Novel Rhein Analogues as Potential Anticancer Agents

Article abstract of DOI:10.1002/cmdc.201100384

Two series of rhein analogues were synthesized with modification at the 3-position. Their cytotoxicities were evaluated using an MTT assay. Among all the compounds synthesized, one compound showed the best potency, with an IC₅₀ value of 2.7μM a

Full text of DOI:10.1002/cmdc.201100384

MED
DOI: 10.1002/cmdc.201100384
Novel Rhein Analogues as Potential Anticancer Agents
Xiaochuan Yang,[a] Guojing Sun,[a] Chunhao Yang,*[a, b] and Binghe Wang*[a]
Two series of rhein analogues were synthesized with modifica-
tion at the 3-position. Their cytotoxicities were evaluated using
an MTT assay. Among all the compounds synthesized, one
compound showed the best potency, with an IC50 value of
2.7 mm against the HeLa cell line and 0.6 mm against the
MOLT4 cell line.
Introduction
Rhein is a natural product isolated from rhubarb (Rheum pal-
matum) that has an anthraquinone scaffold. Studies have
shown that it has moderate anticancer activities against vari-
ous tumor cell lines[1] and is very well tolerated by the human
body when used as a laxative.[2] The anticancer properties of
rhein are less well studied[2b] than those of other anthraqui-
none compounds extracted from rhubarb, such as emodin and
aloe-emodin.[3] Various mechanisms of action have been pro-
posed for rhein based on its cytotoxic effect through the in-
duction of apoptosis,[1a,c,4] p53 up-regulation,[4] inhibition of
ERK phosphorylation,[2a] disruption of mitochondrial func-
tion,[1c,5] and impairment of glucose uptake,[6] among others.[2b]
Despite all these studies, the low-to-moderate activity of rhein
(IC50: 12–100 mm)[1] against tumors means that no further de-
velopment is warranted until its potency can be improved.[2b]
In contrast, several highly potent anthraquinone compounds
such as mitoxantrone and doxorubicin have already been ap-
proved for clinical use. However, many such approved anthra-
quinone drugs have severe cardiac toxicity problems.[7] Fur-
A commonly proposed mechanism for the cytotoxicity of an-
thraquinone compounds is their noncovalent binding to DNA
duplexes, probably through intercalation.[3c,d,9] The binding
event could distort the DNA conformation, leading to subse-
quent inhibition of DNA topoisomerase activities.[3d,9,10] Be-
cause the overall planar structure of anthraquinone is most
likely responsible for its cytotoxicity, we purposely avoided
modifications to this part. Thus, in this study two series of
rhein analogues were designed through modification at the 3-
position. The first series represents replacement of the 3-car-
boxyl group of rhein with an aromatic ring for increased diver-
sity (Scheme 1). The second series features conversion of the
Scheme 1. Synthesis of rhein analogues. Reagents and conditions: a) NaH,
MeI, DMF, ice bath, overnight; b) NaOH in H2O/EtOH, 508C, 1 h; c) Et3N,
Ph2PON3, DMF, RT, 1 h; d) dioxane, reflux, 30 min; e) NaOH in H2O, reflux, 4 h;
f) isopentyl nitrite, CH2I2, THF, 50–608C, 2 days; g) RB(OH)2, Pd(PPh3)4, K2CO3,
DMF, 70–808C; h) PhSH, K2CO3, NMP, 140–1608C.
[a] Dr. X. Yang,+ Dr. G. Sun,+ Dr. C. Yang, Prof. B. Wang
Department of Chemistry and Center for Diagnostics and Therapeutics
Georgia State University, 100 Piedmont Ave., Atlanta, GA 30303-4098 (USA)
E-mail: wang@gsu.edu
thermore, the complex structure of doxorubicin, along with its
main source being from biosynthesis, makes it very costly.[8]
Therefore, we are interested in the development of anthraqui-
none-based anticancer drugs by starting from the rhein scaf-
fold, because it has shown some promise, bears structural simi-
larity to other anthraquinone drugs, is well tolerated in
humans, and is structurally fairly simple. Herein we report the
optimization of rhein at the 3-position.
[b] Dr. C. Yang
State Key Laboratory of Drug Research
Shanghai Institute of Materia Medica
555 Zu Chong Zhi Rd., Shanghai, 21203 (P.R. China)
E-mail: chyang@mail.shcnc.ac.cn
[+] These two authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cmdc.201100384.
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Rhein Analogues as Anticancer Agents
3-carboxyl group into an amide side chain, which is further de-
rivatized with secondary amines, with the purpose of increas-
ing diversity, water solubility, and potential ionic interactions
with the DNA phosphate backbone.[3c,9,11]
with 5d, with replacement of the fluorine atom on the pyri-
dine ring by thiophenol. The demethylation of 5 f was particu-
larly sensitive to experimental conditions. Heating at 1508C for
20 min selectively removed the methyl groups from both pro-
tected anthraquinone hydroxy groups to yield 6 f as the prod-
uct, leaving the methyl group on ꢀR intact. Further demethy-
lation of 6 f to 6g was achieved by increasing the temperature
to 170–1808C and increasing the reaction time to 1 h. Mean-
while, deprotection of compounds 5g–i was unsuccessful; the
reaction did not generate the expected products probably be-
cause the thiophenol demethylation conditions were too
harsh, leading to degradation.
Results and Discussion
Synthesis of the first series of analogues started with methyla-
tion of the phenolic hydroxy groups using iodomethane. This
was followed by conversion of the 3-carboxyl group into an
acyl azide (compound 2). After Curtius rearrangement in diox-
ane and hydrolysis in a solution of sodium hydroxide, com-
pound 3 was obtained with an amino group at the 3-position.
An iodo group was introduced through a Sandmeyer-like reac-
tion of 3 with isopentyl nitrite and diiodomethane in tetrahy-
drofuran. The aromatic groups were installed at the 3-position
through Suzuki coupling of iodo compound 4 with the appro-
priate boronic acids. Afterward, the final products were ob-
tained through deprotection of the hydroxy groups with thio-
phenol in the presence of potassium carbonate in N-methyl-2-
pyrrolidone (Table 1). Compound 4 was also subjected to thio-
phenol-mediated demethylation, but the iodine atom was re-
placed by thiophenol in the reaction, probably through an ad-
dition/elimination reaction due to the strong nucleophilicity of
the deprotonated thiophenol. A similar reaction also occurred
Two cancer cell lines, HeLa and MOLT4, were chosen for cy-
totoxicity evaluations, representing adherent tumor cells and
suspension tumor cells, respectively. MTT assays were per-
formed for quantitative evaluation of in vitro cytotoxicity.[12]
Test results of this series of analogues showed that the most
potent compound, 4a, has an IC50 value at the single-digit mi-
cromolar level against both HeLa and MOLT4 cell lines
(Figure 1). Relative to rhein, the potency increased by at least
30-fold in both cancer cell types with introduction of a phenyl-
thio group at the 3-position. However, the rest of the com-
pounds did not show such improved activity, particularly in
the MOLT4 cell line (Table 2). Analogues 6b and 6c even
showed decreased cytotoxicity against MOLT4 relative to rhein.
In HeLa cells, 6a, 6c, and 6g
showed
a moderate improve-
Table 1. Demethylation reactions in the synthesis of series 1 rhein analogues.
ment in potency. Interestingly,
the difference between 6 f and
6g, with demethylation of the
phenol hydroxy group at the 3-
position, leads to a ~10-fold in-
crease in potency against HeLa
cells. Previous studies have re-
ported that hydroxyanthraqui-
nones with a 3-hydroxy group
have greater anticancer potency
Methylated
R
Demethylated
R’
Yield [%]
54
4
4a
5a
5b
6a
6b
41
47
5c
5d
5e
6c
6d
6e
71
47
78
than those with
a methoxy
group at the 3-position.[1e] Here
we observed similar phenomena
with the side chain phenol hy-
droxy group. In general, for this
series of analogues, direct at-
tachment of an aromatic ring to
the anthraquinone at the 3-posi-
tion does not result in increased
potency. This might be due to
the planar structure of anthra-
quinone being compromised by
steric strain around the biaryl Cꢀ
C bond, leading to decreased
DNA intercalation.[10] Spacing the
aromatic ring away from anthra-
quinone by one sulfur atom ap-
pears to greatly alleviate this sit-
uation.
5 f
6 f
6 f
61
28
6g
5g
5h
–
NA[a]
NA
–
–
NA
NA
NA
NA
5i
[a] NA: not applicable.
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Scheme 2. Synthesis of series 2 rhein analogues. Reagents and conditions:
a) PhSH, K2CO3, NMP, 150–1608C, 1 h; b) chloroacetyl chloride, dioxane, RT,
2 h; c) secondary amine, dioxane, 80–908C.
Figure 2. Series 2 rhein analogues 9a–d.
Figure 1. MTT assay dose–response curves of a) HeLa and b) MOLT4 cells in
the presence of rhein [ : a) IC50 =3.7ꢁ10ꢀ4 m, b) IC50 =3.7ꢁ10ꢀ5 m] and com-
&
pound 4a [ : a) IC50 =3.4ꢁ10ꢀ6 m, b) IC50 =1.4ꢁ10ꢀ6 m].
~
series of analogues were evaluated by using the same method
as for the first series. Generally speaking, compounds in this
second series have much greater potency than the first series.
Among all analogues, compound 8 showed the best activity
(Table 3). The IC50 value of 8 against HeLa approaches that of
the positive control, doxorubicin (Figure 3), and 8 is the only
compound among all the analogues with a sub-micromolar
IC50 value against the MOLT4 cell line. The potent activity of 8
might be attributed to its unique structural feature of combin-
ing an alkylating agent with an intercalation moiety. Such a
proposition has been made in earlier studies.[3a] At this point, it
is important to note that a-chloroacetamide alone is not ex-
Table 2. Cytotoxicity evaluation of series 1 rhein analogues by MTT assay.
IC50 [mm]
Compd
HeLa
MOLT4
Rhein
4a
6a
6b
6c
6d
6e
>100
37
1.4
14[b]
>100[a,b]
>100
35
3.4
16
>100[a,b]
68
>100
>100
>100[a,b]
9.9
22
6 f
6g
29[b]
21[b]
[a] The actual IC50 value should be >100 mm, as fewer than 50% of cells
were killed even at the highest concentration. [b] R2 <0.8 for nonlinear
regression in sigmoidal model fitting; see Supporting Information for fur-
ther details.
Table 3. Cytotoxicity evaluation of series 2 rhein analogues by MTT assay.
IC50 [mm]
Compd
HeLa
MOLT4
rhein
>100
37
7
17
10
8
9a
9b
9c
9d
2.7
6.1
5.8
13[a]
33
0.6
3.0
3.1
25
4.1
0.04
The second series of compounds was designed with a focus
on modifying the 3-amine of rhein analogues. As illustrated in
Scheme 2, compound 7 was obtained after demethylation of 3
using the same method as for the first series of analogues. The
3-amino group of 7 was acylated with chloroacetyl chloride to
yield 8. Four secondary amines were then treated with amide
8 to give compounds 9a–d (Figure 2). The cytotoxicities of this
doxorubicin
0.98
[a] R2 <0.8 for nonlinear regression in sigmoidal model fitting; see Sup-
porting Information for further details.
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Rhein Analogues as Anticancer Agents
Conclusions
In summary, two series of rhein analogues were synthesized
through modification at the 3-position. Their cytotoxicities
were determined by MTT assays against the HeLa and MOLT4
cell lines. Among all 14 compounds generated, compounds 4a
and 8 stood out for their significantly higher cytotoxicity than
the others. Especially important is compound 8, which has an
IC50 value similar to that of doxorubicin against HeLa cells and
is active at sub-micromolar concentrations against MOLT4.
Experimental Section
Chemistry
General: Rhein was purchased from Nanjing ZeLang Medical Tech-
nology Co. (P.R. China) and used directly without further purifica-
tion. Other starting materials and solvents were purchased from Al-
drich or Acros. For all reactions, analytical grade solvents were
used. Anhydrous solvents were used for all moisture-sensitive reac-
1
tions. H and 13C NMR spectra were recorded on a Bruker 400 NMR
spectrometer in deuterated solvent with TMS (d=0.00 ppm) or re-
sidual solvent as the internal reference. Deuterium solvents were
purchased from Cambridge Isotope Laboratories, Inc. Mass spectra
were recorded on a Waters Micromass LC-Q-TOF micro-spectrome-
ter or an ABI4800 MALDI-TOF-TOF mass spectrometer at the Geor-
gia State University Mass Spectrometry Facilities.
1,8-Dimethoxy-3-methylcarboxylate-anthraquinone: Rhein (10 g,
35 mmol) was suspended in dry DMF (300 mL) in a round-bottom
flask, and the mixture was cooled in an ice bath under N2. The sus-
pension was treated with NaH (9 g, 225 mmol; 60% dispersed in
mineral oil) and the color of the mixture turned from yellow to
deep red. The reaction flask outlet was connected to a bubbler
sealed with mineral oil. As the bubbling reached a steady and slow
speed, MeI (18 mL, 290 mmol) was added through a syringe in one
shot. The mixture was kept in the ice bath, with the reaction tem-
perature slowly increasing to RT as the ice melting away. After stir-
ring overnight, the reaction mixture was diluted with H2O (1 L),
and the aqueous suspension was repeatedly extracted with CH2Cl2
(1ꢁvol) until TLC indicated no significant amount of product in the
extraction. The combined organic extracts were concentrated to
~250 mL. MeOH (4ꢁvolume) was added to dilute the solution, and
the mixture was cooled at 48C in a refrigerator. The desired prod-
uct precipitated from solution as a yellow solid (8.9 g, 77%).
1H NMR (400 MHz, CDCl3): d=8.46 (d, 1H, J=1.6 Hz), 7.94 (d, 1H,
J=1.2 Hz), 7.87–7.85 (dd, 1H, J=0.8, 7.6 Hz), 7.67 (t, 1H, J=
8.0 Hz), 7.32 (d, 1H, J=8.4 Hz), 4.07 (s, 3H), 4.02 (s, 3H), 4.00 ppm
(s, 3H); 13C NMR (100 MHz, CDCl3): d=183.3, 182.4, 165.6, 159.7,
135.0, 134.9, 134.8, 134.4, 126.9, 124.0, 120.0, 119.2, 118.4, 118.3,
56.9, 56.7, 52.9 ppm; HRMS: m/z [M+H]+ calcd for C18H15O6:
327.0869, found: 327.0857.
Figure 3. MTT assay dose–response curves of a) HeLa and b) MOLT4 cells in
the presence of compound 8 [ : a) IC50 =2.7ꢁ10ꢀ6 m, b) IC50 =6.3ꢁ10ꢀ7 m]
&
and doxorubicin [ : a) IC50 =9.8ꢁ10ꢀ7 m, a) IC50 =3.8ꢁ10ꢀ8 m].
~
pected to be able to account for the observed cytotoxicity, as
published studies have shown that it is only mildly cytotoxic,
with an IC50 value of ~0.1 mm (against CHO cells).[13] Besides 8,
compound 7 also showed higher potency than most com-
pounds in the first series except 4a. These phenomena sug-
gest that the amine/amide modification has an improved
chance of success than aryl derivatization at the 3-position.
Previous reports by other research groups suggest that the
ring structure side chains are not critical for the high cytotoxic-
ity of these anthraquinone compounds,[14] and the dicationic
side chain gives better activity than the monocationic ones.[3c]
In the second series, we found that 9b shows better activity
than 9c and 9d, but similar activity to that of 9a. Compound
9b shares similar structural features with mitoxantrone, but it
has a cyclic instead of a linear diaminoalkyl side chain. There
have been previous studies on the anticancer properties of
aminoanthraquinone, but the alkylamino side chains were
functionalized at the 1, 2, 4, 5, and 8-position(s).[3c,9,11,14,15]
Herein we demonstrate that 3-position amine/amide modifica-
tion can also significantly potentiate the anticancer activity of
anthraquinone.
1,8-Dimethoxy-3-carboxy-anthraquinone: 1,8-Dimethoxy-3-meth-
ylcarboxylate-anthraquinone (8.9 g, 27 mmol) was suspended in
EtOH (45 mL) and treated with a solution of NaOH in EtOH/H2O
(0.46m, 90 mL, 1:1 v/v). The mixture was stirred at 508C for 1 h,
and the reaction color turned from yellow to deep red. The sus-
pension was cooled in an ice bath and acidified with HCl (1m). The
solution color changed to light yellow and precipitation was ob-
served. The precipitate was isolated by filtration to give the desired
product as
[D6]DMSO): d=8.17 (d, 1H, J=1.6 Hz), 7.89 (d, 1H, J=1.2 Hz),
a
yellow solid (8.9 g, 100%). 1H NMR (400 MHz,
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7.76–7.69 (m, 2H), 7.54 (d, 1H, J=8.0 Hz), 3.99 (s, 3H), 3.93 ppm (s,
3H); 13C NMR (100 MHz, [D6]DMSO): d=182.5, 180.6, 165.6, 158.8,
158.7, 135.4, 134.3, 134.2, 133.9, 126.1, 123.4, 119.1, 118.4, 118.2,
118.1, 56.4, 56.3 ppm; HRMS (ESIꢀ): m/z [MꢀH]ꢀ calcd for C17H12O6:
311.0556, found: 311.0547.
1,8-Dimethoxy-3-(3’,5’-dimethyl-isoxazol-4’-yl)anthraquinone
(5a): Yield: 50 mg, 92%. 1H NMR (400 MHz, CDCl3): d=7.84–7.82
(dd, 1H, J=0.8, 7.6 Hz), 7.73 (d, 1H, J=1.6 Hz), 7.65 (t, 1H, J=
8.0 Hz), 7.34–7.31 (dd, 1H, J=0.8, 8.4 Hz), 7.14 (d, 1H, J=1.6 Hz),
4.02 (s, 3H), 4.01 (s, 3H), 2.48 (s, 3H), 2.33 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=183.9, 182.5, 166.5, 160.0, 159.7, 158.3, 136.7,
135.3, 134.8, 134.2, 124.0, 123.2, 119.3, 119.2, 118.5, 118.2, 115.8,
56.8, 56.7, 12.0, 11.1 ppm; HRMS (ESI+): m/z [M+H]+ calcd for
C21H18NO5: 364.1185, found: 364.1169.
1,8-Dimethoxy-anthraquinone-3-carboxyl azide (2): 1,8-Dime-
thoxy-3-carboxy-anthraquinone (8.9 g, 28 mmol) was dissolved in a
mixture of DMF (93 mL) and Et3N (4.1 mL, 57 mmol). The deep red
solution was cooled in an ice bath and treated dropwise with di-
phenylphosphoryl azide (6.2 mL, 29 mmol) while stirring. The solu-
tion was warmed to RT and stirred for 1 h. The mixture was diluted
with H2O (1.2 L), and the suspension was filtered to give the de-
1,8-Dimethoxy-3-(thiophen-2’-yl)anthraquinone
(5b):
Yield:
1
45 mg, 87%. H NMR (400 MHz, CDCl3): d=8.08 (d, 1H, J=2.0 Hz),
7.87–7.85 (dd, 1H, J=0.8, 7.6 Hz), 7.65 (t, 1H, J=8.0 Hz), 7.55–7.54
(dd, 1H, J=1.2, 3.6 Hz), 7.46 (d, 1H, J=1.2 Hz), 7.43–7.42 (dd, 1H,
J=0.8, 5.2 Hz), 7.32 (d, 1H, J=8.0 Hz), 7.17–7.15 (dd, 1H, J=4.8,
3.6 Hz), 4.08 (s, 3H), 4.02 ppm (s, 3H); 13C NMR (100 MHz, CDCl3):
d=184.1, 182.4, 160.4, 159.8, 142.5, 139.9, 135.5, 134.9, 134.0,
128.7, 127.3, 125.6, 124.2, 122.8, 119.2, 118.5, 116.3, 114.6, 56.8,
56.7 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C20H15O4S:
351.0691, found: 351.0682.
sired product as
a
light yellow solid (9.0 g, 94%). 1H NMR
(400 MHz, CDCl3): d=8.43 (d, 1H, J=1.6 Hz), 7.90 (d, 1H, J=
1.2 Hz), 7.86–7.84 (dd, 1H, J=0.8, 7.6 Hz), 7.67 (t, 1H, J=8.0 Hz),
7.33 (d, 1H, J=8.0 Hz), 4.07 (s, 3H), 4.02 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=183.1, 182.3, 171.4, 159.9, 159.8, 135.3, 135.1,
134.7, 134.6, 127.8, 124.0, 120.0, 119.3, 118.5, 117.6, 57.1, 56.8 ppm;
HRMS (ESI+): m/z [M+H]+ calcd for C17H12N3O5: 338.0777, found:
338.0769.
1,8-Dimethoxy-3-(4’-dimethylamino-3’-methylphenyl)anthraqui-
1
none (5c): Yield: 63 mg, 100%. H NMR (400 MHz, CDCl3): d=8.05
1,8-Dimethoxy-3-aminoanthraquinone (3): Acyl azide 2 (9.0 g,
27 mmol) was refluxed in dry dioxane (200 mL) for 30 min under
N2. TLC monitoring showed the disappearance of 2. The mixture
was concentrated in vacuo and diluted with aq NaOH (1m,
400 mL). The suspension was refluxed for 4 h and then cooled to
RT. The precipitate was removed by filtration, rinsed with acetone,
and discarded. The filtrate was extracted repeatedly with CH2Cl2
(1ꢁvol) until TLC indicated no significant amount of product in the
extraction, and the organic layers were combined and concentrat-
ed in vacuo to give the desired product as a deep red solid (4.0 g,
(d, 1H, J=1.6 Hz), 7.86–7.84 (dd, 1H, J=1.2, 7.6 Hz), 7.62 (t, 1H, J=
8.0 Hz), 7.51–7.48 (m, 2H), 7.45 (d, 1H, J=1.6 Hz), 7.31–7.29 (dd,
1H, J=0.8, 8.4 Hz), 7.10 (d, 1H, J=8.0 Hz), 7.17–7.15 (dd, 1H, J=
4.8, 3.6 Hz), 4.07 (s, 3H), 4.01 (s, 3H), 2.77 (s, 6H), 2.41 ppm (s, 3H);
13C NMR (100 MHz, CDCl3): d=184.4, 182.8, 160.3, 159.7, 153.8,
146.9, 135.1, 135.0, 133.9, 132.8, 132.4, 130.2, 125.4, 124.3, 122.2,
119.2, 118.8, 118.3, 117.3, 115.9, 56.8, 56.7, 44.1, 19.1 ppm; HRMS
(ESI+): m/z [M+H]+ calcd for C25H24O4N: 402.1705, found:
402.1704.
1
53%). H NMR (400 MHz, CDCl3): d=7.78 (d, 1H, J=7.6 Hz), 7.55 (t,
1,8-Dimethoxy-3-(6’-fluoropyridin-3’-yl)anthraquinone
(5d):
1
1H, J=8.0 Hz), 7.25 (m, 1H), 7.03 (d, 1H, J=2.0 Hz), 6.44 (d, 1H,
J=2.0 Hz), 3.96 (s, 3H), 3.91 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3): d=184.8, 181.8, 162.3, 159.8, 151.9, 136.6, 135.0, 133.3,
124.5, 119.1, 118.6, 115.7, 104.7, 102.7, 56.8, 56.5 ppm; HRMS
(ESI+): m/z [M+H]+ calcd for C16H14NO4: 284.0923, found:
284.0914.
Yield: 46 mg, 99%. H NMR (400 MHz, CDCl3): d=8.53 (d, 1H, J=
1.6 Hz), 8.10 (td, 1H, J=2.0, 8.0 Hz), 8.01 (d, 1H, J=1.6 Hz), 7.86 (d,
1H, J=8.0 Hz), 7.67 (t, 1H, J=8.0 Hz), 7.42 (s, 1H), 7.33 (d, 1H, J=
8.4 Hz), 7.01–7.07 (dd, 1H, J=2.8, 8.8 Hz), 4.09 (s, 3H), 4.03 ppm (s,
3H); 13C NMR (100 MHz, CDCl3): d=184.0, 182.5, 160.5, 159.8,
146.5, 146.3, 142.4, 140.2, 140.1, 135.6, 134.9, 134.3, 133.3, 124.1,
123.6, 119.3, 118.6, 117.6, 116.2, 110.3, 109.9, 57.0, 56.8 ppm; HRMS
(ESI+): m/z [M+H]+ calcd for C21H15NO4F: 364.0985, found:
364.0977.
1,8-Dimethoxy-3-iodo-anthraquinone (4): Aminoanthraquinone 3
(2.0 g, 7.1 mmol), isopentyl nitrite (6.0 mL, 45 mmol) and diiodome-
thane (15 mL, 186 mmol) were mixed and stirred in dry THF
(200 mL) at 50–608C for 2 days under N2. The mixture was concen-
trated in vacuo, and the residue was purified by column chroma-
tography (EtOAc/hexane, 1:1) to give the desired product as a
1,8-Dimethoxy-3-(4’-tert-butoxymethyl-phenyl)anthraquinone
1
(5e): Yield: 30 mg, 55%. H NMR (400 MHz, CDCl3): d=8.06 (s, 1H),
7.85 (s,1H, J=5.2 Hz), 7.65 (s, 3H), 7.47 (s, 3H), 7.30 (m, 1H), 4.52
(s, 2H), 4.07 (s, 3H), 4.01 (s, 3H), 1.32 ppm (s, 9H); 13C NMR
(100 MHz, CDCl3): d=184.3, 182.8, 160.2, 159.7, 146.8, 141.1, 138.2,
135.2, 135.0, 134.0, 128.2, 127.3, 124.2, 122.7, 119.2, 118.3, 117.6,
116.4, 73.8, 63.9, 56.8, 56.7, 27.9 ppm; HRMS (ESI+): m/z [M+H]+
calcd for C27H27O5: 431.1858, found: 431.1863.
1
yellow solid (1.4 g, 50%). H NMR (400 MHz, CDCl3): d=8.14 (d, 1H,
J=1.6 Hz), 7.80–7.78 (dd, 1H, J=0.8, 8.0 Hz), 7.64 (t, 1H, J=
8.0 Hz), 7.60 (d, 1H, J=1.2 Hz), 7.30 (d, 1H, J=8.0 Hz), 4.00 (s, 3H),
3.99 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=182.9, 182.3, 159.7,
159.6, 135.0, 134.3, 128.2, 127.1, 123.8, 123.3, 119.2, 118.5, 100.7,
57.0, 56.7 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C16H12O4I:
394.9780, found: 394.9785.
1,8-Dimethoxy-3-(4’-methoxyphenyl)anthraquinone (5 f): Yield:
1
56 mg, 98%. H NMR (400 MHz, CDCl3): d=8.03 (d, 1H, J=1.6 Hz),
7.86–7.84 (dd, 1H, J=1.2, 7.6 Hz), 7.63 (m, 3H, J=8.4, 7.6 Hz), 7.43
(d, 1H, J=2.0 Hz), 7.30 (d, 1H, J=8.4 Hz), 7.01 (d, 2H, J=8.8 Hz),
4.07 (s, 3H), 4.01 (s, 3H), 3.87 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3): d=184.4, 182.8, 160.5, 160.3, 159.7, 146.5, 135.2, 135.1,
134.0, 131.7, 128.6, 124.2, 122.3, 119.2, 118.4, 117.2, 115.8, 114.7,
56.8, 56.7, 55.6 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C23H19O5:
375.1232, found: 375.1247.
General procedure for the synthesis of 5a–i by Suzuki coupling
of
4 with RB(OH)2: A mixture of 4 (0.13 mmol), RB(OH)2
(0.23 mmol), Pd(PPh3)4 (0.013 mmol) and K2CO3 (0.38 mmol) in dry
DMF (5 mL) was heated at 70–808C for 1!16 h under N2. The mix-
ture was then diluted with CH2Cl2 (40 mL) and washed with H2O (2
or 3ꢁ50 mL). The organic layer was concentrated in vacuo, and
the residue was purified by column chromatography (EtOAc/
hexane or EtOAc/CH2Cl2). After removal of the solvent, the solid
was further purified by dissolving in a minimal amount of CH2Cl2
and then precipitated through hexane addition.
1,8-Dimethoxy-3-(4’-acetylphenyl)anthraquinone (5g): Yield:
50 mg, 81%. 1H NMR (400 MHz, CDCl3): d=8.07–8.05 (m, 3H, J=
1.6, 8.0 Hz), 7.85–7.83 (dd, 1H, J=0.8, 7.6 Hz), 7.76 (d, 2H, J=
2298
www.chemmedchem.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2011, 6, 2294 – 2301

Rhein Analogues as Anticancer Agents
8.4 Hz), 7.65 (t, 1H, J=8.4, 7.6 Hz), 7.48 (d, 1H, J=1.6 Hz), 7.32 (d,
1H, J=8.0 Hz), 4.09 (s, 3H), 4.02 (s, 3H), 2.66 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=197.7, 184.0, 182.6, 160.3, 159.8, 145.4, 143.7,
137.2, 135.3, 134.9, 134.2, 129.2, 127.6, 124.1, 123.4, 119.2, 118.4,
117.9, 116.5, 56.9, 56.7, 26.9 ppm; HRMS (ESI+): m/z [M+H]+ calcd
for C24H19O5: 387.1232, found: 387.1241.
1H, J=8.4 Hz), 7.53–7.49 (m, 2H), 7.42 (s, 1H), 7.26 (d, 1H, J=
8.4 Hz), 7.06 (d, 1H, J=8.0 Hz), 2.80 (s, 6H), 2.40 ppm (s, 3H);
13C NMR (100 MHz, CDCl3): d=192.3, 182.1, 163.2, 162.6, 154.5,
150.0, 137.0, 133.9, 133.8, 132.2, 131.4, 130.3, 125.5, 124.7, 120.7,
120.2, 118.7, 118.6, 116.2, 114.2, 44.0, 19.2 ppm; HRMS (ESIꢀ): m/z
[M+H]+ calcd for C23H20O4N: 374.1392, found: 374.1397.
1,8-Dimethoxy-3-(furan-2’-yl)anthraquinone (5h): Yield: 34 mg,
78%. 1H NMR (400 MHz, CDCl3): d=8.06 (s, 1H), 7.83 (d, 1H, J=
7.6 Hz), 7.61–7.52 (m, 3H), 7.27 (t, 1H, J=8.4, 4.0 Hz), 6.88 (d, 1H,
J=3.2 Hz), 6.52 (s, 1H), 4.05 (s, 3H), 3.99 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3): d=184.0, 182.0, 160.7, 160.0, 152.6, 143.8, 136.0,
135.7, 135.2, 133.8, 124.8, 123.0, 119.4, 118.9, 114.7, 112.8, 112.5,
108.8, 56.9 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C20H15O5:
335.0919, found: 335.0935.
1,8-Dihydroxy-3-(6’-phenylthio-pyridin-3’-yl)anthraquinone (6d):
Yield: 11 mg, 47%. 1H NMR (400 MHz, CDCl3): d=12.01 (s, 1H),
11.98 (s, 1H), 8.76 (s, 1H), 8.00 (d, 1H, J=1.6 Hz), 7.83 (dd, 1H, J=
1.2, 7.6 Hz), 7.74 (dd, 1H, J=2.4, 8.4 Hz), 7.68–7.62 (m, 3H), 7.45–
7.43 (m, 4H), 7.29 (dd, 1H, J=1.2, 8.4 Hz), 7.03 ppm (d, 1H, J=
8.4 Hz); 13C NMR (100 MHz, CDCl3): d=192.8, 181.7, 163.6, 163.4,
163.0, 148.2, 146.7, 137.5, 135.4, 135.1, 134.8, 134.0, 130.9, 130.5,
130.0, 129.7, 125.1, 121.5, 121.4, 120.4, 118.4, 116.3, 115.5 ppm;
HRMS (ESI+): m/z [M+H]+ calcd for C25H16NO4S: 426.0800, found:
426.0800.
1,8-Dimethoxy-3-(pyridin-3’-yl)anthraquinone (5i): Yield: 35 mg,
1
100%. H NMR (400 MHz, CDCl3): d=8.93 (s, 1H), 8.68 (s, 1H), 8.03
(d, 1H, J=1.6 Hz), 7.99 (d, 1H, J=8.0 Hz), 7.84 (d, 1H, J=7.6 Hz),
7.64 (t, 1H, J=8.0 Hz), 7.46 (d, 1H, J=1.2 Hz), 7.43 (m, 1H), 7.32 (d,
1H, J=8.4 Hz), 4.09 (s, 3H), 4.02 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3): d=183.9, 182.5, 160.3, 159.7, 150.0, 148.3, 143.4, 135.4,
135.0, 134.8, 134.7, 134.2, 123.9, 123.3, 119.1, 118.4, 117.6, 116.2,
56.8, 56.7 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C21H16NO4:
346.1079, found: 346.1084.
1,8-Dihydroxy-3-(4’-tert-butoxymethyl-phenyl)anthraquinone
(6e): Yield: 22 mg, 78%. 1H NMR (400 MHz, CDCl3): d=12.08 (s,
1H), 12.04 (s, 1H), 8.04 (d, 1H, J=1.6 Hz), 7.81 (dd, 1H, J=1.2,
7.6 Hz), 7.67–7.63 (m, 3H), 7.48 (s, 1H), 7.45 (m, 2H), 7.27 (dd, 1H,
J=1.2, 7.6 Hz), 4.51 (s, 2H), 1.33 ppm (s, 9H); 13C NMR (100 MHz,
CDCl3): d=192.6, 181.9, 163.1, 162.7, 150.0, 141.9, 137.2, 137.1,
134.0, 133.8, 128.2, 127.4, 124.8, 121.7, 120.3, 119.0, 116.1, 114.7,
73.9, 63.9, 27.9 ppm; HRMS (ESI+): m/z [M+H]+ calcd for C25H23O5:
403.1545, found: 403.1543.
General procedure for the synthesis of 4a, 6a-f by thiophenol
demethylation:
A
mixture of 1,8-dimethoxy-anthraquinone
(0.07 mmol), PhSH (0.40 mmol) and K2CO3 (0.40 mmol) in dry N-
methyl-2-pyrrolidone (NMP) (4 mL) was heated at 140–1608C for
20–60 min under N2. The mixture was then diluted with H2O
(150 mL), and the aqueous suspension was extracted with EtOAc
(3ꢁ100 mL). The combined organic layers were and concentrated
in vacuo. The residue was purified by column chromatography
(EtOAc/hexane).
1,8-Dihydroxy-3-(4’-methoxyphenyl)anthraquinone (6 f): Yield:
18 mg, 61%. H NMR (400 MHz, CDCl3): d=12.06 (s, 1H), 12.00 (s,
1
1H), 8.05 (d, 1H, J=1.6 Hz), 7.83 (d, 1H, J=7.2 Hz), 7.64 (m, 3H,
J=8.8, 7.2 Hz), 7.44 (d, 1H, J=1.6 Hz), 7.27 (d, 1H, J=8.4 Hz), 7.00
(d, 2H, J=8.8 Hz), 3.87 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=
192.7, 182.1, 163.5, 162.9, 161.4, 150.0, 137.1, 134.4, 134.2, 131.0,
128.8, 124.8, 121.0, 120.2, 118.7, 116.5, 115.0, 114.6, 55.7 ppm;
HRMS (ESIꢀ): m/z [MꢀH]ꢀ calcd for C21H13O5: 345.0763, found:
345.0767.
1,8-Dihydroxy-3-(phenylthio)anthraquinone (4a): Yield: 10 mg,
54%. 1H NMR (400 MHz, CDCl3): d=12.10 (s, 1H), 12.09 (s, 1H),
7.80–7.77 (dd, 1H, J=1.2, 7.6 Hz), 7.65 (t, 1H, J=8.0 Hz), 7.60–7.57
(m, 3H), 7.50 (d, 2H, J=1.6 Hz), 7.48 (d, 1H, J=1.6 Hz), 7.30–7.27
(dd, 1H, J=1.2, 7.6 Hz), 6.80 ppm (d, 1H, J=1.6 Hz); 13C NMR
(100 MHz, CDCl3): d=192.0, 181.8, 163.1, 162.6, 152.9, 137.1, 135.5,
133.6, 133.5, 130.4, 129.4, 125.0, 120.2, 119.6, 118.1, 116.1,
113.2 ppm; HRMS (ESIꢀ): m/z [MꢀH]ꢀ calcd for C20H11O4S:
347.0378, found: 347.0377.
1,8-Dihydroxy-3-(4’-hydroxyphenyl)anthraquinone (6g): A mix-
ture of 6 f (15 mg, 0.043 mmol), PhSH (13 mL, 0.13 mmol) and
K2CO3 (36 mg, 0.26 mmol) in dry NMP (1 mL) was heated at 170–
1808C for 1 h under N2. The mixture was then diluted with H2O
(20 mL) and acidified with HCl (5m). The aqueous suspension was
extracted with EtOAc (1ꢁvol), and concentrated in vacuo. The resi-
due was purified by column chromatography (EtOAc/hexane, 1:4).
1,8-Dihydroxy-3-(3’,5’-dimethyl-isoxazol-4’-yl)anthraquinone
(6a): Yield: 10 mg, 41%. 1H NMR (400 MHz, CDCl3): d=12.12 (s,
1H), 12.06 (s, 1H), 7.85 (d, 1H, J=7.2 Hz), 7.75 (d, 1H, J=1.6 Hz),
7.72 (t, 1H, J=8.0 Hz), 7.33 (d, 1H, J=7.6 Hz), 7.20 (d, 1H, J=
1.6 Hz), 2.53 (s, 3H), 2.38 ppm (s, 3H); 13C NMR (100 MHz, CDCl3):
d=192.7, 181.7, 167.1, 163.0, 162.8, 140.4, 137.6, 134.3, 133.7,
125.1, 123.8, 120.4, 120.3, 116.0, 115.3, 115.0, 12.3, 11.3 ppm; HRMS
(ESIꢀ): m/z [MꢀH]ꢀ calcd for C19H12O5N: 334.0715, found: 334.0709.
1
Yield: 4 mg, 28%. H NMR (400 MHz, [D6]DMSO): d=11.97 (s, 2H),
9.99 (s, 1H), 7.90 (d, 1H, J=1.6 Hz), 7.80 (t, 1H, J=8.0 Hz), 7.73–
7.70 (m, 3H), 7.56 (d, 1H, J=1.6 Hz), 7.38 (dd, 1H, J=1.2, 8.0 Hz),
6.92 ppm (d, 2H, J=8.4 Hz); 13C NMR (100 MHz, [D6]DMSO): d=
191.2, 181.4, 162.1, 161.3, 159.2, 148.6, 137.3, 133.7, 133.3, 128.6,
127.8, 124.5, 119.6, 119.4, 116.7, 116.1, 114.0 ppm; HRMS (ESIꢀ): m/
z [MꢀH]ꢀ calcd for C20H11O5: 331.0606, found: 331.0614.
1,8-Dihydroxy-3-aminoanthraquinone (7): A mixture of 3 (1.7 g,
6.0 mmol), PhSH (3.3 mL, 30 mmol) and K2CO3 (4.1 g, 30 mmol) in
dry NMP (100 mL) was heated at 150–1608C for 1 h under N2. The
mixture was then diluted with CH2Cl2 (400 mL) and washed with
brine (4ꢁ500 mL). The organic layer was concentrated in vacuo.
The residue was diluted with H2O (250 mL) and hexane (250 mL),
and a precipitate formed at the organic/aqueous interface. The
precipitate was collected by filtration to give the desired product
1,8-Dihydroxy-3-(thiophen-2’-yl)anthraquinone
(6b):
Yield:
10 mg, 47%. 1H NMR (400 MHz, CDCl3): d=12.05 (s, 2H), 8.07 (s,
1H), 7.86 (d, 1H, J=6.8 Hz), 7.66 (t, 1H, J=7.6 Hz), 7.58 (s, 1H),
7.46 (m, 2H), 7.29 (d, 1H, J=8.0 Hz), 7.15 ppm (s, 1H); 13C NMR
(100 MHz, CDCl3): d=192.4, 181.9, 163.6, 163.0, 143.4, 142.1, 137.2,
134.7, 134.1, 128.9, 128.5, 126.7, 125.0, 120.3, 119.8, 117.7, 116.4,
115.0 ppm; HRMS (ESIꢀ): m/z [MꢀH]ꢀ calcd for C18H9O4S: 321.0222,
found: 321.0236.
1
as a deep red solid (1.5 g, 98%). H NMR (400 MHz, [D6]DMSO): d=
1,8-Dihydroxy-3-(4’-dimethylamino-3’-methylphenyl)anthraqui-
none (6c): Yield: 20 mg, 71%. H NMR (400 MHz, CDCl3): d=12.13
(s, 1H), 12.05 (s, 1H), 8.03 (s, 1H), 7.81 (d, 1H, J=7.2 Hz), 7.64 (t,
12.42 (s, 1H), 12.23 (s, 1H), 7.70–7.63 (m, 2H), 7.30 (d, 1H, J=
8.0 Hz), 7.16 (s, 2H), 7.04 (s, 1H), 6.25 ppm (s, 1H); 13C NMR
(100 MHz, [D6]DMSO): d=187.5, 181.9, 164.9, 161.0, 157.5, 135.9,
1
ChemMedChem 2011, 6, 2294 – 2301
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
2299

C. Yang, B. Wang, et al.
MED
134.7, 133.1, 124.3, 119.0, 115.9, 108.6, 105.4, 102.0 ppm; HRMS
(ESIꢀ): m/z [MꢀH]ꢀ calcd for C14H8O4N: 254.0453, found: 254.0441.
Biology
MTT assay: Both HeLa and MOLT4 cell lines were purchased from
the ATCC. MOLT4 cells were cultured in RPMI-1640 medium, while
HeLa cells were cultured in MEM medium. Both media were sup-
plemented with 10% fetal bovine serum and 1% penicillin/strepto-
mycin. For the cytotoxicity assays, cells were seeded into 96-well
plate (2.5ꢁ104 in 100 mL per well for HeLa; 1.0ꢁ105 in 200 mL per
well for MOLT4). Test compounds were dissolved or suspended in
DMSO to make 10–20 mm stock solutions and diluted with culture
medium to various concentrations (final DMSO concentration <
0.5%). Addition of test compound was performed immediately
after seeding (MOLT4) or after adherent cells reached 40–50% con-
fluence (HeLa). After incubation for 64–72 h at 378C in a humidi-
fied atmosphere with 5% CO2, MTT (10 mL, 5 mgmLꢀ1 in phos-
phate-buffered saline) was added to each well, and the plate was
incubated for another 4 h. The culture medium was then aspirated
and DMSO (100 mL) was added to each well. The 96-well plate was
read using a microarray reader for optical density at 490 nm. All
tests were performed in triplicate and the optical absorption read-
out was normalized to percentage of maximum cytotoxicity. Data
were processed using GraphPad Prism 4, and the dose–response
curves were fitted to a sigmoidal (or “logarithmic”) model to calcu-
late IC50 values. For compounds with IC50 values <100 mm, the MTT
assay was repeated.
1,8-Dihydroxy-3-(2’-chloro-acetamido)anthraquinone (8): Chlor-
oacetyl chloride (0.7 mL, 8.8 mmol) was injected slowly into a solu-
tion of 7 (1.5 g, 5.9 mmol) in dry dioxane (60 mL). The mixture was
stirred at RT for 2 h. The reaction mixture was then diluted with
H2O (300 mL), and the suspension was extracted with CH2Cl2 (2ꢁ
200 mL). The combined organic extracts were and concentrated in
vacuo. Purification by column chromatography (CH2Cl2/EtOAc, 2:1)
1
gave the desired product as an orange solid (0.51 g, 26%). H NMR
(400 MHz, CDCl3): d=12.07 (s, 1H), 12.01 (s, 1H), 8.43 (s, 1H), 7.88
(s, 1H), 7.82 (d, 1H, J=7.2 Hz), 7.68–7.63 (m, 2H), 7.29 (d, 1H, J=
8.4 Hz), 4.21 ppm (d, 1H, J=2.4 Hz); 13C NMR (100 MHz, CDCl3): d=
191.9, 181.5, 164.8, 164.4, 163.0, 144.8, 137.2, 135.2, 133.9, 125.2,
120.4, 116.3, 113.4, 113.2, 111.5, 43.1 ppm; HRMS (ESIꢀ): m/z
[MꢀH]ꢀ calcd for C16H9O5NCl: 330.0169, found: 330.0175.
General procedure for the synthesis of 9a–d: A mixture of 8
(0.3 mmol) and secondary amine (1.5 mmol) in dry dioxane (9 mL)
was heated at 80–908C for 2 h. The reaction mixture was concen-
trated in vacuo, and the residue was dissolved in a minimal
amount of CH2Cl2. The solution was then diluted with hexane (2ꢁ
volume) and stored at ꢀ208C. Precipitation was observed, and fil-
tration gave the desired product as a yellow solid.
1,8-Dihydroxy-3-(2’-diethylaminoacetamido)anthraquinone (9a):
1
Yield: 42 mg, 36%. H NMR (400 MHz, CDCl3): d=12.16 (s, 2H), 9.90
Acknowledgements
(s, 1H), 8.03 (d, 1H, J=2.0 Hz), 7.82 (d, 1H, J=7.6 Hz), 7.66 (t, 1H,
J=7.6, 8.4 Hz), 7.57 (d, 1H, J=2.0 Hz), 7.29 (d, 1H, J=8.4 Hz), 3.21
(s, 2H), 2.69 (q, 4H, J=7.2 Hz), 1.12 ppm (t, 6H, J=7.2 Hz);
13C NMR (100 MHz, CDCl3): d=191.4, 181.9, 171.2, 164.9, 162.7,
145.6, 136.9, 134.8, 133.7, 125.1, 120.2, 116.1, 112.5, 112.1, 111.2,
58.2, 49.2, 12.6 ppm; HRMS (ESIꢀ): m/z [MꢀH]ꢀ calcd for
C20H19O5N2: 367.1294, found: 367.1296.
Financial support from the Chinese Academy of Sciences
(SIMM0907 KF-08) and the Georgia State University Molecular
Basis of Disease Program is gratefully acknowledged.
Keywords: alkylating agents · anthraquinones · anticancer
agents · cytotoxicity · DNA intercalators · rhein analogues
1,8-Dihydroxy-3-(2’-(4’’-methylpiperazin-1’’-yl)acetamido)anthra-
quinone (9b): Yield: 54 mg, 45%. 1H NMR (400 MHz, [D6]DMSO):
d=11.97 (s, 2H), 10.51 (s, 1H), 7.97 (d, 1H, J=2.0 Hz), 7.80–7.76
(m, 2H), 7.72–7.70 (dd, 1H, J=1.2, 7.6 Hz), 7.37–7.35 (dd, 1H, J=
1.2, 8.4 Hz), 3.38 (s, 2H), 3.22 (s, 4H), 2.90 (s, 4H), 2.75 ppm (s, 3H);
13C NMR (100 MHz, [D6]DMSO): d=190.0, 180.9, 168.9, 162.7, 161.1,
146.2, 136.7, 134.0, 133.1, 124.1, 119.1, 115.6, 111.3, 110.9, 59.8,
52.3, 48.8, 42.0 ppm; HRMS (ESI+): m/z [M+H]+ calcd for
C21H22O5N3: 396.1559, found: 396.1556.
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1,8-Dihydroxy-3-(2’-morpholino-acetamido)anthraquinone (9c):
Yield: 100 mg, 82%. H NMR (400 MHz, [D6]DMSO): d=11.80–11.40
1
(brs, 2H), 10.47 (s, 1H), 7.90 (d, 1H, J=2.0 Hz), 7.78–7.74 (m, 2H),
7.66 (d, 1H, J=7.2 Hz), 7.33 (d, 1H, J=8.4 Hz), 3.66 (t, 4H, J=
4.4 Hz), 3.22 (s, 2H), 2.54 ppm (t, 4H, J=4.4 Hz); 13C NMR (100 MHz,
[D6]DMSO): d=190.2, 181.1, 169.6, 163.0, 161.3, 146.5, 137.0, 134.1,
133.2, 124.4, 119.4, 115.7, 111.4, 111.1, 66.0, 62.0, 53.1 ppm; HRMS
(ESI+): m/z [M+H]+ calcd for C20H19O6N2: 383.1243, found:
383.1228.
1,8-Dihydroxy-3-(2’-piperidinyl-acetamido)anthraquinone (9d):
Yield: 55 mg, 47%. 1H NMR (400 MHz, [D6]DMSO): d=12.50–11.50
(brs, 2H), 9.65 (s, 1H), 7.92 (d, 1H, J=2.0 Hz), 7.81–7.78 (dd, 2H,
J=1.2, 7.6 Hz), 7.64–7.60 (m, 2H), 7.27–7.25 (d, 1H, J=8.4 Hz), 3.11
(s, 2H), 2.58 (t, 4H, J=5.2 Hz), 1.69 (m, 4H), 1.53 ppm (t, 2H, J=
5.6 Hz); 13C NMR (100 MHz, [D6]DMSO): d=191.6, 181.8, 169.9,
165.0, 162.9, 145.9, 136.9, 135.1, 134.0, 125.0, 120.2, 116.3, 112.7,
112.3, 111.3, 63.1, 55.3, 26.5, 23.8 ppm; HRMS (ESI+): m/z [M+H]+
calcd for C21H21O5N2: 381.1450, found: 381.1442.
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Received: August 6, 2011
Published online on September 26, 2011
ChemMedChem 2011, 6, 2294 – 2301
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
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