The synthesis and biological activity of novel anthracenone-pyranones and anthracenone-furans

Article abstract of DOI:10.1016/j.bmc.2015.04.032

Abstract An efficient and divergent methodology for the synthesis of new anthracenone-pyranones and anthracenone-furans is described. Key reactions discussed in these syntheses include an aldehyde promoted annulation with a β-keto-sulfoxide, a domino alkyne insertion/carbonylation/Nu-acylation and a DMEDA promoted Castro-Stephens reaction. We also report the in vitro growth inhibition of these compounds in a range of human cancer cells. The natural product BE-26554A displayed good cell growth activity on BE2-C neuroblastoma and SMA glioblastoma cell lines at 0.17 and 0.16 μM (GI₅₀), respectively. Of note, were a CF₃ functionalised anthracenone 4-pyranone (chromone) derivative 22, and an anthracenone-furan derivative 54 which displayed 0.20 μM and 0.38 μM growth inhibition, respectively, in the BE2-C neuroblastoma cell line.

Full text of DOI:10.1016/j.bmc.2015.04.032

Bioorganic & Medicinal Chemistry 23 (2015) 3552–3565
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
The synthesis and biological activity of novel anthracenone-
pyranones and anthracenone-furans
James E. Rixson a, James R. Abraham a, Yuki Egoshi a,b, Brian W. Skelton c, Kelly Young d, Jayne Gilbert d,
Jennette A. Sakoff d, Kersten M. Gericke e, Adam McCluskey f, , Scott G. Stewart a,
⇑
⇑
a The School of Chemistry and Biochemistry, The University of Western Australia, Crawley, WA 6009, Australia
b Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan
c Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Crawley, WA 6009, Australia
d Department of Medical Oncology, Calvary Mater Newcastle Hospital, Edith Street, Waratah, 2298 NSW, Australia
e Bayer Pharma AG, Medicinal Chemistry, 42096 Wuppertal, Germany
f Chemistry Building, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and divergent methodology for the synthesis of new anthracenone-pyranones and anthra-
cenone-furans is described. Key reactions discussed in these syntheses include an aldehyde promoted
Received 7 February 2015
Revised 2 April 2015
Accepted 9 April 2015
Available online 22 April 2015
annulation with
a b-keto-sulfoxide, a domino alkyne insertion/carbonylation/Nu-acylation and a
DMEDA promoted Castro–Stephens reaction. We also report the in vitro growth inhibition of these com-
pounds in a range of human cancer cells. The natural product BE-26554A displayed good cell growth
activity on BE2-C neuroblastoma and SMA glioblastoma cell lines at 0.17 and 0.16
Of note, were a CF3 functionalised anthracenone 4-pyranone (chromone) derivative 22, and an anthra-
lM (GI50), respectively.
Keywords:
Anthrapyranones
Natural products
Growth inhibition
Human cancer cells
Castro–Stephens reaction
cenone-furan derivative 54 which displayed 0.20
l
M and 0.38
lM growth inhibition, respectively, in
the BE2-C neuroblastoma cell line.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
(leukemia L-1210),5 however this compound shows little, if any,
DNA sequence selectivity compared to pluramycin (1).6
The structural class of anthrapyranones have a remarkable
range of biological activity mainly as anti-bacterial agents, anti-tu-
mour and anti-fungal compounds. Some examples in this family of
compounds include pluramycin A (1), kidamycin, altromycin B,
hedamycin topopyronone C (2), k-indomycinone1 and the antibi-
otic saptomycin E (3) (Fig. 1). Generally, the molecular mode of
action of this class compounds is thought to go through an interca-
lation with the major groove of DNA along with covalent bonding
with N7 of guanine. The effectiveness of this mode of action, is reli-
ant on substituents at the C5, C8 and C10 positions (mostly carbo-
hydrates) and the C2 epoxide moiety for the guanine alkylation
process.2–4 In one early study an altromycin B-DNA adduct was
investigated using two-dimensional 1H–15N HMBC experiments
to identify the epoxide alkylation position in DNA. Interestingly,
neopluramycin, which differs from pluramycin (1) in that it has a
single olefin in place of the epoxide, also has anti-tumour activity
Simple epoxide-anthrapyranones have also been isolated, for
example, in 1994, the Banyu Pharma group isolated the natural
product BE-26554A (4) from Streptomyces A26554 cultures.7 In this
early report and brief study, the natural product epoxide (4) was
described to have an IC50 value of 0.001 lM (or 10 nM) against
P338 Leukaemia cells. Unfortunately, any indication of the epoxide
stereochemistry was not identified in this isolation study. Aside
from the anthrapyranones, the 4-pyranone ring system alone has
also been reported to effect murine leukaemia cell (L1210)
growth.8
Several groups have developed syntheses of anthrapyranones,
most commonly through various approaches to the 4-pyranone
ring system D ring. These key reactions include; the Baker–
Venkataraman rearrangement with cyclisation,9,10 a 6-endo-dig
cyclisation of alkyne ketones,11–15 a Friedel–Crafts acylation16
and cyclisation of b-diketones17,18 among others.19,20 In 2013, we
described a racemic synthesis of anthrapyranones through the
annulation of a b-keto-sulfoxide and an aldehyde.21 Interestingly,
a recent report on a non-metal mediated synthetic ring forming
processes on simple chromones has come to light22 along with
the oxidative alkylation of these ring systems.23
⇑
Corresponding authors.
E-mail addresses: Adam.McCluskey@newcastle.edu.au (A. McCluskey), scott.
stewart@uwa.edu.au (S.G. Stewart).
http://dx.doi.org/10.1016/j.bmc.2015.04.032
0968-0896/Ó 2015 Elsevier Ltd. All rights reserved.

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3553
either using a Castro–Stevens reaction or the related Sonogashira
palladium catalysed process. Thus treatment of benzoyl protected
phenol 5 with phenyl copper acetylene 6 provided the yne-one 7 in
excellent yield (95%).24 Subjection of compound 7 to sulphuric acid
provided the phenyl 4-pyranone 8 in 55% yield through hydration
of the alkyne and cyclisation through a phenoxide. Alternatively,
hydration using p-TsOH provided a crude mixture of the iso-
CH3
O
D
H3C
O
CH3
O
CH3
HO
OH
A
O
O
OH
O
O
O
H
H3C
O
O
N(CH3)2
CH3 HO
OH
H
O
propyl-ether 4-pyranone and phenol-4-pyranone
8 (1:3.7 by
NMR analysis of the crude product).26
Topopyronone C 2
H3C
N(CH3)2
As we required an alkyl, or alkenyl, substituent at the C2 posi-
tion to begin SAR studies, an alkyl substituted alkyne was incorpo-
rated into the initial C–C bond forming process. Following several
unsuccessful reaction trails with the benzoyl protected derivative
OH
1
Pluramycin A
CH3
O
H3C
CH3
CH3
O
O
2
5
the corresponding benzyl protected phenol 9 was used
AcO
H3C
O
OH
O
O
OH
O
O
H
(Scheme 1b). Treating compound 9 with the alkyne alcohol 10 gave
the desired alkyne in excellent yield (91%). Oxidation of this pro-
duct with Dess–Martin periodinane furnished yne-one 11, in 88%
yield. Unfortunately, treatment with p-TsOH did not provide any
pyranone compound 26, however revisiting the previously used
sulfuric acid conditions only resulted in 33% of the desired alkyl
anthrapyranone 12. As this annulation process was low yielding
O
O
N(CH3)2
CH3
CH3
O
Saptomycin E 3
4
BE-26554A
Figure 1. Chemical structures of selected natural product anthrapyranones.
we decided to pursue
a more efficient synthetic route.
Unfortunately, following the piperidine and aminovinyl ketone
method devised by the Shvartsberg group,24 only afforded a com-
plex mixture of products.
The varying biological activity of the pluramycin class of com-
pounds, with different substitution at C2, reflects the importance
of this region of the molecule. As part of furthering our investiga-
tions into this class of compounds we were interested in develop-
ing efficient syntheses of the anthracenone ring system with
varying D-rings, as well as investigating the role which this ring
system plays in the biological activity. In our synthetic studies sev-
eral approaches to the 4-pyranone core of the anthrapyranones
were developed. Initially, an approach using an acid induced ring
closure of anthraquinone-yne-ones was conceived (Scheme 1a).
This tactic has been pursued by several groups including that of
Shvartsberg.24,25 The anthraquinone-yne-one could be prepared
A synthetic route through key b-keto sulfoxide 13 was ulti-
mately successful in the efficient preparation of the 4-pyranone
ring system bearing an alkyl side chain.21,27–29 Eventually this
intermediate 13 was also used en route to the natural product
( )-BE-26554A (4) (Scheme 2).21 The b-keto-sulfoxide-annulation
procedure with propionaldehyde was especially high yielding
(81%) which provided the impetus to expand this reaction to other
aldehydes. Coupled with the Augustine olefination procedure by
Krohn et al., this sequence could provide a range of substituted
4-pyranone derivatives.10,30
We next examined this first group of compounds (4, 8 and 12,
14 and 16) for in vitro cell growth inhibition against a panel of nine
human cancer cell lines including: HT29 (colorectal carcinoma);
MCF-7 (breast adenocarcinoma); A2780 (ovarian carcinoma);
H460 (lung carcinoma); A431 (epidermoid carcinoma); DU145
(prostate carcinoma); BE2-C (neuroblastoma); SJG2 (glioblas-
toma); MIA (pancreatic carcinoma) and SMA (glioblastoma). As in
previous investigations,31–33 an initial screen was carried out
O
(a)
6
Ph
O
O
O
OBz
O
O
O
OBz
OH
Cu
O
I
DMF, reflux, 2 h
95% yield
CH3
CH3
5
7
Ph
O
H2SO4,
60 °C, 2 h, 55%
O
1.
H
O
S
O
O
OH
OCH3
O
O
O
O
O
CH3
NEt3,toluene,
reflux, 20 h, 81%
O
O
O
8
2. Ag(II)O, dioxane,
HNO3, rt, 15 mins
78%
CH3
CH3
(b)
OCH3
13
i)
14
57%
10 OH
Hex
O
n
BrClCH2,
O
O
OBn
O
O
OBn
pyridine
Pd(PPh3)2Cl2
(10 mol%), 91%
DMF, 2 h, rt,
I
ii) DMP, CH2Cl2
88%
BCl3, CH2Cl2
-40 °C, 15 min
96%
CH3
CH3
OH
O
O
O
O
O
O
9
11
O
O
O
O
nHex
H2SO4,
60 °C, 2 h, 33%
CH3
CH3
OH
O
O
16
O
15
O
m-CPBA,
CH2Cl2, reflux
6 h, 60%
CH3
O
12
( ) BE-256554A 4
Scheme 2. Summary of the final stages of the synthesis of ( )-BE-26554A (4).21
Scheme 1. Synthesis of (a) phenyl and (b) alkyl anthrapyranones.

3554
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
treating each of the cell lines at a compound concentration of
25 M. If, in this preliminary assay, the compound was considered
CF3 moiety rendered 21 insoluble in the assay medium, however
the phenol 22 demonstrated enhanced cytotoxicity across the
l
potent with a high percentage inhibition (>90% across all cell lines
evaluated or >100% against more than two cell lines) and suitably
soluble (in the DMSO/water solution), then a more detailed dose
response evaluation was conducted. This allowed determination
of the compound GI50 and these values are presented in Table 1.
Unfortunately, the C2 hexyl and phenyl substituted anthrapyra-
none compounds (8 and 12, respectively) were not potent as cell
growth inhibitors in any of the cancer cell lines tested. The racemic
mixture of the natural product ( )-4 however was highly growth
inhibitory across the range of the cancer cell lines. Of particular
note was the effect against BE2-C, SMA and A2780 cell lines, at
panel of cell lines examined with GI50 values of 0.2–2.9 lM, with
the highest level of activity noted with the BE2-C cell line.
Following the promising results of the anthrapyranone com-
pounds (4-pyranone D-ring, Table 1) we investigated a series of
D-ring 2-pyranones to determine if this isomer had an effect on
the biological activity. This series of compounds were prepared
through a domino alkyne insertion/carbonylation/Nu-acylation
reaction, described in our earlier publication (Scheme 3).21 We
have found in previous investigations approached using palladium
mediated domino reactions to be effective for rapid ring formation
and sub-structural diversity.36–40
0.17, 0.16 and 0.29
l
M, respectively. Compound 14 disclosed mod-
In most cases under our reaction conditions the regioisomer 24
predominated in favour of compound 25. Moreover, in many of our
reactions involving various alkynes, the regioisomer 25 was not
observed. For example, the specific formation of regioisomer 41,
confirmed by X-ray crystallographic studies (Fig. 3), is the sole pro-
duct of the reaction with TMS–acetylene.
The simple n-hexyl derivatives 26 and 27 displayed poor
growth inhibition, neither of these analogues progressing to a full
dose response evaluation. The nitrile derivative 29 displayed only
erate cytotoxicity with the exception of only having weak potency
on the SJ-G2 cell line. The alkene precursor 16 was mainly three
times more potent across the range of cell lines tested. It is clear
that in most of the cell lines the epoxide ( )-4 is more active than
the precursor alkene 16, however at this stage it is impossible to
gauge if the epoxide moiety is directly playing a role in the mode
of action of ( )-BE-26554A (4).
A
slight modification of the original synthetic pathway
(Scheme 2) facilitated access to additional anthrapyranone
derivatives (Fig. 2). Condensation of alternate aldehydes with the
b-keto-sulfoxide 13, were also successful in producing alterna-
tively C2-alkyl substituted 4-pyranones (65–83% yield). As in the
original synthetic scheme these products could be subjected to a
silver oxide Ag(II)O oxidation with or without subsequent iso-
propyl deprotection (BCl3) to prepare compounds 18, 21 and 22
(ESI ). The methyl ethers 19 and 20 were accessed through treat-
ment of the parent phenols with CH3I. These modifications allowed
exploration of the A ring alkyl ether and the length of the C2 side
chain as well as the effect of a metabolically stable CF3 group with
21 and 22 on the observed cytotoxicity.34,35
moderate cytotoxicity (GI50 3.2–22 lM), however the isopropyl
derivative 28 was relatively inactive (Table 2).
In most of the remaining 2-pyranone cases (Table 2) the activity
was weak to moderate at ca. 10–40 lM. These systems also
seemed not to indicate a clear difference in activity depending on
the position of the R group (i.e., if the isomer 24 or 25 was tested)
as shown in derivatives 34–37. The exception to the observed
moderate activity in these 2-pyranone examples was found in
the slight improvement in potency of the A ring benzylated deriva-
tive 33. We believe this may simply be driven by the higher
lipophilicity of the OBn derivative compared to the OiPr potentially
leading to greater cell permeability.
Phenol 18 with GI50 values of 1.4–3.2
with 16, and the methyl ethers 19 and 20 showed a slight drop in
activity relative to 4 with GI50 values ranging from 4.1 to 14 and
5.3 to 7.1 lM, respectively.
These data suggest that the phenol-OH moiety is not pivotal to
activity. The combination of O-methylation and introduction of a –
l
M was nearly equipotent
Given the D ring 2-pyranone system overall resulted in no
potency enhancements, we sought an alternative ring system to
confirm if the earlier evaluated 4-pyranone ring system was essen-
tial for potent biological activity. In this regard our attention turned
to the installation of a furan moiety to an anthracenone core. From a
synthetic standpoint, these analogues were also of interest as they
Table 1
Growth inhibition (GI50
, l
M) of several anthrapyran-4-one derivatives against a panel of cancer cell linesa
Compdb HT29c
U87d
MCF-7e
A2780f
H460g
A431h
Du145i
BE2-Cj
SJ-G2d
MIAk
SMAl
4
8
2.0 0.38
—
0.99 0.13 1.3 0.20
0.29 0.01
—
2.1 0.31
—
0.95 0.12 0.84 0.17
0.17 0.04
—
0.8 0.25
—
0.9 0.16
—
0.16 0.05
—
—
—
—
—
12
14
16
17
18
19
20
21
22
—
—
—
—
—
—
—
—
—
—
—
4.8 0.62
1.6 0.12
Insoluble
3.2 0.94
4.5 0.25
5.5 0.058 6.4 0.42
Insoluble
0.94 0.18 2.9 0.85
8.7 3.7
3.4 0.12
4.3 0.88
1.4 0.07
5.8 1.5
1.6 0.23
6.9 2.5
3.9 0.20
5.7 0.77
1.8 0.07
1.9 0.000
1.5 0.06
2.2 0.15
5.9 0.21
16 7.3
4.7 0.99
3.4 0.36
2.0 0.34
3.9 1.9
1.7 0.20
2.8 0.72
14 4.7
1.8 0.06
4.1 0.20
6.4 0.33
2.4 0.22
5.3 0.23
6.4 0.20
1.4 0.27
4.8 0.18
5.3 0.31
1.6 0.10
5.7 0.35
6.6 0.15
1.2 0.15
4.8 0.34
5.3 0.56
1.8 0.26
4.1 0.033
6.1 0.000
1.7 0.13
4.3 0.15
5.3 0.17
1.7 0.15
5.4 0.32
7.1 0.32
1.5 0.19
6.5 1.3
6.0 0.36
0.28 0.035 0.34 0.027 0.87 0.46 0.51 0.20 0.29 0.012 0.20 0.018 0.49 0.007 0.28 0.000 0.48 0.17
M in each cell line for growth inhibition and if potent a full dose response analysis was conducted from which the GI50, lM
a
All compounds were initially assayed at 25
l
value was calculated. This value is the concentration of compound that induces 50% growth inhibition after 72 h exposure. (—) indicates the compound had low growth
inhibition level in the initial assay.
b
All assays were completed in triplicate with the standard error indicated.
Colon carcinoma.
Glioblastoma.
Breast carcinoma.
Ovarian carcinoma.
Lung carcinoma.
Skin carcinoma.
Prostate carcinoma.
c
d
e
f
g
h
i
j
Neuroblastoma.
Pancreatic carcinoma.
Spontaneous murine astrocytoma.
k
l

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3555
OH
O
O
O
OH
O
O
O
O
O
O
OCH3
O
O
O
CH3
CH3
CF3
CH3
CF3
O
17
O
18
O
19
O
O
OH
O
O
OCH3
O
O
O
CH3
CH3
CH3
O
20
O
O
21
22
Figure 3. Structure of the compound 41. Ellipsoids have been drawn at the 50%
probability level (CCDC No. 931990).
Figure 2. Newly prepared anthrapyranone analogues.
are poorly represented in the literature.41,42 Additionally, the furan
oxygen atom would be in a similar position to the previous ana-
logues and it was believed that C2 group on the furan would occupy
a similar region of space as the C2 position of the 4-pyranone. We
envisaged these compounds could be prepared through a Castro–
Stephens protocol.43–46 In several examples ortho-substituted
halides had previously been used in heterocycle synthesis including
both furans and isocoumarins, while in situ quenching of these
reactions have been reported to produce pyrazoles.24,47–50
Initially, a range of copper acetylides were prepared simply by
treating an alcoholic solution of the terminal alkynes with a mix-
ture of excess CuCl in NH4OH (28%) in EtOH. Given the inherent
O
O
O
O
O
O
R
Pd(PPh3)2Cl2,
O
O
OH
CH3
NEt3, CO
Alkyne
I
O
24
+
28-94%
O
CH3
R
O
23
O
CH3
O
25
O
O
O
nHex
nPr
OR
O
O
O
OR
O
O
O
O
O
O
CN
CH3
CH3
CH3
O
26: R = iPr
27: R = H
28: R = iPr
30
29: R = H
O
O
OR2
O
O
R1
R2
R
O
O
O
OR1
O
O
O
O
O
CH3
CH3
CH3
O
O
34: R1 = nBu, R2 = H
35: R1 = H, R2 = nBu
31: R1 = iPr, R2 = H
32: R1 = iPr, R2 = Bn
33: R1 = H, R2 = Bn
38: R = CH3
39: R = OH
36: R1 = C3H6Cl, R2 = H
37: R1 = H, R2 = C3H6Cl
O
O
Ph
Si(CH3)3
O
O
O
O
O
O
CH3
CH3
O
O
41
40
Scheme 3. Products from the domino alkyne insertion/carbonylation/Nu-acylation reaction.

3556
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
Table 2
Growth inhibition (GI50
,
l
M) of the various anthrapyran-2-ones in a panel of human cancer cell linesa
Compdb
HT29c
U87d
MCF-7e
A2780f
H460g
A431h
Du145i
BE2-Cj
SJ-G2d
MIAk
SMAl
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
14 2.7
—
11 0.29
—
5.6 0.10
—
18 1.3
15 2.0
24 2.6
13 0.88
30 0.58
—
11 3.5
—
25 2.2
—
14 1.9
—
14 3.8
16 0.88
12 2.7
17 0.88
30 0.58
—
12 3.4
—
16 0.67
—
5.3 0.70
—
15 1.7
19 4.3
8.8 1.6
14 1.3
20 1.2
—
10 1.7
—
19 0.33
—
7.0 0.13
—
9.5 1.5
21 1.8
12 3.2
12 0.33
28 1.7
—
9.0 1.6
—
16 0.33
—
5.1 0.13
—
19 1.5
19 1.5
25 2.6
20 1.5
22 2.3
—
12 0.33
—
15 0.00
—
4.0 0.29
—
20 1.0
17 2.0
12 3.8
17 0.58
19 1.2
—
3.2 0.52
—
26 1.3
—
8.8 0.31
—
11 1.5
20 1.2
24 2.7
29 6.1
40 3.8
—
11 4.3
—
22 2.1
—
6.7 0.40
—
13 3.3
33 6.6
27 2.7
33 2.4
27 3.9
—
22 9.5
—
9.0 1.8
—
3.9 0.57
—
13 2.9
15 3.4
27 4.7
12 2.0
14 1.2
—
15 6.7
—
14 1.2
—
3.9 0.41
—
13 2.0
20 4.3
17 4.0
12 0.33
23 3.2
—
9.8 6.2
—
23 1.2
—
6.1 0.07
—
12 3.6
19 1.3
16 3.6
12 0.33
30 0.58
—
11 0.44
19 1.7
13 1.3
13 1.2
21 1.2
19 0.67
27 1.7
28 5.8
14 3.4
11 0.44
11 0.00
a
All compounds were initially assayed at 25 lM in each cell line for growth inhibition and if potent a full dose response analysis was conducted from which the GI50, lM
value was calculated. This value is the concentration of compound that induces 50% growth inhibition after 72 h exposure. (—) indicates the compound had a low growth
inhibition level in the initial assay.
b
All assays were completed in triplicate with the standard error indicated.
Colon carcinoma.
Glioblastoma.
Breast carcinoma.
Ovarian carcinoma.
Lung carcinoma.
Skin carcinoma.
Prostate carcinoma.
c
d
e
f
g
h
i
j
Neuroblastoma.
Pancreatic carcinoma.
Spontaneous murine astrocytoma.
k
l
poor solubility of cuprous acetylides these species were analysed by
elemental analysis and used without further purification (ESI ).
Following the original Castro–Stevens protocol we trailed reac-
tions in pyridine at high temperatures in order to solubilise the
copper acetylide. Unfortunately, in each of these examples a large
amount of decomposition was also observed. Given this concern
we attempted to carry out these reactions at a lower temperature
by first improving the solubility of the copper acetylide through
the addition of dimethylethylenediamine (DMEDA), a ligand com-
monly used in the copper catalysed Ullmann–Goldberg
condensation.51
The result from this reaction modification led to a collection of
furans containing electron withdrawing and donating groups being
formed in a range of yields (Table 3 and Fig. 4). The aliphatic,
ketone and nitrile copper acetylides performed most optimally in
the reaction (85–54% yield).
inactive as the corresponding isopropyl ethers 43 and 45.
Shortening of the alkyl chain improved the activity given the n-
propyl 45 displayed good sub-micromolar activity against BE2-C
(0.88 lM) and Du145 (0.86 lM) cell lines. Surprisingly, the benzoyl
derivative 49 (Fig. 5), also containing an isopropoxy group on the
A-ring, was potent and the phenol 50 was not. Possibly the
increase in lipophilicity of derivative 49 has an influence on the
activity of this compound. This substrate is particularly interesting
given its potency in the BE2-C and Du145 cell lines at 0.95 and
0.83 lM respectively.
The butanyl-nitrile and the n-propyl chloride derivatives, 52
and 54, both bearing an A-ring phenol had modest to high activity
across the cell lines evaluated with GI50 values of 0.46–32 and
0.59–23
lM, respectively. The cyano-substituted compound 52
showed strong growth inhibition against Du145 cells of 0.46
lM.
The C2 alkyl chloride moiety (in 53 and 54) was chosen as a mimic
similar to the electrophilic ability of epoxide moiety contained
within pluramycin A (1).
As expected using the alkyl alcohol and the alkyl chloride as
coupling partners resulted in
a lower yield of the furan.
Following the preparation of compound 56 a simple oxidation with
Dess–Martin periodinane allowed for the synthesis of the corre-
sponding ketone 58. As previously described both of these com-
pounds could be deprotected using either BCl3 or p-TsOH to the
phenols 57 and 59 (ESI ).
Through the coupling partner diversity of the previously
described reaction (Table 3) we prepared the anthracenefurans
containing a C2 position hydrogen bond donor or acceptor groups,
as well as aliphatic tethers. Anthracenefurans 43, 45, 47 (C2 phenyl
substitution confirmed by X-ray crystallographic studies, Fig. 5)
and 48 displayed low levels of cytotoxicity (Table 4).
Thus, this was expected to undergo a similar alkylation reaction
with the base guanine. In most of the cell lines, 54 had an improved
activity (GI50 values of 0.38–1.9
with GI50 = 37 M) compared to the simple alkyl derivative 46
(GI50 values of 0.86–6.6 M). Again the growth inhibition activity
of anthracenefuran 54 in BE2-C was excellent at 0.38 M. Of the
lM, on exclusion of SJ-G2 cell line
l
l
l
ketone containing compounds (55, 58 and 59) the derivative 55
was the most effective at inhibiting cell growth with GI50 values
of 0.75–6.8
donor in the side-chain, exhibited moderate GI50 values of 14–35
and 7.3–28 M, respectively.
lM. Compounds 56 and 57, having a hydrogen-bond
l
The other analogues were effective as cell growth inhibition
agents throughout the various cell lines with a few exceptions.
The simple 2-alkyl substituted furans, as the free phenols, had
2. Conclusions
moderate (44, GI50 values of 9.3–32
lM) and good (46, GI50 values
In this study we have designed new synthetic pathways to three
anthracenone-pyranones and anthracenone-furans from related
of 0.86–6.6 M) cell growth inhibition, but were essentially
l

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3557
Table 3
Hex
n
Pr
Ph
n
Synthesis of anthracene-furans through a Castro–Stephens reaction
OR
O
O
OR
O
O
O
OR
O
O
O
R
Cu
R
O
O
OH
O
O
O
42
CH3
CH3
CH3
I
DMEDA
O
45: R = Pr
47:
43: R = iPr
44: R = H
i
R = iPr
PhMe
18 h, 90 °C
CH3
CH3
46: R = H
48:
R = H
O
23
O
Cl
CN
OR
Anthrafurans
Furan yielda (%)
Bz
OR
O
O
OR
O
O
O
O
Entry
1
Copper acetylide
Product
CH3
CH3
CH3
85
70
43
Cu
Cu
42a
O
O
O
49: R = iPr
50: R = H
51: R = iPr
52: R = H
53: R = iPr
54: R = H
2
3
45
42b
O
HO
O
nPen
OR
0
—
OR
O
O
O
Cu
Cu
OR
O
O
O
O
42c
CH3
CH3
CH3
O
O
4
5
64
54
47
49
55: R = Pr
i
56: R = iPr
57: R = H
58: R = iPr
59: R = H
42d
O
Figure 4. Prepared novel anthracenone-furan derivatives.
Cu
Cu
3. Experimental
3.1. General protocol
6
N
6
7
80
49
51
53
42e
Starting materials and reagents were available from Sigma–
Aldrich or Merck chemical companies. All reactions were per-
formed under argon and at ambient temperature unless stated
otherwise. All solvents used in reactions were anhydrous unless
noted otherwise. Anhydrous solvents were distilled over the
appropriate drying agent or acquired from a Pure Solv 5-Mid
Solvent Purification System (Innovative Technology Inc.). 1H and
13C Nuclear Magnetic Resonance (NMR) spectra were acquired on
a Varian 300, Varian 400 or a Bruker AV500 Bruker AV600 spec-
trometer and all signals d are reported in parts per million
(ppm). 1H and 13C assignments were made with the aid of DEPT,
COSY, HSQC and HMBC sequences where appropriate. Chemical
shifts were referenced to the residual (partially) undeuterated sol-
vents and reported in parts per million (ppm). Infrared spectra
samples were prepared using the KBr disc method or measured
directly with an ATR adapter and acquired on a Perkin Elmer
Spectrum One spectrometer at 2 cmꢀ1 resolution. Melting points
Cl
Cu
Cu
42f
O
8
65
13
27
55
—
42g
9
OH
42i
Cu
Cu
OH
10
56
42j
were recorded on
a Reichart heated-stage microscope. The
a
Aryl iodide 23, copper acetylide (1.1–1.5 equiv) and DMEDA, (3.5 equiv),
reported retention factors (Rf) were acquired via Thin Layer
Chromatography (TLC) performed on Merck silica gel 60 F254
pre-coated aluminium sheets. Column chromatography was per-
formed using silica gel 60 (0.04–0.063) supplied by Merck.
Chromatography solvents were distilled prior to use. High pressure
reactions were carried out in a high-pressure laboratory autoclave
Model I from Carl Roth. DMEDA is N,N0-dimethylethylenediamine.
Compounds 4, 9, 13–16, 23, 26–41 have been prepared and charac-
terised previously.21 Non-1-yn-3-one (10) was prepared according
to the procedure by Braddock et al.52
toluene (5 mL), 90 °C, 18 h.
aryl iodide precursors. These procedures provided a series of
anthracenone containing compounds exhibiting good to modest
growth inhibition in a range of cancer cell lines. Given these
results, it is evident that the type of D-ring O-heterocycle influ-
ences the cytotoxic effects of these normally DNA-interchelating
class of compounds. Among the forty four compounds tested, those
which displayed potent activity against a variety of tumour cells,
were the natural product BE-26554A (4) and its alkene precursor
16. Other derivatives of note were the potent CF3-alkyl anthra-
cenone-pyranone 22, and the anthracenone-furan derivative 54
3.1.1. General procedure for the deprotection of the isopropyl
group; Method A
TsOHꢁH2O (1.5 equiv) was added to a magnetically stirred solu-
tion or suspension of isopropylether–anthrapyranone in xylene
(0.01–0.04 mM) and heated to reflux for 5–20 min monitoring
showing 0.20
the BE2-C neuroblastoma cell line.
lM and 0.38 lM growth inhibition respectively in

3558
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
Figure 5. Structures of the compounds 47 (molecule 1 only) (CCDC No. 1032509) and 49 (CCDC No. 1032511).
Table 4
Growth inhibition (GI50
,
l
M) of the various anthrafuranones in a panel of human cancer cell lines
Compdb HT29c
U87d
MCF-7e
A2780f
H460g
A431h
Du145i
BE2-Cj
SJ-G2d
MIAk
SMAl
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
—
—
—
—
—
—
—
—
—
—
—
17 1.5
—
1.2 0.62
—
25 2.6
—
6.6 1.7
—
15 2.5
—
2.2 0.21
—
12 2.2
—
1.5 0.15
—
17 1.2
—
3.1 0.63 2.3 0.09
—
—
2.9 0.57 1.77 0.09 0.95 0.13
—
9.4 0.83 9.8 1.1
15 3.2
27 2.2
18 0.58
—
25 2.0
—
21 1.9
—
32 3.4
—
13 2.4
—
9.3 1.8
—
1.3 0.17
—
0.86 0.032 0.88 0.035 1.0 0.065 1.7 0.49
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1.4 0.13
—
11 3.5
1.9 0.09
18 0.88
1.9 0.05
0.88 0.003 4.2 1.2
24 3.5
13 1.7
9.7 0.67
4.7 0.95
2.3 0.49
—
6.1 0.10
11 3.55
18 1.0
1.1 0.26
—
5.9 2.3
4.7 0.82
13 1.9
2.1 0.44
—
6.4 0.83
6.5 2.40
11 0.33
0.83 0.14
—
36 1.7
—
1.7 0.31
—
10 1.4
2.6 1.1
34 2.7
2.2 0.12
—
10 1.7
5.4 3.0
22 2.5
—
—
7.7 1.0
0.46 0.10
25 5.0
23 4.7
0.99 0.11
43 5.1
0.38 0.02
0.75 0.13
20 1.0
19 4.6
4.6 0.78
2.9 0.43
8.4 1.3
32 6.6
25 3.8
37 2.6
4.2 0.89
14 0.67
17 2.4
13 0.67
23 3.8
0.97 0.24 0.66 0.02 0.45 0.009 1.9 0.82 0.59 0.03 0.44 0.02
0.55 0.003 0.69 0.08
2.0 0.07
24 2.7
21 1.5
3.5 0.27
2.1 0.13
2.3 1.4
16 1.0
7.3 0.33
5.0 0.50
2.0 0.067
6.8 2.5
17 1.7
17 3.4
17 0.67
9.6 1.2
1.4 0.09
19 1.0
9.0 2.1
5.8 1.1
4.8 1.5
0.85 0.03
28 3.2
28 5.7
1.9 0.13
2.0 0.17
1.1 0.16
19 0.58
15 2.3
1.8 0.48
29 2.8
12 2.3
2.3 0.29
1.5 0.21
35 2.8
20 2.3
8.4 1.3
5.5 1.8
2.2 0.058 9.7 0.88
1.8 0.033 9.5 0.29
a All compounds were initially assayed at 25
lM in each cell line for growth inhibition and if potent a full dose response analysis was conducted from which the GI50, lM value
was calculated. This value is the concentration of compound that induces 50% growth inhibition after 72 h exposure. (—) indicates the compound had a low cytotoxicity level
in the initial assay.
b
All assays were completed in triplicate with the standard error indicated.
Colon carcinoma.
Glioblastoma.
Breast carcinoma.
Ovarian carcinoma.
Lung carcinoma.
Skin carcinoma.
Prostate carcinoma.
c
d
e
f
g
h
i
j
Neuroblastoma.
Pancreatic carcinoma.
Spontaneous murine astrocytoma.
k
l
every 5 min by tlc (10% EtOAc/PhMe). The reaction mixture was
cooled to room temperature, diluted with NaHCO3 (satd aq) and
extracted with CH2Cl2 (20 mL ꢂ 3), dried over MgSO4 and concen-
trated under reduced pressure. The residue was then purified by
column chromatography (silica, 100% PhMe ? 20% EtOAc/PhMe)
to give the highly coloured phenol as orange to yellow crystalline
solids.
3.1.3. General procedure for the methylation of phenols
MeI (2.0 equiv) was added to a magnetically stirred solution of
phenol–anthraquinone and K2CO3 (3 equiv) in DMF (0.01–
0.04 mM) and heated to 40 °C for 16 h. The reaction mixture was
cooled to room temperature, diluted with H2O and extracted with
CH2Cl2 (20 mL ꢂ 3), dried over MgSO4 and concentrated under
reduced pressure. The resulting residue was then purified by col-
umn chromatography (silica, 100% PhMe ? 30% EtOAc/PhMe) to
give the methylated phenol.
3.1.2. General procedure for the deprotection of the isopropyl
group, Method B
BCl3 (1 M in heptane, 2 equiv) was added dropwise to a magnet-
ically stirred solution of the isopropyl ether (1 equiv) in CH2Cl2 at
ꢀ40 °C. The ensuing mixture was stirred for 15 min before quench-
ing with NaHCO3 (sats 20 mL) and warming to room temperature.
The mixture was treated with water and the solution was
extracted with CH2Cl2, dried over MgSO4, concentrated and the
residue purified by column chromatography.
3.1.3.1. 8-Isopropoxy-3-methyl-9,10-dioxo-2-(3-oxo-3-phenyl-
prop-1-yn-1-yl)-9,10-dihydroanthracen-1-yl
(7). mixture of anthraquinone iodide
benzoate
(277 mg,
A
5
0.526 mmol) and (3-oxo-3-phenylprop-1-yn-1-yl)copper (6)
(152 mg, 0.786 mmol) in DMF (20 mL) was heated to reflux for
1 h. The reaction mixture was concentrated and purified by column
chromatography (silica, 0–5% EtOAc in PhMe) to give the

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3559
anthraquinone 7 (207 mg, 0.392 mmol, 75%) as an orange oil.
Rf = 0.49 (5% EtOAc in PhMe). 1H NMR (500 MHz, CDCl3) d 8.42–
8.33 (m, 2H), 8.10 (d, J = 0.7 Hz, 1H), 8.06–7.99 (m, 2H), 7.87
(‘dd’, J = 7.7, 1.1 Hz, 1H), 7.70 (‘ddd’, J = 7.1, 2.6, 1.3 Hz, 1H), 7.62
(‘dd’, J = 8.3, 7.7 Hz, 1H), 7.60–7.53 (m, 2H), 7.46 (‘tt’, J = 7.5,
1.3 Hz, 1H), 7.31–7.28 (m, 1H), 7.12 (dd, J = 8.3, 7.5 Hz, 2H), 4.49
(hept, J = 6.1 Hz, 1H), 2.74 (d, J = 0.6 Hz, 3H), 1.28 (b‘dd’, J = 13.5,
6.4 Hz, 6H). 13C NMR (126 MHz, CDCl3) d 182.8 (C@O), 180.5
(C@O), 177.3 (C@O), 164.9 (C-Ar), 158.7 (C-Ar), 152.4 (C-Ar),
149.0 (C-Ar), 136.4 (C-Ar), 135.1 (C-Ar), 134.5 (CH-Ar), 134.3 (C-
Ar), 134.3 (CH-Ar), 133.9 (CH-Ar), 130.9 (2 ꢂ CH-Ar), 129.6
(2 ꢂ CH-Ar), 129.5 (C-Ar), 128.7 (2 ꢂ CH-Ar), 128.5 (2 ꢂ CH-Ar),
125.5 (CH-Ar), 125.3 (C-Ar), 124.7 (C-Ar), 123.9 (CH-Ar), 122.7
(C-Ar), 120.1 (CH-Ar), 97.2 (C„C), 84.5 (C„C), 73.9 (CH), 22.0
(2 ꢂ CH3), 21.6 (CH3). IR (Neat, cmꢀ1): 2979 (C-H), 2930 (C-H),
2201 (C„C), 1742 (C@O), 1674 (C@O), 1638, 1583, 1450. HRMS
APCI: (m/z) calculated for C34H25O6 [M+H]+: 529.1651; found:
529.1663.
(Neat, cmꢀ1): 3324 (O-H), 2925 (C-H), 2857 (C-H), 1672 (C@O),
1581 (C@O), 1322, 1281. HRMS APCI: (m/z) calculated for
C
34H37O5 [M+H]+: 525.2641; found: 525.2651.
Dess–Martine Periodinane (455 mg, 1.13 mmol) was added por-
tion-wise to
a solution of anthraquinone alcohol (478 mg,
0.867 mmol) in CH2Cl2 (15 mL) and the mixture stirred at room
temperature for 2 h. The resulting mixture was quenched by the
simultaneous addition of Na2S2O3 (1 M, 10 mL) and NaHCO3 (satd
10 mL) and stirred for 30 min. The organic layer was separated
and the aqueous layer extracted with CH2Cl2 (2 ꢂ 30 mL). The com-
bined organic layers were dried over MgSO4, concentrated and
purified by column chromatography (silica, 0 ? 5% EtOAc in
PhMe) to give the anthraquinone 11 (400 mg, 0.786 mmol, 88%)
as an orange oil. Rf = 0.26 (5% EtOAc in PhMe). 1H NMR
(500 MHz, CDCl3) d 7.88 (d, J = 0.7 Hz, 1H), 7.81 (dd, J = 7.7,
1.1 Hz, 1H), 7.71–7.66 (m, 2H), 7.61 (dd, J = 8.3, 7.7 Hz, 1H), 7.42–
7.36 (m, 2H), 7.36–7.30 (m, 2H), 5.25 (s, 2H), 4.67 (hept,
J = 6.1 Hz, 1H), 2.58 (s, 3H), 2.56 (t, J = 7.3 Hz, 2H), 1.63–1.69 (m,
2H), 1.46 (d, J = 6.0 Hz, 6H), 1.22–1.33 (m, 6H), 0.88 (t, J = 7.0 Hz,
3H). 13C NMR (126 MHz, CDCl3) d 187.8 (C@O), 183.4 (C@O),
181.8 (C@O), 161.2 (C-Ar), 158.1 (C-Ar), 148.4 (C-Ar), 136.9 (C-
Ar), 135.1 (C-Ar), 134.7 (C-Ar), 134.0 (CH-Ar), 129.0 (2 ꢂ CH-Ar),
128.5 (2 ꢂ CH-Ar), 128.4 (CH-Ar), 126.9 (C-Ar), 125.4 (C-Ar),
123.4 (C-Ar), 123.0 (C-Ar), 122.5 (CH-Ar), 119.5 (CH-Ar), 98.2
(C„C), 84.1 (C„C), 73.0 (Ph-CH2), 45.8 (COH), 31.6 (CH2), 28.8
(CH2), 24.1 (CH2), 22.6 (CH2), 22.2 (2 ꢂ CH3), 21.5 (Ar-CH3), 14.13
(CH3). IR (Neat, cmꢀ1): 2957 (C-H); 2929 (C-H), 2858 (C-H), 2195
(C„C), 1670 (C@O), 1582, 1262. HRMS APCI: (m/z) calculated for
3.1.3.2.
11-Hydroxy-5-methyl-2-phenyl-4H-naphtho[2,3-
H2SO4 (98%, 5 mL) was added
h]chromene-4,7,12-trione (8).
to anthraquinone 7 (122 mg, 0.231 mmol) and slowly heated to
60 °C for 1 h. The mixture was poured carefully into H2O (50 mL)
and extracted with CH2Cl2 (3 ꢂ 30 mL), dried (MgSO4), concen-
trated and purified by column chromatography (silica, 0–2%
EtOAc in PhMe) to give the anthrapyranone 8 (49 mg, 0.127 mmol,
55%) as a yellow solid. Rf = 0.33 (2% EtOAc in PhMe). Mp P260 °C.
1H NMR (400 MHz, CDCl3) d 12.99 (s, 1H), 8.32 (dd, J = 6.4, 2.4 Hz,
2H), 8.11 (s, 1H), 7.84 (dt, J = 7.4, 1.0 Hz, 1H), 7.70 (t, J = 7.7 Hz, 1H),
C
34H37O5 [M+H]+: 525.2641; found: 525.2665.
7.65–7.58 (m, 3H), 7.41–7.37 (m, 1H), 6.94 (s, 1H), 3.06 (s, 3H). 13
C
NMR (126 MHz, CDCl3) d 187.6 (C@O), 182.1 (C@O), 179.4 (C@O),
163.4 (C-Ar), 162.8 (CH-Ar), 156.6 (C-Ar), 150.0 (C-Ar), 136.6
(CH-Ar), 136.3 (C-Ar), 132.5 (C-Ar), 132.3 (CH-Ar), 130.8 (C-Ar),
129.4 (2 ꢂ CH-Ar), 127.1 (2 ꢂ CH-Ar), 126.9 (C-Ar), 126.1 (CH-Ar),
125.6 (CH-Ar), 120.1 (C-Ar), 119.6 (CH-Ar), 117.0 (C-Ar), 109.1
(CH-Ar), 24.4 (Ar-CH3). IR (KBr pellet, cmꢀ1): 3463 (O-H), 3065
(C-H), 2924 (C-H), 2852 (C-H), 2651 (C@O), 1636 (C@O), 1462.
HRMS EI+: (m/z) calculated for C24H14O5 [M+H]+: 382.0841; found:
382.0844.
3.1.3.4. 11-Hydroxy-5-methyl-2-hexyl-4H-naphtho[2,3-h]chro-
mene-4,7,12-trione (12). H2SO4 (98%, 5 mL) was added to
anthraquinone 7 (100 mg, 0.236 mmol) and slowly stirred at room
temperature for 4 h. The mixture was poured carefully into H2O
(50 mL) and extracted with CH2Cl2 (3 ꢂ 30 mL), dried (MgSO4),
concentrated and purified by column chromatography (silica,
0 ? 2% EtOAc in PhMe) to give the anthrapyranone 12 (30 mg,
0.078 mmol, 33%) as a yellow solid. Rf = 0.33 (2% EtOAc in PhMe).
Mp = 175–178 °C. 1H NMR (500 MHz, CDCl3) d 12.87 (s, 1H), 8.04
(s, 1H), 7.80 (dd, J = 7.5, 1.1 Hz, 1H), 7.68–7.64 (m, 1H), 7.35 (dd,
J = 8.4, 1.2 Hz, 1H), 6.25 (s, 1H), 3.01 (s, 3H), 2.74 (t, J = 7.6 Hz,
2H), 1.93–1.86 (m, 2H), 1.46 (d, J = 7.2 Hz, 2H), 1.39–1.33 (m,
4H), 0.91 (t, J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) d 187.4
(C@O), 182.1 (C@O), 179.3 (C@O), 169.7 (C-Ar), 162.7 (C-Ar),
156.9 (C-Ar), 149.8 (C-Ar), 136.4 (Ar-CH), 136.0 (C-Ar), 132.4 (C-
Ar), 126.6 (C-Ar), 125.7 (Ar-CH), 125.4 (Ar-CH), 119.9 (C-Ar),
119.4 (Ar-CH), 117.0 (C-Ar), 112.2 (Ar-CH), 34.0 (CH2), 31.6 (CH2),
28.8 (CH2), 26.5 (CH2), 24.4 (CH2), 22.6 (Ar-CH3), 14.2 (CH3).
HRMS APCI: m/z calculated for C24H23O5 [M+H]+: 391.1545; found:
391.1596. IR (Neat, cmꢀ1) 3062 (C-H), 2954 (C-H), 2919 (C-H),
2852 (C-H), 1669 (C@O), 1651 (C@O), 1625 (C@O), 1583 (C@C),
1456, 1269, 776.
3.1.3.3.
1-(Benzyloxy)-8-isopropoxy-3-methyl-2-(3-oxooct-1-
yn-1-yl)anthracene-9,10-dione (11) through 1-(benzyloxy)-2-
(3-hydroxynon-1-yn-1-yl)-8-isopropoxy-3-methylanthracene-
9,10-dione.
A warmed (60 °C) degassed solution of Na2CO3
(310 mg, 2.92 mmol) in H2O (4 mL) was added to a preheated well
stirred mixture of aryl iodide 9 (500 mg, 0.976 mmol), Pd(PPh3)2Cl2
(68 mg, 0.098 mmol) and propargyl alcohol 10 (272 mg,
1.95 mmol) in dioxane (15 mL). The ensuing solution was then
heated to 80 °C for 3 h. The reaction mixture was concentrated
and purified by column chromatography (silica, 0 ? 10% EtOAc in
PhMe) to give the title anthraquinone alcohol (207 mg,
0.392 mmol, 75%) as an orange oil. Rf = 0.36 (10% EtOAc in PhMe).
1H NMR (400 MHz, CDCl3) d 7.79 (s, 1H), 7.76 (d, J = 7.6 Hz, 1H),
7.65 (d, J = 7.1 Hz, 2H), 7.54 (t, J = 8.0 Hz, 1H), 7.35 (‘t’, J = 7.3 Hz,
2H), 7.30 (m, J = 7.2 Hz, 1H), 7.23 (m, J = 10.1 Hz, 1H), 5.20 (s,
2H), 4.61 (hept, J = 6.1 Hz, 1H), 4.53 (bt, J = 6.7 Hz, 1H), 2.45 (s,
3H), 1.99 (s, 1H), 1.74–1.59 (m, 3H), 1.40 (m, 6H), 1.24 (d,
J = 10.8 Hz, 8H), 0.83 (t, J = 6.7 Hz, 3H). 13C NMR (101 MHz,
CDCl3) d 183.6 (C@O), 182.2 (C@O), 159.7 (C-Ar), 158.0 (C-Ar),
146.9 (C-Ar), 137.6 (CH-Ar), 135.2 (C-Ar), 133.8 (CH-Ar), 133.0
(C-Ar), 128.6 (2 ꢂ CH-Ar), 128.4 (2 ꢂ CH-Ar), 128.1 (CH-Ar), 127.0
(C-Ar), 125.7 (C-Ar), 125.6 (C-Ar), 123.3 (CH-Ar), 122.5 (CH-Ar),
119.5 (CH-Ar), 103.5 (C-Ar), 79.3 (C„C), 76.3 (C„C), 73.1 (O-
CH(CH3)2), 63.2 (Ph-CH2), 62.9 (CH-OH), 37.8 (HO-CH2), 37.6
(HO-CH2), 31.8 (CH2), 29.1 (CH2), 29.0 (CH2), 25.3 (CH2), 25.1
(CH2), 22.7 (CH2), 22.2 (2 ꢂ CH3), 21.5 (Ar-CH3), 14.2 (CH3); IR
3.1.3.5. 2-Ethyl-11-hydroxy-5-methyl-4H-naphtho[2,3-h]chro-
mene-4,7,12-trione (17).
Anthra-4-pyranone 17 was pre-
pared according to the general procedure for the deprotection of
the isopropyl group, Method A, using the anthra-4-pyranone 14
(67 mg, 0.151 mmol) in xylene (5 mL). The anthrafuran 17 was
obtained as orange crystals (53 mg, 0.131 mmol, 87%). Rf = 0.27
(10% EtOAc in PhMe); mp = 248–251 °C. 1H NMR (500 MHz,
CDCl3) d 12.86 (s, 1H), 8.05 (s, 1H), 7.80 (dd, J = 7.5, 1.2 Hz, 1H),
7.69–7.63 (m, 1H), 7.35 (dd, J = 8.4, 1.2 Hz, 1H), 6.26 (s, 1H),
3.05–2.95 (m, 2H), 3.00 (s, 3H) 2.80 (q, J = 5.0 Hz, 2H), 1.44 (t,
J = 5.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) d 187.4 (C@O), 182.1
(C@O), 179.4 (C@O), 170.6 (C-Ar), 162.7 (C-Ar), 156.8 (C-Ar),
149.9 (C-Ar), 136.4 (Ar-CH), 136.1 (C-Ar), 132.4 (C-Ar), 126.6 (C-

3560
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
Ar), 125.7 (Ar-CH), 125.4 (Ar-CH), 119.9 (C-Ar), 119.4 (Ar-CH),
117.0 (C-Ar), 111.4 (Ar-CH), 27.4 (CH2), 24.4 (Ar-CH3), 11.0 (CH3).
HRMS APCI: calculated for C20H15O5 [M+H]+: 335.0919; found:
335.0906. IR (Neat, cmꢀ1) 2976 (C-H), 1646 (C@O), 1621 (C@O),
1262, 907.
3.1.4.3. 11-Hydroxy-5-methyl-2-propyl-4H-naphtho[2,3-h]chro-
mene-4,7,12-trione (18). Anthra-4-pyranone 18 was pre-
pared according to the general procedure for the deprotection of
the isopropyl group, Method A. Isopropyl anthra-4-pyranone
(32 mg, 0.082 mmol) in xylene (3 mL) were added to the reaction
flask. The anthrapyranone 18 was obtained as yellow crystals
(26 mg, 0.074 mmol, 90%). Rf = 0.35 (10% EtOAc in PhMe).
Mp = 185–187 °C. 1H NMR (400 MHz, CDCl3) d 12.81 (s, 1H), 7.97
(s, 1H), 7.75 (d, J = 7.3 Hz, 1H), 7.63 (t, J = 7.9 Hz, 1H), 7.31 (d,
J = 8.3 Hz, 1H), 6.22 (s, 1H), 2.97 (s, 3H), 2.70 (t, J = 7.5 Hz, 2H),
1.92 (d, J = 7.4 Hz, 2H), 1.08 (t, J = 7.3 Hz, 3H). 13C NMR (101 MHz,
CDCl3) d 187.2 (C@O), 181.9 (C@O), 179.1 (C-Ar), 169.3 (C-Ar),
162.6 (C-Ar), 156.7 (C-Ar), 149.8 (C-Ar), 136.4 (Ar-CH), 135.9 (C-
Ar), 132.3 (C-Ar), 126.5 (C-Ar), 125.6 (Ar-CH), 125.4 (Ar-CH),
119.7 (C-Ar), 119.3 (Ar-CH), 116.8 (C-Ar), 112.3 (Ar-CH), 35.9
(CH2), 24.3 (CH2), 20.0 (Ar-CH3), 13.7 (CH3). HRMS APCI: m/z calcu-
lated for C21H17O5 [M+H]+: 349.1076; found: 349.1070. IR (Neat,
cmꢀ1) 3073 (C-H), 2962 (C-H), 2927 (C-H), 1663 (C@O), 1637
(C@O), 1582 (C@C), 1456, 1280, 671.
3.1.4. General method for the synthesis of anthra-4-pyranones
via b-ketosulfoxides
Piperidine (catalytic) was added to a solution of b-keto-sulfox-
ide (1 equiv) and aldehyde (2.0 equiv) in toluene (5 mL). The ensu-
ing mixture was slowly heated to reflux for 2–3 h, cooled to room
temperature and purified by column chromatography (silica,
PhMe ? ca. 10–20% EtOAc/PhMe) to give the product pyran-4-
one generally as an orange-yellow solid.21
3.1.4.1. 11-Hydroxy-5-methyl-2-propyl-4H-naphtho[2,3-h]chro-
mene-4,7,12-trione (18): Three steps through 11-isopropoxy-
7,12-dimethoxy-5-methyl-2-propyl-4H-naphtho[2,3-h]chro-
men-4-one.
Anthra-4-pyranone 18 was prepared according
to the general procedure for the synthesis of anthra-4-pyranones
via b-ketosulfoxides. b-Keto-sulfoxide 13 (189 mg, 0.513 mmol)
3.1.4.4. 2-Ethyl-11-methoxy-5-methyl-4H-naphtho[2,3-h]chro-
and butyraldehyde (93
lL, 1.03 mmol) in toluene (5 mL) were
mene-4,7,12-trione (19).
Anthra-4-pyranone 19 was pre-
added to the reaction flask. The anthra-4-pyranone dimethoxy
anthracene was obtained as orange-yellow crystals (153 mg,
4.26 mmol, 83%). Rf = 0.25 (10% EtOAc in PhMe). Mp = 112–
117 °C. 1H NMR (500 MHz, CDCl3) d 7.86 (dd, J = 8.6, 0.9 Hz, 1H),
7.79 (d, J = 1.2 Hz, 1H), 7.45 (dd, J = 8.6, 7.6 Hz, 1H), 6.86 (d,
J = 7.5 Hz, 1H), 6.33 (s, 1H), 4.83–4.72 (m, 1H), 4.03 (s, 3H), 3.96
(s, 3H), 2.96 (d, J = 1.1 Hz, 3H), 2.77 (t, J = 7.5 Hz, 2H), 1.95–1.86
(m, 2H), 1.52 (d, J = 6.0 Hz, 6H), 1.09 (t, J = 7.4 Hz, 3H). 13C NMR
(126 MHz, CDCl3) d 180.1 (C@O), 167.2 (C-Ar), 157.5 (C-Ar), 155.3
(C-Ar), 152.1 (C-Ar), 146.8 (C-Ar), 134.7 (C-Ar), 130.2 (C-Ar),
127.4 (CH-Ar), 126.2 (C-Ar), 120.4 (C-Ar), 120.0 (C-Ar), 119.7
(CH-Ar), 115.8 (C-Ar), 114.6 (CH-Ar), 113.1 (CH-Ar), 108.0 (CH-
Ar), 71.0 (OCH(CH3)2), 63.6 (OCH3), 62.8 (OCH3), 35.8 (CH2), 24.1
(2 ꢂ CH3), 22.0 (Ar-CH3), 20.1 (CH2), 13.75 (CH3). HRMS APCI: cal-
culated for C26H28O5, [M+H]+; 421.2015; found: 421.2025. IR (Neat,
cmꢀ1) 3092 (C-H), 2967 (C-H), 2935 (C-H), 1659 (C@O), 1630,
1363, 656.
pared according to the general procedure for the methylation of
the phenol group using anthra-4-pyranone 17 (68 mg, 0.20 mmol).
The anthrapyranone 19 was obtained as a yellow-orange solid
(61 mg, 0.18 mmol, 86%). Rf = 0.38 (30% EtOAc in PhMe).
Mp = 220–222 °C. 1H NMR (400 MHz, CDCl3) d 7.91 (d, J = 0.7 Hz,
1H), 7.86 (dd, J = 7.7 Hz, 1.1 Hz), 7.68 (‘t’, J = 8.0 Hz, 1H), 7.35 (dd,
J = 8.5 Hz, 0.9 Hz, 1H), 6.21 (s, 1H), 4.04 (s, 3H), 2.96 (d, J = 0.7 Hz,
3H), 2.78 (dq, J = 7.5 Hz, 0.6 Hz, 2H), 1.41 (t, J = 7.5 Hz, 3H). 13C
NMR (151 MHz, CDCl3) d 183.3 (C@O), 180.8 (C@O), 179.7 (C@O),
170.8 (C-Ar), 159.8 (C-Ar), 156.1 (C-Ar), 147.4 (C-Ar), 135.0 (C-
Ar), 134.6 (Ar-CH), 126.6 (C-Ar), 124.6 (Ar-CH), 123.5 (C-Ar),
122.6 (C-Ar), 119.4 (Ar-CH), 118.6 (Ar-CH), 111.1 (Ar-CH), 56.8
(OCH3), 27.4, 24.1 (Ar-CH3), 11.1. HRMS APCI: m/z calculated for
C
21H17O5 [M+H]+: 349.1076; found: 349.1066. IR (KBr Pellet,
cmꢀ1) 2967 (C-H), 2931 (C-H), 2942 (C-H), 1669 (C@O), 1647
(C@O), 1584 (C@C), 1274, 1226, 952.
3.1.4.5.
11-Methoxy-5-methyl-2-propyl-4H-naphtho[2,3-
Anthra-4-pyranone 20 was
3.1.4.2.
h]chromene-4,7,12-trione.
11-Isopropoxy-5-methyl-2-propyl-4H-naphtho[2,3-
HNO3 (4 M, ca. 3.5 mL) was
h]chromene-4,7,12-trione (20).
prepared according to the general procedure for the methylation
of the phenol group using anthra-4-pyranone 18 (30 mg,
0.086 mmol). The anthrapyranone 20 was obtained as a yellow
solid (20 mg, 0.055 mmol, 64%). Rf = 0.26 (20% EtOAc in PhMe);
mp = 214–217 °C. 1H NMR (400 MHz, CDCl3) d 7.93 (d, J = 0.8 Hz,
1H), 7.88 (dd, J = 7.8, 1.1 Hz, 1H), 7.68–7.72 (m, 1H) 7.37 (dd,
J = 8.5, 1.0 Hz, 1H), 6.22 (s, 1H), 4.05 (s, 3H), 2.97 (d, J = 0.7 Hz,
3H), 2.72 (t, J = 7.4 Hz, 2H), 1.92 (dq, 7.4 Hz, 7.4 Hz, 2H), 1.07 (t,
J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) d 183.3 (C@O), 180.9
(C@O), 179.6 (C@O), 169.6 (C-Ar), 159.8 (C-Ar), 156.1 (C-Ar),
147.4 (C-Ar), 135.1 (C-Ar), 134.6 (Ar-CH), 134.6 (Ar-CH), 126.6
(C-Ar), 124.6 (Ar-CH), 123.6 (C-Ar), 122.6 (C-Ar), 119.4 (Ar-CH),
118.6 (Ar-CH), 112.0 (Ar-CH), 56.9 (O-CH3), 36.0 (Ar-CH2), 24.1
(CH2), 20.1 (Ar-CH3), 13.7 (CH3). HRMS APCI: m/z calculated for
added gradually as a steady stream into stirred mixture of
anthra-4-pyranone dimethoxy anthracene (197 mg, 0.485 mmol)
and Ag(II)O (300 mg, 2.42 mmol) in 1,4-dioxane (7 mL) until all
of the suspended Ag(II)O dissolved. The mixture was stirred for
15 min before H2O (20 mL) was added. The mixture was extracted
with CH2Cl2 (3 ꢂ 30 mL), washed with H2O (100 mL), dried over
MgSO4, and the combined organic extracts concentrated and the
residue purified by column chromatography (silica, 100%
PhMe ? 15% EtOAc/PhMe) to give the anthraquinone (157 mg,
0.403 mmol, 83%) as a yellow solid. Rf = 0.35 (10% EtOAc in
PhMe). Mp = 204–206 °C. 1H NMR (600 MHz, CDCl3) d 7.83 (d,
J = 0.5 Hz, 1H), 7.79 (dd, J = 7.6, 0.9 Hz, 1H), 7.59 (t, J = 8.1 Hz 1H),
7.31 (d, J = 8.1 Hz, 1H), 6.17 (s, 1H), 4.64 (hept, J = 6.1 Hz, 1H),
2.91 (s, 3H), 2.69 (t, J = 7.5 Hz, 2H), 1.93–1.85 (m, 2H), 1.45 (d,
J = 6.1 Hz, 6H), 1.05 (t, J = 7.4 Hz, 3H). 13C NMR (151 MHz, CDCl3)
d 183.2 (C@O), 180.4 (C@O), 179.5 (C@O), 169.3 (C-Ar), 158.22
(C-Ar), 155.8 (C-Ar), 146.9 (C-Ar), 135.0 (C-Ar), 134.6 (C-Ar),
134.0 (C-Ar), 126.4 (C-Ar), 125.2 (C-Ar), 124.4 (CH-Ar), 122.9 (C-
Ar), 122.8 (CH-Ar), 119.6 (CH-Ar), 111.9 (CH-Ar), 73.2
(OCH(CH3)2), 35.8 (CH2), 23.9 (CH2), 22.1 (2 ꢂ CH3), 19.7 (CH2),
13.7 (CH3). HRMS APCI: calculated for C24H23O5 [M+H]+:
391.1545; found: 391.1522. IR (Neat, cmꢀ1): 2970 (C-H), 2926
(C-H), 2873 (C-H), 1673 (C@O), 1656 (C@O), 1581 (C@C), 1463,
1285, 750.
C
22H19O5 [M+H]+: 363.1232; found: 363.1245. IR (KBr Pellet,
cmꢀ1) 2927 (C-H), 2842 (C-H), 1671 (C@O), 1648 (C@O), 1585
(C@C), 1301, 1264, 944, 754.
3.1.4.6. 11-Isopropoxy-5-methyl-2-(3,3,3-trifluoropropyl)-4H-
naphtho[2,3-h]chromene-4,7,12-trione (21).
HNO3 (4 M,
ca. 3 mL) was added gradually as a steady stream into stirred mix-
ture of dimethoxy anthracene (140 mg, 0.295 mmol) and Ag(II)O
(183 mg, 1.47 mmol) in 1,4-dioxane (7 mL) until all of the sus-
pended Ag(II)O dissolved. The mixture was stirred for 15 min
before H2O (20 mL) was added. The mixture was extracted with

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3561
CH2Cl2 (3 ꢂ 30 mL), washed with H2O (100 mL), dried (MgSO4),
and the combined organic extracts concentrated. The resulting
residue was purified by column chromatography (silica,
PhMe ? 15% EtOAc/PhMe) to give anthraquinone 21 (113 mg,
0.254 mmol, 86%) as a yellow-orange solid. Rf = 0.18 (10% EtOAc
in PhMe). Mp = 262–263 °C. 1H NMR (500 MHz, CDCl3) d 7.94 (d,
J = 0.8 Hz, 1H), 7.86 (dd, J = 7.7, 1.1 Hz, 1H), 7.65 (dd, J = 8.3,
7.8 Hz, 1H), 7.36 (d, J = 7.8 Hz, 1H), 6.27 (s, 1H), 4.68 (hept,
J = 6.2 Hz, 1H), 3.01 (dd, J = 9.2, 6.4 Hz, 2H), 2.97 (d, J = 0.6 Hz,
3H), 2.87 (ddt, J = 18.2, 10.6, 9.0 Hz, 2H), 1.48 (d, J = 6.1 Hz, 6H).
13C NMR (126 MHz, CDCl3) d 183.3 (C@O), 180.6 (C@O), 179.3
(C@O), 165.0 (C-Ar), 158.4 (C-Ar), 155.7 (C-Ar), 147.3 (C-Ar),
135.3 (C-Ar), 134.8 (C-Ar), 134.3 (CH-Ar), 126.4 (C-Ar), 125.1 (C-
Ar), 124.9 (CH-Ar), 122.9 (CH-Ar), 122.9, 119.8 (CH-Ar), 112.5
(CH-Ar), 73.3 (OC(CH3)2), 30.4 (q, J = 29.8 Hz, CF3), 27.0 (q,
J = 3.5 Hz, CH2CF3), 23.9 (Ar-CH3), 22.1 (2 ꢂ CH3). HRMS APCI: cal-
culated for C24H20O5F3: 445.1263; found: 445.1286. IR (Neat,
cmꢀ1): 3058 (C-H), 2985 (C-H), 2932 (C-H), 1674 (C@O), 1655
(C@O), 1582 (C@C).
(781 mg, 5.98 mmol, 59%) was isolated as a yellow powder and
used without need for further purification. Mp P180 °C decom-
poses. IR (Neat, cmꢀ1) 2955 (C-H), 2937 (C-H), 1930 (C„C), 715.
3.1.5.3. (Phenylethynyl)copper 42d.
Prepared using the gen-
eral procedure for the synthesis of cuprous acetylides using pheny-
lacetylene (1.0 mL, 9.10 mmol). Phenylethynyl-copper 42d
(824 mg, 5.05 mmol, 55%) was obtained as a bright yellow powder
and used without further purification. Mp P180 °C decomposes; IR
(KBr, cmꢀ1) 3048 (C-H), 1930 (C„C), 1906 (C„C), 1595, 1482,
1441, 744, 682. Anal. Calcd for C8H5Cu: C, 58.35; H, 3.06; N, 0.00.
Found: C, 58.60; H, 2.97; N, 0.00.
3.1.5.4. (3-Oxo-3-phenylprop-1-ynyl)copper 6.
Prepared
using the general procedure for the synthesis of cuprous acetylides
using 1-phenyl-2-propyn-1-one (264 mg, 2.03 mmol). 3-Oxo-3-
phenylprop-1-ynyl-copper
6 (216 mg, 1.12 mmol, 55%) was
obtained as a red powder and used without further purification.
Mp P180 °C decomposes; IR (KBr, cmꢀ1) 3057 (C-H), 2923 (C-H),
1932 (C„C), 1906 (C„C), 1611 (C@O), 1575, 1243, 688. Anal.
Calcd for C9H5CuO: C, 56.10; H, 2.62; N, 0.00. Found: C, 56.17; H,
2.64; N, 0.00.
3.1.4.7.
11-Hydroxy-5-methyl-2-(3,3,3-trifluoropropyl)-4H-
(22). Anthra-4-
naphtho[2,3-h]chromene-4,7,12-trione
pyranone 22 was prepared according to the general procedure
for the deprotection of the isopropyl group, Method A, using
anthra-4-pyranone 21 (67 mg, 0.151 mmol). The anthrapyranone
22 was obtained as orange crystals (53 mg, 0.131 mmol, 87%).
Rf = 0.27 (10% EtOAc in PhMe). Mp = 248–251 °C. 1H NMR
(500 MHz, CDCl3) d 12.79 (s, 1H), 8.05 (s, 1H), 7.80 (dd, J = 7.5,
1.2 Hz, 1H), 7.69–7.63 (m, 1H), 7.36 (dd, J = 8.4, 1.2 Hz, 1H), 6.31
(s, 1H), 3.05–2.95 (m, 2H), 3.00 (s, 3H) 2.91–2.78 (m, 2H). 13C
NMR (126 MHz, CDCl3) d 187.3 (C@O), 181.9 (C@O), 178.8 (C-Ar),
165.2 (C-Ar), 162.8 (C-Ar), 156.6 (C-Ar), 150.0 (C-Ar), 136.6 (Ar-
CH), 136.2 (C-Ar), 132.3 (C-Ar), 127.6 (C-Ar), 126.4 (C-Ar), 126.0
(Ar-CH), 125.6 (Ar-CH), 125.4 (C-Ar), 119.8 (C-Ar), 119.6 (Ar-CH),
116.9 (C-Ar), 112.9 (Ar-CH), 30.6 (q, JC-F = 29.9 Hz, CF3), 27.1 (q,
J = 3.5 Hz, CH2CF3), 24.3 (Ar-CH3). HRMS APCI: m/z calculated for
3.1.5.5. (5-Cyanopent-1-ynyl)copper 42e.
Prepared using the
general procedure for the synthesis of cuprous acetylides using 5-
hexynenitrile (0.2 mL, 1.91 mmol). 5-Cyanopent-1-ynyl-copper
42e (102 mg, 1.09 mmol, 57%) was obtained as a yellow powder
and used without further purification. Mp P180 °C decomposes.
IR (Neat, cmꢀ1) 3343 (OH), 2941 (C-H), 2247 (C„N), 1570, 1424,
901. Anal. Calcd for C6H6NCu: C, 46.29; H, 3.89; N, 9.00. Found:
C, 46.34; H, 3.77; N, 9.01.
3.1.5.6. (5-Chloropent-1-ynyl)copper 42f.
Prepared using
the general procedure for the synthesis of cuprous acetylides using
5-chloro-1-pentyne (0.5 mL, 5.04 mmol). 5-Chloropent-1-ynyl-
copper 42f (498 mg, 3.02 mmol, 60%) was obtained as a yellow
powder and used without further purification. Mp P180 °C
decomposes. IR (neat, cmꢀ1) 3576, 2954, (C-H), 1930 (C„C),
1425, 1264, 770, 651; Anal. Calcd for C5H6ClCu: C, 36.37; H, 3.66;
N, 0.00. Found: C, 36.31; H, 3.59; N, 0.00.
C
21H13F3O5: 402.0715; found: 402.0716. IR (Neat, cmꢀ1) 3067 (C-
H), 2925 (C-H), 2853 (C-H), 1659 (C@O), 1636 (C@O), 1584
(C@C), 1456, 1373, 1088, 654.
3.1.5. General method for the synthesis of cuprous acetylide
(Table 3)
3.1.5.7. (3-Oxooct-1-ynyl)copper 42g.
Prepared using the
A solution of alkyne (1 equiv) in EtOH (0.3 M) was added slowly
over 1 min to a magnetically stirred solution of CuCl (1.2 equiv) in
NH4OH (28%, 1.6 M). The mixture was stirred for 15 min upon
which time the cuprous acetylide precipitated. H2O (100 mL per
1 mL of alkyne) is added and the precipitate collected by vacuum
filtration, washed with NH4OH (5%, 25 mL per 100 mL of
alkyne ꢂ 2) plus H2O (25 mL per 1 mL of alkyne ꢂ 2) and dried in
a vacuum desiccator overnight to give the cuprous acetylide as a
coloured powder and which was used without need for further
purification.
general procedure for the synthesis of cuprous acetylides using 1-
octyne-3-one (233 mg, 1.88 mmol). The 3-oxooct-1-ynyl-copper
42g (221 mg, 1.18 mmol, 63%) was obtained as an orange powder
and used without further purification. Mp P180 °C decomposes;
IR (Neat, cmꢀ1) 3676, 2960 (C-H), 2935 (C-H), 2901 (C-H), 1909
(C„C), 1639 (C@O), 1409, 1080, 1066, 1057, 720; Anal. Calcd for
C8H11OCu: C, 51.46; H, 5.94; N, 0.00. Found: C, 51.33; H, 5.87; N, 0.00.
3.1.5.8. ((1-Hydroxycyclohexyl)ethynyl)copper 42i.
using the general procedure for the synthesis of cuprous acetylides
using 1-ethynylcyclohexanol (1.0 g, 8.05 mmol). ((1-
Prepared
3.1.5.1. Oct-1-ynylcopper 42a.
Prepared using the general
Hydroxycyclohexyl)ethynyl)copper 42i (497 mg, 2.66 mmol, 33%)
was obtained as a yellow powder. Mp @ >180 °C decomposes. IR
(Neat, cmꢀ1) 3371 (OH), 2931 (C-H), 2856, 1703 (C„C), 1447,
1067, 964. This copper acetylide was extremely sensitive to the
atmosphere and used without further purification.
procedure for the synthesis of cuprous acetylides using n-octyne
(1.00 mL, 6.78 mmol). The resulting cuprous acetylide 42a
(725 mg, 4.20 mmol, 62%) was isolated as a yellow powder and
used without need for further purification. Mp P180 °C decom-
poses. IR (Neat, cmꢀ1) 2959 (C-H), 2933 (C-H), 2891 (C-H), 2858
(C-H), 2874 (C-H), 1928 (C„C), 1473, 1460, 717. Anal. Calcd for
C8H13Cu: C, 55.63; H, 7.59; N, 0.00. Found: C, 55.65; H, 7.68; N,
0.00.
3.1.6. General method for the synthesis of anthrafuranones
A mixture of aryl iodide 5 (200–300 mg, 1 equiv), cuprous acet-
ylide (1.1–1.5 equiv) and DMEDA, (3.5 equiv) in toluene (5 mL) was
heated to 90 °C for 18 h. The reaction mixture was cooled to room
temperature and purified directly by column chromatography (sil-
ica, ca. 100% PhMe ? 20% EtOAc/PhMe) to give the anthrafurans
usually as yellow to orange solids.
3.1.5.2. Pent-1-ynylcopper 42b.
procedure for the synthesis of cuprous acetylides using n-pentyne
(1.00 mL, 10.14 mmol). The resulting cuprous acetylide 42b
Prepared using the general

3562
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3.1.6.1.
6,11-dione (43).
2-Hexyl-10-isopropoxy-4-methylanthra[1,2-b]furan-
Anthrafuranone 43 was prepared according
to the general method for the synthesis of anthrafuranones using
3.1.6.4. 10-Hydroxy-4-methyl-2-propylanthra[1,2-b]furan-6,11-
dione (46). Anthrafuran 46 was prepared according to the
general procedure for the deprotection of the isopropyl group,
Method A, using anthrafuran 45 (43 mg, 0.119 mmol). The anthra-
furan 46 was obtained as an orange solid (29 mg, 0.091 mmol,
77%). Rf = 0.35 (1% EtOAc in PhMe). Mp = 155–162 °C. 1H NMR
(500 MHz, CDCl3) d 12.72 (s, 1H), 7.89 (s, 1H), 7.76 (d, J = 7.5 Hz,
1H), 7.60 (t, J = 7.6 Hz, 1H), 7.24 (d, J = 8.3 Hz, 1H), 6.48 (s, 1H),
2.89 (t, J = 7.5 Hz, 2H), 2.56 (s, 3H), 1.91–1.81 (m, 2H), 1.08 (t,
J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) d 188.4 (C@O), 182.7
(C@O), 165.6 (C-Ar), 162.4 (C-Ar), 151.5 (C-Ar), 138.0 (C-Ar),
136.4 (C-Ar), 136.3 (Ar-CH), 133.5 (C-Ar), 129.4 (C-Ar), 124.3 (Ar-
CH), 122.7 (Ar-CH), 119.3 (Ar-CH), 116.4 (C-Ar), 116.0 (C-Ar),
101.0 (Ar-CH), 30.8 (CH2CH2CH3), 21.1 (CH2CH2CH3), 19.4
(ArCH3), 13.9 (CH3). HRMS EI: m/z calculated for C20H16O4:
320.1049; found: 320.1051. IR (KBr Pellet, cmꢀ1) 2960 (C-H),
2872 (C-H), 1664 (C@O), 1634 (C@O), 1581 (C@C), 1468, 790, 694.
aryl iodide
(123 mg,
5
(200 mg, 0.474 mmol), oct-1-ynylcopper 42a
0.710 mmol) and
N,N0-dimethylethylenediamine,
(179 lL, 1.66 mmol). The reaction mixture was cooled to room
temperature and purified directly by column chromatography (sil-
ica, 100% PhMe ? 5% EtOAc/PhMe) to give the anthrafuran 43
(163 mg, 0.403 mmol, 85%) as a yellow solid. Rf = 0.35 (5% EtOAc
in PhMe). Mp = 88–92 °C. 1H NMR (500 MHz, CDCl3) d 7.92–7.86
(m, 2H), 7.61 (t, J = 8.0 Hz, 1H), 7.30 (d, J = 8.4 Hz, 1H), 6.48 (d,
J = 0.7 Hz, 1H), 4.73 (hept, J = 6.0 Hz, 1H), 2.92 (t, J = 7.7 Hz, 2H),
2.56 (s, 3H), 1.85–1.78 (m, 2H), 1.50 (d, J = 6.1 Hz, 6H), 1.40–1.47
(m, J = 14.7, 6.9 Hz, 3H), 1.30–1.37 (m, J = 8.9, 5.4 Hz, 5H), 0.90 (t,
J = 7.0 Hz, 3H). 13C NMR (126 MHz, CDCl3) d 184.0 (C@O), 181.8
(C@O), 165.7 (CH-Ar), 158.9 (CH-Ar), 151.5 (C-Ar), 136.6 (C-Ar),
135.9 (C-Ar), 135.8 (C-Ar), 134.2 (CH-Ar), 128.4 (C-Ar), 123.0 (C-
Ar), 121.6 (CH-Ar), 121.3 (CH-Ar), 119.6 (CH-Ar), 118.3 (C-Ar),
100.7 (CH-Ar), 72.3 (OCH(CH3)2), 31.6 (CH2), 29.1, 28.9, 27.5,
22.7, 22.2 (2 ꢂ CH3), 19.2, 14.2 (CH3). HRMS APCI: m/z calculated
for C26H29O4: 405.2066; found: 405.2080. IR (Neat, cmꢀ1) 2979
(C-H), 2920 (C-H), 2850 (C-H), 1663 (C@O), 1579 (C@C), 1238,
950, 749.
3.1.6.5. 10-Isopropoxy-4-methyl-2-phenylanthra[1,2-b]furan-
6,11-dione (47).
The anthrafuran 47 was prepared applying
the general procedure for the synthesis of anthrafurans using aryl
iodide 5 (200 mg, 0.474 mmol) and cuprous phenylacetylide 42d
(117 mg, 0.710 mmol). The anthrafuran 47 (120 mg, 0.303 mmol,
64%) was obtained as a yellow solid. Rf = 0.19 (5% EtOAc in
PhMe). Mp = 215–218 °C. 1H NMR (500 MHz, CDCl3) d 8.06–8.00
(m, 2H), 7.90 (dd, J = 7.6, 1.1 Hz, 1H), 7.89 (d, J = 0.9 Hz, 1H), 7.61
(dd, J = 8.3, 7.6 Hz, 1H), 7.50–7.45 (m, 2H), 7.42–7.38 (m, 1H),
7.33–7.29 (m, 1H), 7.05 (s, 1H), 4.74 (hept, J = 6.1 Hz, 1H), 2.61
(d, J = 0.8 Hz, 3H), 1.54 (d, J = 6.1 Hz, 6H). 13C NMR (126 MHz,
CDCl3) d 183.7 (C@O), 181.3 (C@O), 160.9 (C-Ar), 158.9 (C-Ar),
151.7 (C-Ar), 136.6 (C-Ar), 136.4 (C-Ar), 135.9 (C-Ar), 134.2 (CH-
Ar), 129.6 (CH-Ar), 129.5 (C-Ar), 129.1 (C-Ar), 128.9 (2 ꢂ Ph-H),
125.9 (2 ꢂ Ph-H), 123.1 (C-Ar), 121.9 (C-Ar), 121.6 (CH-Ar), 119.8
(CH-Ar), 118.6 (CH-Ar), 99.7 (CH-Ar), 72.6 (OCH(CH3)2), 22.2
(2 ꢂ CH3), 19.2 (Ar-CH3). HRMS APCI: m/z calculated for
3.1.6.2. 2-Hexyl-10-hydroxy-4-methylanthra[1,2-b]furan-6,11-
dione (44).
Anthrafuran 44 was prepared according to the
general procedure for the deprotection of the isopropyl group,
Method A, using anthrafuran 43 (34 mg, 0.084 mmol). The anthra-
furan 44 was obtained as an orange solid (18 mg, 0.050 mmol,
59%). Rf = 0.50 (2% EtOAc in PhMe). Mp = 126–131 °C. 1H NMR
(500 MHz, CDCl3) d 12.75 (s, 1H), 7.94 (d, J = 0.8 Hz, 1H), 7.78
(dd, J = 7.5, 1.1 Hz, 1H), 7.62 (dd, J = 8.3, 7.6 Hz, 1H), 7.28–7.25
(m, 1H), 6.51 (t, J = 0.9 Hz, 1H), 2.93 (t, J = 7.7 Hz, 2H), 2.59 (d,
J = 0.7 Hz, 3H), 1.83 (dt, J = 15.4, 7.6 Hz, 2H), 1.46 (dt, J = 9.5,
7.1 Hz, 2H), 1.42–1.30 (m, 4H), 0.97–0.88 (m, 3H); 13C NMR
(126 MHz, CDCl3) d 188.5 (C@O), 182.8 (C@O), 166.0 (C-Ar),
162.4 (C-Ar), 151.6 (C-Ar), 138.0 (C-Ar), 136.5 (C-Ar), 136.4 (Ar-
CH), 133.5 (C-Ar), 129.4, 124.4 (Ar-CH), 122.8 (Ar-CH), 119.4 (Ar-
CH), 116.5 (C-Ar), 116.1 (C-Ar), 100.9 (Ar-CH), 31.6 (CH2), 29.1
(CH2), 28.9 (CH2), 27.6 (CH2), 22.7 (CH2), 19.5 (Ar-CH3), 14.2
(CH3). HRMS APCI: m/z calculated for C23H23O4 [M+H]+:
363.1596; found: 363.1605. IR (KBr Pellet, cmꢀ1) 2954 (C-H),
2928 (C-H), 2849 (C-H), 1666 (C@O), 1629 (C@O), 1583 (C@C),
1449, 1256, 750.
C
26H21O4: 397.1440; found: 397.1454. IR (Neat, cmꢀ1) 2968 (C-
H), 2920 (C-H), 2850 (C-H), 1664 (C@O), 1578 (C@C), 1187, 965,
742.
3.1.6.6. 10-Hydroxy-4-methyl-2-phenylanthra[1,2-b]furan-6,11-
dione (48).
Anthrafuran 48 was prepared according to the
general procedure for the deprotection of the isopropyl group
Method A using anthrafuran 47 (45 mg, 0.113 mmol). The anthra-
furan 48 was obtained as orange-red crystals (35 mg, 0.098 mmol,
87%). Rf = 0.50 (5% EtOAc in PhMe). Mp = 246–250 °C. 1H NMR
(400 MHz, CDCl3) d 12.83 (s, 1H), 8.04–8.00 (m, 2H), 7.82 (dd,
J = 7.5, 1.1 Hz, 1H), 7.64 (dd, J = 8.4, 7.5 Hz, 1H), 7.57–7.49 (m,
2H), 7.46 (d, J = 7.4 Hz, 1H), 7.30 (dd, J = 8.4, 1.2 Hz, 1H), 7.13 (s,
1H), 2.69 (d, J = 0.7 Hz, 3H). 13C NMR (101 MHz, CDCl3) d 188.3
(C@O), 182.8 (C@O), 162.5 (Ar), 161.2 (Ar), 151.8 (Ar), 138.5 (Ar),
136.7 (Ar), 136.4, 133.5 (Ar), 130.1 (Ar), 130.1 (Ar), 129.3 (Ar),
129.2 (PhCH), 129.0 (Ar), 125.8 (PhCH), 124.4 (Ar), 123.1 (Ar),
119.5 (Ar), 116.6 (Ar), 116.5 (Ar), 99.8 (Ar), 19.6 (Ar-CH3). HRMS
APCI: m/z calculated for C23H15O4: 355.0970; found: 355.0970. IR
(Neat, cmꢀ1) 3112 (C-H), 2920 (C-H), 1659 (C@O), 1639 (C@O),
1594, 1574, 744.
3.1.6.3.
6,11-dione (45).
10-Isopropoxy-4-methyl-2-propylanthra[1,2-b]furan-
The anthrafuran 45 was prepared applying
the general procedure for the synthesis of anthrafurans using aryl
iodide 5 (300 mg, 0.710 mmol) and cuprous acetylide 42b (111 mg,
0.853 mmol). The anthrafuran 45 (179 mg, 0.494 mmol, 70%) was
obtained as a yellow solid. Rf = 0.27 (2.5% EtOAc in PhMe).
Mp = 159–162 °C. 1H NMR (400 MHz, CDCl3) d 7.93–7.84 (m, 2H),
7.60 (dd, J = 8.3, 7.7 Hz, 1H), 7.29 (d, J = 8.0 Hz, 1H), 6.47 (t,
J = 0.9 Hz, 1H), 4.72 (hept, J = 6.0 Hz, 1H), 2.89 (t, J = 7.6 Hz, 2H),
2.55 (d, J = 0.6 Hz, 3H), 1.90–1.80 (m, J = 15.0, 7.5 Hz, 2H), 1.49 (d,
J = 6.1 Hz, 6H), 1.04 (t, J = 7.4 Hz, 3H). 13C NMR (101 MHz, CDCl3)
d 183.9 (C@O), 181.7 (C@O), 165.4 (C-Ar), 158.8 (C-Ar), 151.4 (C-
Ar), 136.5 (C-Ar), 135.9 (C-Ar), 135.8 (C-Ar), 134.1 (CH-Ar), 128.4
(C-Ar), 123.0 (C-Ar), 121.6 (CH-Ar), 121.3 (CH-Ar), 119.6 (CH-Ar),
118.3 (C-Ar), 100.9 (CH-Ar), 72.3 (OCH(CH3)2), 30.8 (CH2CH2CH3),
22.2 (2 ꢂ CH3), 21.0 (CH2CH2CH3), 19.2 (Ar-CH3), 13.9 (CH3).
HRMS EI: calculated for C23H22O4: 362.1518; found 362.1520. IR
(Neat, cmꢀ1) 2930 (C-H), 2932 (C-H), 1668 (C@O), 1577 (C@C),
1243, 950, 753.
3.1.6.7. 2-Benzoyl-10-isopropoxy-4-methylanthra[1,2-b]furan-
6,11-dione (49).
The anthrafuran 49 was prepared applying
the general procedure for the synthesis of anthrafurans using aryl
iodide 5 (200 mg, 0.474 mmol) and (3-oxo-3-phenylprop-1-ynyl)-
copper 6 (137 mg, 0.710 mmol). The anthrafuran 49 (109 mg,
0.256 mmol, 54%) was obtained as a red solid. Rf = 0.34 (10%
EtOAc in PhMe). Mp = 195–198 °C. 1H NMR (400 MHz, CDCl3) d

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3563
8.48–8.42 (m, 2H), 7.94 (d, J = 0.8 Hz, 1H), 7.89 (dd, J = 7.6, 1.1 Hz,
1H), 7.69–7.65 (m, 2H), 7.57–7.65 (m, 3H), 7.33 (d, J = 7.8 Hz,
1H), 4.70 (hept, J = 6.1 Hz, 1H), 2.66 (d, J = 0.7 Hz, 3H), 1.51 (d,
J = 6.1 Hz, 6H). 13C NMR (101 MHz, CDCl3) d 183.5 (C@O), 182.8
(C@O), 180.4 (C@O), 158.9 (C-Ar), 156.8 (C-Ar), 152.4 (C-Ar),
139.3 (C-Ar), 136.3 (C-Ar), 135.5 (C-Ar), 134.4 (CH-Ar), 133.7 (C-
Ar), 133.6 (CH-Ar), 132.0 (C-Ar), 130.5 (2 ꢂ Ar-H), 128.8 (2 ꢂ Ar-
H), 123.0 (C-Ar), 122.6 (CH-Ar), 122.1 (CH-Ar), 120.1 (CH-Ar),
119.4 (C-Ar), 112.9 (CH-Ar), 73.0 (OCH(CH3)2), 22.2 (2 ꢂ CH3),
19.3 (Ar-CH3). HRMS APCI: calculated for C27H21O5: 425.1389;
found: 425.1391; IR (Neat, cmꢀ1) 3097 (C-H), 2928 (C-H), 2870
(C-H), 1687 (C@O), 1668 (C@O), 1583 (C@C), 1260, 966, 746.
119.6 (Ar-CH), 119.0 (C-Ar), 116.5 (C-Ar), 116.4 (C-Ar), 102.6 (Ar-
CH), 27.6 (CH2), 23.7 (CH2), 19.5 (Ar-CH3), 16.8 (CH3). HRMS
APCI: m/z calculated for C21H16NO4 [M+H]+: 346.1079; found:
346.1070. IR (KBr Pellet, cmꢀ1) 3136 (C-H), 3075 (C-H), 2915 (C-
H), 2245 (C„N), 1655 (C@O), 1636 (C@O), 1574 (C@O), 1456,
1311, 776.
3.1.6.11.
2-(3-Chloropropyl)-10-isopropoxy-4-methylan-
The anthrafuran 53 was
thra[1,2-b]furan-6,11-dione (53).
prepared using the general procedure for the synthesis of anthrafu-
rans. Aryl iodide 5 (200 mg, 0.474 mmol) and (5-chloropent-1-
ynyl)copper 42f (117 mg, 0.710 mmol) were used. The anthrafuran
53 (92 mg, 0.232 mmol, 49%) was obtained as an orange solid.
Rf = 0.29 (5% EtOAc in PhMe). Mp = 120–125 °C; 1H NMR
(500 MHz, CDCl3) d 7.86–7.90 (m, 2H), 7.60 (dd, J = 8.4, 7.7 Hz,
1H), 7.32–7.27 (m, 1H), 4.73 (hept, J = 6.1 Hz, 1H), 3.64 (t,
J = 6.3 Hz, 2H), 3.10 (t, J = 7.4 Hz, 2H), 2.55 (d, J = 0.7 Hz, 3H),
2.35–2.27 (m, 2H), 1.49 (d, J = 6.1 Hz, 6H); 13C NMR (126 MHz,
CDCl3) d 183.8 (C@O), 181.6 (C@O), 163.1 (C-Ar), 158.9 (C-Ar),
151.6 (C-Ar), 136.1 (C-Ar), 136.1 (C-Ar), 135.8 (C-Ar), 134.2 (CH-
Ar), 128.7 (C-Ar), 122.9 (C-Ar), 121.7 (CH-Ar), 121.3 (CH-Ar),
119.6 (CH-Ar), 118.3 (C-Ar), 101.8 (CH-Ar), 72.3 (OCH(CH3)2),
44.1 (CH2Cl), 30.3 (Furan-CH2), 26.1 (CH2), 22.2 (2 ꢂ CH3), 19.2
(Ar-CH3). IR (Neat, cmꢀ1) 2974 (C-H), 2924 (C-H), 1667 (C@O),
1578 (C@C), 1257, 964, 809, 639. HRMS APCI: m/z calculated for
3.1.6.8.
6,11-dione (50).
2-Benzoyl-10-hydroxy-4-methylanthra[1,2-b]furan-
Anthrafuran 50 was prepared according to
the general procedure for the deprotection of the isopropyl group
Method A using anthrafuran 49 (20 mg, 0.047 mmol). The anthra-
furan 50 was obtained as yellow solid (15 mg, 0.039 mmol, 83%).
Rf = 0.29 (5% EtOAc in PhMe). Mp = 246–256 °C. 1H NMR
(500 MHz, CDCl3) d 12.73 (s, 1H), 8.41–8.36 (m, 2H), 8.11 (d,
J = 0.8 Hz, 1H), 7.84 (dd, J = 7.5, 1.1 Hz, 1H), 7.73 (s, 1H), 7.72–
7.70 (m, 1H), 7.68 (dd, J = 8.3, 7.5 Hz, 1H), 7.63 (‘t’, J = 7.6 Hz, 2H),
7.34 (dd, J = 8.4, 1.1 Hz, 1H), 2.75 (d, J = 0.8 Hz, 3H). 13C NMR
(126 MHz, CDCl3) d 187.5 (C@O), 183.0 (C@O), 182.5 (C@O),
162.6 (Ar), 156.9 (Ar), 152.6 (Ar), 141.6 (Ar), 136.7 (Ar), 136.3
(Ar), 133.9 (Ar), 133.9 (Ar), 133.2 (Ar), 130.3 (ArCH), 129.0
(ArCH), 124.9 (Ar), 123.3 (Ar), 119.8 (Ar), 117.6 (Ar), 116.4 (Ar),
113.0 (Ar), 19.7 (Ar-CH3). HRMS APCI: m/z calculated for
C23H22O4Cl: 397.1207; found: 397.1194.
3.1.6.12. 2-(3-Chloropropyl)-10-hydroxy-4-methylanthra[1,2-
b]furan-6,11-dione (54). Anthrafuran 54 was prepared
according to the general procedure for the deprotection of the iso-
propyl group Method using anthrafuran 53 (200 mg,
C
24H15O5: 383.0919; found: 383.0923. IR (Neat, cmꢀ1) 3111 (C-
H), 3079 (C-H), 1667 (C@O), 1643 (C@O), 1633 (C@O), 1591
(C@C), 1541, 749.
A
0.504 mmol). The anthrafuran 54 was obtained as orange-red crys-
tals (175 mg, 0.494 mmol, 98%). Rf = 0.39 (5% EtOAc in PhMe).
Mp = 181–190 °C. 1H NMR (400 MHz, CDCl3) d 12.72 (s, 1H), 7.98
(d, J = 0.6 Hz, 1H), 7.81 (dd, J = 7.5, 1.1 Hz, 1H), 7.64 (dd, J = 8.3,
7.6 Hz, 1H), 7.28 (dd, J = 8.4, 1.1 Hz, 1H), 6.61 (s, 1H), 3.68 (t,
J = 6.3 Hz, 2H), 3.15 (t, J = 7.4 Hz, 2H), 2.62 (s, 3H), 2.37–2.28 (m,
2H). 13C NMR (101 MHz, CDCl3) d 188.4 (C@O), 182.8 (C@O),
163.5 (C-Ar), 162.5 (C-Ar), 151.8 (C-Ar), 138.4 (C-Ar), 136.5 (CH-
Ar), 136.2 (C-Ar), 133.5 (C-Ar), 129.8 (C-Ar), 124.5 (CH-Ar), 122.9
(CH-Ar), 119.5 (CH-Ar), 116.5 (C-Ar), 116.2 (C-Ar), 102.0 (C-Ar),
44.0 (CH2Cl), 30.4 (CH2), 26.1 (CH2), 19.5 (Ar-CH3). HRMS APCI:
m/z calculated for C20H16O4Cl: 355.0737; found: 355.0736. IR
(Neat, cmꢀ1) 2956 (C-H), 1662 (C@O), 1641 (C@O), 1584 (C@C),
1308, 1078, 1006, 794, 751, 564.
3.1.6.9. 4-(10-Isopropoxy-4-methyl-6,11-dioxo-6,11-dihydroan-
thra[1,2-b]furan-2-yl)butanenitrile (51).
The anthrafuran
51 was prepared using the general procedure for the synthesis of
anthrafurans using aryl iodide 5 (200 mg, 0474 mmol) and 5-cya-
nopent-1-ynyl-copper 42e (111 mg, 0.710 mmol). The anthrafuran
51 (147 mg, 0.379 mmol, 80%) was obtained as an orange solid.
Rf = 0.15 (10% EtOAc in PhMe). Mp = 118–128 °C. 1H NMR
(400 MHz, CDCl3) d 7.93–7.82 (m, 2H), 7.61 (t, J = 8.0 Hz, 1H),
7.30 (d, J = 8.3 Hz, 1H), 6.56 (s, 1H), 4.73 (hept, J = 6.0 Hz, 1H),
3.09 (t, J = 7.3 Hz, 2H), 2.54 (s, 3H), 2.50 (t, J = 7.1 Hz, 2H), 2.22
(tt, J = 7.2 Hz, 2H), 1.49 (d, J = 6.0 Hz, 6H). 13C NMR (101 MHz,
CDCl3) d 183.7 (C@O), 181.5 (C@O), 161.8 (CH-Ar), 158.9 (CH-Ar),
151.6 (C-Ar), 136.3 (C-Ar), 135.9 (C-Ar), 135.7 (C-Ar), 134.3 (CH-
Ar), 128.9 (C-Ar), 122.8 (C-Ar), 121.8 (CH-Ar), 121.4 (CH-Ar),
119.6 (CH-Ar), 119.1 (C„N), 118.4 (C-Ar), 102.3 (CH-Ar), 72.4
(OCH(CH3)2), 27.6 (Furan-CH2), 23.6 (CH2CH2CH2), 22.2 (2 ꢂ CH3),
19.2 (Ar-CH3), 16.7 (N„CCH2). HRMS APCI: m/z calculated for
C24H22NO4: 388.1549; found: 388.1555. IR (Neat, cmꢀ1) 2977 (C-
H), 2945 (C-H), 2247 (C„N), 1663 (C@O), 1581 (C@C), 1278,
1241, 969, 746.
3.1.6.13. 2-Hexanoyl-10-isopropoxy-4-methylanthra[1,2-b]fu-
ran-6,11-dione (55).
The anthrafuran 55 was prepared using
the general procedure for the synthesis of anthrafurans using aryl
iodide 5 (200 mg, 0.474 mmol) and 3-oxooct-1-ynyl-copper 42g
(133 mg, 0.710 mmol). The anthrafuran 55 (129 mg, 0.308 mmol,
65%) was obtained as a yellow solid. Rf = 0.20 (5% EtOAc in
PhMe). Mp = 201–202 °C. 1H NMR (600 MHz, CDCl3) d 7.99 (d,
J = 0.7 Hz, 1H), 7.92 (dd, J = 7.6, 1.0 Hz, 1H), 7.66 (t, J = 8.0 Hz,
1H), 7.56 (s, 1H), 7.36 (d, J = 8.2 Hz, 1H), 4.76 (hept, J = 6.0 Hz,
1H), 3.18 (t, J = 7.4 Hz, 2H), 2.67 (s, 3H), 1.86–1.81 (m, 2H), 1.53
(d, J = 6.1 Hz, 6H), 1.46–1.40 (m, 4H), 0.94 (t, J = 7.1 Hz, 3H). 13C
NMR (151 MHz, CDCl3) d 192.5 (Furan-C@O), 183.7 (C@O), 180.8
(C@O), 159.1 (C-Ar), 156.8 (C-Ar), 152.3 (C-Ar), 139.4 (C-Ar),
135.6 (C-Ar), 134.5 (CH-Ar), 134.2 (C-Ar), 132.0 (C-Ar), 122.8 (C-
Ar), 122.1 (CH-Ar), 122.0 (CH-Ar), 119.9 (CH-Ar), 119.6 (C-Ar),
109.2 (CH-Ar), 72.7 (OCH(CH3)2), 39.5 (C@OCH2), 31.5
(C@OCH2CH2), 23.6 (CH2), 22.7 (CH2), 22.2 (2 ꢂ CH3), 19.3 (Ar-
CH3), 14.1 (CH3). HRMS APCI: calculated for C26H27O5: 419.1858;
found: 419.1855. IR (Neat, cmꢀ1) 2927 (C-H), 2870 (C-H), 1687
(C@O), 1668 (C@O), 1582, 1260, 746.
3.1.6.10. 4-(10-Hydroxy-4-methyl-6,11-dioxo-6,11-dihydroan-
thra[1,2-b]furan-2-yl)butanenitrile (52).
Anthrafuran 52
was prepared according to the general procedure for the deprotec-
tion of the isopropyl group Method A using anthrafuran 51 (33 mg,
0.047 mmol). The anthrafuran 52 was obtained as an orange solid
(22 mg, 0.064 mmol, 75%). Rf = 0.20 (5% EtOAc in PhMe). Mp = 241–
243 °C. 1H NMR (500 MHz, CDCl3) d 12.71 (s, 1H), 8.01 (d, J = 0.8 Hz,
1H), 7.82 (dd, J = 7.5, 1.1 Hz, 1H), 7.65 (dd, J = 8.3, 7.5 Hz, 1H), 7.29
(dd, J = 8.4, 1.1 Hz, 1H), 6.66 (s, 1H), 3.14 (t, J = 7.3 Hz, 2H), 2.63 (s,
3H), 2.54 (t, J = 7.0 Hz, 2H), 2.25 (t, J = 7.2 Hz, 2H). 13C NMR
(126 MHz, CDCl3) d 188.4 (C@O), 182.8 (C@O), 162.5 (C-Ar),
162.2 (C-Ar), 151.8 (C-Ar), 138.6 (C-Ar), 136.6 (Ar-CH), 135.9 (C-
Ar), 133.5 (C-Ar), 130.1 (C-Ar), 124.5 (Ar-CH), 123.1 (Ar-CH),

3564
J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3.1.6.14.
2-(1-Hydroxyethyl)-10-isopropoxy-4-methylan-
The anthrafuran 56 was
prepared using the general procedure for the synthesis of
anthrafurans using aryl iodide (200 mg, 0.474 mmol) and
Method B using anthrafuran 58 (50 mg, 0.0138 mmol). The anthra-
thra[1,2-b]furan-6,11-dione (56).
furan 59 was obtained as yellow crystals (21 mg, 0.066 mmol,
48%). Rf = 0.29 (5% EtOAc in PhMe); mp P250 °C, 1H NMR
(400 MHz, CDCl3) d 12.68 (s, 1H), 8.09 (d, J = 0.8 Hz, 1H), 7.84
(dd, J = 7.5, 1.1 Hz, 1H), 7.70–7.65 (m, 1H), 7.61 (s, 1H), 7.33 (dd,
J = 8.4, 1.1 Hz, 1H), 2.78 (s, 3H), 2.73 (d, J = 0.8 Hz, 3H). 13C NMR
(126 MHz, CDCl3) d 188.9 (C@O), 187.5 (C@O), 182.5 (C@O),
162.6 (C-Ar), 156.6 (C-Ar), 152.4 (C-Ar), 141.7 (C-Ar), 136.7 (CH-
Ar), 134.2 (C-Ar), 133.3 (C-Ar), 133.1 (C-Ar), 129.2 (C-Ar), 128.4
(C-Ar), 124.9 (CH-Ar), 123.2 (CH-Ar), 119.8 (CH-Ar), 117.6 (C-Ar),
116.3 (C-Ar), 109.7 (CH-Ar), 27.0 (CH3), 19.6 (Ar-CH3). HRMS
APCI: m/z calculated for C19H13O5: 321.0755; found: 321.0764. IR
(Neat, cmꢀ1) 3362 (C-H), 3100 (C-H), 1689 (C@O), 1668 (C@O),
1591 (C@C), 1558, 1467, 784, 661.
5
(3-hydroxy-3-methylbut-1-ynyl)copper 42h (94 mg, 0.71 mmol).
The anthrafuran 56 (47 mg, 0.128 mmol, 27%) was obtained as a
dark orange oil that formed an amorphous solid mass upon stand-
ing for 2 days under nitrogen. Rf = 0.30 (30% EtOAc in PhMe). 1H
NMR (400 MHz, CDCl3) d 7.90 (dd, J = 7.6, 1.1 Hz, 1H), 7.86 (d,
J = 0.8 Hz, 1H), 7.63 (dd, J = 8.4, 7.7 Hz, 1H), 7.32 (d, J = 8.0 Hz, 1H),
6.65 (d, J = 0.8 Hz, 1H), 5.19 (q, J = 6.5 Hz, 1H), 4.74 (hept,
J = 6.1 Hz, 1H), 2.52 (d, J = 0.6 Hz, 3H), 1.71 (d, J = 6.6 Hz, 3H), 1.50
(dd, J = 6.0, 0.7 Hz, 6H). 13C NMR (101 MHz, CDCl3) d 183.8 (C@O),
181.8 (C@O), 166.4 (C-Ar), 158.9 (C-Ar), 151.5 (C-Ar), 137.0
(C-Ar), 135.8 (C-Ar), 135.7 (C-Ar), 134.5 (CH-Ar), 129.1 (C-Ar),
122.8 (C-Ar), 121.8 (CH-Ar), 121.5 (CH-Ar), 119.8 (CH-Ar), 118.5
(C-Ar), 100.2 (CH-Ar), 72.5 (OCH(CH3)2), 64.0 (C-OH), 22.2
(2 ꢂ CH3), 22.2 (2 ꢂ CH3), 21.3 (CH(OH)CH3), 19.2 (Ar-CH3). HRMS
EI: m/z calculated for C22H20O5: 364.1311; found: 364.1316; IR
(Neat, cmꢀ1) 3430 (OH), 2976 (C-H), 2930 (C-H), 1667 (C@O),
1589 (C@C), 1239, 969.
3.2. Cell culture and stock solutions
Stock solutions were prepared as follows and stored at 20 °C:
analogues were prepared as 20 mM solutions in DMSO. All cell
lines were cultured at 37 °C, under 5% CO2 in air, and were main-
tained in Dulbecco’s modified Eagle’s medium (Trace Biosciences,
Australia) supplemented with 10% foetal bovine serum, 10 mM
sodium bicarbonate penicillin (100 IU/mL), streptomycin
3.1.6.15. 10-Hydroxy-2-(1-hydroxyethyl)-4-methylanthra[1,2-
b]furan-6,11-dione (57).
Anthrafuran 57 was prepared
(100 lg/ml) and glutamine (4 mM).
according to the general procedure for the deprotection of the iso-
propyl group, Method B, using anthrafuran 56 (50 mg,
0.138 mmol). The anthrafuran 57 was obtained as yellow crystals
(22 mg, 0.067 mmol, 49%). Rf = 0.32 (PhMe). Mp = 178–183 °C. 1H
NMR (400 MHz, CDCl3) d 12.71 (s, 1H), 8.02 (s, 1H), 7.82 (d,
J = 7.5 Hz, 1H), 7.65 (t, J = 7.9 Hz, 1H), 7.30 (d, J = 8.4 Hz, 1H), 6.88
(s, 1H), 5.35 (q, J = 6.9 Hz, 1H), 2.66 (s, 3H), 2.05 (d, J = 6.9 Hz,
3H), 1.56 (s, 3H). 13C NMR (101 MHz, CDCl3) d 188.0 (C@O),
182.6 (C@O), 162.6 (C-Ar), 162.4 (C-Ar), 151.8 (C-Ar), 139.4 (C-
Ar), 136.5 (CH-Ar), 135.1 (C-Ar), 133.3 (C-Ar), 130.8 (C-Ar), 124.6
(CH-Ar), 123.0 (CH-Ar), 119.5 (CH-Ar), 116.7 (C-Ar), 116.4 (C-Ar),
102.4 (CH-Ar), 49.7 (HCOH), 23.3 (CH3), 19.5 (Ar-CH3). IR (Neat,
cmꢀ1) 2924 (C-H), 1667 (C@O), 1634 (C@O), 1587 (C@C), 1454,
749.
3.3. MTT in vitro growth inhibition assay
Cells in logarithmic growth were transferred to 96-well plates.
Growth inhibition was determined by plating cells in duplicate in
100
(24 h after plating) when the cells were in logarithmic growth,
100 l medium with or without the test agent was added to each
ll medium at a density of 2500–4000 cells/well. On day 0
l
well. After 72-h drug exposure growth inhibitory effects were eval-
uated using the MTT (3-[4,5-dimethyltriazol-2-yl]-2,5-diphenyl-
tetrazolium bromide) assay and absorbance read at 540 nm.
Percentage growth inhibition was determined at a fixed drug con-
centration of 25 lM. A value of 100% is indicative of total cell
growth inhibition. If the percentage inhibition was >90% across
all cell lines evaluated or >100% against more than two cell lines
and suitably soluble (in the DMSO/water solution), then a more
detailed dose–response evaluation was conducted, allowing for
the calculation of a GI50 value. This value is the drug concentration
at which cell growth is inhibited by 50% based on the difference
between the optical density values on day 0 and those at the end
of drug exposure.
3.1.6.16. 2-Acetyl-10-isopropoxy-4-methylanthra[1,2-b]furan-
6,11-dione
(58).
Dess–Martin
periodinane
(70 mg,
0.165 mmol) was added portionwise to a magnetically stirred solu-
tion of anthrafuran alcohol 56 (50 mg, 0.137 mmol) in CH2Cl2
(2 mL). Stirring continued for 1 h before the solution was treated
with NaHCO3 (satd 2 mL) Na2S2O3 (2 M, 2 mL), H2O (20 mL) and
stirred for a further 1 h. The resulting mixture was extracted with
CH2Cl2 (20 mL ꢂ 3), the combine organic layers were dried over
MgSO4 and concentrated under reduced pressure. The residue
was then purified by column chromatography (silica, 100%
PhMe ? 20% EtOAc/PhMe) to give the anthrafuran ketone 58 a yel-
low crystalline solid. Rf = 0.26 (15% EtOAc in PhMe); mp P250 °C.
1H NMR (400 MHz, CDCl3) d 8.00 (‘d’, J = 0.8 Hz, 1H), 7.93 (‘dd’,
J = 7.6, 1.1 Hz, 1H), 7.65–7.69 (m, 1H), 7.58 (s, 1H), 7.36 (‘d’,
J = 7.4 Hz, 1H), 4.76 (sept, J = 6.0 Hz, 1H), 2.80 (s, 3H), 2.67 (d,
J = 0.8 Hz, 3H), 1.53 (d, J = 6.0 Hz, 6H). 13C NMR (101 MHz, CDCl3)
d 189.7 (C@O), 183.7 (C@O), 180.8 (C@O), 159.1 (C-Ar), 156.7 (C-
Ar), 152.4 (C-Ar), 139.5 (C-Ar), 134.6 (Ar-CH), 132.2 (C-Ar), 122.7
(C-Ar), 122.2 (Ar-CH), 121.8 (Ar-CH), 119.9 (Ar-CH), 119.7 (C-Ar),
109.4 (Ar-CH), 72.7 (CH(CH3)2), 27.2 (C@O(CH3)), 22.2 ((CH3)2),
19.3 (Ar-CH3). C22H18O5 [M+H]+: 362.1154; found: 362.1155. IR
(Neat, cmꢀ1) 3096 (C-H), 2974 (C-H), 2922 (C-H), 1686 (C@O),
1669 (C@O), 1581 (C@C), 1557 (C@C), 1324, 748.
Acknowledgements
The authors would like to thank A/Prof Lindsay Byrne for NMR
assistance and Dr. Tony Reader for mass spectrometry support.
This work received financial support from the Hunter Medical
Research Institute and the Biotechnology Innovation Fund,
AusIndustry, Australia.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2015.04.032.
References and notes
1. Schumacher, R. W.; Davidson, B. S.; Montenegro, D. A.; Bernan, V. S. J. Nat. Prod.
1995, 58, 613.
2. Hansen, M. R.; Hurley, L. H. Acc. Chem. Res. 1996, 29, 249.
3. Lee, S.-J.; Hurley, L. H. J. Am. Chem. Soc. 1999, 121, 8971.
4. Hamilton, P. L.; Arya, D. P. Nat. Prod. Rep. 2012, 29, 134.
5. Koeda, T. H. A. T. J. Antibiot. 1971, 200.
3.1.6.17.
6,11-dione (59).
the general procedure for the deprotection of the isopropyl group
2-Acetyl-10-hydroxy-4-methylanthra[1,2-b]furan-
Anthrafuran 59 was prepared according to

J. E. Rixson et al. / Bioorg. Med. Chem. 23 (2015) 3552–3565
3565
6. Sun, D.; Hansen, M.; Hurley, L. J. Am. Chem. Soc. 1995, 117, 2430.
7. Ojiri, K.; Saito, K.; Nakajima, S.; Suda, H. Jpn. Kokai Tokkyo Koho 1994. JP
06228121 A 19940816.
31. Hill, T. A.; Stewart, S. G.; Ackland, S. P.; Gilbert, J.; Sauer, B.; Sakoff, J. A.;
McCluskey, A. Bioorg. Med. Chem. 2007, 15, 6126.
32. Hill, T. A.; Stewart, S. G.; Sauer, B.; Gilbert, J.; Ackland, S. P.; Sakoff, J. A.;
McCluskey, A. Bioorg. Med. Chem. Lett. 2007, 17, 3392.
8. Bransová, J.; Brtko, J.; Uher, M.; Novotny´, L. Int. J. Biochem. Cell Biol. 1995, 27,
701.
33. Hill, T. A.; Stewart, S. G.; Gordon, C. P.; Ackland, S. P.; Gilbert, J.; Sauer, B.;
Sakoff, J. A.; McCluskey, A. ChemMedChem 2008, 3, 1878.
34. Böhm, H.-J.; Banner, D.; Bendels, S.; Kansy, M.; Kuhn, B.; Müller, K.; Obst-
Sander, U.; Stahl, M. ChemBioChem 2004, 5, 637.
35. Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc. Rev. 2008, 37,
320.
36. Tietze, L. F.; Brasche, G.; Gericke, K. M. Domino Reactions in Organic Synthesis;
Wiley-VCH: Weinheim, 2006.
37. Priebbenow, D. L.; Stewart, S. G.; Pfeffer, F. M. Org. Biomol. Chem. 2011, 9, 1508.
38. Priebbenow, D. L.; Henderson, L. C.; Pfeffer, F. M.; Stewart, S. G. J. Org. Chem.
2010, 75, 1787.
39. Stewart, S. G.; Heath, C. H.; Ghisalberti, E. L. Eur. J. Org. Chem. 2009, 2009, 1934.
40. Stewart, S. G.; Ghisalberti, E. L.; Skelton, B. W.; Heath, C. H. Org. Biomol. Chem.
2010, 8, 3563.
41. Cambie, R.; Larsen, D.; Rutledge, P.; Woodgate, P. Aust. J. Chem. 1987, 40, 215.
42. Boddy, I.; Cambie, R.; Rutledge, P.; Woodgate, P. Aust. J. Chem. 1986, 39, 2075.
43. Stephens, R. D.; Castro, C. E. J. Org. Chem. 1963, 28, 3313.
44. Castro, C. E.; Owsley, D. C. Org. Synth. 1972, 52, 128.
9. Krohn, K.; Vitz, J. Eur. J. Org. Chem. 2004, 2004, 209.
10. Krohn, K.; Tran-Thien, H. T.; Ahmed, I. Eur. J. Org. Chem. 2011, 2011, 2223.
11. O’Keefe, B. M.; Mans, D. M.; Kaelin, D. E.; Martin, S. F. J. Am. Chem. Soc. 2010,
132, 15528.
12. Tietze, L. F.; Singidi, R. R.; Gericke, K. M. Org. Lett. 2006, 8, 5873.
13. Tietze, L. F.; Gericke, K. M.; Singidi, R. R. Angew. Chem., Int. Ed. 2006, 45, 6990.
14. Hsu, D.-S.; Matsumoto, T.; Suzuki, K. Chem. Lett. 2006, 35, 1016.
15. Uno, H.; Sakamoto, K.; Honda, E.; Ono, N. Chem. Commun. 1999, 1005.
16. Fei, Z.; McDonald, F. E. Org. Lett. 2005, 7, 3617.
17. Kitamura, K.; Maezawa, Y.; Ando, Y.; Kusumi, T.; Matsumoto, T.; Suzuki, K.
Angew. Chem., Int. Ed. 2014, 53, 1262.
18. Wright, B. J. D.; Hartung, J.; Peng, F.; Van de Water, R.; Liu, H.; Tan, Q.-H.; Chou,
T.-C.; Danishefsky, S. J. J. Am. Chem. Soc. 2008, 130, 16786.
19. Hauser, F. M.; Rhee, R. P. J. Am. Chem. Soc. 1979, 101, 1628.
20. Foulgoc, L.; Sissouma, D.; Evain, M.; Collet, S.; Guingant, A. Synlett 2012, 768.
21. Rixson, J. E.; Skelton, B. W.; Koutsantonis, G. A.; Gericke, K. M.; Stewart, S. G.
Org. Lett. 2013, 15, 4834.
22. Wang, X.; Cheng, G.; Cui, X. Chem. Commun. 2014, 652.
23. Narayan, R.; Antonchick, A. P. Chem. Eur. J. 2014, 20, 4568.
24. Mzhelskaya, I. D. I. M. A.; Polyakov, N. E.; Moroz, A. A.; Shvartsberg, M. S. Russ.
Chem. Bull. 2004, 53, 2798.
25. Nakatani, K.; Okamoto, A.; Saito, I. Tetrahedron 1996, 52, 9427.
26. Jacubert, M.; Provot, O.; Peyrat, J.-F.; Hamze, A.; Brion, J.-D.; Alami, M.
Tetrahedron 2010, 66, 3775.
45. Haglund, O. N. Synlett 1991, 723.
46. Buccini, M.; Punch, K. A.; Kaskow, B.; Flematti, G. R.; Skelton, B. W.; Abraham, L.
J.; Piggott, M. J. Org. Biomol. Chem. 2014, 12, 1100.
47. Bakunova, S. M.; Bakunov, S. A.; Wenzler, T.; Barszcz, T.; Werbovetz, K. A.;
Brun, R.; Hall, J. E.; Tidwell, R. R. J. Med. Chem. 2007, 50, 5807.
48. Woon, E. C. Y.; Dhami, A.; Mahon, M. F.; Threadgill, M. D. Tetrahedron 2006, 62,
4829.
27. Kozlowski, M. C.; Dugan, E. C.; DiVirgilio, E. S.; Maksimenka, K.; Bringmann, G.
Adv. Synth. Catal. 2007, 349, 583.
28. Paola Gramatica, M. P. G.; Speranza, G.; Manitto, P. Heterocycles 1986, 24, 743.
29. Von Strandtmann, M.; Klutchko, S.; Cohen, M. P.; Shavel, J. J. Heterocycl. Chem.
1972, 9, 171.
49. Boersch, C.; Merkul, E.; Müller, T. J. J. Angew. Chem., Int. Ed. 2011, 50, 10448.
50. Castro, C. E.; Gaughan, E. J.; Owsley, D. C. J. Org. Chem. 1966, 31, 4071.
51. Rixson, J. E.; Chaloner, T.; Heath, C. H.; Tietze, L. F.; Stewart, S. G. Eur. J. Org.
Chem. 2012, 2012, 544.
52. Christopher Braddock, D.; Clarke, J.; Rzepa, H. S. Chem. Commun. 2013, 11176.
30. Augustine, J. K.; Naik, Y. A.; Mandal, A. B.; Chowdappa, N.; Praveen, V. B. J. Org.
Chem. 2007, 72, 9854.