Synthesis and biological evaluation of pyridooxazine-tetrahydroisoquinoline derivatives as MDR modulators

Article abstract of DOI:10.1246/cl.2006.1010

Pyridooxazine-tetrahydroisoquinoline derivatives were designed and synthesized for MDR modulating activity. Pyridooxazin-2-one scaffolds were constructed in a one-pot annulation of N-substituted-2-chloroacetamides with 2-bromo-3-hydroxy pyridine via Smile

Full text of DOI:10.1246/cl.2006.1010

1010
Chemistry Letters Vol.35, No.9 (2006)
Synthesis and Biological Evaluation of Pyridooxazine–Tetrahydroisoquinoline
Derivatives as MDR Modulators
Chen Ma,Ã1 Shao-Jie Liu,1 Liang Xin,1 Qun Zhang,1 Kai Ding,1 J. R. Falck,2 and Dong-Soo ShinÃ3
1School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, P. R. China
2Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, U.S.A.
3Department of Chemistry, Changwon National University, Changwon 641-773, Korea
(Received May 23, 2006; CL-060599; E-mail: chenma@sdu.edu.cn)
Pyridooxazine–tetrahydroisoquinoline derivatives were de-
signed and synthesized for MDR modulating activity. Pyridoox-
azin-2-one scaffolds were constructed in a one-pot annulation of
N-substituted-2-chloroacetamides with 2-bromo-3-hydroxy pyr-
idine via Smiles rearrangement. The Pictet–Spengler cyclization
to form tetrahydroisoquinoline ring afforded target compounds
in 17–37% overall yields. Some of these compounds exhibited
multidrug resistance (MDR) reversing activity.
R1
R4
HO
Br
R1
R4
O
R2
R3
R2
R3
5
Cl
Cl
N
NH
Cl
NH2
O
K2CO3, CH2Cl2
rt
Cs2CO3, CH3CN
reflux
3
4
R1
R1
R2
R3
R2
R3
NaBH4
CH3OH, rt
N
N
HO
R4
Tetrahydroisoquinoline alkaloids are important because of
their occurrence in nature and their physiological properties.1
They possess diverse type of biological activities and are exten-
sively studied over past hundred years. Some tetrahydroisoqui-
noline derivatives such as higenamine, coclaurine, and pyrimi-
doisoquinoline exhibit good biological activities.2
Recently, there has been a growing interest in developing
general and versatile synthetic methods3 for these heterocyclic
systems. As part of our program to the development of novel in-
hibitors of multidrug resistance (MDR) pumps,4 we recently in-
troduced a very efficient entry to the synthesis of tetrahydroiso-
quinolines containing pyridazinone and oxazine moieties 1.5
Herein, we report the synthesis and biological evaluation of
tetrahydroisoquinolines containing pyridine and oxazine moie-
ties 2 (Figure 1).
O
R4
O
N
O
N
6
7
R1
R2
R3
BF3-(C2H5)2O
CH2Cl2, rt
N
O
R4
N
2
Scheme 1.
2a: R1 = R4 = H, R2 = R3 = OCH3
2b: R1 = R4 = H, R2 = OCH3, R3 = CH3
2c: R1 = R3 = R4 = H, R2 = OCH3
2d: R1 = R3 = CH3, R2 = OCH3, R4 =H
2g: R1 = H, R2 = R3 = R4 = OCH3
2h: R1 = R4 = H, R2 = OCH3, R3 = Cl
2i: R1 = R3 = R4 = H, R2 = N(C2H5)2
2j: R1 = R4 = H, R2 = N(C2H5)2, R3 = C2H5
R1
R4
R2
R3
N
O
R1
R2
H3CO
N
N
N
O
H3CO
2
R3
N
N
R4
O
O
O
O
R
N
O
N
N
O
1
2
Figure 1.
O
N
O
N
2e
2f
The synthesis of target compounds 2 was showed in
Scheme 1. By inference, substituted phenylethylamines 3 were
defined as the starting materials. Reaction of substituted phenyl-
ethylamines 3 with 2-chloroacetyl chlorides in dichloromethane
in the presence of potassium carbonate afforded 2-chloroacet-
amides 4 in excellent yields. The reactions occurred at room
temperature for 12 h or at reflux for 2 h. Then, reaction of 2-
chloroacetamides 4 with 2-bromo-3-hydropyridine 5 furnished
pyridooxazin-2-ones 6. The cyclization occurred smoothly in
the presence of cesium carbonate at refluxing acetonitrile via
Smiles rearrangement.6
Figure 2.
the corresponding reducing products 7 in good yield. Towards
the end of the subjection, the treatment of 7 with Lewis acids
such as boron trifluoride–ether in dichloromethane by Pictet–
Spengler cyclization afforded the desired target compounds 2
in 17–37% overall yields (Figure 2). The structures of the
compounds 2 were confirmed by IR, H NMR, 13C NMR, and
elemental analyses.
The appearance of tumor cell resistant to range of cytotoxic
drugs is a serious problem in cancer chemotherapy. This
phenomenon is called MDR. Recently, Robert has reviewed a
1
Reduction of pyridooxazin-2-ones 6 in the presence of
sodium borohydride in methanol at room temperature afforded
Copyright ꢀ 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.9 (2006)
1011
Table 1. The effect of compounds (2a–2j) on the cellular
accumulation of VCR in multidrug-resistant MCF7-ADR human
breast cancer cells
2h showed very potent cytotoxicity while compounds 2e, 2f,
2i, and 2j did not show such cytotoxicity. Replacement of me-
thoxy substituent by alkyl substituent seemed to have a negative
effect (2b and 2d), while the presence of more methoxy substitu-
ents appeared to obviously enhance the activity (2g). The com-
pound 2h (replacement of a methoxy substituent by chlorine) ex-
hibited the most effective activity among these compounds.
In conclusion, the first total synthesis of pyridooxazine–
tetrahydroisoquinolines proceeded efficiently in high overall
yields via Smiles rearrangement and Pictet–Spengler cycliza-
tion. These compounds were evaluated for the discovery of
new multidrug resistance reversal agents. Some compounds
exhibited good activity as modifiers of multidrug resistance.
The results suggested that the introduction of polyalkoxy groups
on phenyl ring was effective for overcoming multidrug resist-
ance. In particular, the compound 2g with trimethoxy groups
on phenyl ring showed the high MDR-modulating activity and
cytotoxic activity, indicating a new drug candidate for MDR
cancer chemotherapy.
VCR accumulationa with a compound concentration of
Compound
1 mg/mL
10 mg/mL
2a
104
135
157
136
115
73
238
192
146
179
362
334
381
125
101
92
2b
2c
2d
2e
2f
2g
141
95
2h
2i
2j
118
97
Verapamil
103
353
aThe amounts of VCR accumulated in multidrug-resistant MCF7-ADR
human breast cancer cells were examined in the presence of 1 and
10 mg/mL of pyridooxazine–tetrahydroisoquinolines. The values ex-
pressed as the relative amounts of VCR accumulated in cancer cells
as compared with the control experiment.
The authors thank the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry
(2004-527) and the Excellent Young Scientist Awarded Founda-
tion of Shandong Province (2005BS11007) for financial assis-
tance.
number of MDR reversing agents for clinical trials.7 However,
the development of new MDR modulators is still in its infancy.
Previously, we reported the inhibitory activity of compounds 1.5
Herein, we observed promising activity of compounds 2 in
reversing MDR.
The effect of compounds (2a–2j) on the cellular accumula-
tion of vincristine (VCR) in multidrug-resistant MCF7-ADR
human breast cancer cells was examined and the results were
showed in Table 1. Verapamil at 1 and 10 mg/mL increased
the VCR accumulation in a dose dependent manner. Among
these compounds, 2a, 2e, 2f, and 2g increased the VCR accumu-
lation as potent as verapamil. Compounds 2b, 2d, and 2h in-
creased moderately the accumulation, while compounds 2c, 2i,
and 2j decreased the VCR accumulation in MCF7-ADR human
breast cancer cells. The results showed that potent compounds
possess polyalkoxy substituents on phenyl ring.
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Table 2. Cytotoxic activity of compounds (2a–2j) against
leukemia HL60 cells and human epidermoid carcinoma KB cells
HL60
IC50 (mg/mL)a
KB
IC50 (mg/mL)a
Compound
2a
2b
2c
2d
2e
2f
8.5
>20
>20
13.4
>20
>20
4.3
3.1
14.2
>20
7.6
4
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>20
1.9
2g
2h
2i
5
6
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1.2
>20
>20
>20
>20
2j
aAll the IC50 values in this text represent the mean of a minimum of
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7
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Published on the web (Advance View) July 29, 2006; doi:10.1246/cl.2006.1010