using the general approach outlined above,
starting from the appropriate 2ꢀ, 3ꢀ or 4ꢀpyridylacetic acid (16a-c) (Scheme 2).
a
Scheme 2. Synthesis of 7ꢀtrifluoroethoxy substituted THIQ derivatives 19a-c.
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Reagents and Conditions: (a) BrCH CO Et, iPr EtN, Bu NI, DMF, rt, 16 h; (b) 2N
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NaOH (aq), EtOH, rt, 16 h; (c) 3ꢀaminomethylpyridine, HATU, iPr EtN, DMF, rt, 16 h;
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h; (ii) NaBH , MeOH, 0 °C to rt, 16 h; (g) BrCH CONHCH Ph, iPr EtN, Bu NI, DMF,
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rt, 16 h; (h) CF CH I, Cs CO , DMF, 100 °C, 2 h.
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The 7ꢀmethylsulfonate derivatives 25a-b (Scheme 3) were prepared from 4ꢀhydroxyꢀ3ꢀ
methoxyphenylacetic acid 20. Protection of the phenolic hydroxyl group as its benzyl
ether gave intermediate 21. Acid 21 was then coupled with 4ꢀhydroxyꢀ3ꢀ
methoxyphenethylamine to give amide 22, followed by sulfonylation of the phenol group
with methanesulfonyl chloride to afford the sulfonate 23. After cyclization to the
tetrahydroisoquinoline 24 and Nꢀalkylation as described above, the benzyl group of 25a
was removed under acidic conditions and the resulting hydroxyl group was converted to
the butyl ether upon treatment with 1ꢀbromobutane to give 25b.
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Scheme 3. Synthesis of 7ꢀsulfonate substituted THIQ derivatives 25a-b.
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Reagents and Conditions: (a) Na, BnBr, MeOH, reflux, 5 h; (b) 4ꢀHydroxyꢀ3ꢀ
methoxyphenylethylamine, HBTU, iPr EtN, DMF, rt, 16 h; (c) MeSO Cl, Et N, CH Cl ,
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The 7ꢀdimethylaminoꢀ6ꢀmethoxytetrahydroisoquinoline derivatives required synthesis
of the phenethylamine 28, which was prepared from 3ꢀmethoxyphenylacetonitrile 26
(Scheme 4), by nitration using tetrabutylammonium nitrate in the presence of
trifluoroacetic anhydride and 18ꢀcrownꢀ6 to give 27, followed by reduction of the nitrile
using boraneꢀTHF complex at 70 °C. The amine 28 was then coupled with 3,4ꢀ
dimethoxyphenylacetic acid to give amide 29. The presence of a strong electron
withdrawing group such as a nitro group on the phenethylamine portion retards the
reactivity of the aromatic system and makes the BischlerꢀNapieralski cyclization
sluggish, so the amide 29 was reduced using Raney nickel to the aniline 30 then protected
as the methyl carbamate using methyl chloroformate and diisopropylethylamine to give
31. BischlerꢀNapieralski cyclization and reduction to the tetrahydroisoquinoline followed
by Nꢀalkylation with the acetamide component gave the acetamide 32 and removal of the
carbamate using 2N sodium hydroxide solution in methanol provided amine 33. This
amine could then be derivatized via sulfonylation, reductive amination or acylation to
give a series of derivatives 34a-e.
a
Scheme 4. Synthesis of 7ꢀdimethylamino substituted THIQ derivatives 34a-e.
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Reagents and Conditions: (a) Bu NNO , (CF CO) O, 18ꢀcrownꢀ6, CH Cl , 0 °C, 30
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(g) BrCH CONHCH Ph, iPr EtN, Bu NI, DMF, rt, 16 h; (h) 2N NaOH, MeOH, 50 °C,
2
2
2
4
4
4
8 h; (i) 34a: HCHO, NaBH(OAc) , 1,2ꢀDCE, rt, 16 h; 34b: PhCHO, NaHCO , MeOH,
3 3
0 °C, 1h, then NaBH , rt, 16 h; (j) 34c: Ac O, iPr EtN, CH Cl , rt, 16 h; 34d: MeSO Cl,
4
2
2
2
2
2
Et N, CH Cl , 0 °C to rt, 16 h; then 3N NaOH, 80 °C, 16 h; 34e: CH (CH ) CO H, BOP,
3
2
2
3
2 2
2
iPr EtN, CH Cl , rt, 16 h.
2
2
2
The bisꢀdimethylamino derivatives 39 and 42 were made in analogous fashion to the
other 7ꢀamino derivatives (Scheme 5). For 39, the phenethylamine 28 was coupled to 4ꢀ
hydroxyꢀ3ꢀnitrophenylacetic acid, then the phenol was converted to the methyl ether
using iodomethane to afford 35. Reduction of both nitro groups with Raney nickel was
followed by formation of the bisꢀ methyl carbamate using methyl chloroformate to form
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2
2
2
2
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2
3
3
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5
5
5
5
5
5
5
6
3
6. Cyclization and then reduction gave the tetrahyroisoquinoline 37 then Nꢀalkylation as
before gave 38. Both methyl carbamates were removed using sodium hydroxide and
reductive amination provided the bisꢀdimethylamino product 39. For 42, amine 28 was
first coupled with 3ꢀnitrophenylacetic acid to afford amide 40 and both nitro groups were
reduced with Raney nickel. Reductive amination gave the bisꢀdimethylamino amide 41,
which was then subjected to BischlerꢀNapieralski conditions, reduced and Nꢀalkylated to
afford the final product 42. Finally, the 1ꢀ(3ꢀpyridylmethyl)benzyl analog 44 was
prepared from intermediate 37, which underwent alkylation using ethyl bromoacetate,
ester hydrolysis, and coupling with 3ꢀaminomethylpyridine to give 43. The final
sequence of carbamate removal and reductive amination with formaldehyde afforded the
desired 44.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
a
Scheme 5. Synthesis of 7ꢀdimethylamino substituted THIQ derivatives 39, 42 and 44.
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23
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25
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32
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34
35
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39
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44
45
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47
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59
60
a
Reagents and Conditions: (a) 4ꢀhydroxyꢀ3ꢀnitrophenylacetic acid, HBTU, iPr EtN,
2
DMF, rt, 16 h; (b) MeꢀI, K CO , DMF, 0ꢀ60 °C, 2 h; (c) Raney Ni, NH NH .H O, EtOH,
2
3
2
2
2
5
0 °C, 90 min; (d) MeOCOCl, iPr EtN, CH Cl , rt, 16 h; (e) (i) POCl , toluene, 90 °C, 2
2 2 2 3
h; (ii) NaBH , MeOH, rt, 16 h; (f) BrCH CONHCH Ph, iPr EtN, Bu NI, DMF, rt, 16 h;
4
2
2
2
4
(
g) 2N NaOH (aq), MeOH, 50 °C, 16 hr; (h) HCHO, NaBH(OAc) , 1,2ꢀDCE, rt, 16 h; (i)
3
3
ꢀnitrophenylacetic acid, HBTU, iPr EtN, DMF, rt, 16 h; (j) BrCH CO Et, iPr EtN,
2 2 2 2
Bu NI, DMF, rt, 16 h; (k) 2N NaOH, EtOH, rt, 16 h; (l) 3ꢀaminomethylpyridine, HATU,
4
iPr EtN, DMF, rt, 16 h.
2
Pharmacological Evaluation. Activity of the target compounds at the OX and OX
1
2
receptors was evaluated in a calcium mobilization based functional assay. The apparent
dissociation constant K was calculated from compoundꢀmediated inhibition of orexin A
e
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5
5
5
5
5
5
6
32, 34, 35, 38
activity as previously described.
Briefly, EC curves of the agonist, orexin A,
50
were obtained alone and together with the test compound, respectively, and the rightꢀshift
of the agonist curve was measured. K values were then calculated using the equation Ke
e
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
ꢀ
+
=
[L]/ ((EC /EC )ꢀ1), where [L] is the test compound concentration, EC is the EC50
50 50 50
ꢀ
of orexin A in the presence of test compound, and EC50 is the EC of orexin A alone. In
50
these assays, the EC for orexin A at OX and OX is 0.13 ± 0.02 nM and 4.2 ± 0.2 nM,
5
0
1
2
respectively. All the compounds that had OX K values < 1 ꢀM were also tested for
1
e
agonist activity at 10 ꢀM final concentration at the OX receptor; none of them showed
1
any agonist activity.
We previously reported SAR studies at three different locations of the THIQ core,
namely the 7ꢀposition, the 1ꢀposition and the acetamide, and had identified structural
3
2, 34, 35
features that led to enhanced potency and OX selectivity at these positions.
At the
1
7
ꢀposition, it was discovered that a modest increase in the chain length, from methoxy to
32
propoxy or trifluoroethoxy groups, led to increased OX potency and selectivity.
1
Similarly, methylsulfonate and dimethylamino groups also led to excellent potency and
selectivity. At the 1ꢀposition of the THIQ core, a series of aromatic systems provided
3
4
similar or slightly improved potency than the initial 3,4ꢀdimethoxybenzyl group. For
3
2
example, we found that pyridylmethyl groups were as potent as the benzyl group. In
this study, we examined the effects of combining these favorable structural modifications
on the OX potency and selectivity. Given the tolerance for substitution at the 1ꢀposition,
1
aromatic groups of different nature were introduced at this position in an effort to
improve the PK properties of these compounds.
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We first examined a series of 7ꢀpropoxy analogs with different substituents at the
ꢀbenzyl position. At the 1ꢀposition, several groups that have previously been
1
demonstrated to be tolerated were introduced. As expected, the naphthyl (12a), 3,4ꢀ
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
dimethylphenyl (12b), and 4ꢀisopropylphenyl (12c) all showed good OX potency,
1
3
4
consistent with our previous findings. The introduction of a nitrogen atom into the
structure (12d, f) did not significantly change the potency, but reduced the lipophilicity of
these compounds from 12c (clogP 7.4 vs. 6.17). The 3ꢀdimethylamino analog 12f was the
most potent of the series with a K value of 21 nM. When a pyridinylmethyl group was
e
introduced at the 4ꢀposition (12g), the clogP was further lowered (5.96), the potency
remained good (K = 96.4 nM), and the selectivity was high (>100ꢀfold). Overall, these
e
results show that substitution at the 1ꢀbenzyl position results in compounds with good
selectivity for the OX receptor over the OX receptor, although clogP remained high.
1
2
Table 1. The effect of changes at the 7ꢀposition on OX antagonism incorporating the
most active 1ꢀposition analogs
O
O
R
1
N
O
N
H
Ar
R2
Ke
(OX
nM)
Ke
(OX
nM)
OX2/
OX
No.
R1
R2
Ar
1
,
2
,
clogP
b
c
1
1
±
6.1
3.6
6
Pr
Pr
Ph
Ph
>10,000 >621 6.86
1
±
21
35
1
2a
a
>82.6 7.29
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2
2
2
2
3
3
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3
3
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3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
±
8.8
4.4
1
2b
Pr
Pr
Ph
Ph
a
a
>347 6.98
>70.9 7.40
1
±
41
42
1
2c
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
173
±
1
2d
Pr
Ph
>10,000
a
>58
6.17
5
2
±
0.6
2.8
12f
Pr
Pr
Ph
Ph
>485 6.17
9
±
6.4
34
1
2g
>10,000 >104 5.96
1750
∗
2
±
9.5
2.2
15a
5b
9a
19b
CF
CF
CF
CF
3
3
3
3
CH
2
2
2
2
3ꢀPy
3ꢀPy
Ph
59
67
>11
0
5.70
5.39
4.47
4.47
± 230
∗
20.4
±
1360
± 150
1
CH
CH
CH
2.9
N
∗
8
± 70
84
1
d
a
a
∗
∗
N
N
d
Ph
>10,000
1
,860 ±
140
1
9c
CF
3
CH
2
Ph
d
a
a
>5.4
4.47
O
∗
43.0
25a
MeSO
MeSO
2
Ph
Ph
>232 5.25
O
±
18
∗
O
5.24
1.0
1,200
± 360
2
5b
2
229
5.19
O
±
a. < 50% inhibition at 10 ꢀM final concentration;
b. Values are the mean of at least three independent experiments in duplicate;
c. Values are the mean of at least two independent experiments in duplicate; for
compounds with K < 100 nM at OX at least three independent experiments in
e
1
duplicate were performed.
d. Compound appeared insurmountable during standard assay procedure, so
incubation was increased to 1 hour.
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Previously reported compound 5, with a trifluoroethoxy substitution at the 7ꢀposition,
3
2
is a highly potent and selective OX antagonist. Both the naphthyl analog 15a and 3,4ꢀ
1
dimethyl analog 15b showed excellent potency, comparable to the propoxy series (12a-
b). The presence of the trifluoroethyl led to lower clogP than the propyl (12b: 6.98 vs.
15b: 5.39). To further reduce clogP, we synthesized 3 different pyridinyl derivatives
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
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54
55
56
57
58
59
60
(
19a-c) at the 1ꢀposition. Although they have lower clogP (4.47), all three compounds
showed significantly lower potency at the OX1 receptor and also displayed
3
5
insurmountable antagonism in the curve shift assays. As previously reported by us,
increasing the receptorꢀtest compound incubation period can help to elucidate whether
this type of antagonism is due to an allosteric mechanism or an orthosteric antagonist
with a slow dissociation rate. For derivatives 19a-c, we found that increasing the
incubation time led to activity profiles consistent with competitive antagonism.
Another group that provided satisfactory results in previous SAR studies was the 7ꢀ
methylsulfonate. Again, these methylsulfonate analogs (25a, b) showed excellent OX1
potency and selectivity. However, both compounds had clogP in the 5ꢀ6 range.
All these structural alterations discussed thus far have resulted in potent and
selective OX antagonists that continue to have high lipophilicity (clogP > 5). Thus, a
1
series of 7ꢀamino compounds were prepared and their potency against OX and OX
1
2
receptors was assayed (Table 2). It was expected that the introduction of the amino
groups not only would reduce clogP or lipophilicity, but would also facilitate the
formation of more soluble ammonium salts.
As can be seen from Table 2, all the compounds in the 7ꢀamino series were
generally tolerated for OX activity. The unsubstituted aniline 33 was active with a K of
1
e
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4
94 nM, but showed little selectivity. Dimethylation of the amino group (34a)
significantly improved the OX potency (494 nM vs. 31.2 nM). The benzylamino analog
1
(34b) was less potent, showing a K value of 352 nM, suggesting larger groups may not
e
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
be well tolerated. When the amino group was acylated (34c, 116 nM) or mesylated (34d,
128 nM), the resulting compounds had good potency and selectivity, as well as lower
clogP (< 4). When the acyl group was elongated, the butyric analog (34e) was less potent
(K = 689 nM), consistent with the limited tolerance for bulk at this position. The
e
methylcarbamate (38) was inactive, and showed increased OX activity as well. The fact
2
that 34a (ꢀNMe ) was more potent than all the NH containing alalogs suggests that the
2
presence of an hydrogen bond donor at this position may be unfavorable for OX activity.
1
Alternatively, the NH group may be forming an intramolecular hydrogen bond with the
methoxy group at the 6ꢀposition, thus limiting the rotational freedom and ability of R1
group to engage in favorable interations with the receptor.
Given the encouraging results with the 3ꢀdimethylamino analog (34a), we
synthesized several additional analogs with amino groups also on the 1ꢀbenzyl position.
While the 3ꢀdimethylamino analog (42) had a K of 148 nM, the corresponding 3ꢀ
e
dimethylaminoꢀ4ꢀmethoxy derivatve (39) was more potent (K = 7.6 nM). Finally, when
e
the benzylacetamide was replaced with the 3ꢀpyridyl group, a potent and more selective
OX antagonist (44) was obtained. Importantly, the clogP value of this compound was
1
3
.07 and PSA was 70, implying that this modification could enhance solubility.
Table 2. 7ꢀAmino tetrahydroisoquinoline derivatives incorporating modifications at the
1ꢀbenzyl position.
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4
5
6
7
8
9
O
O
R1
N
N
N
Ar
H
R2
R3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ke (OX , Ke (OX , OX2/
1 2
No.
R1
H
R2
H
R3
Ar
Ph
Ph
Ph
Ph
Ph
Ph
b
c
clogP
3.87
4.92
6.13
3.76
3.63
4.82
nM)
nM)
OX1
O
∗
∗
∗
∗
∗
∗
4
±
94
32
33
>10,000
>10,000
a
>20
O
O
31.2
3
4a
34b
4c
34d
4e
Me
Me
H
>321
>28
± 3.3
O
O
352
± 34
116
Bn
O
O
3
Ac
H
>10,000
>10,000
>10,000
>86
± 44
O
O
1
±
28
13
MeSO
H
>78
2
O
O
CH (CH )
689
± 73
3
2 2
3
H
>14.5
CO
O
O
O
5
±
92
170
38
MeOCO
H
HN
O
∗
Ph
>10,000
0.1
4.39
8
57
N
O
∗
7
±
.60
2.8
39
Me
Me
Me
Me
Me
Me
Ph
Ph
113
9.1
5.11
5.30
± 220
N
∗
∗
1,360 ±
148
42
44
84
± 36
N
O
3ꢀ
Py
5.7
± 1.0
>10,000 >1,760 3.07
a. < 35% inhibition at 10 ꢀM final concentration;
b. Values are the mean of at least three independent experiments in duplicate;
c. Values are the mean of at least two independent experiments in duplicate; for
compounds with K < 100 nM at OX at least three independent experiments in
e
1
duplicate were performed.
Physiochemical Properties and Preliminary ADME Studies
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7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Compound 44, in general, appeared to have favorable physicochemical properties
which would suggest good solubility and bloodꢀbrain barrier (BBB) permeability
3
9, 40
required for successful CNS agents (Table 3, calculated in ACD Labs).
The lower
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
clogP values suggested 44 (3.07) might have improved solubility over 5 (4.21). When the
kinetic solubility was assessed at pH 7.4, 5 showed a solubility of 77.8 ± 4.1 ꢀM (mean ±
%
CV). Compound 44 was more soluble in aqueous solutions, displaying a kinetic
solubility greater than 200 ꢀM.
We also determined the CNS permeability of 5 and 44. CNS permeability is an
important property for CNS targeting agents, and is generally determined by two factors:
the ability to passively permeate through the BBB and efflux by the transport proteins
37
such as the Pꢀglycoprotein. The apparent permeability of the compounds through
MDCKꢀMDR1 monolayers were determined in both the apicalꢀtoꢀbasolateral (AꢀtoꢀB)
and basolateralꢀtoꢀapical (BꢀtoꢀA) directions. Both compounds showed good apparent
ꢀ6
permeability (Papp > 10 x 10 cm/sec). In general, efflux ratios > 2.5 indicate drug efflux
3
7
occuring. Compounds 5 and 44 had efflux ratios of 3.0 and 3.3, respectively, suggesting
efflux is present for both compounds, albeit relatively weak. Since these MDR1ꢀ
4
1
transfected cells also express endogenous transporters, the observed drug efflux may
indicate these compound are Pꢀgp substrates, but the effects could also be mediated by
the endogenous transportors.
Table 3. Physicochemical and Preliminary ADME Properties of Compounds 6 and 44
Desired value
< 500
5
44
MW
559.6
517.7
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6
7
8
9
ClogP
PSA
1 ꢀ 4
< 70
4.21
82.1
3.07
70.2
14.1,
14.2,
6.3
pKa
< 8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5.4
HBD
HBA
< 3
< 7
1
1
7
7
Solubility (ꢀM)
> 60
77.8 ± 4.1
12.2
> 200
ꢀ6
Papp (10 cm/sec)
AꢀtoꢀB
>
2
14.7
ꢀ6
Papp (10 cm/sec)
BꢀtoꢀA
36.2
3.0
47.8
3.3
Efflux ratio
< 2.5
HBD: Hꢀbond donor; HBA: Hꢀbond acceptor.
Conclusions
The orexin system has been implicated in several important functions, including
addiction. With the growing interest in the role of the orexin system on the reward
pathway and the potential for orexinꢀ1 antagonists as therapeutics in the treatment of drug
addiction, there is a need for the development of orexinꢀ1 selective antagonists. Our
group has previously reported a series of tetrahydroisoquinolineꢀbased antagonists. While
some of the compounds showed high potency and selectivity, they had high lipophilicity
and moderate or low solubility. In this study, we aimed to improve the ADME properties
of the compounds by introducing structural elements that may lead to more optimal
properties. In particular, groups such as propoxy, trifluoroethoxy, methylsulfonate and
dimethylamino at the 7ꢀposition that had been previously demonstrated to be critical for
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OX potency and selectivity have been retained, whereas groups of different nature were
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introduced at the 1ꢀposition which has been shown to tolerate a variety of substituents.
These structural alterations resulted in several compounds with reduced lipophilicity as
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evidenced by the lower clogP and excellent OX potency and selectivity, such as 44
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(clogP = 3.07), which had a dimethylamino groups at the 7ꢀposition and on the 1ꢀbenzyl
group, respectively.
Similar to the previously reported 5 which showed efficacy in several in vivo models,
44 displayed high OX potency (K 5.7 nM vs. 8.5 nM) and excellent selectivity (both
1
e
>
1,000ꢀfold over OX ). These values also represent significant improvement from the
2
commonly used OX antagonist SB334867 (IC = 40 nM, 50x over OX ). Moreover, 44
1
50
2
showed greater kinetic solubility (>200 ꢀM) than 5 (77.8 ꢀM) and good BBB
permeability. Finally, 44 possessed little Pgp activity with an efflux ratio of 3.3. Given its
high OX potency and selectivity, as well as good ADME properties, 44 may serve as an
1
improved molecular tool in the elucidation and validation of the in vivo roles of the OX1
receptor in many orexin related disorders.
Experimental Procedures
General. All solvents and chemicals were reagent grade. Unless otherwise mentioned, all
were purchased from commercial vendors and used as received. Flash column
chromatography was done on a Teledyne ISCO CombiFlash Rf system using prepacked
columns. Solvents used were hexane, ethyl acetate (EtOAc), dichloromethane, methanol
and chloroform:methanol:ammonium hydroxide (80:18:2) (CMAꢀ80). Purity and
characterization of compounds was established by a combination of high pressure liquid
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chromatography (HPLC), thin layer chromatography (TLC), mass spectrometry (MS) and
1
13
nuclear magnetic resonance (NMR) analysis. H and C NMR spectra were recorded on
a Bruker Avance DPXꢀ300 (300 MHz) spectrometer and were determined in chloroformꢀ
d or methanolꢀd4 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
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(ESI). All test compounds were greater than 95% pure as determined by HPLC on an
Agilent 1100 system using an Agilent Zorbax SBꢀPhenyl, 2.1 mm x 150 mm, 5 ꢀm
column with gradient elution using the mobile phases (A) H O containing 0.1%
2
CF COOH and (B) MeCN, with a flow rate of 1.0 mL/min. For ADME analysis, samples
3
were analyzed by LCꢀMS/MS using a CTC PAL autosampler, Thermo Accela UPLC and
+
a Thermo Quantum Ultra triple quadrupole mass spectrometer. The [M+H] adducts of
the test compounds and internal standard were monitored using positive mode
electrospray ionization in multiple reaction monitoring (MRM) mode. The analytes were
injected onto a C18 column and chromatographed using a reverse phase gradient with
0
.1% formic acid in water and 0.1% formic acid in 20/80 isopropyl alcohol/acetonitrile
mobile phases. Peak integrations were performed using Thermo Xcalibur (v 2.4)
software.
Methyl (4-hydroxy-3-methoxyphenyl)acetate (7). To a solution of 4ꢀhydroxyꢀ3ꢀ
methoxyphenylacetic acid (2.50 g, 13.72 mmol) in anhydrous methanol (60 mL) was
added concentrated sulfuric acid (2.02 g, 1.1 mL, 20.59 mmol) and the reaction heated to
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reflux for 3 hr. The reaction was cooled, the solvent was removed under reduced pressure
and NaHCO solution was added. The aqueous solution was extracted three times with
3
dichloromethane and the combined extracts were dried over MgSO and the solvent was
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removed under reduced pressure to give the methyl ester as a yellow oil (2.69 g, 100%).
1
H NMR (300 MHz, CHLOROFORMꢀd) δ 6.84 ꢀ 6.90 (m, 1H), 6.80 (d, J = 1.70 Hz,
1
H), 6.73 ꢀ 6.78 (m, 1H), 5.57 (s, 1H), 3.89 (s, 3H), 3.69 (s, 3H), 3.55 (s, 2H).
-[3-Methoxy-4-(pyridin-2-ylmethoxy)phenyl]acetic acid (8f). Phenol 7 (1.0 g, 5.10
2
mmol), 2ꢀ(bromomethyl)ꢀpyridine hydrobromide (1.93 g, 7.65 mmol), potassium
carbonate (2.82 g, 20.4 mmol) and tetrabutylammonium iodide (0.38 g, 1.02 mmol) were
combined in anhydrous dimethylformamide (50 mL) and heated to 50 °C overnight. The
reaction was cooled, diluted with EtOAc, washed twice with water and with brine, dried
over MgSO and the solvent was removed under reduced pressure. The crude was
4
purified by chromatography on silica (0ꢀ60% EtOAc in hexane) to give the desired ether
1
as an orange oil (0.49 g, 34%). H NMR (300 MHz, CHLOROFORMꢀd) δ 8.58 (d, J =
4.62 Hz, 1H), 7.69 (dt, J = 1.65, 7.70 Hz, 1H), 7.51 ꢀ 7.60 (m, 1H), 7.16 ꢀ 7.25 (m, 1H),
6
.82 ꢀ 6.88 (m, 1H), 6.81 (s, 1H), 6.71 ꢀ 6.78 (m, 1H), 5.27 (s, 2H), 3.91 (s, 3H), 3.69 (s,
H), 3.56 (s, 2H).
3
To the solution of ester (0.49 g, 1.71 mmol) in methanol (15 mL) was added 2N sodium
hydroxide solution (3.4 mL, 6.82 mmol) and the reaction stirred at RT overnight. The pH
was adjusted to between 8 and 9 with 2N HCl then all the solvents were removed under
reduced pressure. The crude was dissolved in methanol as far as possible, the solids were
removed by filtration then the solvent was removed under reduced pressure to give the
1
acid as a yellow solid (0.47 g, 100%). H NMR (300 MHz, METHANOLꢀd ) δ 8.47 ꢀ
4
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8.54 (m, 1H), 7.84 (dt, J = 1.70, 7.72 Hz, 1H), 7.62 (d, J = 7.91 Hz, 1H), 7.30 ꢀ 7.39 (m,
1H), 7.01 (d, J = 1.88 Hz, 1H), 6.83 ꢀ 6.90 (m, 1H), 6.74 ꢀ 6.83 (m, 1H), 5.15 (s, 2H),
3.86 (s, 3H), 3.41 (s, 2H).
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N-[2-(4-Hydroxy-3-methoxyphenyl)ethyl]-2-(naphthalen-2-yl)acetamide (9a). To 2ꢀ
naphthylacetic acid (8a) (0.74 g, 3.97 mmol), 4ꢀhydroxyꢀ3ꢀmethoxyphenethylamine
hydrochloride (0.81 g, 3.97 mmol) and HATU (1.66 g, 4.37 mmol) in anhydrous
dimethylformamide (20 mL) was added diisopropylethylamine (2.06 g, 2.8 mL, 15.90
mmol) and the reaction stirred at RT under N overnight. The reaction was diluted with
2
EtOAc, washed with 2N aqueous HCl solution, NaHCO solution and brine, dried over
3
MgSO and the solvent was removed under reduced pressure to give the amide as a white
4
1
solid (1.33 g, 100%). H NMR (300 MHz, CHLOROFORMꢀd) δ 7.74 ꢀ 7.87 (m, 3H),
7
.62 (s, 1H), 7.47 ꢀ 7.54 (m, 2H), 7.24 ꢀ 7.29 (m, 2H), 6.61 (d, J = 7.91 Hz, 1H), 6.52 (d,
J = 1.88 Hz, 1H), 6.40 (dd, J = 1.88, 7.91 Hz, 1H), 5.38 (br. s., 1H), 3.71 (s, 3H), 3.70 (s,
H), 3.43 (q, J = 6.78 Hz, 2H), 2.63 (t, J = 6.88 Hz, 2H).
-(3,4-Dimethylphenyl)-N-[2-(4-hydroxy-3-methoxyphenyl)ethyl]acetamide (9b).
2
2
This was made by the same method as 9a, using 3,4ꢀdimethylphenylacetic acid (8b).
1
Colorless film. Yield 100%. H NMR (300 MHz, CHLOROFORMꢀd) δ 7.25 ꢀ 7.29 (m,
1H), 7.06 (d, J = 7.54 Hz, 1H), 6.83 ꢀ 6.96 (m, 2H), 6.72 ꢀ 6.79 (m, 1H), 6.59 (d, J = 1.51
Hz, 1H), 6.48 (d, J = 7.91 Hz, 1H), 5.39 (br. s., 1H), 3.83 (s, 3H), 3.46 (s, 2H), 3.42 (q, J
=
6.78 Hz, 2H), 2.65 (t, J = 6.88 Hz, 2H), 2.25 (s, 3H), 2.22 (s, 3H).
N-[2-(4-Hydroxy-3-methoxyphenyl)ethyl]-2-[4-(propan-2-yl)phenyl]acetamide
(
9c). This was made by the same method as 9a using 4ꢀisopropylphenylacetic acid (8c).
1
Colorless film. Yield 71%. H NMR (300 MHz, CHLOROFORMꢀd) δ 7.14 ꢀ 7.21 (m,
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H), 7.05 ꢀ 7.12 (m, 2H), 6.76 (d, J = 8.10 Hz, 1H), 6.61 (d, J = 1.51 Hz, 1H), 6.48 (dd, J
=
=
1.60, 8.01 Hz, 1H), 5.53 (s, 1H), 5.40 (br. s., 1H), 3.84 (s, 3H), 3.50 (s, 2H), 3.43 (q, J
6.78 Hz, 2H), 2.84 ꢀ 2.95 (m, 1H), 2.66 (t, J = 6.97 Hz, 2H), 1.25 (d, J = 6.97 Hz, 6H).
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-[4-(Dimethylamino)phenyl]-N-[2-(4-hydroxy-3-methoxyphenyl)ethyl]acetamide
(9d). This was made by the same method as 9a using 4ꢀdimethylaminophenylacetic acid
1
(8d). White sticky solid. Yield 99%. H NMR (300 MHz, DMSOꢀd ) δ 8.70 (s, 1H), 7.89
6
(t, J = 5.42 Hz, 1H), 7.03 (d, J = 8.57 Hz, 2H), 6.72 (d, J = 1.60 Hz, 1H), 6.61 ꢀ 6.68 (m,
3
H), 6.53 (dd, J = 1.65, 7.96 Hz, 1H), 3.71 (s, 3H), 3.15 ꢀ 3.27 (m, 4H), 2.85 (s, 6H), 2.57
(t, J = 7.30 Hz, 2H).
N-[2-(4-Hydroxy-3-methoxyphenyl)ethyl]-2-(3-nitrophenyl)acetamide (9e). This
was made by the same method as 9a using 3ꢀnitrophenylacetic acid (8e). White sticky
1
solid. Yield 100%. H NMR (300 MHz, CHLOROFORMꢀd) δ 8.13 (d, J = 8.10 Hz, 1H),
8
.08 (s, 1H), 7.44 ꢀ 7.59 (m, 2H), 6.79 (d, J = 8.10 Hz, 1H), 6.62 (d, J = 1.51 Hz, 1H),
.56 (dd, J = 1.70, 8.10 Hz, 1H), 5.57 (s, 1H), 5.51 (br. s., 1H), 3.84 (s, 3H), 3.58 (s, 2H),
6
3.50 (q, J = 6.66 Hz, 2H), 2.72 (t, J = 6.88 Hz, 2H).
N-[2-(4-Hydroxy-3-methoxyphenyl)ethyl]-2-[3-methoxy-4-(pyridin-2-
ylmethoxy)phenyl]acetamide (9f). This was made by the same method as 9a using acid
1
8f. Yellow sticky solid. Yield 69%. H NMR (300 MHz, CHLOROFORMꢀd) δ 8.63 (d, J
=
4.14 Hz, 1H), 7.71 ꢀ 7.81 (m, 1H), 7.59 (d, J = 7.82 Hz, 1H), 7.27 ꢀ 7.32 (m, 1H), 6.67 ꢀ
6.81 (m, 3H), 6.58 (dd, J = 1.98, 8.10 Hz, 1H), 6.55 (d, J = 1.88 Hz, 1H), 6.37 (dd, J =
1.88, 8.01 Hz, 1H), 5.32 (br. s., 1H), 5.23 (s, 2H), 3.85 (s, 3H), 3.80 (s, 3H), 3.46 (s, 2H),
3.37 ꢀ 3.44 (m, 2H), 2.64 (t, J = 6.64 Hz, 2H).
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-Methoxy-1-(naphthalen-2-ylmethyl)-1,2,3,4-tetrahydroisoquinolin-7-ol
(10a).
Amide 9a (1.37 g, 4.09 mmol) was suspended in anhydrous toluene (20 mL) and
phosphorus oxychloride (3.13 g, 1.9 mL, 20.42 mmol) was added slowly. The mixture
was heated to 90 °C for 2 hr, then cooled to RT and quenched cautiously with water. The
reaction was heated for 15 min until the oil formed went into solution. The reaction was
again cooled to RT, the toluene layer was removed and the aqueous layer was adjusted to
pH 8ꢀ9 using 2N aqueous sodium hydroxide solution. It was then extracted 3 times with
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DCM, the combined extracts were dried over MgSO and the solvents were removed
4
under reduced pressure to give the crude dihydroisoquinoline as an orange viscous oil,
which was used in the next step without further purification.
The crude material was dissolved in methanol (40 mL) and cooled in an ice bath.
Sodium borohydride (0.78 g, 20.4 mmol) was added portionwise then the reaction was
allowed to warm slowly to RT overnight. The reaction was quenched with water then the
methanol was removed under reduced pressure. The reaction mixture was diluted with
water and then extracted 3 times with DCM. The combined extracts were dried over
MgSO and the solvents were removed under reduced pressure to give the product as a
4
frothy yellow solid (0.41 g, 31%).
N-Benzyl-2-[7-hydroxy-6-methoxy-1-(naphthalen-2-ylmethyl)-1,2,3,4-
tetrahydroisoquinolin-2-yl]acetamide (11a). Amine 10a (32 mg, 0.100 mmol), Nꢀ
benzyl bromoacetamide (34 mg, 0.150 mmol) and tetrabutylammonium iodide (7 mg,
0
.020 mmol) were combined in anhydrous DMF (1 mL), then diisopropylethylamine (32
mg, 44 mL, 0.250 mmol) was added. The reaction was stirred at RT overnight. The
reaction was diluted with EtOAc and washed with NaHCO solution and brine, then dried
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over MgSO and the solvent was removed under reduced pressure. The crude material
4
was purified by chromatography on silica (0ꢀ75% EtOAc/hexane) to give the desired
1
product as a yellow viscous oil (20 mg, 43%). H NMR (300 MHz, CHLOROFORMꢀd) δ
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.76 (ddd, J = 3.49, 6.08, 11.73 Hz, 2H), 7.65 ꢀ 7.71 (m, 2H), 7.44 ꢀ 7.51 (m, 2H), 7.35
(dd, J = 1.70, 8.29 Hz, 1H), 7.08 ꢀ 7.16 (m, 3H), 6.75 (s, 1H), 6.55 ꢀ 6.65 (m, 4H), 5.52
(s, 1H), 4.13 (dd, J = 8.48, 14.69 Hz, 1H), 3.89 (s, 3H), 3.69 ꢀ 3.76 (m, 1H), 3.44 ꢀ 3.58
(m, 1H), 3.03 ꢀ 3.27 (m, 4H), 2.75 ꢀ 2.99 (m, 3H), 2.43 ꢀ 2.53 (m, 1H). MS (ESI) m/z 467
(M+H).
N-Benzyl-2-{1-[(3,4-dimethylphenyl)methyl]-7-hydroxy-6-methoxy-1,2,3,4-
tetrahydroisoquinolin-2-yacetamide (11b). This was made using the methods outlined
for 10a and 11a, starting from 9b to give 11b as an offꢀwhite sticky solid in 4% overall
yield. MS (ESI) m/z 445 (M+H).
N-Benzyl-2-(7-hydroxy-6-methoxy-1-{[4-(propan-2-yl)phenyl]methyl}-1,2,3,4-
tetrahydroisoquinolin-2-yl)acetamide (11c). This was made using the methods outlined
for 10a and 11a, starting from 9c to give 11c as an offꢀwhite sticky solid in 12% overall
yield. MS (ESI) m/z 459 (M+H).
N-Benzyl-2-{7-hydroxy-6-methoxy-1-[(3-nitrophenyl)methyl]-1,2,3,4-
tetrahydroisoquinolin-2-yl}acetamide (11e). This was made using the methods outlined
for 10a and 11a, starting from 9e to give 11e as an offꢀwhite sticky solid in 8% overall
yield. MS (ESI) m/z 462 (M+H).
N-Benzyl-2-[6-methoxy-1-(naphthalen-2-ylmethyl)-7-propoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl]acetamide (12a). To phenol 11a (20 mg, 0.043 mmol) and
potassium carbonate (18 mg, 0.129 mmol) in dimethylformamide (0.5 mL) was added 1ꢀ
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iodopropane (11 mg, 6 ꢀL, 0.064 mmol) then the reaction was stirred at RT overnight.
The reaction was diluted with EtOAc, washed with NaHCO solution, water and brine,
3
dried over MgSO and the solvent was removed under reduced pressure. The crude was
4
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purified by chromatography on silica (0ꢀ50% EtOAc in hexane) to give the desired
1
product as a yellow solid (17 mg, 77%). m.p. 46ꢀ49 °C. H NMR (300 MHz,
CHLOROFORMꢀd) δ 7.68 ꢀ 7.83 (m, 3H), 7.65 (s, 1H), 7.43 ꢀ 7.52 (m, 2H), 7.34 (dd, J =
1.51, 8.29 Hz, 1H), 7.15 (dd, J = 1.70, 4.90 Hz, 3H), 6.64 ꢀ 6.80 (m, 3H), 6.60 (s, 1H),
6
.48 (s, 1H), 4.19 (dd, J = 8.19, 14.79 Hz, 1H), 3.85 (s, 3H), 3.68 ꢀ 3.83 (m, 3H), 3.44 ꢀ
3
.59 (m, 1H), 3.05 ꢀ 3.32 (m, 4H), 2.83 ꢀ 3.05 (m, 3H), 2.44 ꢀ 2.57 (m, 1H), 1.72 ꢀ 1.88
(m, 2H), 0.98 (t, J = 7.44 Hz, 3H). HRMS (ESI, CH OH) m/z calcd for C H N O [M +
3
33 37
2
3
+
H] 509.2799, m/z found 509.2817.
N-Benzyl-2-{1-[(3,4-dimethylphenyl)methyl]-6-methoxy-7-propoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl}acetamide (12b). Prepared as 12a. White solid. Yield 70%.
1
m.p. 105ꢀ106 °C. H NMR (300 MHz, CHLOROFORMꢀd) δ 7.19 ꢀ 7.37 (m, 4H), 6.86 ꢀ
7.08 (m, 5H), 6.59 (s, 1H), 6.48 (s, 1H), 4.44 (dd, J = 8.19, 14.98 Hz, 1H), 3.89 (t, J =
6
.88 Hz, 2H), 3.82 ꢀ 3.86 (m, 3H), 3.37 ꢀ 3.68 (m, 3H), 3.06 ꢀ 3.33 (m, 2H), 2.78 ꢀ 3.01
(m, 4H), 2.43 ꢀ 2.55 (m, 1H), 2.13 (s, 6H), 1.76 ꢀ 1.93 (m, 2H), 1.04 (t, J = 7.44 Hz, 3H).
+
HRMS (ESI, CH OH) m/z calcd for C H N O [M + H] 487.2955, m/z found
3
31 39
2
3
4
87.2964.
N-Benzyl-2-(6-methoxy-1-{[4-(propan-2-yl)phenyl]methyl}-7-propoxy-1,2,3,4-
tetrahydroisoquinolin-2-yl)acetamide (12c). Prepared as 12a. Pale yellow solid. Yield
1
5
9%. m.p. 80ꢀ81 °C. H NMR (300 MHz, CHLOROFORMꢀd) δ 7.20 ꢀ 7.36 (m, 3H),
7.03 ꢀ 7.14 (m, 7H), 6.58 (s, 1H), 6.41 (s, 1H), 4.37 (dd, J = 7.63, 15.16 Hz, 1H), 3.84 (s,
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