Synthesis and Biological Evaluation of Fused Tricyclic Heterocycle Piperazine (Piperidine) Derivatives As Potential Multireceptor Atypical Antipsychotics

Article abstract of DOI:10.1021/acs.jmedchem.8b01096

Herein, a novel series of multireceptor ligands was developed as polypharmacological antipsychotic agents using the designed multiple ligand approach between dopamine receptors and serotonin receptors. Among them, compound 47 possessed unique pharmacological features, exhibiting high affinities for D₂, D₃, 5-HT_1A, 5-HT_2A, and 5-HT₆ receptors and low efficacy at the off-target receptors (5-HT_2C, histamine H₁, and adrenergic α₁ receptor). Compound 47 showed dose-dependent inhibition of apomorphine- and MK-801-induced motor behavior, and the conditioned avoidance response with low cataleptic effect. Moreover, compound 47 resulted nonsignificantly serum prolactin levels and weight gain change compared with risperidone. Additionally, compound 47 possessed a favorable pharmacokinetic profile with oral bioavailability of 58.8% in rats. Furthermore, compound 47 displayed procognition properties in a novel object recognition task in rats. Taken together, compound 47 may constitute a novel class of atypical antipsychotic drugs for schizophrenia.

Full text of DOI:10.1021/acs.jmedchem.8b01096

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Article
Synthesis and biological evaluation of fused tricyclic heterocycle piperazine
(piperidine) derivatives as potential multi-receptor atypical antipsychotics
Xudong Cao, Yifang Zhang, Yin Chen, Yinli Qiu, Minquan Yu,
Xiangqing Xu, Xin Liu, Bi-Feng Liu, Liangren Zhang, and Guisen Zhang
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.8b01096 • Publication Date (Web): 01 Nov 2018
Downloaded from http://pubs.acs.org on November 1, 2018
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Synthesis and biological evaluation of fused tricyclic heterocycle piperazine
(piperidine) derivatives as potential multi-receptor atypical antipsychotics
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a§
a§
b
b
b
b
Xudong Cao, Yifang Zhang, Yin Chen, Yinli Qiu, Minquan Yu, Xiangqing Xu,
Xin Liu, Bi-Feng Liu, Liangren Zhang, and Guisen Zhang a,b,*
a
a
c
a
Systems Biology Theme, Department of Biomedical Engineering, College of Life
Science and Technology, Huazhong University of Science and Technology,
Wuhan 430074, China
b
Jiangsu Nhwa Pharmaceutical Co., Ltd. 69 Democratic South Road, Xuzhou,
Jiangsu 221116, China
cState Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical
Sciences, Peking University, Beijing 100191, China
§ These authors contributed equally to this work;
*
Author to whom correspondence should be addressed;
E-Mail: gszhang@mail.hust.edu.cn; Tel.: +86-27-87792235; Fax: +86-27-87792170.
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ABSTRACT
Herein,
a
novel series of multi-receptor ligands was developed as
polypharmacological antipsychotic agents using the designed multiple ligand
approach between dopamine receptors and serotonin receptors. Among them,
compound 47 possessed unique pharmacological features, exhibiting high affinities
for D , D , 5-HT , 5-HT and 5-HT receptors and low efficacy at the off-target
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receptors (5-HT , histamine H , and adrenergic α receptor). Compound 47 showed
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dose-dependent inhibition of apomorphine- and MK-801-induced motor behavior, and
the conditioned avoidance response with low cataleptic effect. Moreover, compound
4
7 resulted nonsignificantly serum prolactin levels and weight gain change compared
with risperidone. Additionally, compound 47 possessed a favorable pharmacokinetic
profile with oral bioavailability of 58.8% in rats. Furthermore, compound 47
displayed pro-cognition properties in a novel object recognition task in rats. Taken
together, compound 47 may constitute a novel class of atypical antipsychotic drugs
for schizophrenia.
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INTRODUCTION
Schizophrenia is a chronic neuropsychiatric disorder affecting approximately
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% of the global population and is characterized by a combination of positive
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symptoms (such as hallucinations and delusions), negative symptoms (such as
avolition and psychomotor poverty), disordered thoughts, and cognitive deficits.2
After nearly a century of research, the etiology and pathophysiology of schizophrenia
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remain largely unresolved. Adequate treatment for schizophrenia remains a challenge
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due to the complex pathophysiology. Yet, hyper- and hypo-function of the
dopaminergic signal transduction system clearly contribute to some of the symptoms
of this disorder. The structures of the dopamine D receptors bound to risperidone
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have revealed distinct extended binding sites that could shed light on how to design or
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discover new drugs with fewer side effects than existing therapeutics. Furthermore,
all current antipsychotic medications act by blocking dopamine D receptors, which
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drives their efficacy in treating the positive symptoms of the condition. Despite
tremendous progress in the management of schizophrenia since the introduction of
current therapies, the so-called “typical” and “atypical” antipsychotics still suffer
from several liabilities that limit their overall effectiveness in patients.7
Chlorpromazine and haloperidol are typical antipsychotics with potential antagonistic
activity to D receptor. (Figure 1). Although these agents are effective for controlling
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some of the positive symptoms postulated to arise from hyperdopaminergia in the
mesolimbic pathway of the brain, they are relatively ineffective and may exacerbate
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negative symptoms as well as cognitive dysfunction. Use of these agents also causes
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extrapyramidal
symptoms
(EPSs),
including
tardive
dyskinesia
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hyperprolactinemia. This profile, along with unwanted side effects, has led to find
the new therapeutic strategies, such as favorable polypharmacology, including the
development of multi-receptor agents which targeting specific dopamine receptor
subtypes or a range of receptors, and the discovery of new ligands with a selectivity
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between 5-hydroxytryptamine (5-HT; serotonin) receptors and D receptors, with the
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aim to improve therapeutic profile. Indeed, second-generation antipsychotics (SGAs)
(also known as “atypical drugs”), such as clozapine and olanzapine, show favorable
polypharmacology effects (Figure 1).11
All SGAs antagonize the dopamine D receptor and are effective in alleviating
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the positive symptoms of schizophrenia. Due to their high affinity for serotonin
receptors, particularly the 5-HT1A and 5-HT2A receptors, these agents have also been
shown to treat the positive symptoms, such as hallucinations and delusions with fewer
EPSs.12 First, 5-HT1A receptor agonism alleviates the EPS side effects of
antipsychotics by activating 5-HT receptors located in the primary motor cortex and
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dorsolateral striatum region.13 Second, in the frontal cortex, dopamine release is
increased by the activation of the postsynaptic 5-HT1A receptor, thus potentiating
functions of the mesocortical dopamine pathway, which may inprove negative
symptoms and cognitive deficits in schizophrenia patients.14c,d Furthermore, multiple
preclinical studies supported the hypothesis that 5-HT1A receptor antagonists may
reverse cognitive deficits though its ability to both enhance stimulated glutamate
efflux and stimulated acetylcholine levels. 14a,b,c The 5-HT2A receptor is widely
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expressed in the brain, interacts with neurotransmitter systems, especially acts on
dopaminergic neurotransmission. Blocking the serotonin 5-HT2A receptor
counteracted the effect of D receptor blockade in striatum, thus alleviates the EPS
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side effects. Moreover, 5-HT receptor antagonism has been implicated in the
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enhanced efficacy against negative schizophrenic symptoms.12a,b It is now apparent
that these SGAs, including clozapine and olanzapine, are antagonists at both 5-HT2A
and dopamine D receptors and that activity at both of these receptors is necessary for
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the antipsychotic efficacy of this class of drugs.15 However, the favorable
polypharmacology observed with many atypical antipsychotics was achieved through
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a serendipitous discovery rather than a rational drug design process. Treatment with
these atypical antipsychotics is accompanied by various other risks, such as excessive
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weight gain, hyperglycemia and abnormal blood lipid, which are primarily caused
by high affinity binding to other off-target receptors, such as the histamine H1
1
7–19
receptor, the 5-HT2C receptor, and the α -adrenoceptor.
Moreover, no current
1
antipsychotic drug addresses the cognitive deficits associated with schizophrenia,
which is an equally important component in the etiology of schizophrenia.10
Current hypotheses suggest that cognition-enhancing actions may be due to
11
interactions with the 5-HT or D receptor. The 5-HT receptor modulates multiple
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neurotransmitter systems possibly linked with the cognitive dysfunction of
schizophrenia.12a, 20 Blocking the 5-HT receptor not only enhances prefrontal cortical
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dopamine release, but may also modulate glutamatergic systems by disinhibiting
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GABAergic neurons in the frontal cortex. Given this ability of the 5-HT receptor, a
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large amount of scientific data have indicated that 5-HT receptor ligands are effective
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procognitive agents in preclinical studies. Although the role of this receptor in the
regulation of psychotic symptoms is currently unclear, it may result in cognitive
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improvements though the way: blockade of D recepor in the frontal cortex may
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enhance acetylcholine release. Preclinical studies suggest that the D receptor may
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be proposed as a high pharmacotherapeutic target and D receptor ligands may
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constitute a promising approach to treat the negative and cognitive symptoms in
schizophrenia and drug abuse disorders.24
These observations encouraged us to design multi-target ligands that can
precisely modulate the activity of several monoaminergic receptors (D , D , 5-HT ,
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5-HT2A and 5-HT receptors), expecting that this multifunctional profile will
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contribute to the therapeutic potential for patients with schizophrenia. This three
receptors (D , 5-HT and 5-HT ) have been identified as crucial molecular targets in
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the development of new potential anti-psychotic agents because drugs acting via these
targets effectively treat the positive and negative symptoms. The pharmacological
profile of the newly designed molecules with high affinities for the D and 5-HT
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receptors is presumed to be improved and enhanced with procognitive activities.
Herein, we present the design, synthesis and bio-evaluation of a series of heterocyclic
piperazine (piperidine) analogues as multimodal agents. The most promising molecule
in the whole series was further characterized in extended pharmacological studies.
Tricyclic scaffolds containing an indole and indoline moiety have been barely
explored in medicinal chemistry. Compounds based on the pyrano[2,3,4-cd]indole
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scaffold show high affinity for the 5-HT receptor. A series of potent and selective
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CYP11B1 inhibitors based on the heteroaryl substituted 1,2,5,6-tetrahydro
pyrrolo[3,2,1-ij]quinolin-4-ones have been reported to treat Cushing’s syndrome.26
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Ligands based on the fused tricyclics with substituted 3-(piperidin-4-yl)-1H-indole
that show high binding to D , 5-HT and the human serotonin transporter (hSERT)
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have been reported by Pfizer.27 The structure of compound 1 displays key
pharmacophoric features of many D receptor ligands shown in an earlier publication
2
Figure 2).28
(
Therefore, using the tricyclic heterocycle structure of compound 1 as the
primary scaffold, the privileged structures from known antipsychotic drugs were
introduced into new compounds that simultaneously modulate several receptors using
the designed multiple ligand approach described by Morphy. This approach takes two
separate pharmacophores with distinct pharmacology and integrates them into one
molecule with the attributes of both parent molecules.10a, 29 The privileged structures
from known antipsychotic drugs were covered (Figure 3): (1) phenylpiperazines,
which are known to be important motifs for the functional activity of antipsychotics;
the preclinical and clinical tests demonstrated that compounds incorporating the
2
,3-dichlorophenylpiperazine and 2-methoxyphenylpiperazine scaffolds are useful in
the design of atypical antipsychotics;28a and (2) benzisoxazoles and benzoisothiazoles,
which are important fragments, and some medications containing these moieties have
been approved for human clinical use, including atypical antipsychotics (risperidone,
paliperidone, ziprasidone, and lurasidone). The activities of the piperazine or
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piperidine moiety at D and 5-HT receptors followed by similar structural
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heterocycles have proven useful for antipsychotic efficacy.30 Moreover, the
appropriate linker between the tricyclic heterocycles and the privileged structures is
important for new compounds binding to the desired multi-receptors (D , D , 5-HT ,
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-HT and 5-HT receptors).
2A 6
A series of new compounds in Tables 1–5 was prepared by this strategy, which
were used to identify their pharmacological affinities and determine binding
specificity for the multiple receptors in structure–activity relationship studies. Among
the derivatives prepared, compound 47 not only exhibited high affinity for the desired
multi-target, but was also endowed with low to moderate activities on off-target
receptors (5-HT , H and α receptors) and low hERG channel inhibitiomn.
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Furthermore, compound 47 reversed significantly apomorphine-induced and
MK-801-induced motor behavior with a low propensity to induce catalepsy. In
addition, compound 47 led to negligible weight gain and resulted nonsignificantly
serum prolactin levels change compared with risperidone. Moreover, compound 47
displayed procognitive properties in a novel object recognition task in rats and
showed favorable pharmacokinetic properties. Thus, compound 47 was developed as
atypical antipsychotics to validate the novel approach to treat schizophrenia based on
its unique polypharmacological antipsychotic profile.
CHEMISTRY
The syntheses of 3–54 are shown in Schemes 1 and 2. The new compounds
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8–22, 24, 29–33, and 37–54 were prepared by synthetic route shown in Scheme 1.
Tricyclic heterocycle core 3 was synthesized as the initial building block from
commercially available 1,2,3,4-tetrahydroquinoline or 2,3-dihydro-1H-indole via
N-acylation with 3-chloropropionyl chloride and subsequent Friedel–Crafts
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cyclization with AlCl under molten conditions. The central building blocks 4 and 6
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were produced with the Friedel–Crafts acylation reaction and an appropriate amount
of chloroalkyl chloride. As shown in Scheme 1, compounds 8–22, 24, and 37–48 were
prepared by coupling 4 or 6 with corresponding arylpiperazines or arylpiperidines in
CH CN. Compounds 29–33 and 49–51 were prepared though two method routes. The
3
final compounds were obtained by catalytic reduction of their corresponding ketone
precursors in the presence of triethylsilicon hydride (Et SiH) and trifluoroacetic acid
3
(TFA) from method A. According to method B, the intermediates 5 and 7 were
obtained from the reduction reaction of the corresponding intermediates 4 and 6,
followed by a reaction with the corresponding arylpiperazines or arylpiperidines to
afford the target compounds. Compounds 35, 36, and 52–54 were yielded after further
reduction of their ketone precursors in the presence of NaBH4.
The methyl group-substituted tricyclic heterocycle compounds 23 and 34 was
prepared though the route depicted in Scheme 2. Intermediate 25 was prepared
starting from 1,2,3,4-tetrahydroquinoline and treatment with ethyl acetoacetate and
subsequent sulfuric acid-mediated cyclization to afford the methyl group substituted
tricyclic heterocycle 26. The key building block 27 was obtained by reduction with
Pd/C, which was subsequently coupled with 4-chlorobutanoyl to give the
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corresponding ketone 28. Final compound 23 was prepared by coupling 28 with
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RESULTS AND DISCUSSION
Structure–activity relationships
As previously noted, most of the presently approved atypical antipsychotic
drugs exhibit polypharmacology, with appreciable affinities for a variety of biogenic
amine receptors (such as D , 5-HT
and 5-HT2A receptors). Due to their
2
1A
multi-receptors affinities, ligands contained different chemical groups are of high
pharmacotherapeutic interest in schizophrenia, which has been extensively developed
as a potential strategy to find a novel antipsychotics. In this study, a class of new
compounds by introducing different privileged structures were characterized the
binding to the D , 5-HT and 5-HT receptors.
2
1A
2A
Effect of the tricyclic heterocycle (containing 1,2,3,4-tetrahydroquinoline) on
different privileged structures
In this study, our starting point focused on the impact of various privileged
structures (Table 1, compounds 9–18). Compound 9 bearing a phenylpiperazine
exhibited weak binding to D and 5-HT receptors at micromolar concentrations (D ,
2
1A
2
K = 1764.8 ± 212.4 nM; 5-HT , K = 1856.2 ± 208.1 nM), with low activity to
i
1A
i
5-HT2A receptor (K = 752.3 ± 121.2 nM). Replacing the phenyl ring with its
i
bioisostere, pyridine (10) and pyrimidine (11), resulted in similar affinities as shown
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for compound 9, while a low 5-HT2A affinity for the two compounds was observed
(
10, K = 675.2 ± 102.4 nM; 11, K = 557.4 ± 84.6 nM). Compound 12 showed
i
i
decreased D receptor binding affinity when the methoxy groups was introduced in
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
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2
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4
4
4
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5
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5
5
5
5
5
6
0
1
2
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9
0
1
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8
9
0
the ortho position of phenylpiperazine, while 5-HT1A receptor binding affinity
increased slightly (K = 964.8 ± 125.3 nM), and a good 5-HT receptor affinity with
i
2A
with K values of 178.2 ± 28.5 nM was obtained, compared to compound 9.
i
Compound 13 exhibited good 5-HT and 5-HT receptors affinities with K of 196.1
1
A
2A
i
±
21.3 nM and 207.3 ± 23.4 nM after replacing 2,3-dimethylphenylpiperazine,
compared with risperidone, but weak binding to the D receptor. Introducing a
2
chlorine atom to the 4-position (14) of the phenyl ring did not change the receptor
profile compared with that of compound 9. Derivative 15 of the 2,3-di-Cl-substituted
counterpart maintained potent activities on the 5-HT and 5-HT receptors with Ki
1
A
2A
of 268.6 ± 30.1 nM and 207.4 ± 28.3 nM, respectively. When the privileged structure
phenylpiperazine was replaced with heterocyclic piperazine, compound 16 with
3
-(piperazin-1-yl)benzo[d]isothiazole, a remarkable increase in activity for the D2
receptor (K = 182.1 ± 14.2 nM), and good binding activitie to the 5-HT (K = 128.7
i
1A
i
±
13.0 nM) and 5-HT2A (K = 72.0 ± 8.2 nM) were observed, compared with
i
compound 9. Compounds 17 and 18 showed different affinities for the main targets
when piperazine was replaced by piperidine. Compound 17 with piperidine resulted in
a decrease in D (K = 861.2 ± 54.6 nM), 5-HT (K = 392.0 ± 43.2 nM) and 5-HT
2
i
1A
i
2A
(K = 173.0 ± 28.1 nM) receptor potency by four-, three-, and two-fold, respectively,
i
compared with compound 16. Interestingly, transforming the benzo[d]thiazole moiety
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2
2
2
2
2
2
2
2
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4
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4
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5
5
5
5
5
5
5
5
5
6
to an oxygen-containing benzoheterocycle, such as 6-fluorobenzo[d]isoxazole, in
compound 18 resulted in an increase in D (K = 58.2 ± 6.4 nM) and 5-HT (K =
2
i
1A
i
6
2.9 ± 7.3 nM) receptor potency by three- and two-fold, while 5-HT2A (K = 52.3 ±
i
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
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5
6
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9
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0
1
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8
9
0
5.8 nM) receptor potency increased only slightly, compared to compound 16.
Effect of the different linkers between the tricyclic heterocycle (containing
1,2,3,4-tetrahydroquinoline) and privileged structures
The optimal linker between the tricyclic heterocycle containing
1
,2,3,4-tetrahydroquinoline and the privileged structures was determined in
compound 18. As shown in Table 2, when 4-chlorobutyryl chloride was introduced
and the linker was changed to a longer (4-unit) alkyl chain, compound 19, bearing
2,3-dimethylphenylpiperazine, and compound 20, containing 2,3-dichlorophenyl
piperazine, showed similar affinity for 5-HT , while D and 5-HT receptor potency
1
A
2
1A
decreased slightly (D , K = 185.2 ± 19.5 nM; 5-HT , K = 169.2 ± 17.6 nM for 19;
2
i
1A
i
D , K = 282.5 ± 30.6 nM; 5-HT , K = 149.4 ± 16.7 nM for 20), compared to
2
i
1A
i
compound 18. The privileged structures in ziprasidone and risperidone revealed
slightly different heterocycles (benzoisothiazole vs. benzoisoxazole), and compound
2
1 bearing benzoisothiazole showed increased affinity for the D receptor (K = 91.4 ±
2 i
1
0.7 nM). In addition, both the replacement S with O atom for the heterocycles and
the benzothiazole with a powerful electron-withdrawing substituent (fluorine atom)
on the aromatic ring while benzoisoxazole without F at the same position may have
made compound 22 more favorable for the three receptors compared with compound
2
1. Substituting a hydrogen atom at the R position for a methyl group (23) led to an
3
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approximate three-fold decrease in activity for the D receptor (K = 62.1 ± 7.2 nM),
2
i
while the efficacy for the 5-HT receptors remained the same, compared with
compound 22. When a longer or shorter linker was introduced, the compounds
displayed different affinities for the three receptors. The affinities remained the same
as those of compound 22 when 4-chlorobutyryl chloride (23) was replaced with
5-chloropentanoyl chloride (24), indicating that the compound with a longer linker
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
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3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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5
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9
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0
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8
9
0
(5-unit) may fail to improve the affinities for the three receptors. Compound 8
containing 2-chloroacetyl chloride, a shorter linker (2-unit), resulted in significantly
reduced activities at all three receptors.
Reducing the carbonyl groups and introducing more aliphatic linkers may be
effcet physicochemical properties and drug-likeness. To evaluate the effects of these
modifications, the carbonyl group of the linker was reduced to methylene and a
hydroxymethyl group and the affinities for these compounds were determined (Table
3). When the carbonyl group was reduced by Et SiH in the presence of TFA,
3
compounds containing the benzisoxazolepiperidine moiety with chain lengths of three
(29) or four (33) carbons showed slightly reduced affinities for the receptors,
compared with compound 22. The same affinities were observed when the methyl
group was substituted at the R position (34). Introducing the privileged structures
3
2,3-dichlorophenylpiperazine (30 and 31) and 3-(piperazin-1-yl)benzo[d]isothiazole
(
32) led to a decrease in affinity for the D receptor, while activity against the 5-HT2A
2
receptor was retained (albeit less than that of compound 22). When the carbonyl
group was reduced by sodium borohydride (NaBH ), compounds 35 and 36 with OH
4
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5
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on the carbon chain resulted in a slight change in the D and 5-HT receptors
2
2A
affinities. These results indicate that introducing a carbonyl or hydroxymethyl group
on the linker between the tricyclic heterocycle (containing 1,2,3,4-tetrahydroquinoline)
and the privileged structure benzisoxazolepiperidine moiety moiety resulted in good
activities for the three receptors.
0
1
2
3
4
5
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8
9
0
1
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0
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0
1
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9
0
Effect of the tricyclic heterocycle (containing indoline) on different privileged
structures
We proceeded with our investigation by replacing 1,2,3,4-tetrahydroquinoline
with different substituted indolines on the tricyclic heterocycles (Table 4). First, when
indoline was introduced, the compounds showed moderate affinities for the D2
receptor, regardless of whether the phenyl ring of the privileged structures was
replaced by an electron-donating (37) or electron-withdrawing (38) group. Compound
3
9 with a cyano group on naked aromatic ring showed weaker affinities for the three
receptors. Changing the phenyl ring to benzoisothiazole and benzoisoxazole resulted
in increased affinity of the three receptors for compounds 40 and 41.
Effect of the different linkers between the tricyclic heterocycles (containing indoline)
and the privileged structures
The change of the different sapcer between the tricyclic heterocycle (containing
indoline) and privileged structures was also determined (Table 5). Introducing
4
-chlorobutyryl chloride and the linker changed the compound into a longer (4-unit)
alkyl chain. Compounds with the privileged structures of aripiprazole, risperidone,
and ziprasidone had significantly increased affinities for the three receptors. The
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following order of the three receptors for the analogues with different modifications
was
observed:
2,3-dichlorophenylpiperazine
(42)
<
3-(piperazin-1-yl)
benzo[d]isothiazole (43) < 6-fluoro-3-(4-piperidyl)-1,2-benzisoxazole (44). We then
introduced fluorine substituents at different positions on the tricyclic heterocycle. The
activities of the substitution of F at the seven (45) and nine (46) positions of the
tricyclic heterocycle were retained, although it was little less than that of compound
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
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
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2
3
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8
9
0
1
2
3
4
5
6
7
8
9
0
4
4. Notably, compound (47) bearing benzisoxazolepiperidine moiety, particularly
those with a long (5-unit) linker, had significantly higher activties for D receptor (K
2
i
= 2.9 ± 0.3 nM), 5-HT receptor (K = 8.6 ± 1.1 nM) and 5-HT receptor (K = 0.72
1
A
i
2A
i
±
0.02 nM). In contrast, compound 48, interposed with chain lengths of six carbons,
showed significantly inactive to the three receptors.
To investigate further structure–activity relationships, the carbonyl group of the
linker between the tricyclic heterocycle and benzisoxazolepiperidine moiety was
reduced and the affinities for these compounds was investigated. When the carbonyl
group was reduced to a methylene group, the 5-HT2A receptor affinity of compounds
with different chain lengths led a decrease but not the other two receptors.
Compounds with chain lengths of four carbons (50) showed good activities for D and
2
5
-HT1A receptor with K < 15 nM, whereas compounds with shorter (3-unit) (49) or
i
longer (5-unit) (51) linker had slightly reduced affinities for the two receptors. When
the carbonyl group was reduced by NaBH , compound 54, with a chain length of five
4
carbons, exhibited good binding activitie to the three receptors with K < 15 nM.
i
Affinity for the D receptor following modification of the chain length resulted in
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5
6
analogues in the following order: chain lengths of three carbons (52) < four carbons
(53) < five carbons (54). Compounds 52 and 53 had similar activties for the 5-HT1A
and 5-HT receptors but weaker affinities than those of compound 54.
2
A
0
1
2
3
4
5
6
7
8
9
0
1
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9
0
Overall, compounds 44, 47, 50, 53, and 54 exhibited good activties for the three
receptors. These five compounds especially compound 47 (K = 8.6 ± 1.1 nM) showed
i
higher 5-HT1A affinities than risperidone (K = 182 ± 15 nM). Moreover, compound
i
4
7 (K = 2.9 ± 0.3 nM) displayed a strong binding activity to D2 receptor compared
i
with risperidone (K = 3.7 ± 0.3 nM). Compounds 47 (K = 0.72 ± 0.02 nM) showed
i
i
similar 5-HT2A activity to risperidone (K = 0.18 ± 0.02 nM). These relationships are
i
summarized in Figure 4.
The atypical antipsychotics are less potent D receptor antagonists than
2
conventional antipsychotics and have the distinctive feature of being 5-HT receptor
2
A
antagonists, which improves their neurological safety.31 Thus, the atypical
antipsychotics have demonstrated superior effectiveness, with a diminished incidence
3
2
of EPSs, but are associated with the development of metabolic disturbances. They
trigger many adverse events, such as excessive weight gain, which is primarily a
result of treatment with clozapine and olanzapine, and to a lesser extent risperidone;
the synergistic effects of histamine H and serotonin 5-HT antagonism have been
1
2C
postulated as the reason for the antipsychotic-induced weight gain. Many other
adverse events may be induced by the administration of atypical antipsychotics.
Glucose and lipid abnormalities may be caused by the treatment of clozapine and
olanzapine, while the strong risk of QTc prolongation was tiggered by sertindole and
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ziprasidone. Treating schizophrenia with antipsychotic drugs may trigger orthostatic
3
4
hypotension related to the antagonistic effect of the adrenergic α receptor. These
1
adverse events have been suggested to be closely related to the three off-target
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
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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8
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receptors (5-HT , histamine H , and adrenergic α ). As shown in Table 6, compound
2
C
1
1
5
4 exhibited high binding activity to the two receptors compared to risperidone (54:
5-HT , K = 33.7 ± 4.1 nM; H , K = 43.5 ± 5.2 nM; risperidone: 5-HT , K = 28.2 ±
2
C
i
1
i
2C
i
3
.3 nM; H , K = 46.2 ± 5.1 nM). The other compounds may cause no or little
1 i
treatment-associated weight gain because they have lower 5-HT2C and histamine H1
receptor affinities compared with risperidone. Due to their inactivity to the adrenergic
α receptor (K > 300 nM), the selected compounds except compound 50 (K = 99.3 ±
1
i
i
12.1 nM) may not cause orthostatic hypotension.
Furthermore, the 5-HT receptor has high density in brain areas associated with
6
learning and memory, predominantly in the hippocampus, striatum, nucleus
accumbens, and prefrontal cortex. Its enrichment in those brain regions suggests an
2
0
important role in memory and cognitive processes. Given that blockade of the 5-HT
6
receptor induces glutamatergic and monoaminergic (e.g., dopaminergic and
adrenergic) neurotransmitter release, it was reasonable to consider that 5-HT receptor
6
antagonism could be a promising approach for the improvement of cognitive
2
1
abilities. The dopamine D receptor plays an important role in regulating cortical
3
DA neurotransmission related to cognitive and motivational behaviors, due to its
2
3
selective expression in the striatum and mesolimbic system. Overall, the two desired
target receptors (5-HT and D receptors) have been suggested to help improve
6
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2
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cognitive abilities. In Table 6, the 5-HT receptor affinities of compounds 47, 50, 53,
6
and 54 are higher than risperidone (K = 1260 ± 150 nM). In particular, compounds 47
i
(
K = 5.55 ± 0.6 nM) and 53 (K = 6.36 ± 0.8 nM) displayed significantly higher
i
i
0
1
2
3
4
5
6
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9
0
1
2
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9
0
1
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9
0
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0
1
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0
binding activities to the 5-HT receptor than risperidone. According to Table 6,
6
compound 47 (K = 1.66 ± 0.3 nM) showed higher binding activity to the D receptor
i
3
than risperidone (K = 31.9 ± 3.3 nM), while the other selected compounds had weak
i
affinities for the D receptor. Thus, these results suggest that compound 47 may
3
alleviate cognitive impairment in patients.
Taken together, compounds 44, 47, and 53 showed low binding activity to the
off-target receptors (5-HT , histamine H , and adrenergic α receptors [K > 300
2
C
1
1
i
nM]), while compound 47 exhibited excellent affinities for the desired target receptors
5-HT , K = 5.55 ± 0.6 nM; D , K = 1.66 ± 0.3 nM). Therefore, the three compounds
(
6
i
3
i
were selected to evluate their safety profile.
hERG channel blockade
Cardiotoxicity is a serious side effect often caused by off-target interactions
between drugs and various voltage-gated ion channels in the heart, particularly the
3
5
hERG channel. Unwanted interactions of drugs with this channel can trigger serious
cardiac arrhythmias, such as long QT syndrome, which is characterized by
prolongation of the QT interval and Torsades de pointes.36 The possible lethal
aftermath of drug-induced hERG blockade has significantly affected screening
strategies, drug development, regulation, and approval procedures. Compounds 44, 47,
and 53 were evaluated for their ability to block hERG in a patch-clamp assay.
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Compound 47 (IC > 2000 nM) exhibited a lower hERG inhibition than the others.
5
0
Taken together, compound 47 exhibited excellent in vitro profiles with a higher
affinity for the five desired targets and a lower affinity for the three off-target
receptors and hERG.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
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4
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5
5
5
5
5
5
5
5
5
5
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0
1
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5
6
7
8
9
0
1
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Acute toxicity
The acute toxicity was investigated in terms of LD values. Compound 47 even
5
0
at the highest tested dose (2000 mg/kg) was not lethal in more than half of the mice. It
suggested that compound 47 displayed a good safety profile with a very low acute
toxicity (LD > 2000 mg/kg).
5
0
Intrinsic activity of new multi-receptor compound 47
Compound 47 was selected for further functional characterization based on its
excellent in vitro profiles and good safety properties. In Table 7, compound 47
stimulated the five receptors in an agonist assay and showed minimal agonist activity,
displaying < 20% of the efficacy of the reference compounds, respectively.
Compound 47 blocked five receptors by greater than 90% in an antagonist assay.
Compound 47 functioned as an antagonist at the D2L (IC = 9.20 nM), D (IC =
50
3
50
2
1
5.6 nM), 5-HT1A (IC = 587.8 nM), 5-HT (IC = 257.4 nM) and 5-HT (IC =
50 2A 50 6 50
77.6 nM) receptors.
In vivo behavioral studies on selected analogues of compound 47
Analysis of the data obtained from the receptor binding assays allowed
compound 47 to be selected for testing in several mouse models sensitive to
mesolimbic-mediated antipsychotic-like activity.
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The antagonism of hyperlocomotion induced by dopamine receptor direct
agonists (e.g., apomorphine) or compounds that facilitate dopaminergic tone (e.g.,
amphetamines and AMP) are used in murine models to assess antipsychotic
efficacy.37 The effects of apomorphine decrease significantly in response to D2
receptor antagonists. Many of these compounds demonstrate a potent ability to
attenuate climbing behavior induced by apomorphine in mice, which has been used as
a model for identifying potential antipsychotic activity linked to behavioral agitation,
one positive psychotic symptoms.38 Treatment with Compound 47 can
dose-dependently inhibit the apomorphine induced climbing behavior (Figure 5),
with an ED50 value of 0.61 mg/kg (Table 8). In comparison, the
apomorphine-induced climbing behavior was also attenuated by risperidone (ED ,
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.028 mg/kg) and haloperidol (ED , 0.11 mg/kg), respectively. It indicate that
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compound 47 is a potent blocker of the D receptor, which was also consistent with its
2
potent D receptor antagonistic activity.
2
It is well known that systemic administration of PCP or MK-801 increases the
dopaminergic cell-firing rate in the brain.39 The observation that uncompetitive
NMDA receptor antagonists (e.g., PCP, MK801, and ketamine) induce schizophrenic
symptoms (negative and cognitive symptoms) in healthy subjects and exacerbate
existing psychoses in patients with schizophrenia suggests that endogenous
dysfunction of NMDA receptor-mediated neurotransmission might play an important
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role in the pathophysiology of schizophrenia. The compounds were also tested in the
MK801-induced hyperactivity model. In this test, compound 47 significantly
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dose-dependently decreased the increased locomotor activity induced by MK-801
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Figure 6) with an ED of 0.26 mg/kg (Table 8). In comparison, risperidone and
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haloperidol reversed the MK801-induced hyperactivity with an ED values of 0.011
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and 0.16 mg/kg, respectively.
One of the major obstacles of the use of antipsychotics is their propensity to
produce EPSs. The rodent catalepsy test has been often used to predict the incidence
of EPSs in the antipsychotic drug discovery process.41 Selected compounds were
tested in mice using the horizontal bar test to evaluate the liability for
striatal-mediated side effects and for cataleptogenic potential. This test is sensitive to
catalepsy induced by D receptor antagonist. In Table 8, haloperidol induced
2
significant cataleptic effect (ED , 0.12 mg/kg), consistent with its strong antagonistic
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effect on D receptor. In contrast, compound 47 produced a low potential
2
cataleptogenic effect (ED , 78.62 mg/kg), while the ED of catalepsy induced by
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risperidone is 0.51 mg/kg. Compound 47 with a higher threshold for catalepsy might
induce a lower incidence of extrapyramidal motor side-effects, compared with
risperidone. Compound 47 exhibited a wider range of the therapeutic indices
(128.88–302.38) based on its efficacy (apomorphine or MK-801 models) and its side
effects (catalepsy), while the therapeutic index of risperidone was approximately
18.21–46.36.
The conditioned avoidance response (CAR) test has significant predictive
validity, some construct validity, but little face validity. The CAR test has been used
to assess the antipsychotic activity of potential agents that display high affinities for
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dopamine receptors.42 This test has long been considered an important preclinical
animal model for the study of antipsychotic drugs.43 Both compound 47 and
risperidone effectively inhibited the avoidance response in the rat CAR model
(Figure 7). A nonlinear regression analysis indicating risperidone’s ED was 0.52
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mg/kg, while treatment of compound 47 resulted an ED of 1.46 mg/kg (Table 8).
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Weight gain and serum prolactin
The potential adverse effect profile of compound 47 was also assessed in terms
33
of its ability to induce weight gain and high prolactin levels. Negligible weight gain
was detected by administering compound 47 in mice that experienced chronic dosing
(28 days), whereas risperidone was associated with significantly more weight gain in
the experienced chronic dosing (28 days) (Figure 8). The discrepancies was also
consistent with their different affinities for the histamine H (risperidone, K = 46.2 ±
1
i
5
.1 nM; 47, K = 630.3 ± 5.5 nM) and 5-HT (risperidone, K = 28.2 ± 3.3 nM; 47, K
i 2C i i
= 616.0 ± 65.1 nM) receptors. Moreover, compound 47 resulted nonsignificantly
serum prolactin levels change compared with risperidone (Figure 9).
Besides the aforementioned functional profile, extended pharmacological in
vitro profiling was conducted with compound 47 to investigate its potential off-target
activity (Table 6). The results indicated that compound 47 behaved as an antagonist
of the five receptors (Table 7) and showed weak affinities for off-target receptors
(Table 6). Consequently, similar to other atypical antipsychotics, compound 47
displayed a complex pharmacology with the desired profile, but appeared to produce
some potentially unwanted off-target effects. These effects, resulting from off-target
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receptors (adrenergic α , histamine H , and 5-HT receptors), suggest factors related
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to metabolic disturbances (weight gain), hypotension, and sedation; however, these
states were not observed in this study. The pharmacokinetic properties of compound
47 have been extensively studied in rats, and good pharmacokinetic characteristics
have been demonstrated.
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Pharmacokinetic profile of compound 47
The pharmacokinetic properties of compound 47 have been extensively studied
in rats, and the good pharmacokinetic characteristics are demonstrated in Table 9.
Interestingly, two ways of administration showed similar half-life (t ), t of
1
/2
1/2
intravenous administration (1 mg/kg) was 2.15 ± 0.50 h, while oral administration (10
mg/kg) was associated with a t1/2 of 2.02 ± 0.19 h. Compound 47 showed intravenous
AUC (area under the curve) of 3151.2 ± 402.9 ng·h/mL and oral AUC of 18,539.5 ±
1
584.6 ng·h/mL, respectively. Clearance was 15.4 mL/min/kg following intravenous
administration. The Tmax value was 1.00 ± 0.00 h and the peak serum concentration
was 3733 ± 1635 ng/mL when dosed orally at 10 mg/kg. In sum, compound 47
exhibited a favorable drug-like pharmacokinetic properties with an oral bioavailability
of 58.8 %.
Memory study
Given its promising profile, compound 47 exhibited excellent affinities for
5
-HT (K = 5.55 ± 0.6 nM) and D (K = 1.66 ± 0.3 nM) receptors, so the effect of
6 i 3 i
compound 47 on cognitive performance was evaluated in a novel object recognition
NOR) task in rats, predictive of potential procognitive activity of the drug.22b, 44 The
(
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NOR task is a widely-used behavioral task to assess visual recognition memory, and
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is based on an animal’s innate preference for novelty. The task consists of a training
phase, where rats are presented with two identical objects to explore. Following a
delay interval, memory was assessed by presenting the rats with a trained object and a
novel object. Rats with a memory of the previously presented object will
preferentially explore the novel object. Rats that receive a memory enhancing drug in
conjunction with submaximal training are expected to exhibit improved memory
performance similar to that of untreated animals that received stronger training (i.e.,
more exposure to objects during the training phase). In this study, compound 47 was
orally administered 1 h prior to the acquisition trial and the exploration times for the
two identical objects were recorded (Figure 10A). After a 24 h acquisition trial, one
of the familiar objects was replaced with a novel object, the time spent investigating
each of the objects was recorded (Figure 10B), and the novelty discrimination index
(NDI) was calculated as the percentage of novel object interaction time relative to
total interaction time during the retention trial (Figure 10C). As shown in Figure 10A,
oral administration of compound 47 (0.03−0.3 mg/kg) did not significantly affect total
exploration time during the acquisition trial. As shown in Figure 10B, Risperidone
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(0.2 mg/kg) failed to improve cognitive ability, while Rivastigmine can enhance
recognition memory at 0.3 mg/kg. In contrast, rats treated with 0.1 or 0.3 mg/kg of
compound 47 during the retention trial explored the novel object for a longer time,
indicative of preserved memory for the familiar object presented during the
acquisition trial, whereas rats under the vehicle condition or dosed with 0.03 mg/kg of
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compound 47 did not exhibit differences between exploration times for the familiar
and novel objects, indicating deterioration or loss of memory for the familiar object.
In addition, a 0.3 mg/kg oral dose of compound 47 significantly increased the NDI
(Figure 10C). These results suggest that compound 47 enhanced recognition memory
during the NOR task in rats.
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Selectivity profile of compound 47
The interactions between compound 47 and other receptors related to central
nervous system (CNS) disorders were evaluated, a selectivity profile was created
using additional receptors (including the D , 5-HT , α , H , SERT, NET, DAT,
1
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sigma-1 [σ ] and sigma-2 [σ ], muscarinic M and NMDA receptors). Moreover,
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anticholinergic side effects such as dry mouth, constipation and blurred vision were
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induced by the antitargeting muscarinic M receptors.
Compound 47 showed
1
moderate affinities for D and 5-HT receptors (D , K = 76.9 ± 10.3 nM; 5-HT , K =
1
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1
i
7
i
226.0 ± 33.2 nM), with no significant affinity (K > 1000 nM) for any other putative
i
target. Futhurmore, Compound 47 inhibited D receptor by greater than 90% in an
1
antagonist assay and functioned as an antagonist at the D receptor (IC = 366 nM),
1
50
(Supporting Information).
CONCLUSIONS
A new series of fused tricyclic heterocycle piperazine (piperidine) derivatives
was synthesized, and selected candidates were evaluated as potential new
antipsychotic agents. Among this series, compound 47 was favorable for the binding
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to the five (D , D , 5-HT , 5-HT and 5-HT ) receptors. This compound has a
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desirable selectivity profile against other receptors, including 5-HT , histamine H
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and adrenergic α receptors, which are known to be associated with the adverse
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effects of marketed antipsychotics. Compound 47 was a potent antagonist for those
five receptors and was efficacious in animal models of psychoses. Because it reversed
apomorphine- and MK-801-induced motor behavior, and avoidance behavior in the
CAR test, compound 47 appears to be useful for addressing the positive symptoms of
schizophrenia. Additionally, compound 47 displayed low hERG inhibitory activity,
and no tendency to induce catalepsy. Furthermore, compound 47 was evaluated in the
rat NOR test, and improved visual recognition memory was observed 24 h after
training. Compound 47 may promote the development of a unique CNS-active drug
candidate due to its suitable physicochemical, biophysical, and pharmacokinetic
properties. A thorough preclinical profiling of compound 47 and its analogues is
currently ongoing in our lab and further pharmacological details will be reported
soon.
EXPERIMENTAL SECTION
Chemistry. All commercially available chemicals and reagents were used
without further purification. Reagents were all of analytical grade or of chemical
purity (>95%). Melting points were determined in open capillary tubes and
1
uncorrected. H NMR spectra was recorded on a Bruker Avance III 600 spectrometer
1
at 600 MHz ( H) using CDCl or DMSO-d as solvent. Chemical shifts were given in
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d values (ppm), using tetramethylsilane (TMS) as the internal standard; coupling
constants (J) were given in Hz. Signal multiplicities were characterized as s (singlet),
d (doublet), t(triplet), q (quartet), m (multiplet), br (broad signal). Analytical thin
layer chromatography (TLC) was performed on silica gel GF254. Column
chromatographic purification was carried out using silica gel. Compound purity is
determined by high performance liquid chromatography (HPLC), and all final test
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compounds display purity higher than 95%. HPLC methods used the following:
Shimadzu LC-20AD spectrometer; column, Waters XBridgeTM Sheild RP18
(150×4.6mm，3.5μm); mobile phase, 0.01mol/L KH PO ( 0.2 % Et N, pH = 3.5)
2
4
3
aq./acetonitrile (Merck Company, Germany) 20/80; flow rate, 1.0 mL/min; column
o
temperature, 35 C. UV detection was performed at 210 nm.
General Procedures for the Preparation of Intermediates 3.
1
,2,6,7-tetrahydro pyrido[3,2,1-ij]quinolin-3(5H)-one (3a). Conpound 3a was
synthesized by the followed two step reactions according the literatures with
modifications.26, 27 Step 1: To 1,2,3,4-tetrahydroquinoline (5.0 g, 37.5 mmol) was
added acetone (50 ml), and then 3-chloropropionyl chloride (5.1g, 40.5mmol) was
added slowly. The mixture was heated to reflux for 4 h. Then, it was cooled down and
concentrated. The residue was diluted with water (50 mL) and extracted with 75 mL
ethyl acetate by three times. The ethyl acetate layer was dried with anhydrous MgSO4,
the filtrate was removed under reduced pressure. The obtained crude product was
recrystallized from ethyl acetate to give 3-chloro-1-(3,4-dihydroquinolin
o
1
-
1(2H)-yl)propan-1-one as pale white solid. M.P. 79 – 80 C. Yield: 96.4%; H NMR
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(600 MHz, CDCl ) δ 7.24 – 7.05 (m, 4H), 3.87 (t, J = 6.7 Hz, 4H), 3.00 (t, J = 6.7 Hz,
3
2
H), 2.74 (s, 2H), 2.00 (p, J = 6.6 Hz, 2H). MS (ESI) m/z 224.2 (calcd 224.1 for
+
+
C H ClNO [M+H] ). Step 2: The product (8 g, 35.8 mmol) from the first step was
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heated at 100 °C to melt, and then added anhydrous aluminum chloride (7.2 g, 54.1
mmol) by partions. The reaction was then stirred at 100 °C for 3 h. 100 mL ice water
was added to quench the reaction, until the reaction temperature was cooled down.
The reaction mixture was extracted with 75 mL ethyl acetate by three times. The ethyl
acetate layer was dried with anhydrous MgSO , and then removed under reduced
4
pressure after filtration. The crude product was purified via chromatography
(petroleum ether/EtOAc = 6/1) to afford 1,2,6,7-tetrahydropyrido[3,2,1-ij]quinolin
o
1
-3(5H)-one (3a), as a pale white solid. M.P. 68 – 70 C.Yield: 80.0%; H NMR (600
MHz, CDCl ) δ 7.02 (t, J = 6.9 Hz, 2H), 6.93 (t, J = 7.5 Hz, 1H), 3.95 – 3.84 (m, 2H),
3
2
.94 – 2.86 (m, 2H), 2.81 (t, J = 6.3 Hz, 2H), 2.67 (dd, J = 8.4, 6.5 Hz, 2H), 2.02 –
+
+
1.91 (m, 2H). MS (ESI) m/z 188.2 (calcd 188.1 for C H NO [M+H] ).
1
2
14
5
,6-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3b). A pale white solid. M.P.
o
1
74 – 76 C. Yield: 75.0%; H NMR (600 MHz, CDCl ) δ 7.09 (d, J = 6.9 Hz, 1H),
3
7
.00 (dd, J = 7.4, 0.7 Hz, 1H), 6.93 (td, J = 7.4, 1.7 Hz, 1H), 4.09 (dd, J = 11.5, 5.3
Hz, 2H), 3.20 (t, J = 8.4 Hz, 2H), 2.98 (t, J = 7.7 Hz, 2H), 2.69 (dd, J = 10.6, 4.9 Hz,
+
+
2H). MS (ESI) m/z 174.2 (calcd 174.1 for C H NO [M+H] ).
1
1
12
7
-fluoro-5,6-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-2(4H)-one (3c). A pale white
o
1
solid. M.P. 72 – 73 C. Yield: 72.1%; H NMR (600 MHz, CDCl ) δ 7.00 (d, J = 7.4,
3
1
H), 6.63 (d, J = 7.4, 1H), 4.11 (t, J = 8.4 Hz, 2H), 3.20 (t, J = 8.4 Hz, 2H), 2.98 (t, J
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= 7.7 Hz, 2H), 2.69 (dd, J = 10.6, 4.9 Hz, 2H). MS (ESI) m/z 192.2 (calcd 192.1 for
+
+
C H FNO [M+H] ).
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-fluoro-5,6-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-2(4H)-one (3d). A pale white
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solid. M.P. 80 – 81 C. Yield: 70.3%; H NMR (600 MHz, CDCl ) δ 7.09 (d, J = 6.9
3
Hz, 1H), 6.65 (d, J = 7.4, 1H), 4.12 (t, J = 8.4 Hz, 2H), 3.18 (t, J = 8.4 Hz, 2H), 2.98
(t, J = 7.7 Hz, 2H), 2.69 (dd, J = 10.6, 4.9 Hz, 2H). MS (ESI) m/z 192.2 (calcd 192.1
+
+
for C H FNO [M+H] ).
1
1
11
General Procedures for the Preparation of Intermediates 4 , 6 and 7.
-(2-chloroacetyl)-1,2,6,7-tetrahydropyrido[3,2,1-ij]quinolin-3(5H)-one
9
46
(
(
(
4a). To a suspension of 1,2,6,7-tetrahydropyrido[3,2,1-ij]quinolin-3(5H)-one (3a)
5.0 g, 26.7 mmol) in 25mL 1,2-dichloroethane was added 2-chloroacetyl chloride
3.5 g, 23.9 mmol). Anhydrous aluminium trichloride (7.2g, 54.1 mmol) was added
o
by portions under ice-cooling. The reaction mixture was kept at 0-5 C for 30 min
after all AlCl addition and then the reaction was performed at room temperature for 2
3
h. Then the reaction was quenched with 100 mL ice water. The mixture was extracted
with 75 mL dichloromethane by three times. After being dried over MgSO4,
dichloromethane was removed by evaporation. The crude mixture was purified by
chromatography
(petroleum
ether:
EtOAc
=
4:
1)
to
yield
9
-(2-chloroacetyl)-1,2,6,7-tetrahydro pyrido[3,2,1-ij]quinolin-3(5H)-one (4a). A pale
o
1
white solid. M.P. 68 – 70 C. Yield: 70.3 %; H NMR (600 MHz, CDCl ) δ 7.65 (s,
3
1
6
H), 7.64 (s, 1H), 4.66 (s, 2H), 4.03 – 3.81 (m, 2H), 3.06 – 2.94 (m, 2H), 2.87 (t, J =
.2 Hz, 2H), 2.71 (dd, J = 8.5, 6.6 Hz, 2H), 1.99 (dt, J = 12.2, 6.1 Hz, 2H). MS (ESI)
2
9
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