Total synthesis of dehydroaltenusin

Article abstract of DOI:10.1016/j.tet.2004.05.017

The first total synthesis of dehydroaltenusin, a natural enzyme inhibitor, is described. The key step involves Suzuki-coupling reaction of an aryl triflate prepared from 2,4,6-trihydroxybenzoic acid with a catechol-derived boronic acid or boronic ester. T

Full text of DOI:10.1016/j.tet.2004.05.017

Tetrahedron 60 (2004) 5695–5700
Total synthesis of dehydroaltenusin
c
b
Shinji Kamisuki,a Shunya Takahashi,b Yoshiyuki Mizushina, Shinya Hanashima,
Kouji Kuramochi,d Susumu Kobayashi,d Kengo Sakaguchi,a,d Tadashi Nakatab
and Fumio Sugawaraa,d
,
*
aDepartment of Applied Biological Science, Tokyo University of Science, Noda, Chiba 278-8510, Japan
bRIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan
cDepartment of Nutritional Science, Kobe-Gakuin University, Kobe, Hyogo 651-2180, Japan
dGenome and Drug Discovery Research Center, Tokyo University of Science, Noda, Chiba 278-8510, Japan
Received 14 April 2004; revised 6 May 2004; accepted 10 May 2004
Abstract—The first total synthesis of dehydroaltenusin, a natural enzyme inhibitor, is described. The key step involves Suzuki-coupling
reaction of an aryl triflate prepared from 2,4,6-trihydroxybenzoic acid with a catechol-derived boronic acid or boronic ester. The synthetic
product was evaluated as a potent inhibitor against eukaryotic DNA polymerase a and other DNA polymerases.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
be a g-lactone derivative of b-resorcylic acid monomethyl-
ether based on the chemical and spectroscopic data6 and
later revised to 1 possessing a d-lactone ring by the X-ray
crystallographic analyses (Fig. 1).8 In 1995, 1 was also
reported to inhibit the calmodulin-dependent activity of
myosin light chain kinase (MLCK).9
Eukaryotic multicellular organisms are known to contain at
least 14 types of DNA polymerases.1,2 DNA polymerase a is
an essential enzyme for DNA replication and subsequently
for cell division.1 Aphidicolin, a well-known DNA poly-
merase a inhibitor, has been very useful for studying the
DNA replication system,3 however, there have been no
previous reports of inhibitors capable of distinguishing
among DNA polymerases a, d and e. Recently, we have
isolated a powerful mammalian DNA polymerase a inhibi-
tor (IC50¼0.68 mM) from Acremonium sp. 98H02B04-1 (2)
and revealed it to be dehydroaltenusin (1),4 which was
discovered from mycelium extracts of Alternaria tennuis
and A. kikuchiana by Rosett et al. in 19575 and then from a
variety of fungi.6,7 The structure was initially suggested to
Compound 1 inhibits only mammalian DNA polymerase a
activity, but does not influence the activities of mammalian
DNA polymerase d and e, nor DNA polymerase a from
other vertebrates in vitro, and found to be more potent
inhibitor of DNA polymerase a than aphidicolin.4 We have
also reported 1 suppressed the cell proliferation of the
human gastric cell line NUGC-3 by inhibiting DNA
polymerase a activity.10 The specific inhibitors of mamma-
lian DNA polymerase a are not only molecular tools and
molecular probes to distinguish DNA polymerases and
clarify their biological and in vivo functions, but should also
be considered as a group of potentially useful cancer
chemotherapy agents. However, its low producibility has
prevented such utilization. Furthermore, no total synthesis
of 1 has been reported so far. We report herein the first
synthesis of racemic 1 and its inhibitory activity against a
series of DNA polymerases.11
2. Results and discussion
Figure 1.
2.1. Total synthesis of dehydroaltenusin
Keywords: Dehydroaltenusin; DNA polymerase a; Enzyme inhibitor.
*
Rosett et al. has reported that FeCl3-promoted oxidation of
altenusin 2 afforded 1.5 Therefore, 2 was regarded as our
Corresponding author. Tel.: þ81-48-462-1111-3627; fax: þ81-48-462-
4627; e-mail address: shunyat@riken.go.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.05.017

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S. Kamisuki et al. / Tetrahedron 60 (2004) 5695–5700
Scheme 1. Retrosynthetic scheme of dehydroaltenusin (1).
Scheme 2. Reagents and conditions: (a) acetone, SOCl2, DMAP, DME, rt, 56%; (b) DIAD, Ph3P, MeOH, THF, rt, 89%; (c) Tf2O, pyridine, 0 8C, 94%; (d)
MOMCl, NaH, DMF, 0 8C, 90%; (e) n-BuLi, THF, 278,240 8C, then (i-PrO)3B, Et2O, 278 8C,rt, 95%; (f) (Ph3P)4Pd, K3PO4, KBr, dioxane, 100 8C, 93%;
(g) 2N KOH, EtOH, 60 8C; (h) 10% HCl–MeOH, CH2Cl2, rt, 64% (two steps); (i) BCl3 (10 equiv.), CH2Cl2, 0 8C,rt, 63%; (j) FeCl3, aq. EtOH, rt, 82%.
actual synthetic goal. Our synthetic efforts toward 2
involved Suzuki-coupling12 reaction of an aryltriflate 3
with an aryl boronic acid 4 or boronic ester 5 as a key step
(Scheme 1). Synthesis of the aryltriflate 3 started from
commercially available 2,4,6-trihydroxybenzoic acid 6. The
benzoic acid 6 was reacted with thionyl chloride (SOCl2) in
the presence of N,N-dimethylaminopyridine (DMAP) in
acetone13 to give acetonide 7 in 56% yield, whereas in 43%
yield by Danishefsky’s method (trifluoroacetic acid–
trifluoroacetic anhydride in acetone)14 (Scheme 2).
Danishefsky et al. has accomplished regioselective protec-
tion of 4-hydroxy group of 7 by the Mitsunobu conditions15
with diisopropyl azodicarboxylate–triphenylphosphine in
the presence of benzyl alcohol.14 Regioselective methyl-
ation of 7 was performed according to this method,
affording monomethyl ether 8 in 89% yield. Treatment of
8 with triflic anhydride-pyridine gave the corresponding
triflate 3 in 94% yield. On the other hand, a 4-bromo-
catechol 1016 prepared from 4-methylcatechol (9) was
subjected to methoxymethylation with sodium hydride
(NaH) and methoxymethyl chloride (MOMCl), giving bis-
MOM ether 11 in 90% yield. Halogen–lithium exchange
of 11 with n-butyllithium in tetrahydrofuran (THF) at
278!240 8C followed by trapping with triisopropyl borate
(Et2O, 278 8C!rt) afforded an aryl boronic acid 4 in 95%
yield. This compound was, without purification, employed
to the next coupling reaction, because of its instability.
Introduction of a catechol moiety into 3 was best realized by
using 1.5 mol equiv. of 4 in the presence of tetrakis(tri-
phenylphosphine)palladium (0.05 mol equiv.), potassium

S. Kamisuki et al. / Tetrahedron 60 (2004) 5695–5700
5697
phosphate and potassium bromide in dioxane17 at 100 8C to
2.2. Inhibition studies and discussion
produce a coupled product 12 in 93% yield. Alkaline
hydrolysis of 12 and subsequent acid treatment provided
altenusin 2 in 64% yield. This compound was also obtained
by the action of boron trichloride (BCl3) in dichloromethane
(CH2Cl2) from 12 in a single step (63%). Finally, FeCl3-
promoted oxidation5 of 2 afforded dehydroaltenusin (1) in
82% yield.† The spectroscopic and physical properties of 1
were identical with those of natural 1 (vide infra).
DNA polymerase inhibition assay was performed as
described previously.21,22 Inhibitory activity of the synthetic
compound 1 against the calf DNA polymerase a, rat DNA
polymerase b, calf DNA polymerase d and human DNA
polymerase e was examined and compared with that of
natural 1. As illustrated in Figure 2, the IC50 values of
synthetic and natural 1 for DNA polymerase a were 0.8 and
0.7 mM, respectively, and both compounds had no inhibi-
tory effect on DNA polymerase b, d and e. Therefore, the
inhibitory activity of the two compounds was not
distinguishable.
Furthermore, we have also developed an alternative shorter
route through boronic ester 5 (Scheme 3). 2-Iode-4,5-
methylenedioxytoluene (14)18 obtained from commercially
available 3,4-methylenedioxytoluene (13) was treated wit0h
bis(pinacolato)diboron19 in the presence of dichloro[1,1 -
bis(diphenylphosphino)ferrocene]palladium {PdCl2(dppf),
0.1 mol equiv.} and potassium acetate in N,N-dimethyl-
formamide, giving boronic ester 5 in 81% yield. Triflate 3
was coupled with the boronic ester 5 (1.3 mol equiv.)
using PdCl2(dppf) (0.05 mol equiv.) and potassium
carbonate (3.0 mol equiv.) in 1,2-dimethoxyethane
(DME)20 at 85 8C to provide 15 in 67% yield. Deprotection
of 15 by BCl3 yielded 2, which was transformed into
dehydroaltenusin (1).
Scheme 3. Reagents and conditions: (a) bis(pinacolato)diboron, PdCl2-
(dppf), KOAc, DMF, 80 8C, 81%; (b) 3, PdCl2(dppf), K2CO3, DME, 85 8C,
67%; (c) BCl3, CH2Cl2, rt, 80%; (d) FeCl3, aq. EtOH, rt, 82%.
Figure 2. Dose–response curve of synthetic (a) and natural (b) dehydro-
altenusin. Inhibition activity against eukaryotic DNA polymerase a, b, d
and e are shown as open circle, closed circle, open square, and closed
square symbols, respectively. DNA polymerase activity in the absence of
compound was taken as 100%.
2.3. Conclusion
Scheme 4. Reagents and conditions: (a) 4, (Ph3P)4Pd, K3PO4, KBr,
dioxane, 100 8C, 70%; (b) 2 N KOH, EtOH, 60 8C; (c) 10% HCl–MeOH,
CH2Cl2, rt, 86% (two steps).
In summary, the first synthesis of dehydroaltenusin (1) has
been accomplished in 7 steps with 23% yield or in 6 steps
with 21% overall yield from a commercially available
carboxylic acid 6. These synthetic processes would be quite
useful for preparation of large amounts of 1 suitable for in
vitro and in vivo experiments on DNA polymerase a and
future clinical usage.
†
Our initial approach to 1 was based on the coupling reaction of 4 and
triflate 16 ((Scheme 4)). However, we did not adopt this route for large-
scale synthesis of 1 because preparation of 16 from methyl 2,6-dihydroxy-
4-methoxybenzoate23 was found to be not practical.

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S. Kamisuki et al. / Tetrahedron 60 (2004) 5695–5700
3. Experimental
vigorously stirred, and then extracted with ether. The
extracts were washed with cold dilute HCl solution, water,
sat. NaHCO3 solution, water, brine, dried, and concentrated.
Chromatography on silica gel with hexane!hexane–
EtOAc (6:1) as the eluent yielded 3 (1.50 g, 94%) as
white solids: mp 58–59 8C {hexane–EtOAc (50:1)}; IR
(KBr) 2993, 2954, 2850, 1747, 1624, 1431, 1284, 1203,
1138, 1061 cm21; 1H NMR (400 MHz, CDCl3): d 1.74 (6H,
s), 3.89 (3H, s), 6.49 (1H, d, J¼2.3 Hz), 6.53 (1H, d,
J¼2.3 Hz); 13C NMR (100 MHz, CDCl3): d 25.5, 56.3,
100.9, 101.1, 105.3, 106.6, 118.7 (q, J¼320 Hz), 149.9,
157.1, 158.8, 165.5; HRMS calcd for C12H11F3O7SNa
[MþNa]þ 379.0069, found 379.0058. Anal. Found: C,
40.64; H, 2.93. Calcd for C12H11F3O7S: C, 40.45; H, 3.11.
3.1. General procedures
1H and 13C NMR spectra were recorded at 400 MHz with
Bruker DRX-400 spectrometer, using tetramethylsilan as
the internal standard. IR spectra were recorded with a
HORIBA FREEXACT-II FT-720 spectrophotometer. High-
resolution mass spectra were obtained on Applied Bio-
systems QSTAR Mass Spectrometer using electron spray
ionization (ESI) method. Column chromatography was
performed on Kanto silica gel (spherical, neutral; 40–
50 mm). Merck precoated silica gel 60 F254 0.25 mm
thickness, was used for analytical thin-layer chroma-
tography. All reactions were performed under argon
atmosphere. The solvent extracts were dried with sodium
sulfate, and the solutions were evaporated under diminished
pressure at 30–50 8C.
3.1.4. 1-Bromo-4,5-bis(methoxymethoxy)-2-methylben-
zene (11). To a stirred solution of 10 (5.83 g, 28.7 mmol)
in N,N-dimethylformamide (95 mL) was added sodium
hydride (60% in mineral oil, 2.87 g, 71.8 mmol) by portions
at 0 8C, and then the mixture was stirred at 0 8C for 1 h.
Chloro methylmethylether (5.45 mL, 71.8 mmol) was
added dropwise at 0 8C, and then the mixture was stirred
at 0 8C for 6 h. After addition of sat. NH4Cl solution, the
resulting mixture was extracted with ether. The extracts
were washed with water, brine, dried, and concentrated.
Chromatography on silica gel with hexane–EtOAc
(30:1!20:1) as the eluent yielded 11 (7.54 g, 90%) as a
colorless oil: IR (neat) 2957, 2933, 2829, 1500, 1255, 1151,
3.1.1. 5,7-Dihydroxy-2,2-dimethyl-4H-1,3-benzodioxin-
4-one (7). To a solution of 2,4,6-trihydroxy-benzoic acid
(6) (23.0 g, 135 mmol), N,N-dimethylaminopyridine
(1.65 g, 13.4 mmol), and acetone (25.7 mL, 350 mmol) in
1,2-dimethoxyethane (100 mL) was added dropwise thionyl
chloride (29 mL, 398 mmol) at 0 8C. The mixture was
warmed slowly to rt and then stirred for 2 h. The mixture
was poured into sat. NaHCO3 solution, and extracted with
EtOAc. The extracts were washed with water, dried, and
concentrated. Chromatography on silica gel with hexane–
EtOAc (13:7) as the eluent yielded 7 (16.0 g, 56%) as white
solids: mp 200–201 8C (lit.14 203–204 8C); 1H NMR
(400 MHz, acetone-d6): d 1.72 (6H, s), 3.02 (1H, brs),
6.01 (1H, d, J¼2.2 Hz), 6.08 (1H, d, J¼2.2 Hz,), 10.46 (1H,
s); 13C NMR (100 MHz, acetone-d6): d 25.6, 93.0, 96.2,
98.0, 107.6, 158.1, 164.0, 165.8, 167.2; HRMS calcd for
C10H10O5Na [MþNa]þ 233.0420, found 233.0428.
1080, 1003 cm21 1H NMR (400 MHz, CDCl3): d 2.31
;
(3H, s), 3.51 (6H, s), 5.17 (1H, d, J¼6.7 Hz), 5.20 (1H, d,
J¼6.7 Hz), 7.03 (1H, brs), 7.32 (1H, brs); 13C NMR
(100 MHz, CDCl3): d 22.2, 56.0, 95.2, 95.4, 116.1, 118.5,
120.4, 131.3, 145.5, 146.1; HRMS calcd for C11H15O479Br
81
(C11H15O4 Br) [MþH]þ 290.0154 (292.0134), found
290.0156 (292.0129).
3.1.5. 5-[4,5-Bis(methoxymethoxy)-2-methylphenyl]-7-
methoxy-2,2-dimethyl-4H-1,3-benzodioxin-4-one (12).
To a stirred solution of 11 (2.32 g, 7.97 mmol) in
tetrahydrofuran (21 mL) was added dropwise a 1.59 M
solution of n-butyllithium (5.5 mL, 8.77 mmol) in hexane at
278 8C, and the mixture was stirred at 278!240 8C for
1.4 h. Then a solution of triisopropyl borate (2.02 mL,
8.77 mmol) in ether (7 mL) was added dropwise at 278 8C,
and the mixture was stirred at 278 8C!rt for 1 h and at rt
for 3 h. After addition of 1 M HCl solution, the resulting
mixture was stirred for 45 min, and then extracted with
ether. The extracts were washed with water, brine, dried,
and concentrated to give 4 (1.94 g, 95%), which was
employed to the next without further purification. To a
stirred mixture of the above boric acid 4 (1.12 g,
4.37 mmol), 3 (1.04 g, 2.91 mmol), potassium bromide
(346 mg, 2.91 mmol) and potassium phosphate (928 mg,
4.37 mmol) in dioxane (12 mL) was added tetrakis(tri-
phenylphosphine)palladium (169 mg, 0.15 mmol), and the
mixture was stirred at 100 8C for 10.5 h, cooled, and then
diluted with water. The resulting mixture was extracted with
EtOAc. The extracts were washed with water, brine, dried,
and concentrated. Chromatography on silica gel with
hexane!hexane–EtOAc (4:1!2:1) as the eluent yielded
12 (1.14 g, 93%) as white solids: mp 146–147 8C {hexane–
EtOAc (20:1)}; IR (KBr) 2989, 2958, 2908, 1732, 1612,
3.1.2. 5-Hydroxy-7-methoxy-2,2-dimethyl-4H-1,3-benzo-
dioxin-4-one (8). To a stirred solution of 7 (2.54 g,
12.1 mmol), methanol (0.53 mL, 13.0 mmol) and triphenyl-
phosphine (3.40 g, 13.0 mmol) in tetrahydrofuran (40 mL)
was added dropwise diisopropyl azodicarboxylate (2.6 mL,
13.0 mmol) at 0 8C, and then the mixture was stirred at
0 8C!rt for 4.5 h. The mixture was diluted with EtOAc,
washed with water, brine, dried, and concentrated. Chro-
matography on silica gel with hexane!hexane–EtOAc
(10:1) as the eluent yielded 8 (2.41 g, 89%) as white solids:
mp 108–109 8C {hexane–EtOAc (20:1)}; IR (KBr) 3194,
2985, 2947, 2854, 1697, 1635, 1581, 1192, 1157 cm21; 1H
NMR (400 MHz, CDCl3): d 1.73 (6H, s), 3.82 (3H, s), 6.00
(1H, d, J¼2.3 Hz), 6.15 (1H, d, J¼2.3 Hz), 10.45 (1H, s);
13C NMR (100 MHz, CDCl3): d 25.6, 55.7, 93.1, 94.6,
95.7, 106.9, 156.8, 163.1, 165.2, 167.7; HRMS calcd
for C11H12O5Na [MþNa]þ 247.0576, found 247.0587.
Anal. Found: C, 58.91; H, 5.51. Calcd for C11H12O5: C,
58.93; H, 5.39.
3.1.3. 7-Methoxy-2,2-dimethyl-5-[(trifluoromethyl)-
sulfonyl]-4H-1,3-benzodioxin-4-one (3). To a stirred
solution of 8 (1.0 g, 4.46 mmol) in pyridine (25 mL) was
added dropwise triflic anhydride (0.83 mL, 4.91 mmol) at
210 8C, and then the mixture was stirred at 0 8C for 3.5 h.
After addition of ice–water, the resulting mixture was
1
1577, 1281, 1254, 1149, 1057 cm21; H NMR (400 MHz,

S. Kamisuki et al. / Tetrahedron 60 (2004) 5695–5700
5699
CDCl3): d 1.73 (6H, s), 2.04 (3H, s), 3.50 (3H, s), 3.55 (3H,
s), 3.85 (3H, s), 5.16 (1H, d, J¼6.6 Hz), 5.22 (1H, d, J¼
6.7 Hz), 5.23 (1H, d, J¼6.6 Hz), 5.30 (1H, d, J¼6.7 Hz),
6.44 (1H, d, J¼2.7 Hz), 6.45 (1H, d, J¼2.7 Hz), 6.91 (1H,
s), 7.02 (1H, s); 13C NMR (100 MHz, CDCl3): d 19.4, 25.3,
26.1, 55.7, 56.2, 56.2, 95.4, 95.9, 100.5, 105.0, 105.7, 113.2,
117.0, 117.6, 129.3, 134.1, 144.8, 146.5, 146.6, 158.5,
158.9, 164.6; HRMS calcd for C22H26O8Na [MþNa]þ
441.1519, found 441.1518. Anal. Found: C, 63.02; H, 6.51.
Calcd for C22H26O8: C, 63.15; H, 6.26.
a 10% HCl solution in methanol (3 mL) and the mixture was
stirred at rt for 12 h. After addition of NaHCO3, the resulting
mixture was filtered through a pad of celite, and concen-
trated. The residue was diluted with water, and acidified
with cold HCl solution. The resulting mixture was extracted
with EtOAc, washed with brine, dried and concentrated.
The residue was treated with dichloromethane to give 2
(158 mg, 62% from 12) as crystalline solids. The mother
liquor was purified by preparative TLC {hexane–EtOAc–
AcOH (25:25:1)} to give additional 2 (6 mg, 2%) as
crystalline solids.
3.1.6. 4,4,5,5-Tetramethyl-2-(5-methyl-1,3-benzodioxol-
6-yl)-1,3,2-dioxaborolane (5). To a stirred mixture of 14
(5.27 g, 20.1 mmol), bis(pinacolato)diboron (5.78 g,
22.8 mmol), and potassium acetate (5.99 g, 61.0 mmol) in
N,N0-dimethylformamide (150 mL) was added dichloro-
[1,1 -bis(diphenylphosphino)ferrocene]palladium {PdCl2-
(dppf), 1.42 g, 1.94 mmol}. The mixture was stirred at 80 8C
for 21 h, cooled and then diluted with EtOAc. The resulting
mixture was filtered through a pad of celite, washed with
brine, dried and concentrated. Chromatography on silica gel
with hexane–EtOAc (9:1) as the eluent yielded 5 (4.29 g,
81%) as white solids: mp 64–65 8C; IR (KBr) 2974, 2931,
2885, 1612, 1423, 1369, 1311, 1296, 1146, 1111 cm21; 1H
NMR (400 MHz, CDCl3): d 1.32 (12H, s), 2.47 (3H, s), 5.90
(2H, s), 6.65 (1H, s), 7.21 (1H, s); 13C NMR (100 MHz,
CDCl3): d 21.9, 24.8, 83.2, 100.6, 110.5, 114.7, 140.4,
144.9, 149.7; HRMS calcd for C14H19BO4Na [MþNa]þ
285.1268, found 285.1271. Anal. Found: C, 64.19; H, 7.27.
Calcd for C14H19BO4: C, 64.15; H, 7.31.
(ii) To a stirred solution of 12 (19.4 mg, 0.0464 mmol) in
dichloromethane (1 mL) was added dropwise a 1.0 M
solution of boron trichloride (BCl3) in dichloromethane
(0.46 mL) at 0 8C. The mixture was warmed slowly to rt and
then stirred for 19.5 h. After addition of water, the resulting
mixture was extracted with EtOAc. The extracts was
washed with water, dried and concentrated. Chroma-
tography on silica gel with chloroform–methanol–acetic
acid (95:5:1!90:10:1) as the eluent yielded 2 (8.5 mg,
63%) as crystalline solids.
3.1.9. Altenusin (2) from 15. To a stirred solution of 15
(71.2 mg, 0.208 mmol) in dichloromethane (1 mL) was
added dropwise a 1.0 M solution of BCl3 in dichloro-
methane (1 mL) and then stirred for 19 h. Treatment as
described above yielded 2 (48.1 mg, 80%): mp 192–194 8C
(lit.7 194–196 8C); IR (KBr) 3309, 3012, 2974, 1651, 1612,
1
1577, 1520, 1254, 1207, 1157 cm21; H NMR (400 MHz,
CD3OD): d 1.90 (3H, s), 3.80 (3H, s), 6.16 (1H, d, J¼
2.6 Hz), 6.42 (1H, d, J¼2.6 Hz), 6.48 (1H, s), 6.57 (1H, s);
13C NMR (100 MHz, CD3OD): d 19.3, 55.9, 100.5, 107.0,
111.4, 116.6, 117.3, 127.3, 135.3, 143.2, 144.9, 148.0,
164.9, 165.8, 174.3; HRMS calcd for C15H14O6Na
[MþNa]þ 313.0682, found 313.0691.
3.1.7. 7-Methoxy-2,2-dimethyl-5-(5-methyl-1,3-benzo-
dioxol-6-yl)-4H-1,3-benzodioxin-4-one (15). To a stirred
mixture of 3 (2.33 g, 6.54 mmol), 5 (2.23 g, 8.51 mmol),
potassium carbonate (2.71 g, 19.6 mmol) in 1,2-dimeth-
oxyethane (10 mL) was added PdCl2(dppf) (240 mg,
0.328 mmol), and the mixture was stirred at 85 8C for
10 h, cooled, diluted with EtOAc, and filtered through a pad
of celite. The filtrate was washed successively with water
and brine, dried and concentrated. Chromatography on
silica gel with hexane–EtOAc (9:1!4:1!1:1) as the eluent
yielded 15 (1.50 g, 67%) white solids: mp 170–171 8C
{hexane–EtOAc (5:1)}; IR (KBr) 2997, 2943, 2904, 1732,
3.1.10. Dehydroaltenusin (1). To a stirred solution of 2
(102 mg, 0.35 mmol) in ethanol–water (1:1, 2.2 mL) was
added dropwise a 0.2 M solution of ferric chloride in water
(ca. 4.0 mL) at rt. After 10 min, a yellow precipitate formed
was filtered, washed with water, dried, and recrystallized
from methanol–dichloromethane to 1 (62.1 mg, 61%) as
yellow needles. The mother liquid collected was concen-
trated, subject to chromatography on silica gel {hexane–
EtOAc (1:1)} and recrystallized from methanol–dichloro-
methane to additional 1 (20.6 mg, 21%) as yellow needles:
mp 189–190 8C (lit.5 189–190 8C); IR (KBr) 3383, 3124,
2978, 1674, 1643, 1624, 1392, 1296, 1261, 1227, 1196,
1161, 1076 cm21; 1H NMR (400 MHz, CDCl3): d 1.73 (3H,
s), 3.91 (3H, s), 6.28 (1H, s), 6.41 (1H, s), 6.63 (1H, d, J¼
2.4 Hz), 6.69 (1H, s), 6.73 (1H, d, J¼2.4 Hz), 11.29 (1H, s);
13C NMR (100 MHz, CDCl3): d 29.6, 56.0, 79.1, 99.8,
103.6, 104.3, 116.1, 120.7, 134.9, 145.9., 152.9, 164.5,
166.2, 167.2, 180.6; HRMS calcd for C15H11O6 [M2H]2
287.0561, found 287.0570.
1608, 1577, 1485, 1281, 1203, 1030 cm21 1H NMR
;
(400 MHz, CDCl3): d 1.73 (6H, s), 2.02 (3H, s), 3.85 (3H,
s), 5.95 (1H, d, J¼9.0 Hz), 5.96 (1H, d, J¼9.0 Hz), 6.42
(1H, d, J¼2.5 Hz), 6.45 (1H, d, J¼2.5 Hz), 6.59 (1H, s),
6.70 (1H, s); 13C NMR (100 MHz, CDCl3): d 19.6, 25.2,
26.0, 55.6, 100.5, 100.8, 105.0, 105.7, 108.5, 109.8, 113.1,
128.1, 132.9, 145.2, 146.8, 146.8, 158.5, 158.8, 164.6;
HRMS calcd for C19H18O6Na [MþNa]þ 365.0995, found
365.1001. Anal. Found: C, 66.54; H, 5.53. Calcd for
C19H18O6: C, 66.66; H, 5.30.
3.1.8. Altenusin (2) from 12. (i) A solution of 12 (367 mg,
0.88 mmol) in 2 M KOH–ethanol (1:1, 52 mL) was heated
at 60 8C with stirring for 40 min, cooled and then diluted
with water. The resulting mixture was washed with
dichloromethane. The aqueous layer was acidified with
cold HCl solution, and then extracted with EtOAc. The
extracts were washed with brine, dried, and concentrated to
give a syrup (238 mg), which was dissolved in dichloro-
methane–methanol (2:1, 9 mL). To this solution was added
Acknowledgements
This work was supported in part by Grant-in-Aid for JSPS
Fellows from the Ministry of Education, Culture, Sports,
Science and Technology of Japan, and the Chemical

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S. Kamisuki et al. / Tetrahedron 60 (2004) 5695–5700
Sugawara, F.; Sakaguchi, K.; Mizushina, Y. Biochem.
Pharm. 2002, 63, 421–427.
Biology Project (RIKEN). We express our thanks to Ms E.
Satake (Tokyo University of Science) for the elemental
analyses.
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