Synthetic methods for the preparation of ARQ 501 (β-Lapachone) human blood metabolites

Article abstract of DOI:10.1016/j.bmc.2008.03.073

ARQ 501 (3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b] pyran-5,6-dione), a synthetic version of β-Lapachone, is a promising anti-cancer agent currently in multiple Phase II clinical trials. Promising anti-cancer activity was observed in Phase I and Phase II trials. Metabolism by red blood cells of drugs is an understudied area of research and the metabolites arising from oxidative ring opening (M2 and M3), decarbonylation/ring contraction (M5), and decarbonylation/oxidation (M4 and M6) of ARQ 501 offer a unique opportunity to provide insight into these metabolic processes. Since these metabolites were not detected in in vitro incubations of ARQ 501 with liver microsomes and were structurally diverse, confirmation by chemical synthesis was considered essential. In this report, we disclose the synthetic routes employed and the characterization of the reference standards for these blood metabolites as well as additional postulated structures, which were not confirmed as metabolites.

Full text of DOI:10.1016/j.bmc.2008.03.073

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 5635–5643
Synthetic methods for the preparation of ARQ 501
(b-Lapachone) human blood metabolites
Rui-Yang Yang, Darin Kizer, Hui Wu, Erika Volckova, Xiu-Sheng Miao, Syed M. Ali,
Manish Tandon, Ronald E. Savage, Thomas C. K. Chan and Mark A. Ashwell*
ArQule Inc., 19 Presidential Way, Woburn, MA 01801, USA
Received 14 December 2007; revised 25 March 2008; accepted 28 March 2008
Available online 1 April 2008
Abstract—ARQ 501 (3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b] pyran-5,6-dione), a synthetic version of b-Lapachone, is a prom-
ising anti-cancer agent currently in multiple Phase II clinical trials. Promising anti-cancer activity was observed in Phase I and Phase
II trials. Metabolism by red blood cells of drugs is an understudied area of research and the metabolites arising from oxidative ring
opening (M2 and M3), decarbonylation/ring contraction (M5), and decarbonylation/oxidation (M4 and M6) of ARQ 501 offer a
unique opportunity to provide insight into these metabolic processes. Since these metabolites were not detected in in vitro incuba-
tions of ARQ 501 with liver microsomes and were structurally diverse, confirmation by chemical synthesis was considered essential.
In this report, we disclose the synthetic routes employed and the characterization of the reference standards for these blood metab-
olites as well as additional postulated structures, which were not confirmed as metabolites.
ꢀ 2008 Elsevier Ltd. All rights reserved.
1. Introduction
tissues and is frequently not studied for its metabolic ef-
fects on drug molecules.3 In the course of developing
pharmacokinetic methods for ARQ 501, it was observed
that not only did ARQ 501 partition into red blood cells
but was also metabolized rapidly in whole blood
although not in plasma.4
b-Lapachone (3,4-dihydro-2,2-dimethyl-2H-naphthol[1,
2-b] pyran-5,6-dione), a natural product found in Pau
d’arco trees (Tabebuia impetiginosa), has broad anti-can-
cer activities. ARQ 501, a fully synthetic version of
b-Lapachone, elevates E2F-1 levels leading to the acti-
vation of the cell cycle checkpoint which results in the
selective apoptotic cell death of cancer cells1 and is effec-
tive against human ovarian cancer and prostate cancer
xenografts in mice.2 ARQ 501 is currently in multiple
Phase II clinical trials and promising anti-cancer activity
has been observed.
Figure 1 shows the results from in vitro time course
studies on the metabolism of [14C] ARQ 501 incubated
in human whole blood. Detection and identification of
metabolites was based on radioactive peak monitoring
and molecular ion detection using an accurate radioiso-
tope counting (LC-ARC) system.4 After 180 min incu-
bation at 37 ꢁC, ARQ 501 yielded four major
metabolites (M1, M2, M3, and M5) and two minor
metabolite peaks (M4 and M6). These metabolites were
not detected in in vitro incubations of ARQ 501 with li-
ver microsomes or hepatocytes. They therefore repre-
sented a unique opportunity to examine the effects of
an understudied metabolizing system (red blood cells)
on a promising Phase II drug.
The majority of drugs are metabolized by the liver with
other tissues such as the gastrointestinal tract, the lungs,
the skin, and the kidneys providing almost all the
remainder. There have been countless reports in the sci-
entific community describing studies to elucidate these
processes. However, blood is generally assumed to be
an inert vehicle for the transportation of drugs to target
Herein, we describe the preparation of these novel ARQ
501 human blood metabolites. In addition, we describe
the synthesis of several postulated metabolites suggested
by accurate mass measurements which failed to match
the chromatographic retention times and so were ruled
out as metabolites in this study.
Keywords: Synthesis; Human; Blood; Metabolites; ARQ 501; b-
Lapachone.
*
Corresponding author. Tel.: +1 781 994 0598; fax: +1 781 994
0678; e-mail: mashwell@arqule.com
URL: http://www.arqule.com
0968-0896/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.03.073

5636
R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
Figure 1. Radiochromatograms of [14C] ARQ 501 incubated in human whole blood at rt for 180 min.
2. Results and discussion
reaction. Cyclic anhydride 6 and metabolite M2 were
characterized by 1D and 2D NMR analysis.
2.1. Synthesis of postulated but unconfirmed metabolites,
M1
Metabolite M3 was prepared by regio-specific hydroge-
nation of the cyclic anhydride 6 using catalytic palla-
dium over barium sulfate as shown in Scheme 3. The
reduction occurred exclusively at the carbonyl attached
to the pyran ring, no reduction of the carbonyl attached
to benzene ring or hydrogenation of the double bond
was detected. The structure of metabolite M3 was as-
signed by 1D and 2D NMR analysis. The gHMBC (gra-
dient Heteronuclear Multiple Bond Correlation
spectroscopy) of M3 showed the expected three bond
correlations of the 4-proton with aldehyde carbon and
aldehyde proton with the 4-carbon (Fig. 3). This exper-
iment confirmed that the aldehyde is on the pyran ring
and the carboxylic acid is on the phenyl ring.
Accurate mass measurement experiments indicated that
metabolite M1 was produced by the oxidation of ARQ
501. A characteristic product ion at m/z 121 localized
the oxidation to the phenyl ring. Hydroxylated ring vari-
ants of ARQ 501 1a–d were thus postulated (Fig. 2) and
prepared as shown in Scheme 1. Methoxytetralones 2a–
d were oxidized to the corresponding methoxy-substi-
tuted 2-hydroxy-[1,4]-naphthoquinones 3a–d using the
literature procedures.5 The methoxy-substituted ARQ
501 isomers 5a–d were synthesized through allylation
followed by cyclization in concentrated sulfuric acid.
The treatment of 5a–d with boron tribromide followed
by concentrated sulfuric acid provided the correspond-
ing hydroxylated compounds 1a–d.6 The demethylation
of 5d proceeded in excellent yield (93%) to provide 1d,
presumably due to the neighboring carbonyl group
assistance, while the demethylation of 5a–c provided
low yields (7–27%) of the corresponding products 1a–
c. We ascribe this to the competing destruction of the
dihydropyran ring by boron tribromide. Disappoint-
ingly, the chromatographic retention time of M1 did
not match either of these hydroxylated ARQ 501 com-
pounds. M1 eluted much earlier and the structure re-
mains unconfirmed.
Metabolite M4 was prepared as shown in Scheme 4. The
7 with 3,3-dim-
allylation of 4-hydroxycoumarin
ethylallylbromide provided intermediate 8, which was
cyclized by treatment with sulfuric acid to give metabo-
lite M4.7 The structure of metabolite M4 was assigned
by 1D and 2D NMR analysis.
Metabolite M5 was synthesized by an analogous reac-
tion sequence as described for metabolite M4 except that
1,3-indanedione 9 was used as a starting material. The
allylation of indanedione 9 gave intermediate 10, and
the cyclization of 10 with sulfuric acid in THF gave
metabolite M5 (Scheme 5). The structure of metabolite
M5 was assigned by 1D and 2D NMR analysis.
2.2. Synthesis of blood metabolites M2–M6
Metabolites M2, M3, M5, and M6 have not been previ-
ously reported in the literature. M2 and M3 are prod-
ucts of oxidative ring opening of ARQ 501. Metabolite
M2 was synthesized concisely from ARQ 501 in two
steps as shown in Scheme 2. The oxidation of ARQ
501 with MCPBA (m-chloroperoxybenzoic acid) was
followed by aqueous hydrolysis. No epoxidation was
observed of the double bond in the MCPBA oxidation
Prior to the synthesis of the standard which confirmed
the structure of M4, it was postulated that the accurate
mass of M4 (C14H14O3) corresponded to a phenyl ring
hydroxylated form of M5 (Fig. 4). Two of these postu-
lated metabolites (11b and 11c) were prepared as shown
in Scheme 6. Compound 3c was converted to its corre-
sponding iodonium ylide 12, which was then thermally
transformed to 5-methoxyindan-1,3-dione 13, a method
described in the literature.8 Following allylation and
cyclization, a mixture of methoxy-substituted ring con-
traction compounds 15b and 15c was obtained in a 5:2
ratio. Demethylation of 15b and 15c with boron tribro-
mide resulted in 6:1 mixture of 11b and 11c. The struc-
1
tures of 11b and 11c were assigned based on H NMR
analysis. In compound 11b, the chemical shift of the
phenolic proton appears at lower field (d 10.22) due to
its relationship to para-electron-withdrawing carbonyl
group, as compared to that in 11c (d 10.00) whose elec-
tron-withdrawing carbonyl group is in the meta-posi-
Figure 2. Postulated metabolite structures of M1.

R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
5637
Scheme 1. Synthetic route for postulated structures 1a–d.
Scheme 2. Synthesis of metabolite M2.
sued after the match of M4 was confirmed with the lac-
tone compound as shown in Scheme 4.
Metabolite M6 was prepared as shown in Scheme 7. The
bromination of 2-acetylbenzoic acid 16, followed by
cyclization with sodium acetate provided lactone 18.9
The allylation of 18 afforded intermediate 19, which
was cyclized with sulfuric acid to give M6.
Scheme 3. Synthesis of metabolite M3.
3. Summary
The objective of the present work was to provide struc-
turally unambiguous reference standards, which could
be used to elucidate the underlying mechanisms by
which ARQ 501 is metabolized by red blood cells.
The five major human blood metabolites of ARQ 501
(M2–M6) confirmed in this work indicate that at least
one metabolite, M5 a novel decarbonylation/ring con-
traction product, may arise from a heretofore unknown
mechanism. In addition, metabolites M2 and M3 were
confirmed as oxidative ring opening products, and M4
and M6 as decarbonylation/oxidation products.
Figure 3. Key gHMBC correlations of M3, the direction of the arrows
indicates proton to carbon correlations.
tion. In compound 11c, the C6 proton is in the ortho-po-
sition relative to the electron-donating phenol group,
and appears at higher field (d 6.72) than the correspond-
ing C6 proton in compound 11b (d 7.13) where the C6 is
in meta-position relative to the phenol group. However,
chromatographic retention time of M4 matched neither
11b nor 11c. The synthesis of 11a and 11d was not pur-
With these structurally diverse metabolites available,
work is underway to identify the enzymes responsible
for the biotransformations of ARQ 501 in red blood
cells. Thus, this work provides materials with which to

5638
R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
Scheme 4. Synthesis of metabolite M4.
Scheme 5. Synthesis of metabolite M5.
study an often neglected route of metabolism (blood) of
a drug.
Metabolites (M2–M6) have been studied in pre-clinical
models and do not show anti-cancer activity.
4. Experimentals
Figure 4. Postulated structures of M4.
NMR spectra were recorded on a Varian Mercury
400 MHz NMR spectrometer and calibrated using tetra-
Scheme 6. Synthetic scheme for postulated structures 11b and 11c.

R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
5639
concentrated under reduced pressure to give the prod-
uct as an orange solid (1.03 g, 73%). 1H NMR
(400 MHz, DMSO-d6) d 11.36 (br s, 1H), 7.76 (t,
J = 8.2 Hz, 1H), 7.56 (d, J = 8.6 Hz, 1H), 7.49 (d,
J = 8.6 Hz, 1H), 6.08 (s, 1H), 3.93 (s, 3H); LCMS: m/
z 205 [M+H]+.
4.3. Synthesis of 2-hydroxy-7-methoxy-[1,4]naphthoqui-
none (3b)
Compound 3b was synthesized from 2b in 69% yield
using the same procedure as described for 3a. Mp
220–222 ꢁC; 1H NMR (400 MHz, DMSO-d6) d 11.58
(s, 1H), 7.89 (d, J = 8.6 Hz, 1H), 7.42 (d, J = 2.7 Hz,
1H), 7.35 (dd, J = 8.6, 2.5 Hz, 1H), 6.10 (s, 1H), 3.92
(s, 3H); LCMS: m/z 205 [M+H]+.
Scheme 7. Synthesis of metabolite M6.
methylsilane as an internal reference. Mass spectra were
obtained on
spectrometer.
a
Waters Micromass ZQ mass
4.4. Synthesis of 2-hydroxy-6-methoxy-[1,4]naphthoqui-
none (3c)
4.1. Synthesis of 8-methoxy-1-tetralone (2a)
Compound 3c was synthesized from 2c in 59% yield
using the same procedure as described for 3a. Mp
222–224 ꢁC; 1H NMR (400 MHz, DMSO-d6) d 11.82
(br s, 1H), 7.96 (d, J = 8.6 Hz, 1H), 7.35 (d,
J = 8.6 Hz, 1H), 7.29 (d, J = 8.6 Hz, 1H), 3.92 (s, 3H);
LCMS: m/z 204 [M+H]+.
A solution of 2-methoxy-6-methylbenzoic acid ethyl es-
ter (3.88 g, 20 mmol) in anhydrous tetrahydrofuran
(25 mL) was added dropwise into a solution of lithium
diisopropylamide (LDA) (13.75 mL, 22 mmol, 1.6 M in
tetrahydrofuran) at À78 ꢁC over 15 min. Methyl acry-
late (4.5 mL, 50 mmol) was added and the reaction
was warmed to 0 ꢁC and kept at that temperature for
5 h. The reaction was quenched by the addition of satu-
rated ammonium chloride (100 mL) and extracted with
dichloromethane (3· 200 mL). The combined organic
layers were evaporated under reduced pressure and the
resulting residue dissolved in a mixture of methanol/con-
centrated hydrochloric acid (4:1, 500 mL) and heated at
reflux overnight. The reaction mixture was evaporated
to dryness under reduced pressure and extracted with
dichloromethane (3· 100 mL). The combined organic
layers were washed with brine (100 mL), dried over so-
dium sulfate, and concentrated under reduced pressure.
The crude residue was purified by silica gel chromatog-
raphy (5–35% ethyl acetate in hexane) to give the prod-
4.5. Synthesis of 2-hydroxy-5-methoxy-[1,4]naphthoqui-
none (3d)
Compound 3d was prepared in 92% yield from 2d using
the same procedure as described for 3a.
4.6. Synthesis of 3-hydroxy-5-methoxy-2-(3-methylbut-2-
en-1-yl)-1,4-naphthoquinone (4a)
To a solution of 2-hydroxy-8-methoxy-[1,4]naphtho-
quinone (3a) (1.03 g, 5.0 mmol) in anhydrous dimeth-
ylsulfoxide (5 mL) were added 3,3-dimethylallyl
bromide
(0.65 mL,
5.55 mmol),
triethylamine
(0.77 mL, 5.55 mmol), and sodium iodide (831 mg,
5.55 mmol). The mixture was stirred at rt for 2 h,
heated at 45 ꢁC for 4 h and then poured into water
(100 mL), extracted with dichloromethane (3·
200 mL), washed successively with 10% sodium bicar-
bonate (200 mL), brine (200 mL), and dried over so-
dium sulfate. After filtration and evaporation of the
solvent under reduced pressure, the orange residue
was purified by silica gel chromatography (10–30%
ethyl acetate in hexane) to give the product as a yel-
low solid (150 mg, 11%). Mp 171–173 ꢁC; 1H NMR
(400 MHz, DMSO-d6) d 10.70 (s, 1H), 7.77 (t,
J = 7.8 Hz, 1H), 7.61 (d, J = 7.0 Hz, 1H), 7.48 (d,
J = 7.8 Hz, 1H), 5.12 (m, 1H), 3.92 (m, 3H), 3.10 (d,
J = 7.0 Hz, 2H); LCMS: m/z 273 [M+H]+.
1
uct (1.22 g, 34%) as a yellow oil. H NMR (400 MHz,
DMSO-d6)
d 7.42 (t, J = 8.2 Hz, 1H), 6.94 (d,
J = 8.2 Hz, 1H), 6.87 (d, J = 7.4 Hz, 1H), 3.77 (s, 3H),
2.86 (t, J = 6.2 Hz, 2H), 2.50–2.51 (m, 2H), 1.93 (t,
J = 6.2 Hz, 2H); LCMS: m/z 177 [M+H]+.
4.2. Synthesis of 2-hydroxy-8-methoxy-[1,4]naphthoqui-
none (3a)
Oxygen gas was bubbled into a solution of potassium
tert-butoxide (1 M in tert-butanol, 60 mL, 60 mmol)
for 30 min, 8-methoxytetralone (2a) (1.22 g, 6.93 mmol)
was added, and oxygen was bubbled through the reac-
tion mixture for an additional 4 h. The mixture was
cooled to 0 ꢁC, quenched by the addition of 1 M
hydrochloric acid (100 mL), and extracted with dichlo-
romethane (3· 500 mL). The combined organic layers
were extracted with 1 M sodium hydroxide (3·
200 mL), re-acidified with concentrated hydrochloric
acid (20 mL), and extracted with dichloromethane (3·
500 mL). The combined organic layers were washed
with brine, dried over sodium sulfate, filtered, and
4.7. Synthesis of 3-hydroxy-6-methoxy-2-(3-methyl-bu-2-
enyl)-[1,4]naphthoquinone (4b)
Compound 4b was prepared in 21% yield from 3b using
the same procedure as described for 4a. 1H NMR
(400 MHz, CDCl3) d 8.05 (d, J = 8.4 Hz, 1H), 7.51 (d,
J = 2.8 Hz, 1H), 7.20 (dd, J = 8.8, 2.8 Hz, 1H), 5.20

5640
R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
(m, 1H), 3.29 (d, J = 6.8 Hz, 2H), 1.79 (s, 3H), 1.69 (s,
3H); LCMS: m/z 273 [M+H]+.
4.13. Synthesis of 10-methoxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (5d)
4.8. Synthesis of 2-hydroxy-6-methoxy-3-(3-methylbut-2-
en-1-yl)naphthoquinone (4c)
Compound 5d was prepared in 67% yield from 4d using
the same procedure as described for 5a. Mp 145–146 ꢁC;
1H NMR (400 MHz, CDCl3) d 7.77 (d, J = 8.8 Hz, 1H),
7.60 (t, J = 8.0 Hz, 1H), 7.28 (d, J = 8.0 Hz, 1H), 4.00 (s,
3H), 2.60 (t, J = 6.8 Hz, 2H), 1.79 (t, J = 6.8 Hz, 2H),
1.41 (s, 6 H); LCMS: m/z 273 [M+H]+.
Compound 4c was prepared in 18% yield from 3c using
the same procedure as described for 4a. Mp 113–115 ꢁC;
1H NMR (400 MHz, DMSO-d6) d 10.97 (br s, 1H), 7.95
(d, J = 8.6 Hz, 1H), 7.41 (d, J = 2.7 Hz, 1H), 7.28 (dd,
J = 2.7, 8.6 Hz, 1H), 5.12 (m, 1H), 3.92 (s, 3H), 3.14
(d, J = 7.0 Hz, 2H), 1.70 (s, 3H), 1.62 (s, 3H); LCMS:
m/z 273 [M+H]+. Anal. Calcd for C16H16O4: C, 70.58;
H, 5.92. Found: C, 70.76; H, 5.69.
4.14. Synthesis of 7-hydroxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (1a)
To a solution of 7-methoxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (5a) (50 mg, 0.18
mmol) in anhydrous dichloromethane at 0 ꢁC was added
boron tribromide (0.71 mL, 0.71 mmol, 1.0 M in
dichloromethane) dropwise. After stirring for 15 min,
the mixture was allowed to warm to rt and stirred for
2 h. The reaction mixture was quenched by the addition
of ice water (15 mL), and extracted with dichlorometh-
ane (3· 20 mL). The combined organic layers were dried
and concentrated under reduced pressure. The resulting
residue was taken up in a concentrated sulfuric acid
(5 mL) and stirred at rt for 30 min. The mixture was di-
luted with water (20 mL) and extracted with dichloro-
methane (3· 20 mL). The combined extracts were
dried, concentrated under reduced pressure, and purified
by silica gel chromatography (20–80% ethyl acetate in
hexane) to give the product as a red-orange solid
4.9. Synthesis of 3-hydroxy-8-methoxy-2-(3-methyl-bu-2-
enyl)-[1,4]naphthoquinone (4d)
Compound 4d was prepared in 28% yield from 3d using
the same procedure as described for 4a. Mp 122–124 ꢁC;
1H NMR (400 MHz, CDCl3) d 7.76–7.74 (m, 1H), 7.63–
7.59 (m, 1H), 7.33 (d, J = 8.8 Hz, 1H), 7.07 (s, 1H),
5.24–5.20 (m, 1H), 4.01 (s, 3H), 3.28 (d, J = 8.0 Hz,
2H), 1.79 (s, 3H), 1.67 (s, 3H); LCMS: m/z 273 [M+H]+.
4.10. Synthesis of 7-methoxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (5a)
Concentrated sulfuric acid (5 mL) was added to 3-hy-
droxy-5-methoxy-2-(3-methylbut-2-en-1-yl)-1,4-naph-
thoquinone (4a) (150 mg, 0.87 mmol) at rt. The mixture
was stirred for 1 h and then diluted with ice water
(100 mL). The resulting solution was extracted with
ethyl acetate (3· 100 mL), washed with brine
(100 mL), dried over sodium sulfate, and concentrated
under reduced pressure. The crude solid was purified
by silica gel chromatography (30–50% ethyl acetate in
hexane) to give the product as an orange solid (62 mg,
41%). Mp 156–157 ꢁC; 1H NMR (400 MHz, DMSO-
d6) d 7.57 (t, J = 7.8 Hz, 1H), 7.48 (d, J = 7.4 Hz, 1H),
3.97 (s, 3H), 2.54 (t, J = 6.6 Hz, 1H), 1.84 (t,
J = 6.6 Hz, 2H); LCMS: m/z 273 [M+H]+.
1
(13.6 mg, 27%). Mp 163–165 ꢁC; H NMR (400 MHz,
DMSO-d6) d 11.75 (s, 1H), 7.68 (t, J = 7.8 Hz, 1H),
7.32 (d, J = 7.8 Hz, 1H), 7.12 (d, J = 7.8 Hz, 1H), 2.54
(t, J = 6.6 Hz, 1H), 1.82 (t, J = 6.6 Hz, 2H); LCMS: m/
z 259 [M+H]+.
4.15. Synthesis of 8-hydroxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (1b)
Compound 1b was prepared in 17% yield from com-
pound 5b using the same procedure as described for
1
1a. Mp 211–213 ꢁC; H NMR (400 MHz, DMSO-d6) d
10.49 (s, 1H), 7.61 (d, J = 8.4 Hz, 1H), 7.27 (d,
J = 2.8 Hz, 1H), 7.09 (dd, J = 8.8, 2.8 Hz, 1H), 2.35 (t,
J = 6.4 Hz, 2H), 1.80 (t, J = 6.4 Hz, 2H), 1.40 (s, 6H);
LCMS: m/z 259 [M+H]+.
4.11. Synthesis of 8-methoxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (5b)
Compound 5b was synthesized in 91% yield from 4b
using the same procedure as described for 5a. Mp
162–163 ꢁC; 1H NMR (400 MHz, CDCl3) d 7.71 (d,
J = 8.8 Hz, 1H), 7.55 (d, J = 2.0 Hz, 1H), 7.11 (dd,
J = 8.4, 2.4 Hz, 1H), 3.84 (s, 3H), 2.54 (t, J = 6.4 Hz,
2H), 1.83 (t, J = 6.4 Hz, 2H), 1.45 (s, 6H); LCMS: m/z
273 [M+H]+.
4.16. Synthesis of 9-hydroxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (1c)
Compound 1c was prepared in 7% yield from 5c using
the same procedure as described for 1a. Mp 257–
1
260 ꢁC; H NMR (400 MHz, DMSO-d6) d 10.89 (br s,
1H), 7.82 (d, J = 8.6 Hz, 1H), 7.14 (d, J = 2.3 Hz, 1H),
7.12 (dd, J = 2.3, 8.6 Hz, 1H), 3.90 (s, 3H), 2.38 (t,
J = 6.6 Hz, 2H) 1.80 (t, J = 6.6 Hz, 2H) 1.40 (s, 6H);
LCMS: m/z 273 [M+H]+.
4.12. Synthesis of 9-methoxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (5c)
Compound 5c was prepared in 72% yield from 4c using
the same procedure as described for 5a. Mp 158–160 ꢁC;
1H NMR (400 MHz, DMSO-d6) d 7.91 (d, J = 8.6 Hz,
1H), 7.20 (d, J = 2.3 Hz, 1H), 7.12 (dd, J = 2.7, 8.6 Hz,
1H), 3.90 (s, 3H), 2.39 (t, J = 6.6 Hz, 2H), 1.82 (t,
J = 6.6 Hz, 2H) 1.41 (s, 6H); LCMS: m/z 273 [M+H]+.
4.17. Synthesis of 10-hydroxy-2,2-dimethyl-3,4-dihydro-
2H-benzo[h]chromene-5,6-dione (1d)
Compound 1d was prepared in 93% yield from 5d using
the same procedure as described for 1a. Mp 150–152 ꢁC;

R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
5641
1H NMR (400 MHz, CDCl3) d 12.39 (s, 1H), 7.63 (d,
J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 7.21 (d,
J = 1.6 Hz, 1H), 2.60 (t, J = 8.0 Hz, 2H), 1.83 (t,
J = 8.0 Hz, 2H), 1.43 (s, 6H); LCMS: m/z 258 [M+H]+.
tered and concentrated to dryness under reduced pres-
sure. The residue was purified by preparative reverse
phase HPLC to afford 2-(3-formyl-6,6-dimethyl-5,6-
dihydro-4H-pyran-2-yl)-benzoic acid (M3) as a white
solid (68 mg, 34%). Mp 146–147 ꢁC; 1H NMR
(400 MHz, CDCl3) d 9.20 (s, 1H), 8.10 (dd, J = 8.0,
1.2 Hz, 1H), 7.61 (td, J = 7.6, 1.2 Hz, 1H), 7.56 (td,
J = 7.6, 1.6 Hz, 1H), 7.40 (dd, J = 7.2, 1.2 Hz, 1H),
2.43 (t, J = 6.8 Hz, 2H), 1.79 (t, J = 6.4 Hz, 2H), 1.37
(s, 6 H); 13C NMR (400 MHz, CDCl3) d 191.57,
172.54, 171.26, 135.10, 132.65, 132.48, 131.60, 130.16,
130.10, 114.02, 79.58, 31.87, 26.73, 16.11; LCMS:
m/z 261 [M+H]+; HRMS: Calcd 261.1127. Found:
261.1136.
4.18. Synthesis of 2,2-dimethyl-3,4-dihydro-2H-1,6-diox-
an-dibenzo[a,c]cycloheptene-5,7-dione (6)
A solution of MCPBA (77%, 493 mg, 2.2 mmol) in
dichloromethane (10 mL) was dried over sodium sulfate.
The dried solution was added to a solution of ARQ 501
(484 mg, 2 mmol) in dichloromethane (10 mL) and the
resulting mixture stirred at rt for 24 h. After concentrat-
ing the reaction mixture, dichloromethane (5 mL) was
added and the white solid was filtered off. The filtrate
was concentrated under reduced pressure and the resi-
due purified by chromatography on a silica gel (1–20%
ethyl acetate in hexane) to provide 2,2-dimethyl-3,4-
dihydro-2H-1,6-dioxan-dibenzo[a,c]cycloheptene-5,7-
dione (6) as a white solid (265 mg, 51%). Mp 104–
4.21. Synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyr-
ano[3,2-c]chromen-5-one (M4)
To a solution of 4-hydroxycoumarine (7) (0.30 g,
1.85 mmol) in DMSO (10 mL) was added 3,3-dimethyl-
allyl bromide (0.24 mL, 2.04 mmol), sodium iodide
(0.28 g, 1.85 mmol), and triethylamine (0.28 mL,
2.04 mmol). The reaction was stirred at rt for 2 h, then
heated at 45 ꢁC for 3 h. A mixture of ethyl acetate and
water (5:1, 180 mL) was added to the reaction mixture.
The organic layer was separated and washed with water
(30 mL), brine (50 mL), dried over sodium sulfate, fil-
tered, and concentrated to dryness under reduced pres-
sure. The crude product was purified by silica gel
chromatography (15% ethyl acetate in hexane) to afford
intermediate 8 as a white solid (0.21 g, 49%). LC/MS
was used to confirm the expected [M+H]+ of 231 m/z.
Intermediate 8 (40 mg) was dissolved in concentrated
sulfuric acid (2 mL) and stirred at rt for 1 h. Ice water
(30 mL) was added to quench the reaction. The reaction
mixture was extracted with ethyl acetate (3· 80 mL) and
the combined organic extracts were washed with water
(50 mL), brine (50 mL), dried over sodium sulfate, fil-
tered, and concentrated to dryness under reduced pres-
sure. The crude product was purified by silica gel
chromatography (20% ethyl acetate in hexane) to afford
2,2-dimethyl-3,4-dihydro-2H-pyrano[3,2-c]chromen-5-
one (M4) as a white solid (20 mg, 50 %). Mp 115–
117 ꢁC; 1H NMR (400 MHz, DMSO-d6) d 7.74 (d,
J = 7.2 Hz, 1H), 7.61 (t, J = 8.0 Hz, 1H), 7.39–7.33 (m,
2H), 2.45 (t, J = 6.4 Hz, 2H), 1.87 (t, J = 6.4 Hz, 2H),
1.41 (s, 6H); 13C NMR (400 MHz, CDCl3) d 163.52,
159.38, 152.67, 131.44, 123.85, 122.65, 116.74, 116.43,
99.84, 78.31, 32.14, 26.84, 17.59; LCMS: m/z 231
[M+H]+; HRMS: Calcd 231.1021. Found: 231.1025.
1
107 ꢁC; H NMR (400 MHz, CDCl3) d 7.86–7.80 (m,
2H), 7.65 (td, J = 8.0, 1.2 Hz, 1H), 7.54 (td, J = 8.0,
1.2 Hz, 1H), 2.66 (t, J = 6.8 Hz, 2H), 1.83 (t,
J = 6.8 Hz, 2H), 1.42 (s, 6H); 13C NMR (400 MHz,
CDCl3) d 163.17, 161.70, 156.27, 133.12, 131.67,
130.83, 130.72, 129.55, 126.99, 104.89, 77.99, 31.87,
26.81, 22.06; LCMS: m/z 259 [M+H]+.
4.19. Synthesis of 2-(2-carboxy-phenyl)-6,6-dimethyl-5,6-
dihydro-4H-pyran-3-carboxylic acid (M2)
2,2-Dimethyl-3,4-dihydro-2H-1,6-dioxan-dibenzo[a,c]cy-
cloheptene-5,7-dione (6) (52 mg, 0.2 mmol) was dissolved
in a mixture of THF (5 mL) and water (3 mL), and the
resulting solution stirred at rt for 14 h. The reaction mix-
ture was extracted with ethyl acetate (3· 5 mL) and the
combined organic extracts dried over sodium sulfate.
After filtration and concentration under reduced pressure,
ether (5 mL) was added to the residue and the white solid
collected by filtration to give 2-(2-carboxy-phenyl)-6,6-di-
methyl-5,6-dihydro-4H-pyran-3-carboxylic acid (M2)
(49 mg, 89%). Mp 185–187 ꢁC; 1H NMR (400 MHz,
DMSO-d6) d 12.00 (br, 2H), 7.79 (d, J = 7.2 Hz, 1H),
7.49 (t, J = 7.6 Hz, 1H), 7.40 (t, J = 7.6 Hz, 1H), 7.19 (d,
J = 8.0 Hz, 1H), 2.33 (t, J = 6.4 Hz, 2H), 1.69 (t,
J = 6.4 Hz, 2H), 1.26 (s, 6H); 13C NMR (400 MHz,
DMSO-d6) d 169.01, 168.04, 162.82, 139.62, 131.65,
131.07, 130.86, 129.94, 128.54, 100.99, 76.82, 32.30,
26.85, 20.28; LCMS: m/z 299 [M+Na]+, 277 [M+H]+,
259 [M+HÀH2O]+; HRMS: Calcd 277.1076. Found:
277.1080.
4.22. Synthesis of 2-(3-methylbut-2-enyl)-indan-1,3-dione
(10)
4.20. Synthesis of 2-(3-formyl-6,6-dimethyl-5,6-dihydro-
4H-pyran-2-yl)-benzoic acid (M3)
To a solution of 1,3-indanedione (9) (146 mg, 1.0 mmol)
in chloroform (2 mL) were added 3,3-dimethylallyl bro-
mide (149 mg, 1.0 mmol) and potassium carbonate
(138 mg, 1.0 mmol). The reaction mixture was stirred
at rt for 18 h and then filtered to remove the solid.
The filtrate was immediately loaded onto a silica gel col-
umn and eluted with 10% ethyl acetate in hexane to give
2-(3-methylbut-2-enyl)-indan-1,3-dione (10) as a yellow
solid (35 mg, 16%). Mp 63–65 ꢁC; 1H NMR
To a solution of 2,2-dimethyl-3,4-dihydro-2H-1,6-diox-
an-dibenzo[a,c]cycloheptene-5,7-dione (6) (200 mg,
0.78 mmol) in ethyl acetate (10 mL) was added Pd/
BaSO4 (30 mg). A hydrogen balloon was attached and
the system was evacuated and filled with hydrogen three
times. The reaction mixture was stirred under hydrogen
for 6 h (LCMS showed 60% of product formation with
36% of starting material). The reaction mixture was fil-

5642
R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
(400 MHz, CDCl3) d 7.98–7.95 (m, 2H), 7.85–7.82 (m,
2H), 5.01 (t, J = 1.2 Hz, 1H), 3.06 (t, J = 5.2 Hz, 1H),
2.72 (t, J = 6.8 Hz, 2H), 1.63 (s, 3H), 1.57 (s, 3H);
LCMS: m/z 215 [M+H]+.
2.48 mmol), and potassium carbonate (941 mg,
6.81 mmol) in dichloromethane (25 mL) was stirred
at rt. The reaction was followed closely by LC/MS.
The reaction was stopped when the monoallylation
product (30%) no longer increased, while the diallyla-
tion product (20%) increased more rapidly. The reac-
tion mixture was filtered through Celite and the
filtrate concentrated under reduced pressure. The resi-
due was purified by chromatography on a silica gel (1–
20% ethyl acetate in hexane) to provide the product
(201 mg, 36%). 1H NMR (400 MHz, CDCl3) d 7.88
(dd, J = 7.6, 2.8 Hz, 1H), 7.35–7.31 (m, 2H), 5.03–
4.98 (m, 1H), 3.96 (s, 3H), 3.05 (t, J = 5.6 Hz, 1H),
2.70 (t, J = 6.8 Hz, 2H), 1.63 (s, 3H), 1.57 (s, 3H);
LCMS: m/z 245 [M+H]+.
4.23. Synthesis of 2,2-dimethyl-3,4-dihydro-2H-inde-
no[1,2-b]pyran-5-one (M5)
Concentrated sulfuric acid (5 mL) was added dropwise
to a solution of 2-(3-methylbut-2-en-1-yl)-1H-indene-
1,3(2H)-dione (10) (1.5 g, 7.0 mmol) in THF (100 mL)
at rt. The mixture was stirred for 1 h and then diluted
with ice water (100 mL). The resulting solution was ex-
tracted with ethyl acetate (3· 100 mL), washed with
brine (100 mL), dried over sodium sulfate, and concen-
trated under reduced pressure. The crude solid was puri-
fied by preparative reverse phase HPLC and silica gel
chromatography (100% CHCl3) to give 2,2-dimethyl-
3,4-dihydro-2H-indeno[1,2-b]pyran-5-one (M5) (130
4.27. Synthesis of 8-methoxy-2,2-dimethyl-3,4-dihydro-
2H-indeno[1,2-b]pyran-5-one (15b) and 7-methoxy-2,2-
dimethyl-3,4-dihydro-2H-indeno[1,2-b]pyran-5-one (15c)
1
mg, 8.6%) as a yellow solid. Mp 53–55 ꢁC; H NMR
(400 MHz, DMSO-d6) d 7.41–7.29 (m, 3H), 7.12 (d,
J = 6.8 Hz, 1H), 2.20 (t, J = 6.4 Hz, 2H), 1.78 (t,
J = 6.4 Hz, 2H), 1.41 (s, 6H); 13C NMR (400 MHz,
CDCl3) d 193.62, 173.99, 138.69, 133.99, 131.89,
129.82, 120.91, 117.64, 106.51, 81.28, 32.86, 26.78,
14.47; LCMS: m/z 215 [M+H]+; HRMS: Calcd
215.1076. Found: 215.1080.
5-Methoxy-2-(3-methyl-but-2-enyl)-indan-1,3-dione (14)
(201 mg, 0.82 mmol) was dissolved in THF (5 mL). Con-
centrated sulfuric acid was added dropwise until the
solution turned to orange-dark brown. The reaction
mixture was stirred at rt until the reaction was complete
as indicated by LC/MS. The reaction mixture was then
poured into ice water (50 mL) and extracted with ethyl
acetate (3· 50 mL). The combined organic extracts were
washed with water (3· 50 mL) and dried over sodium
sulfate. After filtration and concentration under reduced
pressure, the residue was purified by chromatography on
a silica gel (5–40% ethyl acetate in hexane) to give the
product (clear oil) (172 mg, 85%) as an approximately
5:2 mixture of two regio-isomers with the major product
identified as 15b: 1H NMR (400 MHz, CDCl3) d 7.29 (d,
J = 8.0 Hz, 1H), 6.68 (d, J = 2.4 Hz, 1H), 6.60 (dd,
J = 7.6, 2.4 Hz, 1H), 3.82 (s, 3H), 2.29 (t, J = 6.4 Hz,
2H), 1.75 (t, J = 6.4 Hz, 2H), 1.42 (s, 6H); LCMS: m/z
245 [M+H]+. Compound 15c: 1H NMR (400 MHz,
CDCl3) d 7.00 (d, J = 2.0 Hz, 1H), 6.98 (d, J = 8.0 Hz,
1H), 6.67 (dd, J = 8.0, 2.4 Hz, 1H), 3.80 (s, 3H),
2.29 (t, J = 6.4 Hz, 2H), 1.75 (t, J = 6.4 Hz, 2H), 1.42
(s, 6H).
4.24. Synthesis of 7-methoxy-1,4-dioxo-3-(phenyliodo-
nio)-1,4-dihydronaphthalen-2-olate (12)
(Diacetoxyiodo)benzene (7.6 g, 23.6 mmol) was added
to a suspension of 2-hydroxy-7-methoxy-[1,4]naphtho-
quinone (3c) (4.8 g, 23.6 mmol) in chloroform (50 mL)
at 0 ꢁC. The reaction mixture was warmed and stirred
at rt for 5 h. After concentration under reduced pres-
sure, ethyl acetate (50 mL) was added to the residue
and the light orange solid product (12) was collected
1
by filtration (6.1 g, 63 %). Mp 204–209 ꢁC; H NMR
(400 MHz, DMSO-d6) d 7.99 (d, J = 8.8 Hz, 1H), 7.86–
7.82 (m, 2H), 7.55–7.49 (m, 1H), 7.43–7.37 (m, 3H),
7.34 (dd, J = 8.4, 2.8 Hz, 1H), 3.90 (s, 3H); LCMS:
m/z 407 [M+H]+.
4.25. Synthesis of 5-methoxy-indan-1,3-dione (13)
4.28. Synthesis of 8-hydroxy-2,2-dimethyl-3,4-dihydro-
2H-indeno[1,2-b]pyran-5-one (11b) and 7-hydroxy-2,2-
dimethyl-3,4-dihydro-2H-indeno[1,2-b]pyran-5-one (11c)
7-Methoxy-1,4-dioxo-3-(phenyliodonio)-1,4-dihydrona-
phthalen-2-olate (12) (3.0 g, 7.39 mmol) as a suspen-
sion in acetonitrile was refluxed overnight. The
reaction mixture was cooled to rt, and filtered. The fil-
trate was concentrated under reduced pressure and the
residue purified by chromatography on a silica gel (5–
40% ethyl acetate in hexane) to give the product as a
yellowish solid (0.4 g, 31%). Mp 118–119 ꢁC; 1H
NMR (400 MHz, CDCl3) d 7.89 (dd, J = 6.8, 2.8 Hz,
1H), 7.36–7.32 (m, 2H), 3.96 (s, 3H), 3.23 (s, 2H);
LCMS: m/z 177 [M+H]+.
An anhydrous dichloromethane solution (3.0 mL) of a
mixture of 15b and 15c (5:2 ratio) (100 mg, 0.41 mmol)
was cooled to 0 ꢁC and boron tribromide (1 M in dichlo-
romethane, 1.0 mL) was added dropwise. The resulting
solution was warmed to rt and stirred for 2 h. LC/MS
indicated completion of the reaction and the reaction
was quenched with ice water (15 mL) and extracted with
dichloromethane (3· 15 mL). The combined organics
were washed with water (4· 15 mL) and dried over so-
dium sulfate. After filtration and concentration under
reduced pressure, the residue was purified by chroma-
tography on silica gel (10–50% ethyl acetate in hexane)
to afford the product as an approximately 6:1 mixture
of two regio-isomers (56 mg, 59%) with the major prod-
4.26. Synthesis of 5-methoxy-2-(3-methyl-but-2-enyl)-
indan-1,3-dione (14)
A mixture of 5-methoxy-indan-1,3-dione (13) (400 mg,
2.27 mmol), 3,3-dimethylallyl bromide (370 mg,
1
uct identified as 11b: H NMR (400 MHz, DMSO-d6) d

R.-Y. Yang et al. / Bioorg. Med. Chem. 16 (2008) 5635–5643
5643
10.22 (s, 1H), 7.13 (d, J = 7.6 Hz, 1H), 6.56–6.50 (m,
4.31. Synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyr-
ano[3,2-c]isochromen-6-one (M6)
2H), 2.15 (t, J = 6.4 Hz, 2H), 1.74 (t, J = 6.4 Hz, 2H),
1.38 (s, 6H); LCMS: m/z 231 [M+H]+. Compound 11c:
1H NMR (400 MHz, DMSO-d6) d 10.00 (s, 1H), 6.91
(d, J = 7.6 Hz, 1H), 6.72 (d, J = 2.0 Hz, 1H), 6.62 (dd,
J = 8.0, 2.4 Hz, 1H), 2.15 (t, J = 6.4 Hz, 2H), 1.74 (t,
J = 6.4 Hz, 2H), 1.38 (s, 6H).
Concentrated sulfuric acid (1 mL) was added dropwise
to 3-(3-methyl-but-2-enyl)-isochroman-1,4-dione (19)
(20 mg, 0.08 mmol) at rt. The mixture was stirred for
30 min and then diluted with ice water (2 mL). The
resulting solution was extracted with dichloromethane
(3· 5 mL), washed with brine (5 mL), dried over so-
dium sulfate, filtered, and concentrated under reduced
pressure. The crude solid was purified by silica
gel chromatography (5–30% ethyl acetate in hexane)
to give 2,2-dimethyl-3,4-dihydro-2H-pyrano[3,2-c]
isochromen-6-one (M6) (6 mg, 30%). 1H NMR
(400 MHz, CDCl3) d 8.24 (d, J = 7.8 Hz, 1H), 7.74–
7.72 (m, 2H), 7.49–7.47 (m, 1H), 2.65 (t, J = 6.6 Hz,
2H), 1.90 (t, J = 6.6 Hz, 2H), 1.39 (s, 6H); LCMS:
m/z 231 [M+H]+; HRMS: Calcd 231.1021. Found:
231.1024.
4.29. Synthesis of isochroman-1,4-dione (18)
To a solution of 2-acetylbenzoic acid (16) (3.19 g,
19.4 mmol) in a mixture of acetic acid/toluene (2:1,
60 mL) was added bromine (1.0 mL, 19.4 mmol) via syr-
inge. The reaction mixture was heated at 50 ꢁC for 18 h,
cooled to rt, and then concentrated under reduced pres-
sure. The crude product was purified by silica gel chro-
matography (30–70% ethyl acetate in hexane) to give a
mixture of 2-(2-bromoacetyl)-benzoic acid (17) and
isochroman-1,4-dione (18) (3.8 g). The mixture was dis-
solved in methanol (250 mL), and sodium acetate
(205 mg, 2.5 mmol) added in portions at rt. The result-
ing mixture was stirred at rt for 4 h, poured into water
(100 mL), extracted with ethyl acetate (3· 100 mL),
washed with brine (200 mL), and dried over sodium sul-
fate. After filtration and concentration under reduced
pressure, the yellow residue was purified by silica gel
chromatography (30–75% ethyl acetate/hexane) to give
isochroman-1,4-dione (18) (1.7 g, 54%) as a white solid.
Acknowledgments
The authors thank Khanh Nguyen for assistance in
the purification of some of the final compounds, Peng-
fei Song for preparing [14C] ARQ 501 blood metabo-
lite samples, and Prof. Michael E. Jung, Department
of Chemistry and Biochemistry, University of Califor-
nia Los Angeles, Los Angeles, CA for helpful
discussion.
1
Mp 151–154 ꢁC; H NMR (400 MHz, CDCl3) d 8.32–
8.29 (m, 1H), 8.12–8.08 (m, 1H), 7.93–7.83 (m, 2H),
5.15 (s, 2H); LCMS: m/z 163 [M+H]+.
4.30. Synthesis of 3-(3-methyl-but-2-enyl)-isochroman-
1,4-dione (19)
References and notes
1. Li, Y.; Li, C. J.; Yu, D.; Pardee, A. B. Mol. Med. 2000, 6,
1008–1015.
2. Li, C. J.; Li, Y. Z.; Pinto, A. V.; Pardee, A. B. Proc. Natl.
Acad. Sci. U.S.A. 1999, 96, 13369–13374.
3. Hindering, P. H. Pharmacol. Rev. 1997, 49, 279–295.
4. Miao, X.-S.; Song, P.; Savage, R. E.; Yang, R.-Y.; Kizer,
D.; Wu, H.; Volckova, E.; Ashwell, M. A.; Chan, T. C. K.
Drug Metab. Dispos. 2008, 36, 64–448.
5. Malerich, J. P.; Maimone, T. J.; Elliott, G. I.; Trauner, D.
J. Am. Chem. Soc. 2005, 127, 6276.
To a solution of isochroman-1,4-dione (18) (502 mg,
3.09 mmol) in THF (5 mL) at À78 ꢁC was added dropwise
lithium diisopropyl amide (prepared by the addition of n-
BuLi (2.1 mL, 3.3 mmol, 1.6 M in hexane) to diisopropyl-
amine (0.48 mL, 3.3 mmol)) at À78 ꢁC. After stirring for
30 min, 3,3-dimethylallyl bromide (506 mg, 3.4 mmol) in
THF(1 mL)wasaddeddropwiseandtheresultingsolution
was stirred for 1 h at À78 ꢁC. After warming to room
temperature, the reaction was quenched with water
(5 mL), extracted with dichloromethane (3· 5 mL), and
dried over sodium sulfate. After filtration and concentra-
tion under reduced pressure, the residue was purified by sil-
ica gel chromatography (5–50% ethyl acetate in hexane) to
give 3-(3-methyl-but-2-enyl)-isochroman-1,4-dione as an
6. Frydman, B.; Marton, L.J. PCT Int. Appl. WO2000066175,
2000.
7. (a) Ahluwalia, V. K.; Arora, K. K.; Mukherjee, I. Hetero-
cycles 1984, 22, 223–227; (b) Shah, R. R.; Desai, S. M.;
Trivedi, K. N. Pharmazie 1983, 38, 439–441; (c) Bravo, P.;
Ticozzi, C.; Viani, F.; Arnone, A. Gazz. Chim. Ital. 1985,
115, 677–684.
8. Hatzigrigoriou, E.; Spyroudis, S.; Varvoglis, A. Liebigs
Ann. Chem. 1989, 167–170.
9. Barcia, J. C.; Cruces, J.; Estevez, J. C.; Estevez, R. J.;
Castedo, L. Tetrahedron Lett. 2002, 43, 5141–5144.
1
oil (19) (20 mg, 2.8%). H NMR (400 MHz, CDCl3) d
8.26 (dd, J = 8.0, 1.2 Hz, 1H), 8.06 (dd, J = 6.8, 2.0 Hz,
1H), 7.88–7.79 (m, 2H), 5.14 (t, J = 5.2 Hz, 1H), 5.04–
4.98 (m, 1H), 2.87–2.69 (m, 2H), 1.61 (s, 3H), 1.57 (s,
3H); LCMS: m/z 231 [M+H]+.