Enantioselective synthesis of dictyoceratin-A (smenospondiol) and -C, hypoxia-selective growth inhibitors from marine sponge

Article abstract of DOI:10.1016/j.bmc.2015.01.021

Total syntheses of (+)-dictyoceratin-C (1) and (+)-dictyoceratin-A (smenospondiol) (2), hypoxia-selective growth inhibitors isolated from marine sponge, were executed. The absolute stereochemistry of the each compound was determined through the enantiosel

Full text of DOI:10.1016/j.bmc.2015.01.021

Bioorganic & Medicinal Chemistry 23 (2015) 966–975
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Enantioselective synthesis of dictyoceratin-A (smenospondiol)
and -C, hypoxia-selective growth inhibitors from marine sponge
⇑
Yuji Sumii, Naoyuki Kotoku , Akinori Fukuda, Takashi Kawachi, Yuta Sumii, Masayoshi Arai,
Motomasa Kobayashi
⇑
Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka 565-0871, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Total syntheses of (+)-dictyoceratin-C (1) and (+)-dictyoceratin-A (smenospondiol) (2), hypoxia-selective
growth inhibitors isolated from marine sponge, were executed. The absolute stereochemistry of the each
compound was determined through the enantioselective total syntheses of them. It revealed that the
unnatural enantiomers of them also exhibited the hypoxia-selective growth inhibitory activity against
human prostate cancer DU-145 cells.
Received 2 December 2014
Revised 13 January 2015
Accepted 13 January 2015
Available online 19 January 2015
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
(+)-Dictyoceratin-C
(+)-Dictyoceratin-A (smenospondiol)
Hypoxia-selective growth inhibitor
Total synthesis
Absolute stereochemistry
1. Introduction
we re-discovered a sesquiterpene phenol dictyoceratin-C (1)4 as
an active constituent, from the Indonesian marine sponge of
Over the past decades, a number of sesquiterpene phenols/
quinones and the related compounds have been isolated from
marine organisms, particularly from algae and sponges.1,2 Some
of these sesquiterpenoids have been found to exhibit a variety of
attractive biological activities such as antimicrobial, antiviral,
cytotoxic, and immunomodulatory activities. In many cases,
however, further biological studies of these compounds have been
limited mainly due to the scarcity of natural supply. Consequently,
the secure supply through chemical synthesis and the precise
evaluation are highly desirable from the viewpoint of medicinal
chemistry and drug discovery.
Dactylospongia elegans (Fig. 1). Structure–activity relationship
study with some sponge-derived sesquiterpenoids revealed that
dictyoceratin-A (smenospondiol) (2),5,6 a closely related compound
possessing a para-hydroxybenzoyl ester moiety, exhibited similar
OCH3
R
O
HO
15
O
COOCH3
ref. 5
H
1
H
OH
8
5
3
12
11
It is known that hypoxia alters the metabolic and proliferative
pathway of tumor cells. And the tumor cells, which have adapted
to the hypoxic environment, aggravate pathology of cancer by
promoting tumor growth, angiogenesis, metastasis, and response
to chemotherapy and irradiation.3 As the hypoxic environment is
rarely observed in normal tissues, the new chemical entities, which
exhibit the hypoxia-selective growth inhibitory activity, are highly
needed as a novel and promising anticancer drug lead.
(+)-dictyoceratin-C (1, R = H)
(+)-dictyoceratin-A (2, R = OH)
(—)-ilimaquinone (3)
confirmed (total synthesis)
ref. 8
OH
?
ref. 6
OH
HO
O
H
COOCH3
H
In our continuing search for novel hypoxia-selective
growth inhibitors against human prostate cancer DU-145 cells,
(+)-aureol (4)
(+)-smenospondiol
(proposed structure)
confirmed (X-ray analysis)
⇑
Corresponding authors. Tel.: +81 6 6879 8215; fax: +81 6 6879 8219.
E-mail addresses: kotoku@phs.osaka-u.ac.jp (N. Kotoku), kobayasi@phs.osaka-u.
Figure 1. Proposed chemical structures of dictyoceratin-C (1) and dictyoceratin-A
(smenospondiol) (2).
ac.jp (M. Kobayashi).
http://dx.doi.org/10.1016/j.bmc.2015.01.021
0968-0896/Ó 2015 Elsevier Ltd. All rights reserved.

Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
967
hypoxia-selective growth inhibitory activity, whereas all the tested
sesquiterpene quinones such as ilimaquinone (3) did not show
hypoxia-selectivity.7
In order to supply sufficient amount of these compounds for
further biological study including in vivo anti-tumor test and to
develop a more promising anticancer drug lead, we engaged in
their synthetic study. Here we report the first enantioselective
total synthesis of 1 and 2 with confirming the absolute stereostruc-
ture and the biological evaluation of them.
bromide, and the following introduction of 8-methyl group and
4-methylene group would afford 1 and 2. Furthermore, the
optically pure enone 5 and its enantiomer (ent-5) could be pre-
pared using an amino acid (phenylalanine) as a chiral catalyst.13
At first, the synthesis of the side chain part of 1 was executed
(Scheme 1). Commercially available 4-hydroxy-3-methylbenzoic
acid (6) was treated with H2SO4 in MeOH to give a corresponding
methyl ester 7.14 After protection of the hydroxyl group of 7 as a
methoxymethyl (MOM) ether, the resulting compound 8 was then
subjected to radical bromination reaction to provide a bromide 9,
the coupling partner of enone 5.
2. Results and discussion
The coupling reaction of 5 and 9 using LHMDS as a base pro-
ceeded smoothly to provide a desired product as a single diastereo-
mer, and the following hydrogenation gave a ketone 10 in good
yield. Then, we examined the introduction of methyl group into
the C-8 position by Wittig methylenation and stereoselective
hydrogenation. To our disappointment, the methylenation reaction
using excess Wittig reagent under heating conditions provided a
styrene derivative 11 as a main product instead of the desired
product 12.15 It clearly indicates that the C-8 ketone in 10 was less
reactive in the Wittig methylenation than the carbonyl in the
methyl ester, probably because of the steric hindrance. Reduction
of the amount of the Wittig reagent or temperature (0 °C–rt) did
not improve the selectivity.
Based on the initial results, we anticipated that the use of more
bulky ester group would reduce the reactivity of the ester carbonyl
and give the desired exo-olefin product, and decided to use
tert-butyl ester as a bulky protecting group. Thus, the condensation
of 6 and tert-BuOH with DCC16 gave the tert-butyl ester 13, and the
following similar four-step transformation, as that used in the case
of a methyl ester described above, provided the desired ketone 16
(Scheme 2). As expected, Wittig reaction toward the carbonyl
group of the tert-butyl ester was completely inhibited, and the
desired methylenation product 17 was obtained in good yield.
The optimized reaction condition (55 °C, 16 h) improved the
reaction yield up to 74%.
2.1. Enantioselective synthesis of (+)-dictyoceratin-C
To date, the absolute stereostructure of 1 and 2 remains unclear,
although the structural similarity and the same sign of their
specific rotation suggested that the absolute stereochemistry of
the two compounds should be the same. There have been only a
few reports regarding the absolute stereostructure of 2. Nakamura
and co-workers first reported the isolation and structure elucida-
tion of dictyoceratin-A, in which they described that the specific
rotation of its degradation product is antipodal to that derived
from (ꢀ)-ilimaquinone (3) (Fig. 1).5 Later, the absolute configura-
tion of (ꢀ)-3 was determined through the similar correlation study
with (+)-aureol (4)8 and total synthesis.9 Considering these litera-
tures and the opposite sign of the optical rotation, the absolute
configuration of 2 might be deduced as shown in Figure 1. On
the other hand, Kondracki and co-workers isolated a sesquiterpe-
noid having the same relative stereostructure as that of dictyocer-
atin-A named smenospondiol.6 They supposed about the absolute
configuration of smenospondiol to be antipodal of dictyoceratin-
A through the chemical conversion, despite the same sign of the
optical rotation for these two compounds was observed. Therefore,
we decided to synthesize both enantiomers of 1 and 2, to confirm
their absolute stereostructure.
Today, several synthetic studies of these sesquiterpene
quinones/phenols with various strategies have been reported.10
One of the most popular strategy for the synthesis of trans-
clerodane type compounds is that the quinone/phenol side chain
is appended through one-pot Birch reduction–alkylation on the
enone moiety of Wieland–Miescher-type diketone.11 On the other
hand, Samadi and co-workers developed a concise and scalable
synthetic method of ilimaquinone (3) through appending the side
chain by simple alkylation toward the enone 5.12 We envisioned
that the similar strategy, as shown in Figure 2, would lead us to
obtain sufficient amount of the compounds. Thus, the coupling
reaction between the common enone 5 and the arylmethyl
After removal of the ketal group under an acidic condition, the
resulting ketone 18 was subjected to Pd–C catalyzed hydrogena-
tion in Et3N/MeOH (50:1)17 to afford the desired product 19 as a
single diastereomer. The stereochemistry of the resulting methyl
group at C-8 was determined by NOE experiment. Acid treatment
of 19 removed all the remained protecting groups providing 20,
which was converted to the methyl ester 21 in quantitative yield
R1O
X
HO
d,e
a-c
COOH
COOR2
7 : R1 = X = H, R2 = CH3
6
8 : R1 = MOM, X = H, R2 = CH3
9 : R1 = MOM, X = Br, R2 = CH3
R
R
HO
MOMO
H
R2O
MOMO
f
COOCH3
COOCH3
favored
H2C=PPh3
H
COOR1
H
H
O
O
O
1 or 2
O
stereoselective
hydrogenation
O
11
10
O
O
Wittig
major product
reaction
R
MOMO
H
R2O
R
R2O
H
COOCH3
Br
COOR1
COOR1
H
O
O
O
O
12
Wittig
O
O
reaction
O
O
5
Scheme 1. Synthesis of methyl ester 10 and attempted Wittig reaction. Reagents
and conditions: (a) H2SO4, MeOH, 60 °C, 67%; (b) MOMCl, K2CO3, DMAP, CH2Cl2,
77%; (c) NBS, AIBN, benzene, 95 °C, 91%; (d) LHMDS, 5, THF, 59%; (e) H2, Pd–C,
AcOEt, 84%; (f) KHMDS, Ph3PCH3Br, THF, 45 °C.
both enantiomers
available
Figure 2. Synthetic strategy of 1 and 2.

968
Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
MOMO
(c 0.96, CHCl3)) was opposite. These results have confirmed the
R1O
X
d,e
b,c
COOtBu
absolute stereostructure of 2 to be the same as that of 1, as well
as that smenospondiol is the same as dictyoceratin-A.
a
HO
COOtBu
H
6
X
COOtBu
13
14 : R1 = MOM, X = H
O
15 : R1 = MOM, X = Br
2.3. Biological evaluation of dictyoceratin-A and -C
16 : X = O
17 : X = CH2
O
f
MOMO
H
HO
With both enantiomers of 1 and 2 in hand, we next evaluated
their growth inhibitory effects against DU145 cells under normoxic
or hypoxic conditions. As shown in Figure 3, both synthetic 1 and 2
showed dose-dependent and hypoxia-selective growth inhibitory
activity against DU145 cells, respectively. And, to our surprise, the
ent-1 and ent-2 showed almost the same activity and selectivity
as those for 1 and 2, respectively. It implies that the pharmacophore
of these compounds might be a para-hydroxybenzoyl ester moiety
of the side chain and the decalin part might not play a crucial role.
i-k
g,h
COOtBu
COOR
H
X
20 : R = H, X = O
21 : R = CH3, X = O
1 : R = CH3, X = CH2
O
X
18 : X = CH2
19 : X = CH3 (α), H (β)
[α]D +17.3 (lit. +16.7)
HO
H
O
O
COOCH3
H
O
O
O
ent-1
[α]D –17.7
ent-5
3. Conclusion
In summary, we succeeded the total synthesis of (+)-dictyocer-
atin-C (1) and (+)-dictyoceratin-A (2), and also confirmed their
absolute stereostructures. This is the first example of the enantio-
selective synthesis of 1 and 2, although the racemic synthesis of 2
has been reported.21 Through their biological evaluation, we found
that the hypoxia-selective growth inhibitory activity of them was
not dependent on the absolute stereochemistry. Development of
more promising hypoxia-targeting anti-tumor drug candidate
through structure–activity relationship study and target protein
analysis of 1 and 2 are currently being studied.
Scheme 2. Synthesis of (+)-1 and ent-1. Reagents and conditions: (a) DCC, tBuOH,
DMAP, CH2Cl2, 99%; (b) MOMCl, K2CO3, DMAP, CH2Cl2, 45 °C, 70%; (c) NBS, AIBN,
benzene, reflux, 76%; (d) LHMDS, 5, THF, ꢀ78 °C to rt, 75%; (e) H2, Pd–C, AcOEt, 99%;
(f) KHMDS, Ph3PCH3Br, THF, 55 °C, 74%; (g) 5% HCl, THF; (h) H2, Pd–C, Et3N/MeOH,
quant (2 steps); (i) 6 N HCl, THF; TFA, CH2Cl2, 97% (2 steps); (j) SOCl2, MeOH, 45 °C,
89%; (k) KHMDS, Ph3PCH3Br, THF, 0 °C, 98%.
by using SOCl2 in MeOH. Finally, Wittig methylenation toward the
C-4 ketone in 21 proceeded to afford dictyoceratin-C (1) in good
yield.
The spectroscopic properties (IR, 1H and 13C NMR, HRMS) of the
synthetic dictyoceratin-C (1) were identical to those of natural
4. Experimental section
4.1. General experimental
product. In addition, the optical rotation of the synthetic 1 ([
+17.3 (c 0.12, CHCl3)) showed good agreement with that of the
naturally occurring one ([
+16.7 (c 0.03, CHCl3)).18 We also
synthesized ent-dictyoceratin-C from ent-5, easily obtained by
using
-phenylalanine as a chiral organocatalyst.12 The optical
rotation of ent-1 ([
a]
D
a
]
D
The following instruments were used to obtain physical data: a
JASCO P-2200 digital polarimeter (L = 50 mm) for specific rota-
tions; a JEOL ECS-300 (1H NMR: 300 MHz, 13C NMR: 75 MHz),
ECA-500 (1H NMR: 500 MHz, 13C NMR: 125 MHz) and an Agilent
NMR system (1H NMR: 600 MHz, 13C NMR: 150 MHz) spectrome-
ter for 1H and 13C NMR data using tetramethylsilane as an internal
standard; a JASCO FT/IR-5300 infrared spectrometer for IR spectra;
a Waters Q-Tof Ultima API mass spectrometer for ESI-TOF MS.
L
a
]
D
ꢀ17.7 (c 0.28, CHCl3)) was opposite to the
natural 1. Therefore, we determined the absolute stereochemistry
of (+)-dictyoceratin-C, as 5R,8R,9S,10R.
2.2. Enantioselective synthesis of (+)-dictyoceratin-A
(smenospondiol)
Silica gel (Kanto, 40–100 lm) and pre-coated thin layer chroma-
We next executed synthesis of 2. At first, the aromatic fragment
was prepared from commercially available 3-methylcatechol (22)
(Scheme 3). Thus, the catechol moiety in 22 was reacted with
2-butanone to give an isobutylidene ketal 2319 in moderate yield.
After regioselective Friedel–Crafts acetylation of 23 with ZnCl2 in
Ac2O, the subsequent haloform reaction toward 24 by using
tography (TLC) plates (Merck, 60F254) were used for column
chromatography and TLC. Spots on TLC plates were detected by
spraying acidic p-anisaldehyde solution (p-anisaldehyde: 25 mL,
c-H2SO4: 25 mL, AcOH: 5 mL, EtOH: 425 mL) or phosphomolybdic
acid solution (phosphomolybdic acid: 25 g, EtOH: 500 mL) with
subsequent heating. Unless otherwise noted, all the reaction was
performed under a N2 atmosphere. After workup, the organic layer
was dried over Na2SO4.
20
Ca(ClO)2 gave a benzoic acid 25. Then compound 25 was con-
verted to the corresponding tert-butyl ester 26 in moderate yield,
by the treatment with SOCl2 in CH2Cl2 and the following addition
of tert-BuOK. The SOCl2 treatment in tert-butanol gave 26 in low
yield, and the carbodiimide-mediated esterification with tert-buta-
nol did not proceed at all. Finally, radical bromination of the
methyl group in 26 provided an aromatic fragment 27.
4.2. Enantioselective synthesis of dictyoceratin-C (1)
4.2.1. (4aR,5R,8aR)-5,8a-Dimethyl-3,4,4a,8a-tetrahydro-2H-
spiro[naphthalene-1,20-[1,3]dioxolan]-6(5H)-one (5)
The starting material, optically pure Wieland–Miescher-type
diketone ((R)- or (S)-5,8a-dimethyl-3,4,8,8a-tetrahydronaphtha-
lene-1,6(2H,7H)-dione) was obtained through the reported
method.13
Using the aromatic fragment 27 and the decalin part 5, the same
transformation sequence as that for 1 [LHMDS-mediated coupling
under heating condition; stereoselective introduction of the C-8
methyl group; removal of all protecting groups by acid hydrolysis
and conversion to the methyl ester; and Wittig olefination]
smoothly proceeded to afford dictyoceratin-A (2). Additionally,
ent-2 was synthesized form ent-5.
26
20
D
(R)-Isomer: [
CH2Cl2)13}.
(S)-Isomer: [
CH2Cl2)13}.
Then,
a
]
ꢀ150 (c 1.0, CH2Cl2) {Lit. [
a]
ꢀ140 (c 0.20,
D
26
20
The spectroscopic properties (IR, 1H and 13C NMR, HRMS) of the
synthetic dictyoceratin-A were identical to those of natural prod-
a]
+150 (c 1.0, CH2Cl2) {Lit. [a]
D D
+140 (c 0.20,
5
and ent-5 were prepared through the reported
uct. The optical rotation of the synthetic 2 [
also showed good agreement with that of the naturally occurring
one ([
+5.8 (c 0.97, CHCl3),5 and that of ent-2 ([
ꢀ11.6
a]D +10.4 (c 0.19, CHCl3)
method,12 starting from the above material of (R)- or (S)-isomer,
respectively.
a
]
D
a]
D

Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
969
O
O
O
OH
O
g,h
f
O
O
c-e
HO
a,b
COOtBu
H
X
COOR
O
R
25 : R = X = H
22
23 : R = H
26 : R = tBu, X = H
27 : R = tBu, X = Br
24 : R =COCH3
O
28
O
OH
O
O
O
HO
O
COOR
i,j
k-m
COOtBu
COOtBu
H
H
H
X
X
33 : R = H, X = O
34 : R = CH3, X = O
2 : R = CH3, X = CH2
29 : X = O
30 : X = CH2
O
31 : X = CH2
X
O
O
32 : X = CH3 (α), H (β)
[α]D +10.4 (lit. +5.8)
OH
HO
H
O
COOCH3
H
O
O
ent-2
[α]D –11.6
ent-5
Scheme 3. Synthesis of (+)-2 and ent-2. Reagents and conditions: (a) 2-butanone, P2O5, toluene, 75 °C, 70%; (b) ZnCl2, Ac2O, 55%; (c) Ca(ClO)2, Na2CO3, NaOH, H2O/1,4-
dioxane, 70 °C, 89%; (d) SOCl2, tBuOK, THF, 52%; (e) NBS, AIBN, benzene, reflux, 60%; (f) LHMDS, 5, THF, ꢀ78 °C to 60 °C, 73%; (g) H2, Pd–C, EtOH, 99%; (h) KHMDS, Ph3PCH3Br,
toluene, 100 °C, 82%; (i) concd HCl, THF; (j) H2, Pd–C, Et3N/MeOH, 99% (2 steps); (k) TFA, THF/H2O, 95%; (l) SOCl2, MeOH, 60 °C, 85%; (m) KHMDS, Ph3PCH3Br, THF, 83%.
Figure 3. Growth inhibition activities of the synthetic 1, ent-1, 2, and ent-2 against DU145 cells. ⁄⁄P <0.01.
4.2.2. Methyl 4-hydroxy-3-methylbenzoate (7)
NMR (125 MHz, CDCl3) d: 166.9, 159.0, 132.2, 129.0, 127.1, 123.0,
112.6, 94.0, 56.1, 51.8, 16.2. IR (KBr): 2951, 1717, 1607,
1501, 1437, 1296, 1263 cmꢀ1. MS (ESI-TOF) m/z: 233 [M+Na]+.
HRMS (ESI-TOF) m/z: 233.0790 Calcd for C11H14O4Na; Found:
233.0796.
Concd H2SO4 (2.0 mL) was added to a solution of 4-hydroxy-3-
methylbenzoic acid (6) (2.0 g, 13.1 mmol) in anhydrous MeOH
(20 mL), and the whole mixture was stirred for 12 h at 60 °C. The
mixture was neutralized with 4 N NaOH and cold H2O was added.
The precipitate was filtered off and washed with cold H2O. The
crystals were dried in vacuo to give 7 (1.46 g, 67%) as a white solid.
The spectroscopic and physical data were identical to those
reported.14
4.2.4. Methyl 3-(bromomethyl)-4-(methoxymethoxy)benzoate
(9)
NBS (1.94 g, 10.9 mmol, 1.05 equiv) and AIBN (136 mg,
0.83 mmol, 0.08 equiv) were added to a solution of 8 (2.18 g,
10.4 mmol) in anhydrous benzene (30 mL), and the whole mixture
was stirred for 16 h at 80 °C. The whole reaction mixture was con-
centrated in vacuo, and the residue was dissolved in Et2O and
washed with satd NaHCO3 aq. Removal of the solvent from the
Et2O extract under reduced pressure gave a crude product, which
was purified by SiO2 column (n-hexane/AcOEt = 10:1) to give 9
(2.74 g, 91%) as a white solid.
4.2.3. Methyl 4-(methoxymethoxy)-3-methylbenzoate (8)
K2CO3 (3.81 g, 27.6 mmol, 2.0 equiv) and MOMCl (1.26 mL,
16.5 mmol, 1.2 equiv) were added to a solution of 7 (2.29 g,
13.8 mmol) in anhydrous DMF (20 mL), and the whole mixture
was stirred for 20 h at 55 °C. The residue mixture was filtered,
and the filtrate was concentrated in vacuo. The residue was dis-
solved in Et2O and washed with satd NH4Cl aq and brine. Removal
of the solvent from the Et2O extract under reduced pressure gave a
crude product, which was purified by SiO2 column (CH2Cl2) to give
8 (2.23 g, 77%) as a colorless liquid.
1H NMR (500 MHz, CDCl3) d: 8.04 (1H, d, J = 2.3 Hz), 7.97 (1H,
dd, J = 8.6, 2.3 Hz), 7.13 (1H, d, J = 8.6 Hz), 5.33 (2H, s), 4.57 (2H,
s), 3.89 (3H, s), 3.52 (3H, s). 13C NMR (125 MHz, CDCl3) d: 166.2,
158.5, 132.4, 131.9, 126.6, 123.3, 113.4, 93.8, 56.4, 51.9, 28.0. IR
(KBr): 1705, 1609, 1503, 1445, 1275, 1150 cmꢀ1. MS (ESI-TOF)
1H NMR (500 MHz, CDCl3) d: 7.83–7.82 (2H, m), 7.04 (1H, d,
J = 8.9 Hz), 5.23 (2H, s), 3.86 (3H, s), 3.46 (3H, s), 2.25 (3H, s). 13C

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Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
m/z: 311/313 [M+Na]+. HRMS (ESI-TOF) m/z: 310.9895 Calcd for
11H1379BrO4Na; Found: 310.9898.
dropwise to a solution of 10 (26.7 mg, 0.06 mmol) in anhydrous
THF (0.3 mL) at rt, and the whole mixture was stirred for 5 h at
45 °C. Satd NH4Cl aq was added to the mixture, and the whole
mixture was extracted with Et2O. Removal of the solvent from
the Et2O extract under reduced pressure gave a crude product,
which was purified by SiO2 column (n-hexane/AcOEt = 8:1) to give
11 (14.9 mg, 58%) as a colorless liquid.
C
4.2.5. Methyl 3-[{(4a0R,50R,8a0R)-50,8a0-dimethyl-60-oxooctahydro-
20H-spiro([1,3]dioxolane-2,10-naphthalen)-50-yl}methyl]-4-
(methoxymethoxy)benzoate (10)
Under an Ar atmosphere, n-BuLi (3.83 mL, of a 1.60 M solution in
hexane, 6.13 mmol, 1.3 equiv) was added to a solution of HMDS
(1.28 mL, 6.13 mmol, 1.3 equiv) in anhydrous THF (3.0 mL) at
ꢀ78 °C, and the whole mixture was stirred for 5 min at ꢀ78 °C
and for 10 min at rt. A solution of 5 (1.11 g, 4.71 mmol) in anhy-
drous THF (5.0 mL) was added dropwise to the mixture via cannula
over 5 min at ꢀ50 °C, and the whole mixture was stirred for 45 min
at 0 °C. A solution of bromide 9 (1.50 g, 5.19 mmol, 1.1 equiv) in
anhydrous THF (5.0 mL) was added dropwise to the mixture via
cannula over 5 min at ꢀ78 °C, and the whole mixture was stirred
for 10 min at ꢀ78 °C, for 40 min at 0 °C and for 1 h at rt. Satd NH4Cl
aq was added to the mixture, and the whole mixture was extracted
with Et2O. Removal of the solvent from the Et2O extract under
reduced pressure gave a crude product, which was purified by
SiO2 column (n-hexane/AcOEt = 3:1) to give a coupling prod-
uct, Methyl 3-[{(4a0R,50R,8a0R)-50,8a0-dimethyl-60-oxo-30,40,4a0,50,60,
8a0-hexahydro-20H-spiro([1,3]dioxolane-2,10-naphthalen)-50-yl}
methyl]-4-(methoxymethoxy)benzoate (1.24 g, 59%) as a white
1H NMR (500 MHz, CDCl3) d: 7.26 (1H, dd, J = 8.6, 2.2 Hz), 7.12
(1H, d, J = 2.2 Hz), 7.05 (1H, d, J = 8.6 Hz), 5.25 (1H, s), 5.15 (1H,
d, J = 6.6 Hz), 5.07 (1H, d, J = 6.6 Hz), 4.97 (1H, s), 3.92–3.86 (4H,
m), 3.47 (3H, s), 2.93 (1H, d, J = 13.5 Hz), 2.84 (1H, d, J = 13.5 Hz),
2.56–2.49 (1H, m), 2.34–2.27 (2H, m), 2.10 (3H, s), 1.98–1.95
(1H, m), 1.70–1.68 (1H, m), 1.59–1.54 (3H, m), 1.47–1.40 (3H,
m), 1.06 (3H, s), 1.03 (3H, s). 13C NMR (125 MHz, CDCl3) d: 217.1,
155.6, 142.7, 134.2, 129.3, 126.3, 124.9, 113.5, 112.8, 110.9, 94.8,
65.0, 64.7, 56.0, 51.6, 45.4, 42.1, 39.8, 35.2, 29.8, 28.5, 22.8, 22.7,
21.9, 20.6, 17.4. IR (KBr): 2950, 1704, 1501, 1459, 1240 cmꢀ1. MS
(ESI-TOF) m/z: 451 [M+Na]+. HRMS (ESI-TOF) m/z: 451.2460 Calcd
for C26H36O5Na; Found: 451.2463.
4.2.7. tert-Butyl 4-hydroxy-3-methylbenzoate (13)
A solution of DCC (14.9 g, 72.5 mmol, 1.1 equiv) in anhydrous
THF (65 mL) was added dropwise to a solution of 6 (10.0 g,
65.9 mmol), DMAP (0.80 g, 6.59 mmol, 0.1 equiv) and tert-butanol
(220 mL) in anhydrous THF (30 mL) over 30 min, and the whole
mixture was stirred for 20 h at rt. The mixture was filtered through
short pad of Celite. Removal of the solvent from the filtrate under
reduced pressure gave a crude product, which was purified by SiO2
column (n-hexane/AcOEt = 5:1) to give 13 (13.6 g, 99%) as a white
solid.
amorphous solid.
26
[
a]
+17.4 (c 1.18, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.82
D
(1H, d, J = 8.6 Hz), 7.70 (1H, s), 7.09 (1H, d, J = 8.6 Hz), 6.90 (1H,
d, J = 10.3 Hz), 5.87 (1H, d, J = 10.3 Hz), 5.18 (1H, d, J = 6.9 Hz),
5.09 (1H, d, J = 6.9 Hz), 3.94–3.88 (4H, m), 3.81 (3H, s), 3.44 (3H,
s), 3.06 (1H, d, J = 13.6 Hz), 2.87 (1H, d, J = 13.6 Hz), 2.25 (1H, d,
J = 12.3 Hz), 1.64–1.60 (2H, m), 1.54–1.52 (1H, m), 1.42 (1H, qd,
J = 12.5, 3.8 Hz), 1.30–1.28 (1H, m), 1.25–1.22 (1H, m), 1.17 (6H,
s). 13C NMR (125 MHz, CDCl3) d: 203.7, 166.9, 159.7, 155.0, 133.5,
129.8, 127.4, 127.0, 122.9, 113.2, 111.6, 94.5, 64.9, 64.5, 56.2,
51.8, 48.9, 45.1, 41.9, 39.7, 29.2, 22.4, 22.0, 21.5, 19.7. IR (KBr):
1H NMR (500 MHz, CDCl3) d: 7.78–7.73 (2H, m), 6.85 (1H, s),
6.82 (1H, dd, J = 8.0, 3.4 Hz), 2.27 (3H, s), 1.59 (9H, s). 13C NMR
(125 MHz, CDCl3) d: 166.7, 158.4, 132.6, 129.1, 124.0, 123.6,
114.5, 81.0, 28.2 (3C), 15.7. IR (KBr): 3341, 1678, 1607 cmꢀ1. MS
(ESI-TOF) m/z: 231 [M+Na]+. HRMS (ESI-TOF) m/z: 231.0997 Calcd
for C12H16O3Na; Found: 231.1030.
2951, 1717, 1665, 1604, 1501, 1439, 1265, 1188 cmꢀ1
. MS
(ESI-TOF) m/z: 467 [M+Na]+. HRMS (ESI-TOF) m/z: 467.2046 Calcd
for C25H32O7Na; Found: 467.2057.
4.2.8. tert-Butyl 4-(methoxymethoxy)-3-methylbenzoate (14)
K2CO3 (36.0 g, 261 mmol, 4.0 equiv) and MOMCl (9.9 mL,
130 mmol, 2.0 equiv) were added to a solution of 13 (13.5 g,
65.1 mmol) in anhydrous DMF (70 mL), and the whole mixture
was stirred for 20 h at 45 °C. The mixture was filtered, and the fil-
trate was concentrated in vacuo. The residue was dissolved in Et2O
and washed with satd NH4Cl aq and brine. Removal of the solvent
from the Et2O extract under reduced pressure gave a crude prod-
uct, which was purified by SiO2 column (n-hexane/AcOEt = 20:1)
to give 14 (11.6 g, 70%) as a colorless liquid.
10% Pd–C (27 mg) was added to a solution of the above coupling
product (124 mg, 0.279 mmol) in anhydrous MeOH (2.5 mL), and
the whole mixture was stirred for 12 h under a H2 atmosphere (bal-
loon). The mixture was filtered through short pad of Celite. Removal
of the solvent from the filtrate under reduced pressure gave a crude
product, which was purified by SiO2 column (n-hexane/
AcOEt = 2:1) to give 10 (105 mg, 84%) as a white amorphous solid.
26
[
a]
ꢀ8.4 (c 0.58, CHCl3). 1H NMR (300 MHz, CDCl3) d: 7.86 (1H,
D
dd, J = 8.7, 2.2 Hz), 7.71 (1H, d, J = 2.2 Hz), 7.11 (1H, d, J = 8.7 Hz),
5.18 (1H, d, J = 6.8 Hz), 5.11 (1H, d, J = 6.9 Hz), 3.94–3.91 (4H, m),
3.87 (3H, s), 3.48 (3H, s), 2.96 (1H, d, J = 13.4 Hz), 2.85 (1H, d,
J = 13.4 Hz), 2.71–2.61 (1H, m), 2.34 (1H, q, J = 7.5 Hz), 2.30–2.24
(1H, m), 2.12–1.95 (1H, m), 1.72–1.67 (1H, m), 1.61–1.55 (2H,
m), 1.53–1.38 (3H, m), 1.26–1.24 (1H, m), 1.04 (3H, s), 1.02 (3H,
s). 13C NMR (125 MHz, CDCl3) d: 216.4, 166.8, 159.7, 133.5, 129.9,
126.5, 122.8, 113.1, 112.6, 94.6, 64.9, 64.6, 56.2, 51.8, 51.2, 46.1,
42.0, 39.6, 34.7, 29.7, 28.6, 22.7, 22.6, 19.9, 17.5. IR (KBr): 2949,
1715, 1605, 1501, 1439, 1262, 1134 cmꢀ1. MS (ESI-TOF) m/z: 469
[M+Na]+. HRMS (ESI-TOF) m/z: 469.2202 Calcd for C25H34O7Na;
Found: 469.2220.
1H NMR (500 MHz, CDCl3) d: 7.80–7.78 (2H, m), 7.03 (1H, d,
J = 8.6 Hz), 5.24 (2H, s), 3.47 (3H, s), 2.26 (3H, s), 1.57 (9H, s). 13C
NMR (125 MHz, CDCl3) d: 165.7, 158.6, 132.0, 128.8, 126.8, 124.9,
112.5, 94.0, 80.4, 56.0, 28.2 (3C), 16.2. IR (KBr): 1709, 1609, 1501,
1300 cmꢀ1. MS (ESI-TOF) m/z: 275 [M+Na]+. HRMS (ESI-TOF) m/z:
275.1259 Calcd for C14H20O4Na; Found: 275.1253.
4.2.9. tert-Butyl 3-(bromomethyl)-4-(methoxymethoxy)benzoate
(15)
NBS (8.16 g, 45.9 mmol, 1.1 equiv) and AIBN (342 mg,
2.09 mmol, 0.05 equiv) were added to a solution of 14 (10.5 g,
41.7 mmol) in anhydrous benzene (130 mL), and the whole mix-
ture was stirred for 16 h under reflux. The mixture was concen-
trated in vacuo, and the residue was dissolved in Et2O and
washed with satd NaHCO3 aq. Removal of the solvent from the
Et2O extract under reduced pressure gave a crude product, which
was purified by SiO2 column (n-hexane/AcOEt = 20:1) to give 15
(10.5 g, 76%) as a white solid and recovered starting material
(2.55 g, 24%).
4.2.6. (4a0R,50R,8a0R)-50-(2-(Methoxymethoxy)-5-(prop-1-en-2-
yl)benzyl)-50,8a0-dimethylhexahydro-20H-spiro[[1,3]dioxolane-
2,10-naphthalen]-60(70H)-one (11)
Under an Ar atmosphere, KHMDS (0.60 mL of a 0.5 M solution in
toluene, 0.30 mmol, 5.0 equiv) was added to Ph3PCH3Br (107 mg,
0.30 mmol, 5.0 equiv) in anhydrous THF (0.3 mL), and the whole
mixture was stirred for 45 min at rt. Above solution was added

Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
971
1H NMR (500 MHz, CDCl3) d: 7.96 (1H, s), 7.91 (1H, d, J = 8.6 Hz),
7.10 (1H, d, J = 8.6 Hz), 5.31 (2H, s), 4.56 (2H, s), 3.51 (3H, s), 1.58
(9H, s). 13C NMR (125 MHz, CDCl3) d: 164.9, 158.2, 132.2, 131.8,
126.4, 125.3, 113.3, 93.9, 80.9, 56.4, 28.4, 28.2 (3C). IR
(KBr): 2363, 1709, 1609, 1501 cmꢀ1. MS (ESI-TOF) m/z: 355/
353 [M+Na]+. HRMS (ESI-TOF) m/z: 353.0364 Calcd for
(20 mL) was added dropwise to the mixture via cannula at 0 °C,
and the whole mixture was stirred for 16 h at 55 °C. Satd NH4Cl
aq was added to the mixture, and the whole mixture was extracted
with Et2O. Removal of the solvent from the Et2O extract under
reduced pressure gave a crude product, which was purified by
SiO2 column (n-hexane/AcOEt = 8:1) to give 17 (1.02 g, 74%) as a
C
14H1979BrO4Na; Found: 353.0367.
white amorphous solid.
26
[
a]
ꢀ58.9 (c 0.91, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.76
D
4.2.10. tert-Butyl 3-[{(4a0R,50R,8a0R)-50,8a0-dimethyl-60-oxoocta
hydro-20H-spiro([1,3]dioxolane-2,10-naphthalen)-50-yl}methyl]-
4-(methoxymethoxy)benzoate (16)
(1H, dd, J = 8.6, 2.3 Hz), 7.64 (1H, d, J = 2.3 Hz), 7.05 (1H, d,
J = 8.6 Hz), 5.15 (1H, d, J = 6.9 Hz), 5.10 (1H, d, J = 6.9 Hz), 4.70
(1H, s), 4.16 (1H, s), 3.99–3.92 (4H, m), 3.46 (3H, s), 2.78 (1H, d,
J = 13.2 Hz), 2.67 (1H, d, J = 13.2 Hz), 2.38–2.36 (1H, m), 2.12–
2.09 (2H, m), 1.98–1.95 (1H, m), 1.70–1.68 (1H, m), 1.62–1.54
(3H, m), 1.56 (9H, s), 1.46–1.44 (2H, m), 1.19–1.17 (1H, m), 1.05
(3H, s), 0.92 (3H, s). 13C NMR (125 MHz, CDCl3) d: 165.9, 159.9,
153.1, 134.0, 128.9, 127.2, 123.9, 113.6, 112.6, 107.6, 94.7, 80.2,
64.8, 64.4, 56.1, 46.7, 43.4, 42.8, 39.5, 32.0, 29.7, 29.4, 28.2 (3C),
23.1, 22.8, 20.9, 19.9. IR (KBr): 1709, 1604, 1497 cmꢀ1. MS
(ESI-TOF) m/z: 509 [M+Na]+. HRMS (ESI-TOF) m/z: 509.2879 Calcd
for C29H42O6Na; Found: 509.2861.
Under an Ar atmosphere, LHMDS (15.9 mL of a 0.89 M solution,
14.2 mmol, 1.6 equiv, prepared from n-BuLi (1.60 M solution in
hexane), HMDS and THF) was added dropwise to a solution of 5
(2.10 g, 8.90 mmol) in anhydrous THF (9.0 mL) via cannula over
5 min at ꢀ45 °C, and the whole mixture was stirred for 50 min at
0 °C. A solution of 15 (3.54 g, 10.7 mmol, 1.2 equiv) in anhydrous
THF (9.0 mL) was added dropwise to the mixture via cannula over
10 min at ꢀ78 °C, and the whole mixture was stirred for 10 min at
ꢀ78 °C, 40 min at 0 °C, and 1 h at rt. Satd NH4Cl aq was added to
the mixture, and the whole mixture was extracted with Et2O.
Removal of the solvent from the Et2O extract under reduced
pressure gave a crude product, which was purified by SiO2 column
4.2.12. tert-Butyl 3-[{(1R,4aR,8aR)-1,4a-dimethyl-2-methylene-
5-oxodecahydronaphthalen-1-yl}methyl]-4-
(methoxymethoxy)benzoate (18)
5% HCl (15 mL) was added to a solution of 17 (606 mg,
1.24 mmol) in THF (20 mL) at 0 °C, and the whole mixture was
stirred for 6 h at rt. Satd NaHCO3 aq was added to the mixture,
and the whole mixture was extracted with AcOEt. Removal of the
solvent from the AcOEt extract under reduced pressure gave a 18
as a colorless amorphous solid, which was used for the next reac-
(n-hexane/AcOEt = 4:1) to give
a
coupling product, 3-[{(4a0R,
50R,8a0R)-50,8a0-dimethyl-60-oxo-30,40,4a0,50,60,8a0-hexahydro-20H-
spiro([1,3]dioxolane-2,10-naphthalen)-50-yl}methyl]-4-(methoxy-
methoxy)benzoate (3.26 g, 75%) as a white amorphous solid.
27
[a]
+17.8 (c 1.02, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.77
D
(1H, dd, J = 8.6, 2.0 Hz), 7.65 (1H, d, J = 2.0 Hz), 7.07 (1H, d,
J = 8.6 Hz), 6.91 (1H, d, J = 10.3 Hz), 5.87 (1H, d, J = 10.3 Hz), 5.17
(1H, d, J = 6.9 Hz), 5.10 (1H, d, J = 6.9 Hz), 3.97–3.87 (2H, m),
3.83–3.82 (2H, m), 3.44 (3H, s), 3.06 (1H, d, J = 13.9 Hz), 2.86 (1H,
d, J = 13.9 Hz), 2.30 (1H, dd, J = 12.7, 2.7 Hz), 1.62–1.58 (2H, m),
1.54 (9H, s), 1.54–1.52 (2H, m), 1.44–1.38 (1H, m), 1.26–1.24
(1H, m), 1.18 (6H, s). 13C NMR (125 MHz, CDCl3) d: 203.6, 165.6,
159.3, 154.8, 133.4, 129.4, 127.5, 126.7, 124.8, 113.1, 111.6, 94.5,
80.3, 64.9, 64.5, 56.1, 48.9, 45.0, 41.9, 39.6, 29.3, 28.2 (3C), 22.4,
22.0, 21.5, 19.7. IR (KBr): 2976, 1709, 1669, 1605 cmꢀ1. MS (ESI-
TOF) m/z: 509 [M+Na]+. HRMS (ESI-TOF) m/z: 509.2515 Calcd for
tion without further purification.
27
[
a]
ꢀ70.6 (c 1.46, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.77
D
(1H, dd, J = 8.6, 2.3 Hz), 7.66 (1H, d, J = 2.3 Hz), 7.06 (1H, d,
J = 8.6 Hz), 5.16 (1H, d, J = 6.9 Hz), 5.12 (1H, d, J = 6.9 Hz), 4.78
(1H, s), 4.33 (1H, s), 3.46 (3H, s), 2.80 (1H, d, J = 13.2 Hz), 2.69
(1H, d, J = 13.2 Hz), 2.52 (1H, td, J = 14.3, 6.3 Hz), 2.43–2.21 (4H,
m), 2.08–2.05 (1H, m), 1.83–1.78 (3H, m), 1.56 (9H, s), 1.52–1.46
(1H, m), 1.41–1.37 (1H, m), 1.14 (3H, s), 1.06 (3H, s), 0.88 (1H, t,
J = 6.9 Hz). 13C NMR (125 MHz, CDCl3) d: 215.1, 165.7, 159.7,
151.7, 133.9, 129.2, 126.7, 124.2, 112.7, 108.8, 94.7, 80.4, 56.2,
49.7, 49.1, 44.0, 39.6, 38.0, 31.5, 28.6, 28.2 (3C), 25.4, 23.3, 22.6,
20.8. IR (KBr): 1707, 1604 cmꢀ1. MS (ESI-TOF) m/z: 465 [M+Na]+.
HRMS (ESI-TOF) m/z: 465.2617 Calcd for C27H38O5Na; Found:
465.2634.
C28H38O7Na; Found: 509.2531.
10% Pd–C (617 mg) was added to a solution of the above cou-
pling product (3.09 g, 6.34 mmol) in AcOEt (30 mL), and the whole
mixture was stirred for 2 h under a H2 atmosphere (balloon). The
mixture was filtered through short pad of Celite. Removal of the
solvent from the filtrate under reduced pressure gave a crude prod-
uct, which was purified by SiO2 column (n-hexane/AcOEt = 3:1) to
4.2.13. tert-Butyl 4-(methoxymethoxy)-3-[{(1S,2R,4aR,8aR)-
1,2,4a-trimethyl-5-oxodecahydronaphthalen-1-
yl}methyl]benzoate (19)
give 16 (3.05 g, 99%) as a white amorphous solid.
26
[a]
ꢀ8.1 (c 1.01, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.77 (1H,
D
dd, J = 8.6, 2.0 Hz), 7.62 (1H, d, J = 2.0 Hz), 7.06 (1H, d, J = 8.6 Hz),
5.14 (1H, d, J = 6.9 Hz), 5.07 (1H, d, J = 6.9 Hz), 3.88–3.84 (4H, m),
3.43 (3H, s), 2.91 (1H, d, J = 13.6 Hz), 2.83 (1H, d, J = 13.6 Hz),
2.63–2.57 (1H, m), 2.32–2.24 (2H, m), 2.05–1.99 (1H, m), 1.66–
1.64 (1H, m), 1.54 (9H, s), 1.52–1.36 (6H, m), 1.00 (6H, s). 13C
NMR (125 MHz, CDCl3) d: 216.4, 165.5, 159.3, 133.3, 129.6, 126.2,
124.6, 113.0, 112.6, 94.5, 80.3, 64.9, 64.6, 56.1, 51.2, 45.9, 42.0,
39.5, 34.8, 29.7, 28.6, 28.1 (3C), 22.7, 22.6, 20.0, 17.5. IR (KBr):
1707, 1605, 1298 cmꢀ1. MS (ESI-TOF) m/z: 511 [M+Na]+. HRMS
(ESI-TOF) m/z: 511.2672 Calcd for C28H40O7Na; Found: 511.2695.
10% Pd–C (1.22 g) was added to a solution of the above product
18 in Et3N/MeOH (30 mL, 50:1), and the whole mixture was stirred
for 12 h under a H2 atmosphere (balloon). The mixture was diluted
with small amount of CHCl3 and filtered through short pad of
Celite. Removal of the solvent from the filtrate under reduced
pressure gave a crude product, which was purified by SiO2 column
(n-hexane/AcOEt = 1:1) to give 19 (554 mg, quantitative yield for
two steps) as a colorless viscous liquid.
27
[
a]
+18.7 (c 1.02, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.80
D
(1H, dd, J = 8.6, 2.3 Hz), 7.66 (1H, d, J = 2.3 Hz), 7.08 (1H, d,
J = 8.6 Hz), 5.18 (1H, d, J = 6.9 Hz), 5.16 (1H, d, J = 6.9 Hz), 3.44
(3H, s), 2.81 (1H, d, J = 14.3 Hz), 2.63–2.54 (2H, m), 2.21–2.18
(2H, m), 2.13–2.10 (1H, m), 1.85–1.79 (1H, m), 1.71–1.61 (1H,
m), 1.56 (9H, s), 1.47 (1H, dt, J = 13.0, 2.4 Hz), 1.43–1.38 (1H, m),
1.34–1.18 (3H, m), 1.15 (3H, s), 1.02 (3H, d, J = 5.7 Hz), 0.93 (3H,
s). 13C NMR (125 MHz, CDCl3) d: 216.0, 165.5, 159.6, 133.6, 129.4,
127.0, 124.6, 113.3, 94.4, 80.5, 56.2, 49.1, 47.3, 42.3, 37.4, 37.2,
35.8, 32.3, 28.2 (3C), 26.8, 25.3, 22.0, 18.8, 18.0, 17.6. IR (KBr):
4.2.11. tert-Butyl 3-[{(4a0R,50R,8a0R)-50,8a0-dimethyl-60-
methyleneoctahydro-20H-spiro([1,3]dioxolane-2,10-
naphthalen)-50-yl}methyl]-4-(methoxymethoxy)benzoate (17)
Under an Ar atmosphere, KHMDS (45.3 mL of a 0.5 M solution in
toluene, 22.6 mmol, 8.0 equiv) was added to Ph3PCH3Br (8.09 g,
22.6 mmol, 8.0 equiv), and the whole mixture was stirred for 1 h
at rt. A solution of 16 (1.38 g, 2.83 mmol) in anhydrous THF

972
Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
1707, 1605, 1456 cmꢀ1. MS (ESI-TOF) m/z: 467 [M+Na]+. HRMS
(ESI-TOF) m/z: 467.2773 Calcd for C27H40O5Na; Found: 467.2793.
160.0, 159.2, 135.0, 129.3, 125.2, 121.6, 115.3, 102.8, 52.0, 48.0,
42.0, 40.2, 37.0, 36.5, 36.3, 33.0, 27.8, 27.7, 23.2, 20.5, 17.62,
17.59. IR (KBr): 3341, 1686, 1601, 1426, 1287 cmꢀ1. MS (ESI-TOF)
m/z: 379 [M+Na]+. HRMS (ESI-TOF) m/z: 379.2249 Calcd for C23H32
O3Na; Found: 379.2266.
4.2.14. 4-Hydroxy-3-[{(1S,2R,4aR,8aR)-1,2,4a-trimethyl-5-
oxodecahydronaphthalen-1-yl}methyl]benzoic acid (20)
6 N HCl (20 mL) was added to a solution of 19 (541 mg,
1.24 mmol) in THF (20 mL) at 0 °C and stirred for 12 h at rt. The
whole mixture was concentrated in vacuo. TFA (10 mL) was added
to a solution of the above residue in dry CH2Cl2 (10 mL) at 0 °C, and
the whole mixture was stirred for 2 h at rt. The mixture was
concentrated in vacuo to give a crude product, which was purified
by SiO2 column (n-hexane/AcOEt = 1:1 contained with 1% AcOH) to
4.2.17. (ꢀ)-Dictyoceratin-C (ent-1)
ent-1 was synthesized through the same procedures as those for
26
1, using ent-5 as a starting material. [
a]
ꢀ17.7 (c 0.28, CHCl3).
D
4.3. Enantioselective synthesis of dictyoceratin-A (2)
give 20 (414 mg, 97%) as a white solid.
4.3.1. 2-Ethyl-2,4-dimethylbenzo[d][1,3]dioxole (23)
+26.7 (c 1.05, MeOH). 1H NMR (500 MHz, CD3COCD3) d:
A solution of P2O5 (12.6 g, 88.8 mmol, 1.0 equiv) in 2-butanone
(162 mL) was added to a solution of 2,3-dihydroxytoluene (22)
(10.9 g, 87.8 mmol) in anhydrous toluene (162 ml), and the whole
mixture was stirred for overnight at 75 °C. The mixture was filtered
through short pad of Celite. Removal of the solvent from the filtrate
under reduced pressure gave a crude product, which was purified by
SiO2 column (n-hexane) to give 2319 (11.0 g, 70%) as a colorless oil.
1H NMR (500 MHz, CDCl3) d: 6.67 (1H, t, J = 8.0 Hz), 6.59 (1H, d,
J = 8.0 Hz), 6.58 (1H, d, J = 8.0 Hz), 2.20 (3H, s), 1.94 (2H, q,
J = 7.4 Hz), 1.61 (3H, s), 1.01 (3H, t, J = 7.4 Hz). 13C NMR
(125 MHz, CDCl3) d: 147.1, 146.0, 122.7, 120.4, 118.9, 118.6,
105.7, 32.2, 24.0, 14.7, 7.5.
27
[
a]
D
7.76 (1H, d, J = 2.3 Hz), 7.72 (1H, dd, J = 8.3, 2.3 Hz), 6.91 (1H, d,
J = 8.3 Hz), 2.78 (1H, d, J = 14.2 Hz), 2.73 (1H, d, J = 14.2 Hz), 2.63
(1H, td, J = 14.0, 7.1 Hz), 2.31 (1H, dd, J = 13.7, 2.0 Hz), 2.09–2.00
(3H, m), 1.88–1.83 (1H, m), 1.67–1.63 (1H, m), 1.38–1.34 (4H,
m), 1.17 (1H, d, J = 2.0 Hz), 1.15 (3H, s), 1.05 (3H, d, J = 6.0 Hz),
0.96 (3H, s). 13C NMR (125 MHz, CD3OD) d: 219.0, 170.2, 162.3,
135.9, 130.7, 125.9, 121.8, 115.7, 50.5, 49.3, 43.4, 38.4, 37.9, 37.0,
33.8, 27.8, 26.8, 23.0, 19.3, 18.4, 17.9. IR (KBr): 3156, 1682, 1603,
1279 cmꢀ1. MS (ESI-TOF) m/z: 367 [M+Na]+. HRMS (ESI-TOF) m/z:
367.1885 Calcd for C21H28O4Na; Found: 367.1887.
4.2.15. Methyl 4-hydroxy-3-[{(1S,2R,4aR,8aR)-1,2,4a-trimethyl-
5-oxodecahydronaphthalen-1-yl}methyl]benzoate (21)
4.3.2. 1-(2-Ethyl-2,7-dimethylbenzo[d][1,3]dioxol-5-
SOCl2 (0.35 mL, 4.82 mmol, 4.5 equiv) was added to a solution
of 20 (367 mg, 1.06 mmol) in anhydrous MeOH (11 mL), and the
whole mixture was stirred for 24 h at 45 °C. Removal of the solvent
from the mixture under reduced pressure gave a crude product,
which was purified by SiO2 column (n-hexane/AcOEt = 2:1) to give
yl)ethanone (24)
ZnCl2 (4.68 g, 34.3 mmol, 1.0 equiv) was added to a solution of
23 (6.10 g, 34.2 mmol) in Ac2O (31 mL) at 0 °C, and the whole mix-
ture was stirred for 2.5 h at 0 °C and for 1.5 h at rt. The mixture was
concentrated in vacuo. Satd NaHCO3 aq was added to the residue,
and the whole mixture was extracted with Et2O. Removal of the
solvent from the Et2O extract under reduced pressure gave a crude
product, which was purified by SiO2 column (n-hexane/
AcOEt = 20:1) to give 24 (4.12 g, 55%) as a colorless oil.
1H NMR (500 MHz, CDCl3) d: 7.34 (1H, d, J = 1.1 Hz), 7.19 (1H, d,
J = 1.1 Hz), 2.51 (3H, s), 2.24 (3H, s), 1.96 (2H, q, J = 7.4 Hz), 1.63
(3H, s), 1.01 (3H, t, J = 7.4 Hz). 13C NMR (125 MHz, CDCl3) d:
196.3, 150.3, 147.5, 130.9, 125.6, 120.6, 117.7, 105.2, 32.2, 26.2,
23.9, 14.5, 7.2. IR (KBr): 2982, 1676, 1489, 1427, 1302,
1235 cmꢀ1. MS (ESI-TOF) m/z: 243 [M+Na]+. HRMS (ESI-TOF) m/z:
243.0997 Calcd for C13H16O3Na; Found: 243.1000.
21 (338 mg, 89%) as a white solid.
27
[
a]
+25.9 (c 1.07, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.75–
D
7.72 (2H, m), 6.75 (1H, d, J = 8.0 Hz), 6.58 (1H, br s), 3.86 (3H, s),
2.73 (1H, d, J = 14.3 Hz), 2.67 (1H, d, J = 14.3 Hz), 2.58 (1H, td,
J = 14.0, 7.2 Hz), 2.24 (1H, d, J = 12.9 Hz), 2.17 (1H, dd, J = 14.3,
5.2 Hz), 2.09–2.05 (1H, m), 1.79 (1H, qd, J = 12.9, 6.4 Hz), 1.65–
1.62 (1H, m), 1.48–1.45 (1H, m), 1.41–1.38 (1H, m), 1.28–1.25
(3H, m), 1.16 (3H, s), 1.14–1.13 (1H, m), 1.02 (3H, d, J = 5.7 Hz),
0.94 (3H, s). 13C NMR (125 MHz, CDCl3) d: 217.3, 167.2, 159.3,
134.8, 129.5, 124.7, 121.6, 115.3, 51.9, 49.2, 47.5, 42.3, 37.5, 37.1,
35.7, 32.3, 26.7, 25.2, 22.0, 18.9, 18.0, 17.5. IR (KBr): 3333, 1688,
1603, 1427, 1283 cmꢀ1. MS (ESI-TOF) m/z: 381 [M+Na]+. HRMS
(ESI-TOF) m/z: 381.2042 Calcd for C22H30O4Na; Found: 381.2047.
4.3.3. 2-Ethyl-2,7-dimethylbenzo[d][1,3]dioxole-5-carboxylic
acid (25)
4.2.16. (+)-Dictyoceratin-C (1)
Ca(ClO)2 (16.8 g, 118 mmol, 5.0 equiv) was dissolved in H2O
(23.6 mL) and stirred for 10 min at 60 °C. A solution of Na2CO3
(12.5 g, 118 mmol, 5.0 equiv) and NaOH (3.6 g, 89.7 mmol,
3.8 equiv) in H2O (23.6 mL) was added dropwise to the mixture
at rt, and the whole mixture was stirred for 5 min at 60 °C. The
mixture was filtered, and the filtrate was stirred at 60 °C. A solu-
tion of 24 (5.20 g, 23.6 mmol) in 1,4-dioxane (23.6 mL) was added
dropwise to the mixture, and the whole mixture was stirred for 3 h
at 70 °C. Satd NaHSO3 aq was added to the mixture, and the whole
mixture was stirred for 1 h at rt. 5% HCl was added to the mixture,
and the whole mixture was extracted with Et2O. Removal of the
solvent from the Et2O extract under reduced pressure gave a crude
product, which was purified by SiO2 column (n-hexane/AcOEt/
AcOH = 25:5:3) to give 25 (4.69 g, 89%) as a white solid.
Under an Ar atmosphere, KHMDS (12.3 mL of a 0.5 M solution in
toluene, 6.14 mmol, 9.5 equiv) was added to Ph3PCH3Br (2.19 g,
6.14 mmol, 9.5 equiv), and the whole mixture was stirred for 1 h
at rt. A solution of 21 (231 mg, 0.643 mmol) in anhydrous THF
(12 mL) was added dropwise to the mixture via cannula at 0 °C,
and the whole mixture was stirred for 12 h at rt. Satd NH4Cl aq
was added to the mixture, and the whole mixture was extracted
with Et2O. Removal of the solvent from the Et2O extract under
reduced pressure gave a crude product, which was purified by
SiO2 column (n-hexane/AcOEt = 8:1) to give 1 (205 mg, 98%) as a
white solid.
27
[
a]
+17.3 (c 0.12, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.77
D
(1H, s), 7.77–7.74 (1H, m), 6.77 (1H, d, J = 8.0 Hz), 6.01 (1H, s),
4.41 (1H, s), 4.36 (1H, s), 3.87 (3H, s), 2.68 (1H, d, J = 14.3 Hz),
2.64 (1H, d, J = 14.3 Hz), 2.33 (1H, td, J = 13.7, 5.2 Hz), 2.08 (2H, d,
J = 13.7 Hz), 1.93–1.89 (1H, m), 1.61–1.56 (1H, m), 1.47 (1H, dt,
J = 12.2, 3.2 Hz), 1.41–1.38 (3H, m), 1.31–1.27 (1H, m), 1.22–1.19
(1H, m), 1.06 (3H, s), 1.02 (3H, d, J = 6.9 Hz), 0.96 (1H, dd,
J = 12.0, 1.7 Hz), 0.88 (3H, s). 13C NMR (125 MHz, CDCl3) d: 167.6,
1H NMR (500 MHz, CDCl3) d: 12.29 (1H, br), 7.54 (1H, d,
J = 1.1 Hz), 7.30 (1H, d, J = 1.1 Hz), 2.24 (3H, s), 1.98 (2H, q,
J = 7.4 Hz), 1.65 (3H, s), 1.02 (3H, t, J = 7.4 Hz). 13C NMR
(125 MHz, CDCl3) d: 172.3, 151.0, 147.3, 127.2, 122.0, 120.9
118.1, 107.2, 32.3, 24.0, 14.5, 7.3. IR (KBr): 2980, 2943, 1684,
1424, 1306, 1225, 1182 cmꢀ1. MS (ESI-TOF) m/z: 245 [M+Na]+.

Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
973
HRMS (ESI-TOF) m/z: 245.0791 Calcd for C12H14O4Na; Found:
245.0790.
J = 13.7 Hz), 2.68 (0.5H, d, J = 13.7 Hz), 2.40–2.35 (1H, m), 1.96–
1.91 (2H, m), 1.69–1.66 (1H, m), 1.63–1.56 (6H, m), 1.55 (9H, s),
1.50–1.44 (2H, m), 1.232 (1.5H, s), 1.225 (1.5H, s), 1.21 (1.5H, s),
1.20 (1.5H, s), 1.02 (1.5H, t, J = 7.4 Hz), 0.98 (1.5H, t, J = 7.4 Hz).
13C NMR (125 MHz, CDCl3) d: 203.5 (0.5C), 203.3 (0.5C), 165.56
(0.5C), 165.54 (0.5C), 155.2 (0.5C), 155.0 (0.5C), 150.4 (0.5C),
150.2 (0.5C), 147.09 (0.5C), 147.06 (0.5C), 127.6 (0.5C), 127.5
(0.5C), 127.1 (0.5C), 126.9 (0.5C), 124.73 (0.5C), 124.71 (0.5C),
120.5 (0.5C), 120.4 (0.5C), 118.3 (0.5C), 118.1 (0.5C), 111.7, 107.1
(0.5C), 107.0 (0.5C), 80.3, 65.0, 64.50 (0.5C), 64.47 (0.5C), 49.3,
45.13 (0.5C), 45.07 (0.5C), 41.6 (0.5C), 41.4 (0.5C), 38.8 (0.5C),
38.7 (0.5C), 32.3 (0.5C), 32.2 (0.5C), 29.31 (0.5C), 29.28 (0.5C),
28.2 (3C), 24.1 (0.5C), 23.7 (0.5C), 22.4 (0.5C), 22.34 (0.5C), 22.33
(0.5C), 22.28 (0.5C), 21.13 (0.5C), 21.07 (0.5C), 19.7 (0.5C), 19.6
(0.5C), 7.5 (0.5C), 7.3 (0.5C). IR (KBr): 2980, 1707, 1669, 1437,
1381, 1304, 1167 cmꢀ1. MS (ESI-TOF) m/z: 535 [M+Na]+. HRMS
(ESI-TOF) m/z: 535.2672 Calcd for C30H40O7Na; Found: 535.2682.
4.3.4. tert-Butyl 2-ethyl-2,7-dimethylbenzo[d][1,3]dioxole-5-
carboxylate (26)
SOCl2 (2.0 mL, 27.4 mmol, 2.0 equiv) was added to a solution of
25 (3.00 g, 13.5 mmol) in anhydrous THF (27 mL) at 0 °C, and the
whole mixture was stirred for 30 min at rt. tert-BuOK (54.0 mL of
a 1.0 M solution in THF, 54.0 mmol, 4.0 equiv) was added dropwise
to the mixture at 0 °C, and the whole mixture was stirred for
30 min at rt. H2O was added to the mixture and the whole mixture
was extracted with Et2O. Removal of the solvent from the Et2O
extract under reduced pressure gave a crude product, which was
purified by SiO2 column (n-hexane/AcOEt = 30:1) to give 26
(1.95 g, 52%) as a colorless oil.
1H NMR (500 MHz, CDCl3) d: 7.38 (1H, s), 7.18 (1H, s), 2.21 (3H,
s), 1.95 (2H, q, J = 7.4 Hz), 1.62 (3H, s), 1.56 (9H, s), 1.00 (3H, t,
J = 7.4 Hz). 13C NMR (125 MHz, CDCl3) d: 165.3, 149.6, 147.0,
125.7, 124.6, 120.2, 117.5, 106.6, 80.1, 32.1, 28.0 (3C), 23.8, 14.4,
7.2. IR (KBr): 2980, 1709, 1312, 1169 cmꢀ1. MS (ESI-TOF) m/z:
301 [M+Na]+. HRMS (ESI-TOF) m/z: 301.1416 Calcd for C16H22O4
Na; Found: 301.1429.
4.3.7. tert-Butyl 7-(((4a0R,50R,8a0R)-50,8a0-dimethyl-60-
oxooctahydro-20H-spiro[[1,3]dioxolane-2,10-naphthalen]-50-
yl)methyl)-2-ethyl-2-methylbenzo[d][1,3]dioxole-5-
carboxylate (29)
10% Pd–C (1.0 g) was added to a solution of 28 (2.13 g,
4.16 mmol) in EtOH (20 mL), and the whole mixture was stirred
for 2 h under a H2 atmosphere (balloon). The mixture was filtered
through short pad of Celite. Removal of the solvent from the filtrate
under reduced pressure gave 29 (2.05 g, 99%, diastereomeric mix-
ture) as a white amorphous, which was used for the next reaction
without further purification.
4.3.5. tert-Butyl 7-(bromomethyl)-2-ethyl-2-
methylbenzo[d][1,3]dioxole-5-carboxylate (27)
NBS (1.76 g, 9.89 mmol, 1.1 equiv) and AIBN (118 mg,
0.72 mmol, 0.08 equiv) were added to a solution of 26 (2.50 g,
8.98 mmol) in anhydrous benzene (36 mL), and the whole mixture
was stirred for 2 h under reflux. Satd NaHCO3 aq was added to the
mixture, and the whole mixture was extracted with CH2Cl2.
Removal of the solvent from the CH2Cl2 extract under reduced
pressure gave a crude product, which was purified by SiO2 column
(n-hexane/AcOEt = 20:1) to give 27 (1.91 g, 60%) as a white solid.
1H NMR (500 MHz, CDCl3) d: 7.53 (1H, d, J = 1.1 Hz), 7.28 (1H, d,
J = 1.1 Hz), 4.46 (1H, d, J = 10.1 Hz), 4.42 (1H, d, J = 10.1 Hz), 1.99
(2H, q, J = 7.4 Hz), 1.66 (3H, s), 1.56 (9H, s), 1.01 (3H, t,
J = 7.4 Hz). 13C NMR (125 MHz, CDCl3) d: 164.9, 149.7, 147.9,
125.5, 125.0, 122.1, 117.9, 109.1, 80.9, 32.4, 28.2 (3C), 26.5, 24.2,
7.2. IR (KBr): 2980, 1711, 1485, 1447, 1312, 1235, 1165 cmꢀ1. MS
(ESI-TOF) m/z: 379/381 [M+Na]+. HRMS (ESI-TOF) m/z: 379.0521
Calcd for C16H2179BrO4Na; Found: 379.0541.
1H NMR (500 MHz, CDCl3) d: 7.27 (0.5H, s), 7.26 (0.5H, s), 7.194
(0.5H, s), 7.191 (0.5H, s), 3.95–3.80 (4H, m), 2.96 (0.5H, d,
J = 13.7 Hz), 2.88 (0.5H, d, J = 13.7 Hz), 2.69 (0.5H, d, J = 13.7 Hz),
2.66 (0.5H, d, J = 13.7 Hz), 2.51–2.32 (2H, m), 2.23–2.20 (1H, m),
1.99–1.85 (3H, m), 1.68–1.64 (2H, m), 1.61 (1.5H, s), 1.57 (1.5H,
s), 1.54 (9H, s), 1.48–1.41 (5H, m), 1.09 (4.5H, s), 1.07 (1.5H, s),
1.02 (1.5H, t, J = 7.7 Hz), 0.99 (1.5H, t, J = 7.4 Hz). 13C NMR
(125 MHz, CDCl3) d: 216.3 (0.5C), 216.0 (0.5C), 165.53 (0.5C),
165.51 (0.5C), 150.5 (0.5C), 150.3 (0.5C), 147.0, 126.83 (0.5C),
126.75 (0.5C), 124.7, 120.54 (0.5C), 120.50 (0.5C), 118.3 (0.5C),
118.2 (0.5C), 112.7 (0.5C), 112.6 (0.5C), 107.19 (0.5C), 107.16
(0.5C), 80.3, 64.94 (0.5C), 64.92 (0.5C), 64.7, 51.8 (0.5C), 51.6
(0.5C), 44.8 (0.5C), 44.7 (0.5C), 42.12 (0.5C), 42.07 (0.5C), 38.6
(0.5C), 38.5 (0.5C), 35.2 (0.5C), 35.0 (0.5C), 32.3 (0.5C), 32.1 (0.5C),
29.9, 28.2 (3C), 28.1 (0.5C), 28.0 (0.5C), 23.9 (0.5C), 23.8 (0.5C),
22.6, 22.5 (0.5C), 22.4 (0.5C), 21.32 (0.5C), 21.30 (0.5C), 16.74
(0.5C), 16.73 (0.5C), 7.5 (0.5C), 7.4 (0.5C). IR (KBr): 2978, 1707,
1439, 1304, 1165 cmꢀ1. MS (ESI-TOF) m/z: 537 [M+Na]+. HRMS
(ESI-TOF) m/z: 537.2828 Calcd for C30H42O7Na; Found: 537.2844.
4.3.6. tert-Butyl 7-(((4a0R,50R,8a0R)-50,8a0-dimethyl-60-oxo-
30,40,4a0,50,60,8a0-hexahydro-20H-spiro[[1,3]dioxolane-2,10-
naphthalen]-50-yl)methyl)-2-ethyl-2-
methylbenzo[d][1,3]dioxole-5-carboxylate (28)
Under an Ar atmosphere, LHMDS (6.2 mL of a 1.0 M solution in
THF, 6.2 mmol, 1.5 equiv) was added dropwise to a solution of 5
(980 mg, 4.15 mmol) in anhydrous THF (5.5 mL) via cannula over
5 min at ꢀ78 °C, and the whole mixture was stirred for 1 h with
gradually warming to 0 °C. A solution of 27 (1.78 g, 4.98 mmol,
1.2 equiv) in anhydrous THF (10 mL) was added dropwise to the
mixture via cannula over 5 min at ꢀ78 °C, and the whole mixture
was stirred for 1.5 h with gradually warming to 60 °C and for
12 h at 60 °C. Satd NH4Cl aq was added to the mixture, and the
whole mixture was extracted with CH2Cl2. Removal of the solvent
from the CH2Cl2 extract under reduced pressure gave a crude prod-
uct, which was purified by SiO2 column (n-hexane/AcOEt = 5:1) to
give 28 (1.55 g, 73%, inseparable diastereomeric mixture) as a
white amorphous.
4.3.8. tert-Butyl 7-(((4a0R,50R,8a0R)-50,8a0-dimethyl-60-
methyleneoctahydro-20H-spiro[[1,3]dioxolane-2,10-
naphthalen]-50-yl)methyl)-2-ethyl-2-
methylbenzo[d][1,3]dioxole-5-carboxylate (30)
Under an Ar atmosphere, KHMDS (56 mL of a 0.5 M solution in
toluene, 28 mmol, 7.2 equiv) was added to Ph3PCH3Br (11.1 g,
30.7 mmol, 7.9 equiv), and the whole mixture was stirred for 1 h
at 100 °C. A solution of 29 (2.00 g, 3.89 mmol) in anhydrous tolu-
ene (19.5 mL) was added dropwise to the mixture via cannula at
rt, and the whole mixture was stirred for 1.5 h at 100 °C. Satd NH4
Cl aq was added to the mixture, and the whole mixture was
extracted with Et2O. Removal of the solvent from the Et2O extract
under reduced pressure gave a crude product, which was purified
by SiO2 column (n-hexane/AcOEt = 18:1) to give 30 (1.64 g, 82%,
diastereomeric mixture) as a white amorphous.
1H NMR (500 MHz, CDCl3) d: 7.25 (0.5H, d, J = 1.7 Hz), 7.23
(0.5H, d, J = 1.7 Hz), 7.18 (0.5H, d, J = 1.7 Hz), 7.17 (0.5H, d,
J = 1.7 Hz), 6.95 (0.5H, d, J = 10.3 Hz), 6.93 (0.5H, d, J = 9.7 Hz),
5.90 (0.5H, d, J = 9.7 Hz), 5.85 (0.5H, d, J = 10.3 Hz), 3.98 (1H, q,
J = 6.9 Hz), 3.92 (1H, q, J = 6.8 Hz), 3.88–3.81 (2H, m), 3.12 (0.5H,
d, J = 13.7 Hz), 3.02 (0.5H, d, J = 13.7 Hz), 2.71 (0.5H, d,
1H NMR (500 MHz, CDCl3) d: 7.32 (0.5H, d, J = 1.7 Hz), 7.29
(0.5H, d, J = 1.7 Hz), 7.17 (1H, br s), 4.75 (1H, d, J = 1.1 Hz), 4.39

974
Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
(0.5H, d, J = 1.1 Hz), 4.37 (0.5H, d, J = 1.1 Hz), 3.99–3.89 (4H, m),
2.68–2.57 (2H, m), 2.29–2.27 (1H, m), 2.18–2.11 (1H, m), 2.05–
2.00 (1H, m), 1.94–1.91 (3H, m), 1.69–1.67 (1H, m), 1.62–1.56
(3H, m), 1.55 (9H, s), 1.54–1.42 (5H, m), 1.22–1.14 (1H, m), 1.061
(1.5H, s), 1.058 (1.5H, s), 1.01–0.98 (6H, m). 13C NMR (125 MHz,
CDCl3) d: 165.7, 153.01 (0.5C), 152.98 (0.5C), 150.83 (0.5C),
150.78 (0.5C), 146.6, 127.5, 123.7 (0.5C), 123.6 (0.5C), 120.1
(0.5C), 120.0 (0.5C), 119.2 (0.5C), 119.1 (0.5C), 113.48 (0.5C),
113.46 (0.5C), 108.12 (0.5C), 108.07 (0.5C), 106.64 (0.5C), 106.61
(0.5C), 80.1, 65.0 (0.5C), 64.4 (0.5C), 46.1 (0.5C), 46.0 (0.5C),
43.30 (0.5C), 43.27 (0.5C), 42.80 (0.5C), 42.77 (0.5C), 39.9 (0.5C),
39,7 (0.5C), 32.2 (0.5C), 32.0 (0.5C), 31.8 (0.5C), 31.7 (0.5), 29.74
(0.5C), 29.67 (0.5C), 29.5 (0.5C), 29.4 (0.5C), 28.2 (3C), 23.8, 22.81
(0.5C), 22.78 (0.5C), 22.72, 20.7, 20.6, 20.5, 7.4 (0.5C), 7.3 (0.5C).
IR (KBr): 2982, 2943, 1707, 1439, 1377, 1304, 1165 cmꢀ1. MS
(ESI-TOF) m/z: 535 [M+Na]+. HRMS (ESI-TOF) m/z: 535.3036 Calcd
for C31H44O6Na; Found: 535.3052.
147.2 (0.5C), 147.1 (0.5C), 126.9 (0.5C), 126.8 (0.5C), 124.6 (0.5C),
124.5 (0.5C), 120.0, 118.6 (0.5C), 118.5 (0.5C), 107.24 (0.5C),
107.16 (0.5C), 80.5, 49.0, 47.42 (0.5C), 47.35 (0.5C), 42.3, 37.4,
37.24 (0.5C), 37.22 (0.5), 36.1 (0.5C), 36.0 (0.5C), 32.4, 32.18
(0.5C), 32.16 (0.5C), 28.2 (3C), 26.8 (0.5C), 26.7 (0.5C), 25.4
(0.5C), 25.3 (0.5C), 24.2 (0.5C), 23.4 (0.5C), 21.6 (0.5C), 17.9
(0.5C), 17.8 (0.5C), 17.3 (0.5C), 17.2 (0.5C), 7.5 (0.5C), 7.2 (0.5C).
IR (KBr): 2976, 2934, 1707, 1435, 1304, 1165 cmꢀ1. MS (ESI-TOF)
m/z: 493 [M+Na]+. HRMS (ESI-TOF) m/z: 493.2930 Calcd for C29H42
O5Na; Found: 493.2941.
4.3.11. 3,4-Dihydroxy-5-(((1S,2R,4aR,8aR)-1,2,4a-trimethyl-5-
oxodecahydronaphthalen-1-yl)methyl)benzoic acid (33)
TFA (40 mL) was added to a solution of 32 (1.34 g, 2.95 mmol)
in THF/H2O (7:3, 10 mL) at 0 °C, and the whole mixture was stirred
for 4 h at 40 °C and for 1 h at 50 °C. Removal of the solvent from the
filtrate under reduced pressure gave a crude product, which was
purified by SiO2 column (CHCl3/MeOH/H2O = 30:3:1, lower phase)
4.3.9. tert-Butyl 7-(((1R,4aR,8aR)-1,4a-dimethyl-2-methylene-5-
oxodecahydronaphthalen-1-yl)methyl)-2-ethyl-2-
to give 33 (1.01 g, 95%) as a white amorphous.
+23.8 (c 0.932, MeOH). 1H NMR (500 MHz, CD3COCD3) d:
26
[
a]
D
methylbenzo[d][1,3]dioxole-5-carboxylate (31)
8.92 (1H, br), 7.88 (1H, br), 7.38 (1H, d, J = 1.7 Hz), 7.35 (1H, d,
J = 1.7 Hz), 2.75 (1H, d, J = 14.0 Hz), 2.71 (1H, d, J = 14.0 Hz), 2.60
(1H, td, J = 14.2, 7.4 Hz), 2.28 (1H, br d, J = 12.0 Hz), 2.02–1.97
(2H, m), 1.81 (1H, qd, J = 13.0, 3.4 Hz), 1.69–1.59 (1H, m), 1.35–
1.32 (4H, m), 1.18–1.15 (2H, m), 1.12 (3H, s), 1.03 (3H, d,
J = 5.7 Hz), 0.93 (3H, s). 13C NMR (125 MHz, CD3COCD3) d: 214.8,
167.9, 150.3, 144.7, 127.1, 125.3, 121.1, 114.7, 49.7, 48.6, 42.9,
37.8, 37.6, 36.6, 33.5, 27.5, 26.1, 22.6, 19.1, 18.3, 17.9. IR (KBr):
3206, 2955, 1688, 1439, 1296, 1225 cmꢀ1. MS (ESI-TOF) m/z: 383
[M+Na]+. HRMS (ESI-TOF) m/z: 383.1834 Calcd for C21H28O5Na;
Found: 383.1852.
Concd HCl (5 mL) was added to a solution of 30 (1.61 g,
3.14 mmol) in THF (45 mL) at 0 °C, and the whole mixture was stir-
red for 30 min at rt. H2O was added to the mixture, and the whole
mixture was extracted with Et2O. Removal of the solvent from the
Et2O extract under reduced pressure gave 31 (1.50 g, quant, diaste-
reomeric mixture) as a white amorphous, which was used next
reaction without further purification.
1H NMR (500 MHz, CDCl3) d: 7.34 (0.5H, d, J = 1.7 Hz), 7.31
(0.5H, d, J = 1.7 Hz), 7.18 (1H, s), 4.84 (1H, s), 4.54 (0.5H, d,
J = 1.1 Hz), 4.51 (0.5H, d, J = 1.1 Hz), 2.71 (0.5H, d, J = 14.0 Hz),
2.70 (0.5H, d, J = 14.0 Hz), 2.61 (0.5H, d, J = 14.0 Hz), 2.60 (0.5H, d,
J = 14.0 Hz), 2.54–2.52 (1H, m), 2.34–2.24 (4H, m), 2.09–2.04 (1H,
m), 1.93–1.90 (2H, m), 1.86–1.72 (3H, m), 1.57 (1.5H, s), 1.56
(1.5H, s), 1.55 (9H, s), 1.47–1.42 (2H, m), 1.15 (3H, s), 1.13 (1.5H,
s), 1.11 (1.5H, s), 1.00–0.98 (3H, m). 13C NMR (125 MHz, CDCl3)
d: 215.03 (0.5C), 215.01 (0.5C), 165.57 (0.5C), 165.56 (0.5C),
151.6 (0.5C), 151.5 (0.5C), 150.7 (0.5C), 150.6 (0.5C), 146.8, 127.2,
124.1 (0.5C), 124.0 (0.5C), 120.3 (0.5C), 120.2 (0.5C), 118.7 (0.5C),
118.6 (0.5C), 109.3 (0.5C), 109.2 (0.5C), 107.0 (0.5C), 106.9 (0.5C),
80.4, 49.4 (0.5C), 49.2 (0.5C), 49.1 (0.5C), 49.0 (0.5C), 43.94
(0.5C), 43.92 (0.5C), 39.68 (0.5C), 39.66 (0.5C), 37.90 (0.5C), 37.88
(0.5C), 32.2 (0.5C), 32.0 (0.5C), 31.54 (0.5C), 31.52 (0.5C), 28.6,
28.2 (3C), 25.41 (0.5C), 25.38 (0.5C), 23.8, 23.02 (0.5C), 22.99
(0.5C), 22.2 (0.5C), 22.1 (0.5C), 21.7 (0.5C), 21.5 (0.5C), 7.5 (0.5C),
7.3 (0.5C). IR (KBr): 2982, 2944, 1707, 1439, 1377, 1304,
1165 cmꢀ1. MS (ESI-TOF) m/z: 491 [M+Na]+. HRMS (ESI-TOF) m/z:
491.2773 Calcd for C29H40O5Na; Found: 491.2793.
4.3.12. Methyl 3,4-dihydroxy-5-(((1S,2R,4aR,8aR)-1,2,4a-
trimethyl-5-oxodecahydronaphthalen-1-yl)methyl)benzoate
(34)
SOCl2 (0.44 mL, 6.00 mmol, 4.0 equiv) was added to a solution
of 33 (538 mg, 1.49 mmol) in anhydrous MeOH (7.5 mL), and the
whole mixture was stirred for 2.5 h with gradually warming to
60 °C and for 30 min at 60 °C. Removal of the solvent from the fil-
trate under reduced pressure gave a crude product, which was
purified by SiO2 column (n-hexane/AcOEt = 2:1) to give 34
(477 mg, 85%) as a white solid.
26
[
a]
+24.8 (c 1.05, MeOH). 1H NMR (500 MHz, CD3COCD3) d:
D
8.89 (1H, s), 7.95 (1H, s), 7.38 (1H, d, J = 2.3 Hz), 7.34 (1H, d,
J = 2.3 Hz), 3.78 (3H, s), 2.78 (1H, d, J = 14.0 Hz), 2.75 (1H, d,
J = 14.0 Hz), 2.64 (1H, td, J = 13.9, 7.1 Hz), 2.31 (1H, br d,
J = 15.5 Hz), 2.10–2.08 (1H, m), 1.87 (1H, qd, J = 13.0, 3.7 Hz),
1.73–1.64 (1H, m), 1.41–1.29 (4H, m), 1.21–1.19 (2H, m), 1.16
(3H, s), 1.06 (3H, d, J = 6.3 Hz), 0.97 (3H, s). 13C NMR (125 MHz,
CD3COCD3) d: 214.9, 167.2, 150.3, 144.7, 126.7, 125.3, 120.8,
114.3, 51.9, 49.7, 48.5, 42.9, 37.8, 37.6, 36.6, 33.4, 27.5, 26.0,
22.5, 19.0, 18.3, 17.9. IR (KBr): 3355, 2953, 1701, 1439, 1302,
1225 cmꢀ1. MS (ESI-TOF) m/z: 397 [M+Na]+. HRMS (ESI-TOF) m/z:
397.1991 Calcd for C22H30O5Na; Found: 397.1997.
4.3.10. tert-Butyl 2-ethyl-2-methyl-7-(((1S,2R,4aR,8aR)-1,2,4a-
trimethyl-5-oxodecahydronaphthalen-1-
yl)methyl)benzo[d][1,3]dioxole-5-carboxylate (32)
10% Pd–C (2.11 g) was added to a solution of 31 (1.47 g,
3.14 mmol) in Et3N (29.5 mL) and MeOH (2 drops), and the whole
mixture was stirred for 6 h under a H2 atmosphere (balloon). The
mixture was filtered through short pad of Celite. Removal of the
solvent from the filtrate under reduced pressure gave 32 (1.46 g,
99%) as a white amorphous, which was used for the next reaction
without further purification.
4.3.13. (+)-Dictyoceratin-A (2)
Under an Ar atmosphere, KHMDS (13.2 mL of a 0.5 M solution in
toluene, 6.6 mmol, 10.3 equiv) was added to Ph3PCH3Br (2.62 g,
7.33 mmol, 11.5 equiv), and the whole mixture was stirred for
1 h at rt. Above solution (24 mL, about 4.2 mmol of Ph3P@CH2,
6.6 equiv) was added dropwise to a solution of 34 (241 mg,
0.64 mmol) in anhydrous THF (24.5 mL), and the whole mixture
was stirred for 1 h at rt. Satd NH4Cl aq was added to the mixture,
and the whole mixture was extracted with AcOEt. Removal of the
solvent from the AcOEt extract under reduced pressure gave a
crude product, which was purified by SiO2 column (n-hexane/
1H NMR (500 MHz, CDCl3) d: 7.253 (0.5H, s), 7.249 (0.5H, s),
7.21 (0.5H, d, J = 1.1 Hz), 7.20 (0.5H, d, J = 1.1 Hz), 2.66–2.54 (3H,
m), 2.18–2.13 (3H, m), 1.94–1.91 (2H, m), 1.83–1.78 (1H, m),
1.71–1.64 (1H, m), 1.58 (1.5H, s), 1.56 (1.5H, s), 1.54 (9H, s),
1.51–1.49 (1H, m), 1.35–1.25 (4H, m), 1.24–1.21 (1H, m), 1.15
(3H, s), 1.00–0.97 (6H, m), 0.92 (3H, s). 13C NMR (125 MHz, CDCl3)
d: 215.89 (0.5C), 215.87 (0.5C), 165.3, 150.8 (0.5C), 150.7 (0.5C),

Y. Sumii et al. / Bioorg. Med. Chem. 23 (2015) 966–975
975
AcOEt = 18:1) to give dictyoceratin-A (2) (200 mg, 83%) as a white
solid.
Acknowledgements
+10.4 (c 0.19, CHCl3). 1H NMR (500 MHz, CDCl3) d: 7.49
26
[a]
The authors thank Dr. Kazutake Tsujikawa (Osaka University)
for providing the DU145 cells. The authors are grateful to the
Hoansha Foundation, the Uehara Memorial Foundation, the Naito
Foundation, and Osaka University Project MEET for financial sup-
port. This study was also financially supported by Grant-in-Aid
for Scientific Research (Nos. 26242074, 22241053 and 26860065),
and Platform for Drug Discovery, Informatics, and Structural Life
Science, from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan.
D
(1H, d, J = 2.0 Hz), 7.40 (1H, d, J = 2.0 Hz), 5.90 (2H, S), 4.41 (1H,
s), 4.37 (1H, s), 3.87 (3H, s), 2.68 (1H, d, J = 14.3 Hz), 2.65 (1H, d,
J = 14.3 Hz), 2.34 (1H, td, J = 13.7, 5.0 Hz), 2.09 (2H, d, J = 14.3 Hz),
1.93–1.91 (1H, m), 1.60–1.55 (1H, m), 1.47 (1H, dt, J = 11.6,
2.7 Hz), 1.43–1.35 (3H, m), 1.33–1.19 (2H, m), 1.06 (3H, s), 1.03
(3H, d, J = 6.3 Hz), 0.96 (1H, d, J = 11.5 Hz), 0.88 (3H, s). 13C NMR
(125 MHz, CDCl3) d: 167.7, 160.1, 148.7, 142.3, 127.4, 125.2,
120.3, 114.0, 102.8, 52.1, 48.0, 42.1, 40.2, 37.0, 36.5, 36.3, 33.0,
27.9, 27.7, 23.2, 20.6, 17.64, 17.59. IR (KBr): 3341, 1686, 1601,
1426, 1287 cmꢀ1
.
MS (ESI-TOF) m/z: 395 [M+Na]+. HRMS
Supplementary data
(ESI-TOF) m/z: 395.2198 Calcd for C23H32O4Na; Found: 395.2214.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2015.01.021.
4.3.14. (–)-Dictyoceratin-A (ent-2)
ent-2 was synthesized through the same procedures as those for
2, using ent-5 as a starting material. [
26
a]
ꢀ11.6 (c 0.96, CHCl3).
D
References and notes
4.4. Biological evaluation of dictyoceratin-C (1), dictyoceratin-A
(2) and those enantiomers
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The DU145 cells in the culture medium were plated into each
well of 96-well plates (1 ꢁ 104 cells/well/200
lL) for 4 h in a
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humidified atmosphere of 5% CO2 at 37 °C (normoxic condition).
Then, the plates were incubated for 12 h in the 94% nitrogen, 5%
CO2, and 1% O2 (hypoxic condition) inducing hypoxia related genes,
such as HIF-1a. After 12 h incubation, testing compounds were
added, and then the plates were incubated for an additional 24 h
in the hypoxic condition. The cell proliferation was detected by
the MTT method. The growth inhibition rate was calculated as per-
centage of parallel negative controls. The anti-proliferative activi-
ties of the testing compounds under normoxic condition were
also evaluated by MTT method.
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