Synthesis and antimalarial and antituberculosis activities of a series of natural and unnatural 4-methoxy-6-styryl-pyran-2-ones, dihydro analogues and photo-dimers

Article abstract of DOI:10.1016/j.bmc.2011.12.053

Previous studies have identified the 3,6-dialkyl-4-hydroxy-pyran-2-one marine microbial metabolites pseudopyronines A and B to be modest growth inhibitors of Mycobacterium tuberculosis and a range of tropical diseases including Plasmodium falciparum and Leishmania donovani. In an effort to expand the structure-activity relationship of this compound class towards infectious diseases, a library of natural product and natural product-like 4-methoxy-6-styryl-pyran-2-ones and a subset of catalytically reduced examples were synthesized. In addition, the photochemical reactivity of several of the 4-methoxy-6-styryl-pyran-2-ones were investigated yielding head-to-head and head-to-tail cyclobutane dimers as well as examples of asymmetric aniba-dimer A-type dimers. All compounds were evaluated for cytotoxicity and activity against M. tuberculosis, P. falciparum, L. donovani, Trypanosoma brucei rhodesiense and Trypanosoma cruzi. Of the styryl-pyranones, natural product 3 and non-natural styrene and naphthalene substituted examples 13, 18, 21, 22 and 23 exhibited antimalarial activity (IC₅₀ <10 μM) with selectivity indices (SI) >10. Δ⁷ Dihydro analogues were typically less active or lacked selectivity. Head-to-head and head-to-tail photodimers 5 and 34 exhibited moderate IC₅₀s of 2.3 to 17 μM towards several of the parasitic organisms, while the aniba-dimer-type asymmetric dimers 31 and 33 were identified as being moderately active towards P. falciparum (IC₅₀ 1.5 and 1.7 μM) with good selectivity (SI ～80). The 4-tert-butyl aniba-dimer A analogue 33 also exhibited activity towards L. donovani (IC₅₀ 4.5 μM), suggesting further elaboration of this latter scaffold could lead to the identification of new leads for the dual treatment of malaria and leishmaniasis.

Full text of DOI:10.1016/j.bmc.2011.12.053

Bioorganic & Medicinal Chemistry 20 (2012) 1482–1493
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and antimalarial and antituberculosis activities of a series
of natural and unnatural 4-methoxy-6-styryl-pyran-2-ones, dihydro
analogues and photo-dimers
Stephen T. McCracken a, Marcel Kaiser b,c, Helena I. Boshoff d, Peter D.W. Boyd a, Brent R. Copp a,
⇑
a School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
b Swiss Tropical and Public Health Institute, Socinstrasse 57, PO Box, CH-4002 Basel, Switzerland
c University of Basel, CH-4003 Basel, Switzerland
d Tuberculosis Research Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Previous studies have identified the 3,6-dialkyl-4-hydroxy-pyran-2-one marine microbial metabolites
pseudopyronines A and B to be modest growth inhibitors of Mycobacterium tuberculosis and a range of trop-
ical diseases including Plasmodium falciparum and Leishmania donovani. In an effort to expand the struc-
ture–activity relationship of this compound class towards infectious diseases, a library of natural
product and natural product-like 4-methoxy-6-styryl-pyran-2-ones and a subset of catalytically reduced
examples were synthesized. In addition, the photochemical reactivity of several of the 4-methoxy-6-sty-
ryl-pyran-2-ones were investigated yielding head-to-head and head-to-tail cyclobutane dimers as well
as examples of asymmetric aniba-dimer A-type dimers. All compounds were evaluated for cytotoxicity
and activity against M. tuberculosis, P. falciparum, L. donovani, Trypanosoma brucei rhodesiense and Trypan-
osoma cruzi. Of the styryl-pyranones, natural product 3 and non-natural styrene and naphthalene substi-
Received 10 November 2011
Revised 21 December 2011
Accepted 23 December 2011
Available online 2 January 2012
Keywords:
Malaria
Tuberculosis
Natural product
Pyran-2-one
tuted examples 13, 18, 21, 22 and 23 exhibited antimalarial activity (IC50 <10
indices (SI) >10.
7 Dihydro analogues were typically less active or lacked selectivity. Head-to-head and
head-to-tail photodimers 5 and 34 exhibited moderate IC50s of 2.3 to 17 M towards several of the parasitic
organisms, while the aniba-dimer-type asymmetric dimers 31 and 33 were identified as being moderately
active towards P. falciparum (IC50 1.5 and 1.7
M) with good selectivity (SI ꢀ80). The 4-tert-butyl aniba-
dimer A analogue 33 also exhibited activity towards L. donovani (IC50 4.5 M), suggesting further elabora-
lM) with selectivity
Photochemical dimerisation
D
l
l
l
tion of this latter scaffold could lead to the identification of new leads for the dual treatment of malaria and
leishmaniasis.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
trypomastigotes,9 while 2 and 4, isolated from Piper sanctum, were
growth inhibitors of Mycobacterium tuberculosis H37Rv with MICs
4-Methoxy-6-styryl-2H-pyran-2-ones are polyketide synthase-
derived natural products commonly reported from fungi and prim-
itive angiosperms.1,2 The most well known representatives of this
class of compounds are the kavapyrones being neuroactive and
potentially hepatotoxic metabolites of Kava (Piper methysticum).3
The related dihydrostyryl- and styryl-pyrones 1, 2 and 3, isolated
from a number of sources, including Alpinia speciosa4 and Polygala
sabulosa,5 exhibit plant growth inhibiting properties4 as well as
anxiolytic6 and antinociceptive7 (visceral pain) effects in mice.
There are however few reports of the evaluation of this family of
natural products for activity towards infectious diseases such as
trypanosomiasis, leishmaniasis, malaria or tuberculosis.8–10 Pyrone
3 displays weak activity against American Trypanosoma cruzi blood
of 32 lg/mL and 4 l
g/mL respectively.10
OCH3
5
8
2
13
O
O
Δ
10
R1
R2
1
R1 = R2 = H, Δ saturated
2 R1 = R2 = OCH2O, Δ saturated
3 R1 = R2 = OCH3
4
R1 = R2 = H
Styryl-pyrones such as
photochemically-induced dimerization, to form symmetrical
4 are also known to undergo
⇑
Corresponding author. Tel.: +64 9 373 7599x88284; fax: +64 9 373 7422.
E-mail address: b.copp@auckland.ac.nz (B.R. Copp).
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.12.053

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
1483
head-to-head (5)11,12 or head-to-tail (6)13,14 cyclobutane dimers or
OR1
O
unsymmetrical dimers (7).15,16 Although examples of each dimer
class have been reported as natural products, it is still unclear
whether they are true natural products or artifacts generated dur-
ing the process of isolation and purification. Head-to-tail and
asymmetric dimers related to 6 and 7, isolated from extracts of
the Colombian medicinal plant Achyrocline bogotensis, were re-
cently reported to modulate cytokine production by chemically
stimulated human peripheral blood mononuclear cells.17
R2
O
8 R1 = H, R2 = n-C H
9 R1 = H, R2 = n-C5H11
15
5
10
R
1 = CH , R2 = 7n-C H
3
11
2. Chemistry
MeO
R1
R2
R2
MeO
R1
Target styryl-pyrones were chosen to explore the effects of ste-
ric bulk, lipophilicity and extended conjugation on biological activ-
ity. To this end, the pyrones were prepared by aldol condensation
of 4-methoxy-6-methyl-2H-pyran-2-one 1119 and a variety of aryl
aldehydes (Scheme 1, Table 1).20 Thus a solution of pyrone 11 and
the appropriate aldehyde in anhydrous MeOH was added to a sus-
pension of magnesium methoxide in anhydrous methanol and the
resulting mixture heated at reflux for 6 h. Upon cooling, the solvent
was removed in vacuo and the crude product purified by either
recrystallization or silica gel column chromatography.
O
O
O
O
7
5
8
OMe
13
R2
MeO
10
O
O
3
R1
R2
O
R1
O
5 R1 = R2 = H
31
6
R1 = R2 = H
The synthesisand characterization of target pyrones 3,5,21,22 4,4,23
12,4 13,4 15,22,24 and 1820 have been previously reported and in all
cases the spectroscopic and spectrometric data observed in the cur-
rent study agreed with the previously reported values. The remain-
ing new compounds were fully characterized by MS and NMR, and
the data observed was consistent with the structures (see Experi-
mental). Diffusion of hexane into a solution of 3 in acetone and slow
evaporation of a methanolic solution of 14 yielded crystals of a suit-
able quality for X-ray analysis. The crystal structures of 3 and 14 and
details of the crystallographic studies are given in the Supplemen-
tary data. Noteworthy in both cases is that these particular pyrones
pack in the crystal unit cell in head-to-tail fashion, with alignment of
R1 = R2 = OCH2O
29 R1 = R2 = OMe
R2
R1
10
8
OMe
13
5'
3'
6'
7
5
O
7'
O
MeO
8'
O
3
10'
O
R2
D
5 and 7 at intermolecular distances of 3.6–3.7 Å and 3.5–3.9 Å for
D
13'
3 and 14, respectively (see Supplementary data). Previous studies
have concluded that 3.6–4.1 Å is a typical intermolecular distance
for cinnamic acid analogues to achieve [2+2] cycloaddition.25 The
alignment and intermolecular distances have a direct bearing on
the observed solid state photochemical reactivities of these pyrones
to yield aniba-dimer-type products (see later).
R1
7
R
1 = R2 = H
30
R
1 = R2 = OMe
32 R1 = tBu, R2 = H
34
R1 = H, R2 = O-(4-tBu-phenyl)
Catalytic hydrogenation20 of pyrones 3, 4, 14, 15, 17, 21, 22, and
23 with 10% Pd/C under a hydrogen atmosphere yielded exclu-
sively the D7 dihydro analogues 255, 126, 24, 25, 26, 27, 28, and
29, respectively, in yields of 49–96% (Table 2). The new compounds
prepared were fully characterized by MS and NMR, and the data
observed was consistent with the structures (see Experimental).
Slow evaporation of a H2O–MeOH solution of 2 gave crystals suit-
able for X-ray analysis, the structure and details of which are given
in Supplementary data. Reduction of D7 led to loss of overall pla-
narity of the molecule, compared to styryl-pyrones 3 and 14.
As noted earlier, the solid state photodimerization of 4-methoxy-
6-styryl-2H-pyran-2-one 4 has been extensively studied and is
known to yield three distinct dimer products, 5–7.11–16 The three
established photocyclization products arise from [2+2] cycloaddi-
tions of styryl-pyrones in either head-to-head (5) or head-to-tail
During our recent study of the structures and anti-infective bio-
activities of the marine microbial pyrones pseudopyronines A (8)
and B (9), the latter was found to be a modest growth inhibitor of
Mycobacterium tuberculosis (MIC 2.7
desiense (IC50 42 M), Leishmania donovani (IC50 4.8
modium falciparum (K1 strain, chloroquine resistant) (IC50 48
l
M), Trypanosoma brucei rho-
M) and Plas-
M)
l
l
l
while the methylether analogue of pseudopyronine A 10 was simi-
larly active towards L. donovani, less active towards M. tuberculosis
(MIC 45
(IC50 14
l
M) but more potent towards both T. brucei rhodesiense
lM) and P. falciparum (IC50 11
l
M).18 In continuation of
our interest in this class of natural products, we have synthesized
a library of natural and unnatural 4-methoxy-6-styryl-2H-pyran-
2-ones, and a selection of D7 dihydro and photochemically dimer-
ized analogues, and evaluated their abilities to act as growth inhib-
itors of the neglected disease target organisms M. tuberculosis, L.
donovani, T. brucei rhodesiense, T. cruzi and P. falciparum.
(6) orientations or cycloaddition between
D
5 of one molecule with
D7 of a second molecule (7). Preliminary studies of the propensity
of styryl-pyrones 3, 4, 12–23 to undergo photochemical reactions
identified 3, 4, 14, 15, 17 and 22 as being reactive and yielding of sta-
ble products. Samples of these pyrones were each suspended in
water (ꢀ1 mL) with vigorous stirring and exposed to a 300 W sun-
lamp from a distanceof 15 cm for 5 h. Under these conditionspyrone
4 afforded dimers 511,12 and 714–16 in isolatable quantities. Trace
quantities of dimer 613,14 in the crude product mixture were de-
tected by 1H NMR spectroscopy but could not be purified from the
OMe
OMe
a
O
O
R
O
O
11
3, 4, 12 23
-
Scheme 1. Reagents: (a) RCHO, Mg(OMe)2, MeOH.

1484
S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
Table 1
6-Styryl-pyran-2H-ones and their biological activities
Entry
No.
Structure
M. tb.a
T.b. rhod.b
T. cruzic
L. don.d
P. falc.e
L6f
SI Pf.g
OCH3
O
1
3
>350
31
170
270
3.0
160
54
H3CO
H3CO
O
OCH3
O
2
3
4
>440
>370
120
290
64
190
270
13
12
160
180
12
15
O
OCH3
12
>330
O2N
O
O
OCH3
4
5
13
14
>370
>350
38
44
240
49
20
6.0
5.3
190
32
O
O
O
O2N
OCH3
26
24
4
O
OCH3
6
7
15
16
>370
>310
47
180
230
5.6
4.9
16
13
3
3
O
O
O
O
OCH3
O
8.8
43
30
O
O
OCH3
O
8
9
17
18
>270
>390
34
40
25
6.3
6.7
64
10
29
O
O
OCH3
150
>350
220
190
O
O

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
1485
Table 1 (continued)
Entry
No.
Structure
M. tb.a
T.b. rhod.b
T. cruzic
L. don.d
P. falc.e
L6f
26
SI Pf.g
OCH3
O
10
19
170
290
>300
>300
7.2
4
O
(H3C)2N
OCH3
O
11
12
20
21
>460
>360
76
18
>410
240
47
17
140
110
8
O
O
OCH3
34
4.6
24
O
O
OCH3
O
13
22
>360
2.7
>320
>320
1.3
28
22
O
OMe
O
O
14
23
>260
119
>240
>240
8.6
>240
>28
O
O
OMe
a
b
c
d
e
f
Mycobacterium tuberculosis H37Rv grown in GAST medium, MIC (lM). Highest test concentration was 100 lg/mL.
Trypanosoma brucei rhodesiense. IC50
Trypanosoma cruzi. IC50 M).
Leishmania donovani. IC50 M).
Plasmodium falciparum. IC50 M).
L6 rat skeletal myoblast cell line. IC50
(
l
M).
(
l
(
l
(l
(
lM).
g
Selectivity index for Plasmodium falciparum against L6. All data is the mean value from duplicate assays.
other major products of the reaction. The 1H NMR data observed for
5 agreed with those reported for the cis-trans-cis head-to-head di-
mer previously obtained as a natural product from the leaves of Ani-
ba gardneri (though the structure was originally assigned as 6-cis-
styryl-4-methoxy-2-pyrone)15 or as a synthetic photodimerization
product.11,12 The 1H NMR data observed for 7 also agreed with those
previously reported for aniba-dimer-A.14 Photodimerization of pyr-
one 3 gave the previously reported natural products 30 and 31,22
while pyrones 14, 15, 17 and 22 each gave a single product of 33
(asymmetric), 32 (head-to-head), 35 (asymmetric), and 34 (head-
to-tail) respectively (Table 3). The structures and relative configura-
tion of asymmetric dimers 33 and 35 were readily established by
interpretation of 2D NMR data and comparison with NMR chemical
shifts observed for aniba-dimer A (7). Dimer 32 was judged to be of
head-to-head orientation by comparison of NMR chemical shifts
with that of 5, and by ESI-MS-MS analysis, which identified a major
fragment of the pseudomolecular parent ion to be m/z 277.0690
([M+H]+, calcd for C14H13O6 277.0707), which is only possible for a
head-to-head dimer. A similar ion was observed in ESI-MS-MS anal-
ysis of 5. The cis-trans-cis relative configuration of 32 was assumed
to match that of 5, which has been rigorously established.12 In con-
trast, 2-naphthalene dimer 34 was determined to be of head-to-tail
orientation, based upon ESI-MS-MS analysis which only detected a
fragment at m/z 279.1005 ([M+H]+, calcd for C18H15O3 279.1021).
Similar retro-[2+2] fragmentation was observed for dimers 6 and
30 (see Experimental).
MeO
O
O
8
7
8'
7'
MeO
O
O
34
3. Biological results and discussion
3.1. Overview
The resultant library of 6-styryl-pyran-2-ones, dihydro ana-
logues and photodimers were evaluated for anti-tuberculosis,

1486
S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
Table 2
Alkyl-pyran-2H-ones and their biological activities
entry
No.
R/structure
M. tb.a
T.b. rhod.b
T. cruzic
L. don.d
P. falc.e
L6f
SI Pfg
OCH3
O
1
1
>430
280
240
190
>22
290
-
O
OCH3
2
3
2
>360
>330
>330
>330
>18
150
-
O
O
O
O
OCH3
24
170
78
55
24
11
95
9
O
O
OCH3
O
4
5
25
26
>340
200
>310
270
>17
>310
-
H3CO
H3CO
O
OCH3
O
O
130
65
36
15
7.2
50
7
O
OCH3
6
7
27
28
270
180
85
72
76
65
55
42
>18
110
-
O
O
OCH3
16
91
6
O
O
OMe
O
O
8
29
>260
200
>240
>240
3.6
50
14
O
O
OMe
a
b
c
d
e
f
Mycobacterium tuberculosis H37Rv grown in GAST medium, MIC (lM). Highest test concentration was 100 lg/mL.
Trypanosoma brucei rhodesiense. IC50
Trypanosoma cruzi. IC50 M).
Leishmania donovani. IC50 M).
Plasmodium falciparum. IC50 M).
L6 rat skeletal myoblast cell line. IC50
(
l
M).
(
l
(
l
(l
(
lM).
g
Selectivity index for Plasmodium falciparum against L6. All data is the mean value from duplicate assays.
anti-parasitic and cytotoxic activities. Anti-tuberculosis testing
was carried out against the Mycobacterium tuberculosis H37Rv
strain grown in GAST medium. The reported MIC was determined
as the minimal concentration of test compound leading to 100%
growth inhibition. To investigate the potential of the compounds
to act as drug leads against human African trypanosomiasis

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
1487
Table 3
Dimeric pyranones and their biological activities
entry
No.
R
M. tb.a
T.b. rhod.b
T. cruzic
L. don.d
P. falc.e
L6f
SI Pfg
OMe
O
MeO
R
O
O
R
O
1
2
30
34
3,4-Dimethoxyphenyl
2-Naphthyl
>170
>180
6.2
4.9
38
90
75
10
3.1
2.3
22
95
7
42
O
O
O
O
MeO
OMe
R
R
3
4
5
32
Phenyl
>220
>180
15
32
nd
17
nd
3.8
nd
51
nd
13
nd
Benzo[3,4]dioxomethylene
ndh
OMe
R
O
O
MeO
O
R
O
5
6
7
8
7
Phenyl
3,4-Dimethoxyphenyl
4-tert-Butyl-phenyl
3-(4-tert-Butyl-phenoxy)-phenyl
>220
>170
>180
>130
13
61
21
>120
28
130
71
27
79
4.5
66
7.1
1.5
1.7
4.4
>200
120
130
>28
80
76
31
33
35
>120
>120
>27
a
b
c
Mycobacterium tuberculosis H37Rv grown in GAST medium, MIC (lM). Highest test concentration was 100 lg/mL.
Trypanosoma brucei rhodesiense. IC50
Trypanosoma cruzi. IC50 M).
M).
M).
L6 rat skeletal myoblast cell line. IC50
(
l
M).
(
l
(l
d
e
f
Leishmania donovani. IC50
Plasmodium falciparum. IC50
(l
(
lM).
g
h
Selectivity index for Plasmodium falciparum against L6. All data is the mean value from duplicate assays.
nd: Not determined.
(HAT), American trypanosomiasis, leishmaniasis or malaria, their
abilities to inhibit the growth of Trypanosoma brucei rhodesiense
(strain STIB 900, trypomastigote stage), T. cruzi (strain Tulahuen
C2C4, amastigote stage), Leishmania donovani (strain MHOM-ET-
67/L82, amastigote/axenic stage) and Plasmodium falciparum
(strain K1, IEF stage) were evaluated. In order to establish selectiv-
ity indices, the cytotoxicity of compounds towards the rat skeletal
myoblast cell line L6 were also determined. Summaries of these as-
say results are presented in Tables 1–3, with compounds grouped
into the three different classes of 6-styryl-pyran-2-ones (Table 1),
their dihydro analogues (Table 2) and photodimers (Table 3).
varying between 1.3 and 17 lM (Table 1). Of particular note was
the potency of antimalarial activity coupled with lack of cytotoxic-
ity towards the L6 cell line of dimethoxy 3 (entry 1), para-nitro 13
(entry 4), aryl-diene 18 (entry 9), both naphthalene analogues 21
and 22 (entries 12 and 13) and dipyrone 23 (entry 14). In all cases,
these pyrones exhibited antimalarial activity with IC50 <10 lM,
and with a selectivity index greater than 10, identifying them as
potentially useful starting points for further structure–activity
optimization studies. Only two examples of styryl-pyran-2-ones,
16 and 22, achieved activity towards Trypanosoma brucei rhodes-
iense with IC50 <10 lM. In the case of the former compound, broad
ranging anti-parasitic activity was observed suggesting a general
mechanism related to toxicity. Collectively, the styryl-pyran-2-
ones exhibited only modest to poor activity towards T. cruzi and
L. donovani. There was no apparent correlation of specific structural
features with biological activity in this series of compounds.
3.2. Anti-tuberculosis activity
Overall, none of the library compounds exhibited any apprecia-
ble level of anti-tuberculosis activity. This finding was somewhat
surprising given the reported activities of the styryl-pyranone 4
and dihydro analogue 2 natural products towards M. tuberculosis
The
tent and lacked selectivity against the parasitic targets (Table 2)
compared to their
7 counterparts. Three examples were identified
as being more active growth inhibitors of P. falciparum (24, 26, 29;
entries 3, 5 and 8) with IC50s of 11, 7.2 and 3.6 M respectively,
D
7 dihydro analogues 1, 2, and 24–29 were typically less po-
H
37Rv.10 When compared to the moderately antimycobacterial
D
activities observed for 3,6-dialkyl-pyranones 8–10 and other 6-al-
kyl substituted pyranones18 the current results indicate that the
presence of aryl–alkenyl/alkyl substitution at C-6 is detrimental
to activity.
l
however they lacked selectivity (SI 9, 7 and 14 respectively) versus
the L6 cell line, limiting their therapeutic potential.
Symmetrical head-to-tail dimers 30 and 34 (Table 3, entries 1
and 2) and head-to-head dimer 5 (Table 3, entry 3) were found
to be moderate growth inhibitors of two organisms, P. falciparum
and T. brucei rhodesiense. In the cases of 5 and 34, limited cytotox-
icity towards the L6 cell line identifies both classes of dimers as
3.3. Anti-parasitic activity
On the whole, the library of 6-styryl-pyran-2-ones exhibited
moderate activity towards Plasmodium falciparum, with IC50s

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S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
being useful starting points for further development. In contrast,
5.2. General procedure for the preparation of 6-substituted 4-
the asymmetric aniba-dimer A-type compounds 7, 31, 33 and 35
methoxy-2H-pyran-2-ones
exhibited antimalarial activity (IC50 1.5–7.1 lM) with moderate
selectivity versus the L6 cell line. Of special note is the identifica-
tion of tert-butyl-phenyl dimer 33 as a dual organism growth
To a suspension of magnesium methoxide, freshly prepared by
gently heating Mg (104 mg) in anhydrous MeOH (10 mL), were
added 4-methoxy-6-methyl-2-pyrone (11)19 (200 mg, 1.4 mmol)
and aldehyde (1.7 mmol) under nitrogen.20 The reaction mixture
was heated at reflux for 6 h, allowed to cool and dried in vacuo.
The solid was then suspended in acetic acid (3.3 M, 20 mL) and ex-
tracted with dichloromethane (4 Â 50 mL), and the combined or-
ganic layers washed with water (2 Â 50 mL) and dried in vacuo.
Purification of the resultant pyrone was achieved either by tritur-
ation with diethylether followed by recrystallization from MeOH
or by silica gel column chromatography eluting with 0–1% MeOH
in dichloromethane.
inhibitor exhibiting anti-leishmanial (IC50 4.5
lM) and anti-malar-
ial (IC50 1.7 M) activities. Although limited in scope, the results
l
presented in Table 3 suggest that enhanced lipophilicity analogues
of asymmetric aniba-dimer A-type compounds have the potential
to act as novel scaffolds for the development of anti-malarial or
dual organism anti-malarial and anti-leishmanial drugs.
4. Conclusions
A library of natural product and natural product-like 4-meth-
oxy-6-styryl-pyran-2-ones, selected D7 dihydro analogues and
photodimers have been synthesized and several candidates iden-
tified as potential anti-malarial or dual organism anti-malarial/
anti-T. brucei rhodesiense or anti-malarial/anti-leishmanial agents.
Overall the styryl-pyranones were moderate growth inhibitors of
P. falciparum but in many cases lacked selectivity. Similar conclu-
sions were drawn for the D7 dihydro analogues. Cyclobutane
head-to-tail and head-to-head photodimers were found to repre-
sent a new dual organism P. falciparum/T. brucei rhodesiense
inhibiting scaffold while asymmetric dimers related to aniba-di-
mer A inhibited P. falciparum and in one example, also inhibited
L. donovani. Further exploration of structure–activity relation-
ships of these latter photodimers is somewhat constrained by
the method of their synthesis—the crystal packing of styryl-pyr-
anone subunits dictates the nature of the resultant dimeric prod-
uct. We are currently exploring how the judicious choice of
functionalization of the benzenoid ring of 4-methoxy-6-styryl-
pyran-2-ones can be used to direct crystal packing and to facil-
itate the preparation of new leads for the treatment of neglected
diseases.
5.2.1. 6-[2-(3,4-Dimethoxyphenyl)ethenyl]-4-methoxy-2H-
pyran-2-one (3)
From pyrone (201 mg, 1.4 mmol) and 3,4-dimethoxybenzalde-
hyde (285 mg, 1.7 mmol). Repeated recrystallization from MeOH
gave the product as a yellow crystalline solid (115 mg, 28%). Mp
162–163 °C (lit.22 160–162 °C); Rf = 0.42 (3% MeOH:CH2Cl2); IR
(ATR) 1700, 1550, 1408, 1252, 1153 cmÀ1
;
1H NMR (CDCl3,
300 MHz) d 7.42 (1H, d, J = 15.8 Hz, H-8), 7.05 (1H, dd, J = 8.3,
1.9 Hz, H-14), 7.00 (1H, d, J = 1.9 Hz, H-10), 6.84 (1H, d, J = 8.3 Hz,
H-13), 6.43 (1H, d, J = 15.8 Hz, H-7), 5.88 (1H, d, J = 2.2 Hz, H-5),
5.44 (1H, d, J = 2.2 Hz, H-3), 3.90 (3H, s, OMe-11), 3.88 (3H, s,
OMe-12), 3.79 (3H, s, OMe-4);13C NMR (CDCl3, 75 MHz) d 171.2
(C-4), 164.1 (C-2), 158.9 (C-6), 150.4 (C-12), 149.2 (C-11), 135.6
(C-8), 128.2 (C-9), 121.6 (C-14), 116.5 (C-7), 111.2 (C-13), 109.3
(C-10), 100.5 (C-5), 88.4 (C-3), 55.9 (2xOMe), 55.8 (OMe); (+)-
ESIMS m/z 289 [M+H]+, (+)-HRESIMS m/z 289.1070 (calcd for
C16H17O5 289.1071).
Crystallographic data (excluding structure factors) for the struc-
ture of compound 3 have been deposited with the Cambridge Crys-
tallographic Data Centre as Supplementary Publication No. CCDC
831983. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
(fax: +44-(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
"p0095">Crystal data: C16H16O5, M 288.30, T 93(2) K, Triclinic,
5. Experimental
5.1. Chemistry: general methods
ꢀ
P1, a = 8.6990(7) Å, b = 9.3889(8) Å, c = 10.0485(8) Å,
Mass spectra were recorded on either a VG-7070 or a Bruker
micrOTOF Q II mass spectrometer. Infrared spectra were run as
dry films on sodium chloride or ATR crystal and acquired with
a Perkin Elmer Spectrum One Fourier Transform infrared spec-
a
= 89.624(7)°, b = 68.010(6)°,
c
= 67.643(6)°, V = 694.90(10) Å3,
Z = 2, Dc = 1.378 Mg/m3, = 0.103 mmÀ1, F(000) = 304, crystal size
l
0.18 Â 0.16 Â 0.10 mm3, Hmax = 28.17°, index ranges À11< = h< =
11, À12< = k< = 12, À13< = l< = 13, reflections collected = 8711,
independent reflections = 3359 [R(int) = 0.0688], data/restraints/
parameters 3359/0/193. All non hydrogen atoms were identified
after isotropic refinement of the initial solution. Full matrix least-
squares refinement on F2 was carried out to give R indices
trometer with
a Universal ATR Sampling Accessory. Melting
points were obtained on an Electrothermal melting point appara-
tus and are uncorrected. 1H NMR (300.13 or 400.13 MHz) and 13C
NMR (75.47 or 100.62 MHz) spectra were run on a Bruker Avance
300 MHz or a Bruker DRX 400 MHz spectrometer. Chemical shifts
are expressed in parts per million (ppm) relative to TMS in 1H
NMR and to deuterated solvent in 13C NMR (CDCl3: 13C
77.0 ppm). Complete assignment of 1H and 13C NMR resonances
was based on interpretation of standard 2D NMR data. Pressur-
ized (flash) column chromatography was performed on Kieselgel
60 0.063–0.200 mesh (Merck) silica gel. Analytical thin layer
chromatography (TLC) was carried out on 0.2 mm thick plates
of Kieselgel F254 (Merck). Reactions were heated by immersion
in oil or by use of DrySynTM MULTI reaction block kit while the
temperature was taken from a thermometer touching the bottom
of the pyrex bath. Microanalyses were carried out by the Camp-
bell Laboratory, University of Otago, Dunedin, New Zealand. 4-
Methoxy-6-methyl-2-pyrone (11) was prepared by a literature
method.19 The 1H NMR data observed for pyrones 35, 426, 124,
134, 1524, 1820, dihydro styryl pyrones 126 and 25, and dimers
5,11,12 7,14 30,22 and 31,22 agreed with those previously reported
in the literature.
[I > 2r(I)], R1 = 0.0730, wR2 = 0.2232 and GOF = 1.084.
5.2.2. 4-Methoxy-6-styryl-2H-pyran-2-one (4)
From pyrone (200 mg, 1.4 mmol) and benzaldehyde (180 lL,
1.8 mmol). Recrystallization from MeOH gave the product as a
white microcrystalline solid (153.1 mg, 47%). Mp 137–138 °C
(lit.23 134–136 °C); Rf = 0.78 (3% MeOH:CH2Cl2); IR (smear) mmax
3076, 1719, 1635, 1607, 1555, 1446, 1406, 1256, 1152, 1001,
954, 831, 748, 685 cmÀ1 13C NMR (CDCl3, 100 MHz) d 171.1 (C-
;
4), 164.0 (C-2), 158.6 (C-6), 135.8 (C-8), 135.2 (C-9), 129.4 (C-12),
128.9 (C-11), 127.4 (C-10), 118.6 (C-7), 101.3 (C-5), 88.9 (C-3),
55.9 (OMe); EIMS m/z 228 [M]+; HREIMS m/z 228.0788 (calcd for
C
14H12O3 228.0786); Anal. Calcd for C14H12O3: C, 73.67; H, 5.30.
Found: C, 73.63; H, 5.44. 1H NMR data agreed with literature.23
5.2.3. 4-Methoxy-6-(3-nitrostyryl)-2H-pyran-2-one (12)
From pyrone (202 mg, 1.4 mmol) and 3-nitrobenzaldehyde
(259 mg, 1.7 mmol). Recrystallization from MeOH gave the product

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
1489
as a yellow amorphous solid (115 mg, 29%). Mp 235–236 °C;
Rf = 0.76 (3% MeOH:CH2Cl2); IR (ATR) mmax 3078, 1726, 1526,
yellow crystalline solid (155 mg, 40%). Mp 231–232 °C (lit.24
234–235 °C); Rf = 0.43 (3% MeOH:CH2Cl2); 13C NMR (CDCl3,
100 MHz) d 171.1 (C-4), 164.0 (C-2), 158.8 (C-6), 148.9 (C-12),
148.3 (C-11), 135.5 (C-8), 129.7 (C-9), 123.5 (C-14), 116.8 (C-7),
108.6 (C-10), 105.9 (C-13), 101.4 (C-15), 100.7 (C-5), 88.5 (C-3),
55.9 (OMe); EIMS m/z 272 [M]+; HREIMS m/z 272.0686 (calcd for
1347, 1257 cmÀ1
; d 8.37 (1H, t,
1H NMR (CDCl3, 300 MHz)
J = 1.8 Hz, H-10), 8.17 (1H, ddd, J = 8.1, 2.2, 1.0 Hz, H-12), 7.75
(1H, br d, J = 7.7 Hz, H-14), 7.55 (1H, t, J = 8.0 Hz, H-13), 7.52 (1H,
d, J = 16.0 Hz, H-8), 6.70 (1H, d, J = 16.0 Hz, H-7), 6.02 (1H, d,
J = 2.2 Hz, H-5), 5.53 (1H, d, J = 2.2 Hz, H-3), 3.84 (3H, s, OMe);
13C NMR (CDCl3, 75 MHz) d 170.7 (C-4), 163.5 (C-2), 157.4 (C-6),
148.8 (C-11), 137.0 (C-9), 133.6 (C-14), 132.9 (C-8), 130.0 (C-13),
123.6 (C-12), 121.5 (C-7), 121.1 (C-10), 102.9 (C-5), 89.7 (C-3),
56.1 (OMe); EIMS m/z 273 [M]+; HREIMS m/z 273.0637 (calcd for
C
15H12O5 272.0685); Anal. Calcd for C14H12O3: C, 66.17; H, 4.44.
Found: C, 66.12; H, 4.53. IR and 1H NMR data agreed with
literature.24
5.2.7. 4-Methoxy-6-(3-phenoxy-styryl)-2H-pyran-2-one (16)
C
14H11NO5 273.0637). 1H NMR data agreed with literature.4
From pyrone (200 mg, 1.4 mmol) and 3-phenoxybenzaldehyde
(295
chromatography eluting with 1% MeOH in dichloromethane gave
the product as yellow oil (104 mg, 23%). Rf = 0.58 (2%
MeOH:CH2Cl2); IR (ATR) mmax 3078, 1721, 1641, 1607, 1554,
1484, 1233 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.42 (1H, d,
J = 16.0 Hz, H-8), 7.35 (2H, m, H-18), 7.32 (1H, m, H-13), 7.21
(1H, m, H-14), 7.13 (1H, m, H-19), 7.11 (1H, m, H-10), 7.01 (2H,
m, H-17), 6.97 (1H, m, H-12), 6.51 (1H, d, J = 16.0 Hz, H-7), 5.92
(1H, d, J = 2.0 Hz, H-5), 5.48 (1H, d, J = 2.0 Hz, H-3), 3.81 (3H, s,
OMe); 13C NMR (CDCl3, 100 MHz) d 171.0 (C-4), 163.8 (C-2),
158.3 (C-6), 157.9 (C-11), 156.7 (C-16), 137.0 (C-9), 135.1 (C-8),
130.2 (C-13), 129.9 (C-18), 123.6 (C-19), 122.5 (C-14), 119.7 (C-
12), 119.3 (C-7), 119.1 (C-17), 116.9 (C-10), 101.6 (C-5), 89.0 (C-
3), 55.9 (OMe); EIMS m/z 320 [M]+; HREIMS m/z 320.1051 (calcd
for C20H16O4 320.1049).
lL, 1.7 mmol). Purification by repeated silica gel column
5.2.4. 4-Methoxy-6-(4-nitrostyryl)-2H-pyran-2-one (13)
From pyrone (199 mg, 1.4 mmol) and 4-nitrobenzaldehyde
(258 mg, 1.7 mmol). Recrystallization from MeOH gave the product
as an orange solid (21 mg, 5%). Mp 213–214 °C (lit4 211.5–214 °C);
Rf = 0.77 (3% MeOH:CH2Cl2); IR (smear) mmax 3081, 1694, 1610,
1591, 1553, 1513, 1448, 1337, 1254, 1154, 955, 810 cmÀ1; 1H NMR
(CDCl3, 400 MHz) d 8.23 (2H, d, J = 8.8 Hz, H-11), 7.62 (2H, d,
J = 8.8 Hz, H-10), 7.51 (1H, d, J = 16.0 Hz, H-8), 6.70 (1H, d,
J = 16.0 Hz, H-7), 6.03 (1H, d, J = 2.1 Hz, H-5), 5.54 (1H, d, J = 2.1 Hz,
H-3), 3.84 (3H, s, OMe); 13C NMR (CDCl3, 100 MHz) d 170.6 (C-4),
163.4 (C-2), 157.3 (C-6), 147.8 (C-12), 141.4 (C-9), 132.9 (C-8),
127.9 (C-10), 124.2 (C-11), 122.6 (C-7), 103.3 (C-5), 89.9 (C-3),
55.1 (OMe); EIMS m/z 273 [M]+; HREIMS m/z 273.06323 (calcd for
a
;
C
14H11NO5 273.06372). 1H NMR data agreed with literature.4
5.2.5. 4-Methoxy-6-(4-tert-butyl-styryl)-2H-pyran-2-one (14)
From pyrone (201 mg, 1.4 mmol) and 4-tert-butylbenzaldehyde
5.2.8. 4-Methoxy-6-(3-(4-tert-butyl-phenoxy)-styryl)-2H-pyran-
2-one (17)
(290
l
L, 1.7 mmol). Repeated recrystallization from MeOH gave
From pyrone (202 mg, 1.4 mmol) and 3-(4-tert-butyl-phen-
oxy)benzaldehyde (434 mg, 1.7 mmol). Repeated recrystallization
from MeOH gave the product as a white microcrystalline solid
(121 mg, 22%). Mp 138–139 °C; Rf = 0.64 (2% MeOH:CH2Cl2); IR
the product as a white microcrystalline solid (104 mg, 25%). Mp
146–147 °C; Rf = 0.77 (3% MeOH:CH2Cl2); IR (ATR) mmax 2960,
1713, 1638, 1552, cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.48 (1H, d,
;
J = 16.0 Hz, H-8), 7.43 (2H, m, H-10), 7.39 (2H, m, H-11), 6.54
(1H, d, J = 16.0 Hz, H-7), 5.92 (1H, d, J = 2.2 Hz, H-5), 5.47 (1H, d,
J = 2.2 Hz, H-3), 3.81 (3H, s, OMe), 1.32 (9H, s, H-14); 13C NMR
(CDCl3, 100 MHz) d 171.1 (C-4), 164.1 (C-2), 158.9 (C-6), 152.9
(C-12), 135.7 (C-8), 132.4 (C-9), 127.3 (C-10), 125.9 (C-11), 117.8
(C-7), 100.9 (C-5), 88.6 (C-3), 55.9 (OMe), 34.8 (C-13), 31.2 (C-
14); EIMS m/z 284 [M]+; HREIMS m/z 284.1412 (calcd for
(ATR) mmax 2959, 1717, 1638, 1565, 1505, 1442, 1242 cmÀ1 1H
;
NMR (CDCl3, 400 MHz) d 7.42 (1H, d, J = 16.0 Hz, H-8), 7.36 (2H,
m, H-18), 7.31 (1H, m, H-13), 7.20 (1H, m, H-14), 7.10 (1H, br m,
H-10), 6.97 (1H, m, H-12), 6.95 (2H, m, H-17), 6.52 (1H, d,
J = 16.0 Hz, H-7), 5.92 (1H, d, J = 2.2 Hz, H-5), 5.48 (1H, d,
J = 2.2 Hz, H-3), 3.81 (3H, s, OMe), 1.33 (9H, s, H-21); 13C NMR
(CDCl3, 100 MHz) d 171.0 (C-4), 163.9 (C-2), 158.3 (C-6), 158.2
(C-11), 154.1 (C-16), 146.6 (C-19), 136.9 (C-9), 135.2 (C-8), 130.1
(C-13), 126.7 (C-18), 122.0 (C-14), 119.4 (C-12), 119.2 (C-7),
118.7 (C-17), 116.8 (C-10), 101.6 (C-5), 89.0 (C-3), 55.9 (OMe),
34.3 (C-20), 31.5 (C-21); EIMS m/z 376 [M]+; HREIMS m/z
C18H20O3 284.1412); Anal. Calcd for C18H20O3: C, 76.03; H, 7.09.
Found: C, 75.87; H, 7.35.
Crystallographic data (excluding structure factors) for the struc-
ture of compound 14 in this paper have been deposited with the
Cambridge Crystallographic Data Centre as Supplementary Publi-
cation No. CCDC 831984. Copies of the data can be obtained, free
of charge, on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK, (fax: +44-(0)1223-336033 or e-mail: deposit@
ccdc.cam.ac.uk).
376.1674 (calcd for
C24H24O4 376.1675); Anal. Calcd for
C24H24O4: C, 76.57; H, 6.43. Found: C, 76.69; H, 6.58.
5.2.9. 4-Methoxy-6-(4-phenyl-1,3-butadienyl)-2H-pyran-2-one
(18)
Crystal data: C18H20O3, M 284.34, T 93(2) K, Triclinic, P21/n,
From pyrone (201 mg, 1.4 mmol) and cinnamaldehyde (450 lL,
a = 14.6633(5) Å, b = 7.1228(3) Å, c = 15.6152(6) Å,
113.468(3)°,
= 90°, V = 1496.01(10) Å3, Z = 4, Dc = 1.262 Mg/m3,
= 0.085 mmÀ1
a
= 90°, b =
3.6 mmol). Recrystallization from MeOH gave the product as a yel-
low solid (23 mg, 6%). Mp 189–190 °C (lit.20 188.5–190 °C);
Rf = 0.81 (3% MeOH:CH2Cl2); 13C NMR (CDCl3, 100 MHz) d 171.0
(C-4), 164.0 (C-2), 158.7 (C-6), 138.3 (C-10), 136.4 (C-11), 136.3
(C-8), 128.8 (C-13), 128.6 (C-14), 127.1 (C-9), 127.0 (C-12), 122.0
(C-7), 100.9 (C-5), 88.7 (C-3), 55.9 (OMe); EIMS m/z 254 [M]+; HRE-
IMS m/z 254.0936 (calcd for C16H14O3 254.0943); Anal. Calcd for
c
l
,
F(000) = 608, crystal size 0.44 Â 0.12 Â 0.12
mm3, Hmax = 27.99°, index ranges À19< = h< = 19, À9< = k< = 9,
À20< = l< = 20, reflections collected = 18895, independent reflec-
tions = 3588 [R(int) = 0.0656], data/restraints/parameters 3588/0/
202. All non hydrogen atoms were identified after isotropic refine-
ment of the initial solution. Full matrix least-squares refinement
C
14H12O3: C, 75.57; H, 5.55. Found: C, 75.28; H, 5.68. IR and 1H
on F2 was carried out to give R indices [I > 2
wR2 = 0.1007 and GOF = 1.013.
r
(I)], R1 = 0.0465,
NMR data agreed with literature.20
5.2.10. 4-Methoxy-6-(4-(4-dimethylaminophenyl)-1,3-butadie
nyl)-2H-pyran-2-one (19)
From pyrone (200 mg, 1.4 mmol) and 4-dimethylaminocinnam-
aldehyde (298 mg, 1.7 mmol) and heating with magnesium meth-
oxide in MeOH under nitrogen for 22 h. Recrystallization from
5.2.6. 6-[2-(1,3-Benzodioxo-5-yl)ethenyl]-4-methoxy-2H-pyran-
2-one (15)
From pyrone (201 mg, 1.4 mmol) and piperanal (260 mg,
1.7 mmol). Recrystallization from MeOH gave the product as a

1490
S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
MeOH gave the product as a red solid (21 mg, 5%). Mp 239–240 °C;
Rf = 0.86 (3% MeOH:CH2Cl2); IR (ATR) max 1720, 1595, 1541, 1523,
1258 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.33 (2H, m, H-12), 7.28
MeOH gave the product as a yellow solid (72.4 mg, 27%). Mp
330 °C (decomp.); Rf = 0.15 (3% MeOH:CH2Cl2); IR (ATR) max 3078,
1726, 1640, 1556, 1409 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.50
m
m
;
;
(1H, m, H-8), 6.75 (1H, m, H-10), 6.70 (1H, m, H-9), 6.65 (2H, m,
H-13), 6.02 (1H, d, J = 15.2 Hz, H-7), 5.79 (1H, d, J = 2.0 Hz, H-5),
5.41 (1H, d, J = 2.0 Hz, H-3), 3.78 (3H, s, OMe), 2.98 (6H, s, H-16);
13C NMR (CDCl3, 100 MHz) d 171.2 (C-4), 164.3 (C-2), 159.4 (C-6),
150.7 (C-14), 139.1 (C-10), 137.4 (C-8), 128.4 (C-12), 124.6 (C-
11), 122.7 (C-9), 119.2 (C-7), 112.1 (C-13), 99.7 (C-5), 87.9 (C-3),
55.8 (OMe), 40.2 (C-16); EIMS m/z 297 [M]+; HREIMS m/z
297.1365 (calcd for C18H19NO3 297.1365).
(4H, s, H-10), 7.48 (2H, d, J = 16.0 Hz, H-8), 6.60 (2H, d, J = 16.0 Hz,
H-7), 5.96 (2H, d, J = 2.0 Hz, H-5), 5.50 (2H, d, J = 2.0 Hz, H-3), 3.83
(6H, s, OMe); 13C NMR (CDCl3, 100 MHz) d 171.0 (C-4), 163.9 (C-2),
158.4 (C-6), 136.3 (C-9), 134.8 (C-8), 128.0 (C-10), 119.3 (C-7),
101.8 (C-5), 89.1 (C-3), 56.0 (OMe); FABMS m/z 379 [M+H]+;
HRFABMS m/z 379.1188 (calcd for C22H19O6 379.1182).
5.3. General procedure for catalytic hydrogenation of pyrones
5.2.11. 4-Methoxy-6-[2-(2-furyl)ethenyl]-2H-pyran-2-one (20)
Pyrone was dissolved in MeOH/CHCl3 (5 mL, 1:1) and stirred
under a hydrogen atmosphere (balloon) for 2 h in the presence of
10% Pd/C. The suspension was filtered and the solvent evaporated
in vacuo. Purification by silica gel column chromatography eluting
with MeOH (0–1%) in dichloromethane gave the product.
From pyrone (200 mg, 1.4 mmol) and furfuraldehyde (145 lL,
1.8 mmol). Purification by recrystallization from MeOH gave the
product as a yellow solid (66 mg, 21%). Mp 174–175 °C; Rf = 0.46
(3% MeOH:CH2Cl2); IR (ATR) mmax 3091, 2917, 1697, 1634, 1543,
1449, 1145, 943 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.43 (1H, d,
;
J = 1.5 Hz, H-12), 7.23 (1H, d, J = 15.6 Hz, H-8), 6.49 (1H, m, H-
10), 6.47 (1H, m, H-7), 6.44 (1H, m, H-11), 5.89 (1H, d, J = 2.2 Hz,
H-5), 5.45 (1H, d, J = 2.2 Hz, H-3), 3.81 (3H, s, OMe); 13C NMR
(CDCl3, 100 MHz) d 171.0 (C-4), 163.9 (C-2), 158.4 (C-6), 151.6
(C-9), 144.0 (C-12), 122.6 (C-8), 116.5 (C-7), 113.3 (C-10), 112.3
(C-11), 101.2 (C-5), 88.7 (C-3), 55.9 (OMe); EIMS m/z 218 [M]+;
HREIMS m/z 218.0575 (calcd for C12H10O4 218.0579); Anal. Calcd
for C12H10O4: C, 66.05; H, 4.62. Found: C, 66.34; H, 4.85.
5.3.1. 7,8-Dihydro-4-methoxy-6-styryl-2H-pyran-2-one (1)
From pyrone 4 (24.9 mg, 0.11 mmol) and Pd/C (10%, 6.8 mg) to
give product 1 as a white solid (16.9 mg, 67%). Mp 99–100 °C (lit.26
96–97 °C); Rf = 0.59 (3% MeOH:CH2Cl2); EIMS m/z 230 [M]+; HRE-
IMS m/z 230.0939 (calcd for C14H14O3 230.0943); Anal. Calcd for
C
14H14O3: C, 73.03; H, 6.13. Found: C, 73.30; H, 6.11. 1H and 13C
NMR data agreed with the literature.26
5.3.2. 6-[2-(1,3-Benzodioxo-5-yl)ethyl]-4-methoxy-2H-pyran-2-
one (2)
5.2.12. 4-Methoxy-6-[2-(1-naphthyl)ethenyl]-2H-pyran-2-one
(21)
From pyrone 15 (17.9 mg, 0.066 mmol) and Pd/C (10%, 4.8 mg)
to give product 2 as white crystals (13.0 mg, 72%). Mp 143–
144 °C (lit.5 138–140 °C); Rf = 0.39 (3% MeOH:CH2Cl2); IR (smear)
From pyrone (200 mg, 1.4 mmol) and 1-napthaldehyde (233 lL,
1.7 mmol). Purification by repeated recrystallization from MeOH
gave the product as a yellow solid (160 mg, 40%). Mp 120–121 °C;
mmax 3108, 2927, 1705, 1645, 1567, 1239 cmÀ1 1H NMR (CDCl3,
;
Rf = 0.83 (3% MeOH:CH2Cl2); IR (ATR)
m
max 3079, 1724, 1636, 1556,
400 MHz) d 6.71 (1H, d, J = 7.8 Hz, H-13), 6.64 (1H, d, J = 1.6 Hz,
H-10), 6.60 (1H, dd, J = 7.8, 1.6 Hz, H-14), 5.91 (2H, s, H2-15),
5.70 (1H, d, J = 2.3 Hz, H-5), 5.40 (1H, d, J = 2.1 Hz, H-3), 3.77 (3H,
s, OMe), 2.88 (2H, t, J = 7.6 Hz, H2-8), 2.68 (2H, t, J = 7.6 Hz, H2-7);
13C NMR (CDCl3, 100 MHz) d 171.1 (C-4), 164.9 (C-2), 164.2 (C-6),
147.7 (C-11), 146.1 (C-12), 133.6 (C-9), 121.2 (C-14), 108.7 (C-
10), 108.3 (C-13), 100.9 (C-15), 100.3 (C-5), 87.7 (C-3), 55.8
(OMe), 35.7 (C-7), 32.6 (C-8); EIMS m/z 274 [M]+; HREIMS m/z
274.0841 (calcd for C15H14O5 274.0841); Anal. Calcd for
1411 cmÀ1; 1H NMR (CDCl3, 400 MHz) d 8.29 (1H, d, J = 15.7 Hz, H-
8), 8.23 (1H, d, J = 8.2 Hz, H-16), 7.85 (2H, m, H-12, 13), 7.72 (1H,
d, J = 7.2 Hz, H-10), 7.58 (1H, m, H-15), 7.52 (1H, m, H-14), 7.47
(1H, m, H-11), 6.66 (1H, d, J = 15.7 Hz, H-7), 5.99 (1H, d, J = 2.2 Hz,
H-5), 5.53 (1H, d, J = 2.2 Hz, H-3), 3.85 (3H, s, OMe); 13C NMR (CDCl3,
100 MHz) d 171.0 (C-4), 164.0 (C-2), 158.6 (C-6), 133.7 (C-12a),
132.7 (C-9), 132.6 (C-8), 131.4 (C-16a), 129.8 (C-12), 128.6 (C-13),
126.7 (C-15), 126.2 (C-14), 125.4 (C-11), 124.1 (C-10), 123.6 (C-
16), 121.3 (C-7), 101.6 (C-5), 89.0 (C-3), 55.9 (OMe); EIMS m/z 278
[M]+; HREIMS m/z 278.0942 (calcd for C18H14O3 278.0943).
C15H14O5: C, 65.69; H, 5.15. Found: C, 65.76; H, 5.23.
Crystallographic data (excluding structure factors) for the struc-
ture of compound 2 have been deposited with the Cambridge Crys-
tallographic Data Centre as Supplementary Publication No. CCDC
831985. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
(fax: +44-(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
5.2.13. 4-Methoxy-6-[2-(2-naphthyl)ethenyl]-2H-pyran-2-one
(22)
From pyrone (201 mg, 1.4 mmol) and 2-napthaldehyde
(269 mg, 1.7 mmol). Purification by repeated recrystallization from
MeOH gave the product as a yellow crystalline solid (138 mg, 35%).
Mp 201–202 °C; Rf = 0.56 (3% MeOH:CH2Cl2); IR (ATR) mmax 3081,
ꢀ
Crystal data. C15H14O5, M 274.26, T 98(2) K, Triclinic, P1,
a = 8.0036(2) Å, b = 8.3760(3) Å, c = 10.5599(3) Å,
a = 90.8060(10)°,
1709, 1638, 1549, 1448, 1408, 1251 cmÀ1
;
1H NMR (CDCl3,
b = 105.8980(10)°,
c
= 110.4210(10)°. V = 633.31(3) Å3, Z = 2, Dc =
400 MHz) d 7.87 (1H, d, J = 1.0 Hz, H-16), 7.82 (3H, m, H-11, H-
12, H-15), 7.64 (1H, d, J = 15.9 Hz, H-8), 7.63 (1H, m, H-10), 7.48
(2H, m, H-14 and H-13), 6.68 (1H, d, J = 15.9 Hz, H-7), 5.96 (1H,
d, J = 2.2 Hz, H-5), 5.49 (1H, d, J = 2.2 Hz, H-3), 3.81 (3H, s, OMe);
13C NMR (CDCl3, 100 MHz) d 171.0 (C-4), 164.0 (C-2), 158.7 (C-6),
135.8 (C-8), 133.8 (C-11a), 133.4 (C-15a), 132.7 (C-9), 128.9 (C-
16), 128.6 (C-11), 128.4 (C-15), 127.7 (C-12), 126.9 (C-13), 126.6
(C-14), 123.2 (C-10), 118.8 (C-7), 101.3 (C-5), 88.8 (C-3), 55.9
(OMe); EIMS m/z 278 [M]+; HREIMS m/z 278.0945 (calcd for
1.438 Mg/m3,
l
= 0.109 mmÀ1, F(000) = 288, crystal size 0.43 Â
0.29 Â 0.20 mm3, Hmax = 27.98°, index ranges À10< = h< = 10,
À11< = k< = 10, À13< = l< = 13, reflections collected = 15272, inde-
pendent reflections = 3024 [R(int) = 0.0243], data/restraints/param-
eters 3024/0/182. All non hydrogen atoms were identified after
isotropic refinement of the initial solution. Full matrix least-squares
refinement on F2 was carried out to give R indices [I > 2
R1 = 0.0342, wR2 = 0.0944 and GOF = 1.033.
r(I)],
C18H14O3 278.0943).
5.3.3. 4-Methoxy-6-[2-(4-tert-butylphenyl)ethyl]-2H-pyran-2-
one (24)
5.2.14. 6,6’-(1E,1’E)-2,2’-(1,4-Phenylene)bis(ethene-2,1-diyl)bis
(4-methoxy-2H-pyran-2-one) (23)
From pyrone (200 mg, 1.4 mmol) and terephthaldicarboxalde-
hyde (95 mg, 0.7 mmol). Purification by recrystallization from
From pyrone 14 (19.3 mg, 0.068 mmol) and Pd/C (10%, 5.2 mg)
to give product 24 as a white solid (17.4 mg, 90%). Mp 77–79 °C;
Rf = 0.42 (3% MeOH:CH2Cl2); IR (ATR) mmax 2959, 1713, 1567,
1451, 1411, 1248 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.31 (2H, d,
;

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
1491
J = 8.3 Hz, H-11/13), 7.11 (2H, d, J = 8.3 Hz, H-10/14), 5.75 (1H, d,
J = 2.1 Hz, H-5), 5.41 (1H, d, J = 2.1 Hz, H-3), 3.77 (3H, s, OMe),
2.92 (2H, m, H2-8), 2.73 (2H, m, H2-7), 1.30 (9H, s, H-16); 13C
NMR (CDCl3, 100 MHz) d 171.2 (C-4), 165.0 (C-2), 164.6 (C-6),
149.3 (C-12), 136.8 (C-9), 127.9 (C-10/14), 125.5 (C-11/13), 100.1
(C-5), 87.7 (C-3), 55.8 (OMe), 35.4 (C-7), 34.4 (C-15), 32.3 (C-8),
31.3 (C-16); (+)-ESIMS m/z 287 [M+H]+, (+)-HRESIMS m/z
287.1639 (calcd for C18H23O3 287.1642).
133.5 (C-15a), 132.1 (C-11a), 128.2 (C-11⁄), 127.6 (C-12⁄), 127.5
(C-15⁄), 126.7 (C-10), 126.6 (C-16), 126.1 (C-13⁄), 125.5 (C-14⁄),
100.4 (C-5), 87.7 (C-3), 55.8 (OMe), 35.3 (C-7), 32.9 (C-8); (+)-
ESIMS m/z 281 [M+H]+, (+)-HRESIMS m/z 281.1172 (calcd for
C18H17O3 281.1172).
5.3.8. 6,6’-(2,2’-(1,4-Phenylene)bis(ethane-2,1-diyl))bis(4-
methoxy-2H-pyran-2-one) (29)
From pyrone 23 (19.7 mg, 0.052 mmol) and Pd/C (10%, 4.9 mg)
to give 29 as a white solid (9.8 mg, 49%). Mp 196–198 °C;
Rf = 0.06 (3% MeOH:CH2Cl2); IR (ATR) mmax 1710, 1651, 1566,
5.3.4. 6-[2-(3,4-Dimethoxyphenyl)ethyl]-4-methoxy-2H-pyran-
2-one (25)
1450, 1413, 1250, 1143 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.08
;
From pyrone 3 (20.8 mg, 0.072 mmol) and Pd/C (10%, 3.9 mg) to
give 25 as a white solid (20.1 mg, 96%). Mp 71-73 °C; (lit.27 74–
75 °C); Rf = 0.18 (3% MeOH:CH2Cl2); IR (ATR) mmax 1709, 1651,
(4H, s, H-10), 5.70 (2H, d, J = 2.2 Hz, H-5), 5.39 (2H, d, J = 2.2 Hz,
H-3), 3.77 (6H, s, OMe), 2.92 (4H, m, H2-8), 2.70 (4H, m, H2-7);
13C NMR (CDCl3, 100 MHz) d 171.1 (C-4), 164.8 (C-2), 164.3 (C-6),
138.0 (C-9), 128.5 (C-10), 100.2 (C-5), 87.7 (C-3), 55.8 (OMe),
35.4 (C-7), 32.4 (C-8); (+)-ESIMS m/z 405 [M + Na]+, (+)-HRESIMS
m/z 405.1316 (calcd for C22H22NaO6 405.1309).
1569, 1518, 1453, 1241, 1136 cmÀ1 1H NMR (CDCl3, 400 MHz) d
;
6.77 (1H, d, J = 8.1 Hz, H-13), 6.69 (1H, dd, J = 8.1, 1.9 Hz, H-14),
6.66 (1H, d, J = 1.9 Hz, H-10), 5.69 (1H, d, J = 2.2 Hz, H-5), 5.40
(1H, d, J = 2.2 Hz, H-3), 3.84 (3H, s, OMe-11⁄), 3.83 (3H, s, OMe-
12⁄), 3.76 (3H, s, OMe-4), 2.91 (2H, m, H2-8), 2.71 (2H, m, H2-7);
13C NMR (CDCl3, 100 MHz) d 171.2 (C-4), 165.1 (C-2), 164.3 (C-6),
148.8 (C-11), 147.5 (C-12), 132.4 (C-9), 120.1 (C-14), 111.6 (C-
10), 111.3 (C-13), 100.4 (C-5), 87.6 (C-3), 55.8 (OMe), 55.7 (OMe),
35.7 (C-7), 32.4 (C-8); (+)-ESIMS m/z 313 [M+Na]+, (+)-HRESIMS
m/z 313.1056 (calcd for C16H18NaO5 313.1046).
5.4. General procedure for photodimerization of 6-styryl-pyran-
2-ones
6-Styryl-pyran-2-one was suspended, with stirring, in water
and exposed to a sun lamp (300 W, 15 cm from vial) for three 5 h
periods at which time the resulting crude product was purified
by repeated column chromatography eluting with 0–5% MeOH in
dichloromethane.
5.3.5. 4-Methoxy-6-[2-(3-(4-tert-butylphenoxy)phenyl)ethyl]-
2H-pyran-2-one (26)
From pyrone 17 (21.2 mg, 0.056 mmol) and Pd/C (10%, 3.8 mg)
5.4.1. 6,6’-(3,4-Diphenylcyclobutane-1,2-diyl)bis(4-methoxy-
2H-pyran-2-one) (5) and Aniba-dimer-A (7)
to give 26 as
a
colorless oil (19.6 mg, 92%). Rf = 0.49 (3%
MeOH:CH2Cl2); IR (smear) mmax 2960, 1721, 1568, 1247 cmÀ1
;
1H
From pyrone 4 (43.0 mg, 0.19 mmol) to give the head-to-tail di-
mer 511,12 (8.0 mg, 19%) and aniba-dimer A14–16 7 (4.2 mg, 10%),
both as amorphous colorless solids.
NMR (CDCl3, 400 MHz) d 7.33 (2H, m, H-18/20), 7.22 (1H, t,
J = 7.8 Hz, H-13), 6.90 (2H, m, H-17/21), 6.87 (1H, m, H-14), 6.83
(1H, m, H-12), 6.81 (1H, m, H-10), 5.71 (1H, d, J = 2.1 Hz, H-5),
5.40 (1H, d, J = 2.1 Hz, H-3), 3.77 (3H, s, OMe), 2.93 (2H, m, H2-8),
2.72 (2H, m, H2-7), 1.32 (9H, s, H-23);13C NMR (CDCl3, 75 MHz) d
171.1 (C-4), 164.8 (C-2), 164.2 (C-6), 157.8 (C-11), 154.5 (C-16),
146.2 (C-19), 141.7 (C-9), 129.8 (C-13), 126.5 (C-18,20), 122.9 (C-
14), 118.4 (C-17/21), 118.3 (C-10), 116.6 (C-12), 100.3 (C-5), 87.7
(C-3), 55.8 (OMe), 35.2 (C-7), 34.3 (C-22), 32.7 (C-8), 31.5 (C-23);
(+)-ESIMS m/z 401 [M+Na]+, (+)-HRESIMS m/z 401.1725 (calcd for
C24H26NaO4 401.1723).
Data for 5: Mp 82–84 °C (lit.11 103–105 °C; lit.12 170–172 °C);
Rf = 0.24 (3% MeOH:CH2Cl2); IR (ATR)
mmax 2918, 1714, 1646, 1563,
1454, 1409, 1239 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.12 (4H, m,
;
H-11,13), 7.06 (2H, m, H-12), 6.95 (4H, m, H-10,14), 5.99 (2H, d,
J = 2.3 Hz, H-5), 5.36 (2H, d, J = 2.3 Hz, H-3), 4.50 (2H, m, H-8), 4.11
(2H, m, H-7), 3.75 (6H, s, OMe); 13C NMR (CDCl3, 100 MHz) d 171.0
(C-4), 164.3 (C-2), 162.4 (C-6), 137.9 (C-9), 128.2 (C-11,13), 127.7
(C-10,14), 126.7 (C-12), 101.5 (C-5), 88.0 (C-3), 55.9 (OMe), 44.9
(C-8), 44.0 (C-7); (+)-ESIMS m/z 457 [M+H]+, (+)-HRESIMS m/z
457.1650 (calcd for C28H25O6 457.1646); (+)-HRESIMSMS (parent
m/z 457) fragment m/z 277.0701 (calcd for C14H13O6 277.0707),
229.0853 (calcd for C14H13O3 229.0859).
5.3.6. 4-Methoxy-6-[2-(1-naphthyl)ethyl]-2H-pyran-2-one (27)
From pyrone 21 (21.1 mg, 0.076 mmol) to give 27 as a white so-
lid (16.0 mg, 75%). Mp 75–77 °C; Rf = 0.40 (3% MeOH:CH2Cl2); IR
Data for 7: Mp 178–180 °C (lit.15 178–179 °C; lit.14 185–188 °C);
(ATR) mmax 3078, 1714, 1647, 1563, 1465, 1257, 1138 cmÀ1 1H
;
Rf = 0.20 (3% MeOH:CH2Cl2); IR (ATR)
mmax 3078, 1704, 1647, 1623,
1567, 1244 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.41 (2H, m, H-
;
NMR (CDCl3, 400 MHz) d 8.02 (1H, d, J = 8.4 Hz, H-16), 7.86 (1H, d,
J = 7.8 Hz, H-13), 7.73 (1H, d, J = 8.2 Hz, H-12), 7.50 (2H, m, H-15/
H-14), 7.38 (1H, t, J = 7.6 Hz, H-11), 7.30 (1H, d, J = 7.6 Hz, H-10),
5.71 (1H, d, J = 2.2 Hz, H-5), 5.42 (1H, d, J = 2.2 Hz, H-3), 3.76 (3H,
s, OMe), 3.42 (2H, m, H2–8), 2.86 (2H, m, H2-7); 13C NMR (CDCl3,
100 MHz) d 171.1 (C-4), 164.9 (C-2), 164.4 (C-6), 135.9 (C-9),
133.9 (C-12a), 131.5 (C-16a), 128.9 (C-13), 127.3 (C-12), 126.2 (C-
10/15), 125.6 (C-11⁄), 125.5 (C-14⁄), 123.2 (C-16), 100.3 (C-5),
87.8 (C-3), 55.8 (OMe), 34.8 (C-7), 30.2 (C-8); (+)-ESIMS m/z 281
[M+H]+, (+)-HRESIMS m/z 281.1174 (calcd for C18H17O3 281.1172).
10’,14’), 7.29 (8H, m, H-10,11,12,13,14,11’,12’,13’), 6.94 (1H, d,
J = 15.9 Hz, H-8’), 6.59 (1H, d, J = 15.9 Hz, H-7’), 5.91 (1H, d,
J = 2.2 Hz, H-5), 5.34 (1H, d, J = 2.2 Hz, H-3), 5.28 (1H, s, H-3’),
4.35 (1H, t, J = 10.3 Hz, H-8), 4.16 (1H, d, J = 11.1 Hz, H-7), 3.71
(3H, s, OMe-4), 3.59 (1H, d, J = 10.3 Hz, H-5’), 3.27 (3H, s, OMe-
4’); 13C NMR (CDCl3, 100 MHz) d 170.5 (C-4), 169.9 (C-4’), 164.6
(C-2⁄), 163.9 (C-2’⁄), 158.6 (C-6), 135.9 (C-9’), 135.6 (C-9), 131.5
(C-8’), 128.7, 128.5, 128.3, 127.8 (C-11,12,13,11’,12’,13’), 127.5
(C-10/14), 126.9 (C-10’/14’), 124.4 (C-7’), 102.7 (C-5), 91.8 (C-3’),
88.7 (C-3), 79.4 (C-6’), 55.9 (OMe-4), 55.4 (OMe-4’), 54.5 (C-7),
45.7 (C-5’), 39.2 (C-8); (+)-ESIMS m/z 479 [M+Na]+, (+)-HRESIMS
m/z 479.1453 (calcd for C28H24NaO6 479.1465).
5.3.7. 4-Methoxy-6-[2-(2-naphthyl)ethyl]-2H-pyran-2-one (28)
From pyrone 22 (19.4 mg, 0.070 mmol) to give 28 as a white so-
lid (16.3 mg, 84%). Mp 72–74 °C; Rf = 0.42 (3% MeOH:CH2Cl2); IR
(ATR) mmax 3082, 1722, 1649, 1564, 1412, 1250, 1142 cmÀ1 1H
;
5.4.2. 6,6’-(2,4-Bis(3,4-dimethoxyphenyl)cyclobutane-1,3-diyl)
bis(4-methoxy-2H-pyran-2-one) (30) and 11,12,11’,12’-
Tetramethoxy-aniba-dimer-A (31)
From pyrone 3 (19.9 mg, 0.069 mmol) to give the head-to-tail
dimer 30 as an amorphous colorless solid (4.1 mg, 14%) and asym-
metric dimer 31 as an amorphous yellow solid (6.9 mg, 35%).
NMR (CDCl3, 400 MHz) d 7.77 (3H, m, H-11,12,15), 7.61 (1H, br s,
H-16), 7.43 (2H, m, H-13,14), 7.29 (1H, dd, J = 8.4, 1.6 Hz, H-10),
5.71 (1H, d, J = 2.1 Hz, H-5), 5.40 (1H, d, J = 2.1 Hz, H-3), 3.74 (3H,
s, OMe), 3.13 (2H, m, H2-8), 2.83 (2H, m, H2-7); 13C NMR (CDCl3,
100 MHz) d 171.2 (C-4), 165.1 (C-2), 164.2 (C-6), 137.2 (C-9),

1492
S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
Data for 30: Mp 86–88 °C (lit.22 112–114 °C); Rf = 0.09 (3%
MeOH:CH2Cl2); IR (ATR) max 2918, 2849, 1706, 1641, 1563, 1515,
1454, 1409, 1249, 1142, 1023 cmÀ1 13C NMR (CDCl3, 100 MHz) d
101.5 (C-5), 87.9 (C-3), 55.6 (OMe-4), 45.3 (C-7), 44.0 (C-8); (+)-
ESIMS m/z 557 [M+H]+, (+)-HRESIMS m/z 557.1963 (calcd for
36H29O6 557.1959); (+)-HRESIMSMS (parent m/z 557) fragment
m
;
C
170.6 (C-4), 164.0 (C-2), 162.9 (C-6), 148.9 (C-11), 148.2 (C-12),
129.8 (C-9), 119.4 (C-14), 111.04 (C-10⁄), 110.96 (C-13⁄), 101.3
(C-5), 87.8 (C-3), 56.0 (OMe-11), 55.82 (OMe-12), 55.76 (OMe-4),
45.5 (C-7), 43.5 (C-8); (+)-ESIMS m/z 577 [M+H]+, (+)-HRESIMS m/
z 577.2073 (calcd for C32H33O10 577.2068); (+)-HRESIMSMS (parent
m/z 577) fragment m/z 289.1055 (calcd for C16H17O5 289.1071). 1H
and 13C NMR chemical shifts agreed with the literature, however
the previously reported assignments of C-2 and C-4 should be
reversed.22
m/z 279.1005 (calcd for C18H15O3 279.1021).
5.4.6. 11,11’ Di (4-tert-butyl-phenoxy) aniba-dimer-A (35)
From pyrone 17 (19.9 mg, 0.026 mmol) to give 35 as an amor-
phous colorless solid (9.7 mg, 49%). Mp 103–104 °C; Rf = 0.36 (3%
MeOH:CH2Cl2); IR (ATR) mmax 2960, 1713, 1626, 1568, 1507, 1444,
1240 cmÀ1
; d 7.34 (4H, m, H-
1H NMR (CDCl3, 400 MHz)
18,20,18’,20’), 7.26 (2H, m, H-13,13’), 7.17 (1H, d, J = 7.9 Hz, H-
14’), 6.98 (1H, br s, H-10’), 6.90 (8H, m, H-10,12,14,17,21,
12’,17’,21’), 6.85 (1H, m, H-8’), 6.53 (1H, d, J = 15.9 Hz, H-7’), 5.89
(1H, d, J = 2.1 Hz, H-5), 5.35 (1H, d, J = 2.1 Hz, H-3), 5.26 (1H, s, H-
3’), 4.28 (1H, t, J = 10.2 Hz, H-8), 4.09 (1H, d, J = 10.2 Hz, H-7), 3.72
(3H, s, OMe-4), 3.55 (1H, d, J = 10.2 Hz, H-5’), 3.34 (3H, s, OMe-4’),
1.33 (9H, s, H-23,23’), 1.32 (9H, s, H-23,23’); 13C NMR (CDCl3,
100 MHz) d 170.4 (C-4), 169.7 (C-4’), 164.3, 163.7 (C-2,2’), 158.4
(C-6), 158.0, 157.8 (C-11,11’), 154.3, 154.3 (C-16,16’), 146.5, 146.3
(C-19,19’), 137.6 (C-9,9’), 131.2 (C-8’), 130.0, 129.6 (C-13,13’),
126.65, 126.60 (C-18,20,18’,20’), 124.8 (C-7’), 121.8 (C-14), 120.8
Data for 31: Mp 99–100 °C (lit.22 195–197 °C); Rf = 0.05 (3%
MeOH:CH2Cl2); (+)-ESIMS m/z 599 [M+Na]+, (+)-HRESIMS m/z
599.1881 (calcd for C32H32NaO10 599.1888). 1H and 13C NMR data
were in agreement with literature values, however the previously
reported assignments of C-2 and C-4 should be reversed.22
5.4.3. 6,6’-(3,4-Di(benzo[d][1,3]dioxo-5-yl)cyclobutane-1,2-diyl)
bis(4-methoxy-2H-pyran-2-one) (32)
From pyrone 15 (19.3 mg, 0.071 mmol) to give 32 as an amor-
phous colorless solid (2.0 mg, 10%) and unreacted starting material
15 (5.6 mg, 29%). Mp 101–103 °C; Rf = 0.14 (3% MeOH:CH2Cl2); IR
(ATR) mmax 2905, 1706, 1646, 1561, 1490, 1445, 1408, 1237,
(C-14’),
118.6,
118.4,
118.2,
117.9,
117.8
(C-
10,12,17,21,12’,17’,21’), 117.3 (C-10’), 102.6 (C-5), 91.8 (C-3’), 88.8
(C-3), 79.2 (C-6’), 55.9 (OMe-4), 55.5 (OMe-4’), 54.4 (C-7), 45.6 (C-
5’), 38.9 (C-8), 34.3 (C-22,22’), 31.5 (C-23,23’); (+)-ESIMS m/z 753
[M + H]+, (+)-HRESIMS m/z 753.3402 (calcd for C48H49O8 753.3422).
1034 cmÀ1 1H NMR (CDCl3, 400 MHz) d 6.62 (2H, d, J = 8.0 Hz, H-
;
13), 6.46 (2H, dd, J = 8.0, 1.7 Hz, H-14), 6.43 (2H, d, J = 1.7 Hz, H-
10), 5.96 (2H, d, J = 2.1 Hz, H-5), 5.86 (4H, br s, H2–15), 5.35 (2H,
d, J = 2.1 Hz, H-3), 4.35 (2H, m, H-8), 3.96 (2H, m, H-7), 3.75 (6H,
s, OMe-4); 13C NMR (CDCl3, 100 MHz) d 171.0 (C-4), 164.2 (C-2),
162.2 (C-6), 147.7 (C-11), 146.3 (C-12), 131.8 (C-9), 120.8 (C-14),
108.1 (C-10), 101.4 (C-5), 100.9 (C-15), 88.1 (C-3), 55.9 (OMe-4),
44.8 (C-8), 44.4 (C-7); (+)-ESIMS m/z 545 [M+H]+, (+)-HRESIMS m/
z 545.1435 (calcd for C30H25O10 557.1959), (+)-HRESIMSMS (parent
m/z 545) fragment m/z 277.0690 (calcd for C14H13O6 277.0707).
5.5. Biological assays
5.5.1. Anti-tuberculosis activity
Procedures for the determination of MIC against M. tuberculosis
H
37Rv in 7H9 broth have been reported elsewhere.28 In the present
study, the protocol was modified slightly by utilizing 1:1000 di-
luted cultures rather than 1:100 and by growth of M. tuberculosis
H
37Rv in GAST medium29 which does not contain bovine serum
5.4.4. 12,12’-Di-tert-butyl-aniba-dimer-A (33)
albumin. Positive control was isoniazid which gave MIC 0.22
(0.03 g/mL).
lM
From pyrone 14 (20.6 mg, 0.036 mmol) to give 33 as an amor-
phous colorless solid (9.5 mg, 46%). Mp 130–131 °C; Rf = 0.26 (3%
MeOH:CH2Cl2); IR (ATR) mmax 2960, 1713, 1626, 1567, 1455,
l
5.5.2. Anti-protozoal activity
1390, 1244 cmÀ1
;
1H NMR (CDCl3, 400 MHz) d 7.35 (4H, s, H-
The in vitro activities against the protozoan parasites T.b. rho-
desiense, T. cruzi, L. donovani, and P. falciparum and cytotoxicity
assessment against L6 cells were determined as reported else-
where.30 The following strains, parasite forms and positive controls
were used: T.b. rhodesiense, STIB900, trypomastigote forms, melar-
10’,11’,13’,14’), 7.34 (2H, d, J = 9.9 Hz, H-11,13), 7.16 (2H, d,
J = 8.3 Hz, H-10,14), 6.91 (1H, d, J = 15.9 Hz, H-8’), 6.55 (1H, d,
J = 15.9 Hz, H-7’), 5.89 (1H, d, J = 2.1 Hz, H-5), 5.33 (1H, d,
J = 2.1 Hz, H-3), 5.27 (1H, s, H-3’), 4.33 (1H, t, J = 10.4 Hz, H-8),
4.14 (1H, d, J = 10.4 Hz, H-7), 3.70 (3H, s, OMe-4), 3.53 (1H, d,
J = 10.4 Hz, H-5’), 3.24 (3H, s, OMe-4’), 1.30 (9H, s), 1.29 (9H, s,
H-16,16’); 13C NMR (CDCl3, 100 MHz) d 170.5 (C-4), 170.1 (C-4’),
164.8, 164.0 (C-2,2’), 158.8 (C-6), 151.4 (C-12’), 150.9 (C-12),
133.1 (C-9’), 132.6 (C-9), 131.1 (C-8’), 127.2 (C-10,14), 126.6 (C-
10’,14’), 125.7 (C-11’,13’), 125.3 (C-11,13), 123.6 (C-7’), 102.6 (C-
5), 91.7 (C-3’), 88.7 (C-3), 79.5 (C-6’), 55.8 (OMe-4), 55.2 (OMe-
4’), 54.5 (C-7), 45.8 (C-5’), 38.8 (C-8), 34.6, 34.5 (C-15,15’), 31.3,
31.2 (C-16,16’); (+)-ESIMS m/z 591 [M+Na]+, (+)-HRESIMS m/z
591.2711 (calcd for C36H40NaO6 591.2717).
soprol, IC50 of 0.01
gote forms in L6 rat myoblasts, benznidazole, IC50 of 1.4
(0.352 g/mL); L. donovani, MHOM/ET/67/L82, axenic amastigote
forms, miltefosine, IC50 of 0.5 M (0.213 g/mL); P. falciparum, K1
(chloroquine and pyrimethamine resistant), erythrocytic stages,
chloroquine, IC50 of 0.20 M (0.065 g/mL) and L6 cells, rat skeletal
lM (4 ng/mL); T. cruzi, Tulahuen C2C4, amasti-
lM
l
l
l
l
l
myoblasts, podophyllotoxin, IC50 of 0.01 lM (0.004 lg/mL).
Acknowledgments
We thank the University of Auckland and Auckland Medical
Research Foundation for funding. This research was supported in
part by the Intramural Research Program of the NIH, NIAID. We also
thank M. Cal, S. Sax, and C. Stalder (Swiss TPH) for assistance with
parasitic assays, Dr M. Schmitz for assistance with NMR data acqui-
sition, and Ms. R. Imatdieva for MS data. STM wishes to acknowledge
theTertiary Education Commission of New Zealand for a scholarship.
5.4.5. 6,6’-(2,4-Di(naphthalen-2-yl)cyclobutane-1,3-diyl)bis(4-
methoxy-2H-pyran-2-one) (34)
From pyrone 22 (21.3 mg, 0.077 mmol) to give 34 as an amor-
phous colorless solid (4.1 mg, 19%). Mp 130–131 °C; Rf = 0.20 (3%
MeOH:CH2Cl2); IR (ATR) mmax 3055, 2946, 1714, 1644, 1564,
1454, 1410, 1246, 1146 cmÀ1 1H NMR (CDCl3, 400 MHz) d 7.80
;
(8H, m, ArH), 7.45 (6H, m, ArH), 5.77 (2H, d, J = 2.2 Hz, H-5), 5.13
(2H, d, J = 2.2 Hz, H-3), 4.67 (2H, m, H-8), 4.48 (2H, m, H-7), 3.60
(6H, s, OMe-4); 13C NMR (CDCl3, 100 MHz) d 170.4 (C-4), 163.8
(C-2), 162.6 (C-6), 134.9 (C-9), 133.3, 132.5 (C-11a,15a), 128.3,
127.9, 127.6, 126.2, 126.1, 125.9, 125.8 (C-10,11,12,13,14,15,16),
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2011.12.053. These data

S. T. McCracken et al. / Bioorg. Med. Chem. 20 (2012) 1482–1493
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