Synthesis of gerfelin and related analogous compounds

Article abstract of DOI:10.1271/bbb.60287

Gerfelin, an inhibitor of human geranylgeranyl diphosphate (GGPP) synthase that has been isolated from a culture broth of Beauveria felina QN22047, was synthesized in 4 and 3 steps starting from 2,4-dihydroxy-6-methylbenzoic acid and 3,4,5-trihydroxytolue

Full text of DOI:10.1271/bbb.60287

Biosci. Biotechnol. Biochem., 70 (10), 2523–2528, 2006
Synthesis of Gerfelin and Related Analogous Compounds
Md. Sadequl ISLAM,1 Mitsuhiro KITAGAWA,2 Masaya IMOTO,2
y
1;
Takeshi KITAHARA,1;3 and Hidenori WATANABE
1Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences,
The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
2Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University,
3-4-11 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
3Center for Basic Research, The Kitasato Institute, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan
Received May 23, 2006; Accepted May 29, 2006; Online Publication, October 7, 2006
[doi:10.1271/bbb.60287]
R1
Gerfelin, an inhibitor of human geranylgeranyl
diphosphate (GGPP) synthase that has been isolated
from a culture broth of Beauveria felina QN22047, was
O
R2
O
HO
O
HO
O
synthesized in 4 and 3 steps starting from 2,4-dihy-
droxy-6-methylbenzoic acid and 3,4,5-trihydroxytolu-
ene, respectively. An effective ligand, 2-(di-tert-butyl-
phosphino)biphenyl, was used in the palladium-cat-
alyzed diaryl ether-forming reaction. Five analogous
compounds of gerfelin were also synthesized for a study
of the structure-activity relationship.
OH
OH
R1 =OH, R2 =CO2H (Gerfelin, 1)
R1 =R2 =CO2Me (3)
2
R1 =CO2H, R2 =CO2Me (4)
R1 =R2 =CO2H (5)
R1 =CO2Me, R2 =CO2H (6)
Fig. 1. Structures of Gerfelin and Analogous Compounds.
Key words: gerfelin; geranylgeranyl diphosphate syn-
thase; enzyme inhibitor
O
O
O
O
In the course of screening for an inhibitor of
geranylgeranyl diphosphate (GGPP) synthase, Imoto
and his co-workers have isolated gerfelin 1 from a
culture broth of Beauveria felina QN22047 and reported
that gerfelin inhibited human GGPP synthase activity
with an IC50 value of 3.5 mg/ml.1,2) The compound also
inhibited the farnesyl diphosphate (FPP) synthesizing
activity of GGPP synthase.
We were fascinated by this simple structure with its
interesting bioactivity and started the synthesis of 1 and
its analogs to learn about the structure-activity relation-
ship (SAR). We report in this paper the synthesis of
gerfelin (1) and its analogs (2–6) in short steps and their
biological activities.
O
O
+
OH
TfO
O
O
A
B
O
O
Pd-catalyzed
Gerfelin, 1
Ullmann reaction
+
OTf
HO
D
C
Scheme 1. Retrosynthesis of Gerfelin 1.
groups of 3,4,5-trihydroxytoluene (7) were protected
as an acetonide by acid-catalyzed transacetalization with
2,2-dimethoxypropane to give 8 in a 98% yield, and the
remaining alcohol was converted into a triflate (9, 96%,
Scheme 2).
On the other hand, the right-hand segments (11 and
12) were prepared from the known 2,2-dihydoxy-6-
methylbenzoic acid (10)3) by acetalization and triflation.
Acetonide 11 was first obtained in a 40% yield from 10
with acetone in the presence of TFA-TFAA,4) but a
Result and Discussion
As shown in the retrosynthesis of gerfelin
(Scheme 1), it would be possible to form an ether
linkage by the Pd-catalyzed Ullmann-type diaryl ether
formation between the phenol of the left-hand segment
(A) and triflate of the right-hand segment (B), or vice
versa (C and D).
To prepare the left-hand segment, two hydroxyl
y
To whom correspondence should be addressed. Tel: +81-3-5841-5119; Fax: +81-3-5841-8019; E-mail: ashuten@mail.ecc.u-tokyo.ac.jp

2524
Md. S. ISLAM et al.
O
O
a
O
O
b
a
2
HO
OH
OR
O
X
O
O
OH
O
O
17
15 (X =Br)
16 (X =OTf)
8 (R =H)
9 (R =OTf)
7
b
c
OH
O
O
CO2R1
CO2R1
CO2H
O
c or d
CO2R2
CO2R2
b
HO
RO
O
11 (R =H)
O
HO
O
10
O
b
12 (R =OTf)
O
OH
3 (R1=R2=Me)
4 (R1=H, R2=Me)
5 (R1=R2=H)
18 (R1=R2=Me)
19 (R1=H, R2=Me)
20 (R1=R2=H)
O
d
f
e
e
O
f
1
8 + 12
6 (R1=Me, R2=H)
21 (R1=Me, R2=H)
O
O
O
13
Scheme 3. Synthesis of Gerfelin Analogs (2–6).
Reagents and conditions: (a) 8, K2CO3, DMF, rt [94% from 15
(40 h); 58% from 16 (48 h)]. (b) TFA, H2O, rt, 1.5 h (99% for 2, 3
and 5, 98% for 4, 68% for 6). (c) MeO2CCꢀCCO2Me, 170–180 ꢁC
for 1.5 h, then 190–200 ꢁC for 3.5 h (86%). (d) NaOH, H2O–EtOH,
rt, 1 h (95%). (e) LiOH, THF–MeOH–H2O, 60 ꢁC, 75 h (77%). (f)
Ac2O, rt for 1.5 h, then MeOH, 45 ꢁC for 12 h [65% (þ20% of 19)].
P(t-Bu)2
e
9 + 11
13
14
Scheme 2. Synthesis of Gerfelin 1.
Reagents and conditions: (a) Me2C(OMe)2, acetone, p-TsOH
.
H2O, PhH, reflux, 75 h (98%). (b) Tf2O, Et3N, CH2Cl2, 0 ꢁC, 40 min
(96% for 9; 98% for 12). (c) acetone, TFA, TFAA, 0 ꢁC to rt, 24 h
(40%). (d) acetone, SOCl2, DMAP, DME, rt, 2.5 h (85%). (e)
Pd(OAc)2, Ph3P or 14, K3PO4, toluene, 95 ꢁC [1.7% by Ph3P (55 h);
60% by 14 (18 h)]. (f) TFA, H2O, rt, 6.5 h (89%).
via Michael addition-ꢀ-elimination, and 17 was obtained
in a high yield (94% from 15, 58% from 16; Scheme 3).
Removal of the protecting acetonide group quantitative-
ly afforded a pyronyl analog (2).
The reaction of 17 with dimethyl acetylenedicarbox-
ylate at 170–200 ꢁC gave Diels-Alder-decarboxylated
product 18 in an 86% yield. Dimethyl ester 18 was
converted to half methyl ester 19 (1 M aq NaOH in
EtOH, rt, 95% yield), and diacid 20 (LiOH, H2O–THF–
MeOH, 60 ꢁC, 77%). Another half ester (21) could be
prepared in a 65% yield from diacid 20 by the formation
of a phthalic anhydride and subsequent methanolysis.
Acid-catalyzed hydrolysis of the acetonide groups of
18–21 afforded 3–6, respectively.
The inhibitory activities of our synthetic analogs (2–
5) were evaluated by an in vitro GGPP synthase assay.1)
Although 3–5 were found to be two to four times less
active than gerfelin, 2 exhibited no bioactivity. This
result suggests that the 2-hydroxybenzoic acid moiety as
well as the catechol moiety1) played important roles in
the bioactivity of gerfelin.
better result (85%) was obtained by using acetone and
thionyl chloride in the presence of DMAP.5) The
reaction of 11 with Tf2O in the presence of TEA gave
98% of triflate 12.
With both the left and right-hand segments in hand,
we next investigated the Pd catalyzed Ullmann-type
diaryl ether formation between 8 (ꢀA) and 12 (ꢀB).
When triphenylphosphine was used as a ligand of the
palladium catalyst, coupled product 13 was only
obtained in a poor yield (1.7%). However, the use of
the bulkier ligand, 2-(di-tert-butylphosphino)biphenyl
(14),6) instead of triphenylphosphine dramatically im-
proved the yield to 60% [14 (0.05 eq.), Pd(II)(OAc)2
(0.05 eq.) and K3PO4 (2 eq.) in toluene at 95 ꢁC]. On
the other hand, another combination of the triflate and
phenol [9 (ꢀC) and 11 (ꢀD)] afforded no desired
product, even when 14 was used as the ligand. Finally,
treatment of 13 with aq. TFA gave 89% of gerfelin (1),
whose spectroscopic data were identical to those
reported for the natural compound.
Experimental
General. All reactions (except hydrolysis) were
performed under argon in oven-dried glassware. Ben-
zene, toluene and tetrahydrofuran were distilled from
Na/benzophenone, dichloromethane was distilled from
P2O5, and acetone was distilled from anhydrous CaCl2.
1H- and 13C-NMR spectra were recorded by a JEOL
JNM–AL 300 FT NMR system at 300 MHz and 75
MHz, respectively, using deuterated solvents CDCl3,
Our next plan was to synthesize some related analogs
(2–6) of gerfelin. We adopted commercially available
4-hydroxy-6-methyl-2-pyrone as the starting material
which was converted to the known bromide (15)7) and
triflate (16).8) The coupling reaction of 15 or 16 with 8
proceeded under the basic condition (K2CO3 in DMF)

Synthesis of Gerfelin and Analogs
2525
(CD3)2SO and CD3OD. Chemical shifts are reported in
ppm relative to an internal solvent peak. IR spectra were
recorded by a JASCO FT/IR–230 spectrometer. Melting
point (mp) data were measured by Yanaco micro-
melting point apparatus and are uncorrected. Refractive
indices were measured by an ATAGO NAR-1T refrac-
tometer. Column chromatography was performed with
Silica Gel 60N (spherical, neutral) 63–210 mm or Silica
Gel 60N (spherical, neutral) 40–100 mm purchased from
Kanto Chemical Co., Tokyo, Japan.
136.8, 149.7. Anal. Found: C, 42.40; H, 3.59%. Calcd.
for C11H11F3O5S: C, 42.31; H, 3.55%.
7-Hydroxy-2,2,5-trimethyl-4H-1,3-benzodioxin-4-one
(11).
Method A: Trifluoroacetic anhydride (8.25 ml) and
acetone (1.65 ml) were added to an ice-cooled suspen-
sion of 10 (1.50 g, 8.92 mmol) in trifluoroacetic acid
(13 ml). The reaction mixture was warmed slowly to
room temperature while continuously stirring. After
24 h, the resulting slightly yellow homogeneous solution
was evaporated in vacuo, and the residue was poured
into a saturated aqueous solution of NaHCO3. This was
then extracted with EtOAc, successively washed with
water and brine, dried over anhydrous MgSO4 and
filtered. The filtrate was concentrated to leave a yellow
solid which was purified by silica gel column chroma-
tography, using hexane/EtOAc (4:1 to 7:3) as the eluent,
to afford 741 mg (40%) of 11 as a white solid. A small
portion was recrystallized from ethyl acetate to afford an
analytical sample as colorless needles. Mp 199–200 ꢁC.
2,2,6-Trimethylbenzodioxol-4-ol (8). A mixture of 7
.
(2.83 g, 20.2 mmol), p-TsOH H2O (121 mg) and 2,2-
dimethoxypropane (9.9 ml, 80.5 mmol) in acetone (97
ml) and benzene (362 ml) was heated and refluxed with
azeotropic removal of methanol through a column of
˚
MS 4 A (55 g). Further amounts of 2,2-dimethoxypro-
pane (4 ꢂ 9:9 ml, 4 ꢂ 80:5 mmol), acetone (1 ꢂ 61 ml),
.
benzene (1 ꢂ 50 ml) and p-TsOH H2O (121 mg) were
added during reflux. After 75 h, the reaction mixture
was allowed to cool to room temperature, concentrated
in vacuo, diluted with 1 M aq NaOH (60 ml), and the
separated aqueous layer was washed with Et2O (50 ml).
The aqueous solution was then neutralized by adding
pieces of dry-ice while stirring and extracted with Et2O
(3 ꢂ 100 ml). The combined ethereal solution was dried
over anhydrous MgSO4, filtered and concentrated in
vacuo to afford 3.55 g (98%) of almost pure 8. A small
portion was recrystallized from hexane–ethyl acetate to
give colorless crystals as an analytical sample. Mp 53–
54 ꢁC. IR ꢁmax (CDCl3 solution) cmꢃ1: 3437 (OH), 1214
1
IR ꢁmax (nujol) cmꢃ1: 1689 (C=O), 1290 (C–O). H-
NMR ꢂH (CD3OD): 1.65 (6H, s, Me2), 2.53 (3H, s, Ar-
Me), 6.20 (1H, d, J ¼ 2:4 Hz, ArH), 6.39 (1H, d, J ¼
2:4 Hz, ArH). 13C-NMR ꢂC (CD3OD): 25.6, 28.9, 105.5,
108.2, 109.5, 118.2, 149.9, 163.8, 166.1, 168.8. Anal.
Found: C, 63.38; H, 5.90%. Calcd. for C11H12O4: C,
63.45; H, 5.81%.
Method B: To a stirred and cooled solution containing
10 (67.5 mg, 0.401 mmol), DMAP (3 mg, 6 mol %), 1,2-
dimethoxyethane (1 ml), and acetone (38 ml, 0.518
mmol) was added thionyl chloride (42 ml, 0.58 mmol)
at 0 ꢁC. The mixture was allowed to warm to room
temperature, and stirring was continued for 2.5 h. An
aqueous NaHCO3 solution (5 ml) was added, and the
mixture was extracted with ethyl acetate. The organic
solution was washed with water, dried over anhydrous
MgSO4 and filtered. The filtrate was concentrated in
vacuo, and the residue was purified by silica gel column
chromatography, using hexane/ethyl acetate (4:1) as
the eluent, to afford 70.6 mg (85%) of 11 as a solid. Its
1H-NMR data were identical to those obtained by
method A.
1
(C–O), 1052 (C–O), 981 (C–O). H-NMR ꢂH (CDCl3):
1.68 (6H, s, Me2), 2.22 (3H, s, Ar-Me), 4.93 (1H, s,
OH), 6.23 (1H, s, ArH) and 6.27 (1H, s, ArH). 13C-NMR
ꢂC (CDCl3): 21.2, 25.7, 102.5, 102.8, 110.3, 118.5,
131.6, 138.7, 148.3. Anal. Found: C, 66.65; H, 6.83%.
Calcd. for C10H12O3: C, 66.65; H, 6.71%.
2,2,6-Trimethylbenzodioxol-4-yl trifluoromethanesul-
fonate (9). To a stirred suspension of 8 (58 mg,
0.32 mmol) in dichloromethane (1 ml) was added trieth-
ylamine (50 ml, 0.35 mmol, 1.1 eq.). After 10 min, the
reaction mixture was cooled to 0 ꢁC, and trifluoro-
methanesulfonic anhydride (57 ml, 0.34 mmol, 1.06 eq.)
was added dropwise. After a further 40 min, a saturated
aqueous ammonium chloride solution (ca. 3 ml) was
added, and the mixture was poured into water and
extracted with CHCl3 (3 ꢂ 20 ml). The organic solution
was washed with brine (8 ml), dried with anhydrous
MgSO4 and filtered. After concentrating under reduced
pressure, the crude product was purified by silica gel
column chromatography, using n-hexane/ethyl acetate
(9:1) as the eluent, to afford 96.6 mg (96%) of 9 as a
colorless liquid. n2D4:1 1.4552. IR ꢁmax (CDCl3 solution)
cmꢃ1: 1426 (S=O), 1217 (S=O). 1H-NMR ꢂH (CDCl3):
1.70 (6H, s, Me2), 2.28 (3H, s, Ar-Me), 6.53 (1H, s,
ArH) and 6.56 (1H, s, ArH). 13C-NMR ꢂC (CDCl3):
21.1, 25.6, 109.3, 114.5, 118.7, 120.7, 131.4, 131.9,
2,2,5-Trimethyl-4-oxo-4H-1,3-benzodioxin-7-yl tri-
fluoromethanesulfonate (12). To a stirred suspension of
11 (202 mg, 0.97 mmol) in dichloromethane (3 ml) was
added 152 ml (1.07 mmol, 1.1 eq.) of triethylamine. After
10 min at room temperature, the mixture was cooled to
0 ꢁC, and trifluoromethanesulfonic anhydride (171 ml,
1.02 mmol, 1.05 eq.) was added dropwise. After 40 min,
saturated aqueous ammonium chloride (ca. 10 ml) was
added to the mixture. This was extracted with CHCl3
(3 ꢂ 40 ml), and the organic solution was washed with
brine (10 ml), dried over anhydrous MgSO4 and filtered.
The filtrate was concentrated in vacuo and purified by
silica gel column chromatography, using hexane/ethyl
acetate (9:1) as the eluent, to afford 323 mg (98%) of 12

2526
Md. S. ISLAM et al.
as a colorless solid. An analytical sample was obtained
by recrystallization from hexane as colorless plates. Mp
50–51 ꢁC. IR ꢁmax (CDCl3 solution) cmꢃ1: 1744 (C=O),
6-Methyl-4-(2,2,6-trimethyl-1,3-benzodioxol-4-yloxy)-
pyran-2-one (17).
From bromide 15. A mixture of 15 (500 mg, 2.64
mmol), 8 (477 mg, 2.64 mmol) and K2CO3 (365 mg,
2.64 mmol) in DMF (16 ml) was stirred at room temper-
ature. After 40 h, saturated aqueous ammonium sulfate
(12 ml) was added, and the mixture extracted with ethyl
acetate (200 ml). The organic solution was successively
washed with brine (15 ml) and water (15 ml), dried over
anhydrous MgSO4, and filtered. The filtrate was con-
centrated in vacuo, and the residue was purified by silica
gel column chromatography (10% ethyl acetate in
hexane) to give 714 mg (94%) of a colorless crystalline
solid. An analytical sample was obtained as colorless
plates by recrystallization from ethyl acetate–hexane.
Mp 135–136 ꢁC. IR ꢁmax (CDCl3 solution) cmꢃ1: 1732
(C=O), 1226 (C–O). 1H-NMR ꢂH (CDCl3): 1.67 (6H, s,
Me2), 2.26 (6H, s, 2 ꢂ Ar-Me), 5.31 (1H, br. s, ArH),
5.99 (1H, br. s, ArH), 6.36 (1H, br. s, ArH), 6.51 (1H, br.
s, ArH). 13C-NMR ꢂC (CDCl3): 20.0, 21.1, 25.7, 90.7,
99.7, 107.8, 114.5, 119.7, 132.1, 133.8, 135.9, 149.5,
163.1, 164.7, 169.6. Anal. Found: C, 66.66; H, 5.67%.
Calcd. for C16H16O5: C, 66.66; H, 5.59%.
1
1428 (S=O), 1210 (S=O). H-NMR ꢂH (CDCl3): 1.72
(6H, s, Me2), 2.72 (3H, s, Ar-Me), 6.78 (1H, d, J ¼
2:4 Hz, ArH), 6.84 (1H, d, J ¼ 2:4 Hz, ArH). 13C-NMR
ꢂC (CDCl3): 22.3, 25.6, 106.1, 108.4, 112.2, 118.2,
118.6, 146.9, 152.8, 158.2, 159.1. Anal. Found: C,
42.45; H, 3.26%. Calcd. for C12H11F3O6S: C, 42.36; H,
3.26%.
2,2,5-Trimethyl-7-(2,2,6-trimethylbenzodioxol-4-yloxy)-
4H-1,3-benzodioxin-4-one (13). A mixture of palladium
(II) acetate (95% purity, 8 mg, 0.034 mmol), 14 (10 mg,
0.034 mmol), 8 (155.7 mg, 0.86 mmol), 12 (245 mg, 0.72
mmol) and K3PO4 (98% purity, 312 mg, 1.44 mmol) in
toluene (3 ml) was stirred and heated at 95 ꢁC. After
18 h, the reaction mixture was allowed to cool to room
temperature, diluted with ether (40 ml), filtered and
concentrated in vacuo to give 351 mg of a brown paste.
This crude product was purified by silica gel column
chromatography (10% ethyl acetate in hexane) to afford
158 mg (60%) of 13 as crystals with recovery of the
starting materials [8 (11.1 mg, 8.6%) and 12 (23 mg,
9.4%)] and small amount of a hydrolyzed compound
(11). Recrystallization from hexane–ethyl acetate af-
forded colorless plates for analysis. Mp 115–116 ꢁC. IR
ꢁmax (CDCl3 solution) cmꢃ1: 1734 (C=O), 1148 (C–O).
1H-NMR ꢂH (CDCl3): 1.66 (6H, s, Me2), 1.68 (6H, s,
Me2), 2.26 (3H, s, ArMe), 2.64 (3H, s, ArMe), 6.30 (1H,
d, J ¼ 2:4 Hz, ArH), 6.39 (1H, s, ArH), 6.49 (1H, s,
ArH), 6.54 (1H, d, J ¼ 2:4 Hz, ArH). 13C-NMR ꢂC
(CDCl3): 21.2, 22.3, 25.6, 25.8, 101.8, 105.1, 106.7,
107.0, 113.9, 114.8, 119.3, 132.0, 135.8, 136.2, 145.7,
149.4, 158.7, 160.3, 162.6. Anal. Found: C, 68.25; H,
6.04%. Calcd. for C21H22O6: C, 68.10; H, 5.99%.
From triflate 16. In the same manner as that just
described, 16 (73.6 mg, 0.285 mmol) and 8 (51.5 mg,
0.286 mmol) were reacted for 48 h to afford 48 mg
(58%) of 17, whose spectral data were identical with
those obtained from bromide 15.
4-(2,3-Dihydroxy-5-methylphenoxy)-6-methyl-2H-py-
ran-2-one (2). A mixture of 17 (76.0 mg, 0.263 mmol),
water (9 drops) and TFA (0.9 ml) was stirred at room
temperature for 1.5 h. Concentration in vacuo gave an
off-white solid which was chromatographed in a silica
gel column, using ethyl acetate–hexane (1:1 to 1:0), to
afford 64.8 mg (99%) of 2 as colorless crystals. Re-
crystallization from ethyl acetate afforded colorless
crystals as an analytical sample. Mp 215–216 ꢁC. IR
ꢁmax (nujol) cmꢃ1: 3365 (OH), 3205 (OH), 1686 (C=O).
1H-NMR ꢂH (CD3OD): 2.20 (3H, s, Me), 2.27 (3H, s,
Me), 5.12 (1H, s, ArH), 6.19 (1H, s, ArH), 6.35 (1H, s,
ArH), 6.59 (1H, s, ArH). 13C-NMR ꢂC (CD3OD): 19.8,
20.8, 90.7, 101.4, 113.9, 115.4, 130.7, 136.1, 141.3,
148.4, 165.0, 167.7, 173.2. Anal. Found: C, 62.80; H,
5.14%. Calcd. for C13H12O5: C, 62.90; H, 4.87%.
Gerfelin (1). To a stirred mixture of 13 (17.3 mg,
0.047 mmol) and distilled water (4 drops) was added
TFA (0.8 ml) at 0 ꢁC, and then the mixture was allowed
to warm slowly to room temperature. After 6.5 h, the
reaction mixture was concentrated in vacuo to give an
off-white solid. The crude product was purified by silica
gel column chromatography (hexane/ethyl acetate 7:3
to 1:1) to afford 12.1 mg (89%) of 1 as a white solid.
Recrystallization from ethyl acetate–benzene afforded
colorless crystals which melted at 175–177 ꢁC. IR ꢁmax
(nujol) cmꢃ1: 3040 (OH), 1662 (C=O), 1630 (aromatic
C=C), 1606 (aromatic C=C), 1188 (C–O), 1151 (C–O).
1H-NMR ꢂH (DMSO-d6): 2.12 (3H, s, Me), 2.38 (3H, s,
Me), 6.01 (1H, d, J ¼ 2:4 Hz, ArH), 6.24 (1H, d, J ¼
2:4 Hz, ArH), 6.26 (1H, d, J ¼ 2:1 Hz, ArH), 6.49 (1H,
d, J ¼ 2:1 Hz, ArH), 8.41 (1H, s, OH), 9.30 (1H, s, OH).
13C-NMR ꢂC (DMSO-d6): 20.4, 22.7, 100.7, 109.0,
110.4, 113.2, 113.4, 128.0, 135.4, 141.8, 147.0, 161.5,
162.5, 172.3. ESI-HRMS: calcd. for C15H14O6Na ½M þ
Naꢄþ, 313.0688; found, 313.0692.
Dimethyl 3-methyl-5-(2,2,6-trimethyl-1,3-benzodiox-
ol-4-yloxy)phthalate (18). A mixture of 17 (281 mg,
0.974 mmol) and dimethyl acetylenedicarboxylate (346
mg, 2.43 mmol) was heated at 170–180 ꢁC for 1.5 h and
then at 190–200 ꢁC for 3.5 h. After cooling to room
temperature, the excess acetylenedicarboxylate was
evaporated by a vacuum pump to give 523 mg of a
brown viscous oil. This crude product was purified by
silica gel column chromatography, using hexane–ethyl
acetate (9:1) as the eluent, to afford 324 mg (86%) of
18 as a colorless paste. n2D4:5 1.5078. IR ꢁmax (CDCl3
1
solution) cmꢃ1: 1732 (C=O), 1136 (C–O). H-NMR ꢂH

Synthesis of Gerfelin and Analogs
2527
(CDCl3): 1.65 (6H, s, Me2), 2.25 (3H, s, Ar-Me), 2.33
(3H, s, Ar-Me), 3.85 (3H, s, OMe), 3.92 (3H, s, OMe),
6.34 (1H, s, ArH), 6.46 (1H, s, ArH), 7.01 (1H, d, J ¼
2:6 Hz, ArH) and 7.36 (1H, d, J ¼ 2:6 Hz, ArH). 13C-
NMR ꢂC (CDCl3): 19.3, 21.2, 25.7, 52.5, 52.6, 106.3,
114.0, 115.4, 119.2, 122.5, 129.4, 129.8, 131.9, 135.6,
136.9, 137.8, 149.3, 157.2, 166.1, 169.6. ESI-HRMS:
calcd. for C21H22O7Na ½M þ Naꢄþ, 409.1263; found,
409.1231.
room temperature for 1.5 h and then concentrated in
vacuo. The residue was diluted with MeOH (16 ml) and
stirred at 45 ꢁC for 12 h. The reaction mixture was
concentrated in vacuo, and the crude product was
purified by silica gel column chromatography, using
CHCl3/MeOH (200:1) as the eluent, to afford 139.6 mg
(65%) of 21 as a white solid and 42 mg (20%) of 19.
Recrystallization from ethyl acetate–hexane afforded
colorless needles for analysis. Mp 158–159 ꢁC. IR ꢁmax
(CDCl3 solution) cmꢃ1: 3200–2800 (OH), 1721 (C=O).
1H-NMR ꢂH (CDCl3): 1.66 (6H, s, Me2), 2.26 (3H, s,
Ar-Me), 2.42 (3H, s, Ar-Me), 3.87 (3H, s, OMe), 6.36
(1H, s, ArH), 6.47 (1H, s, ArH), 7.02 (1H, d, J ¼ 2:4 Hz,
ArH) and 7.34 (1H, d, J ¼ 2:4 Hz, ArH). ESI-HRMS:
calcd. for C20H20O7Na ½M þ Naꢄþ, 395.1107; found,
395.1144.
2-Methoxycarbonyl-3-methyl-5-(2,2,6-trimethyl-1,3-
benzodioxol-4-yloxy)benzoic acid (19). A mixture of 18
(61 mg, 0.16 mmol) and 1 M NaOH–EtOH (1:1, 2 ml)
was stirred at room temperature for 1 h, diluted with
water (5 ml), acidified carefully to pH 5–6 with 0.5 N
HCl, and then quickly extracted with EtOAc. The
organic solution was dried over anhydrous MgSO4,
filtered and concentrated in vacuo. The crude product
was purified by silica gel column chromatography, using
ethyl acetate–hexane (1:1 to 1:0) as the eluent, to afford
56 mg (95%) of 19 as a white solid. Mp 137–138 ꢁC. IR
ꢁmax (CDCl3 solution) cmꢃ1: 3200–2500 (OH), 1734
Dimethyl 5-(2,3-dihydroxy-5-methyl-phenoxy)-3-meth-
ylphthalate (3). In the same manner as that described for
deprotecting 13 to gerfelin (1), 18 (81 mg, 0.21 mmol)
afforded 71.8 mg (99%) of 3 as a white solid. Re-
crystallization from ethyl acetate–hexane afforded col-
orless crystals for analysis. Mp 135–136 ꢁC. IR ꢁmax
1
(C=O). H-NMR ꢂH (CDCl3): 1.65 (6H, s, Me2), 2.26
1
(3H, s, Me), 2.33 (3H, s, Me), 3.90 (3H, s, OMe), 6.35
(1H, s, ArH), 6.47 (1H, s, ArH), 7.06 (1H, d, J ¼ 2:3 Hz,
ArH), 7.43 (1H, d, J ¼ 2:3 Hz, ArH). 13C-NMR ꢂC
(CDCl3): 19.2, 21.2, 25.7, 52.5, 106.4, 113.9, 116.0,
119.2, 123.2, 128.7, 129.9, 132.0, 135.7, 136.7, 137.8,
149.3, 157.2, 169.5, 170.8. Anal. Found: C, 64.64; H,
5.57%. Calcd. for C20H20O7: C, 64.51; H, 5.41%.
(CDCl3 solution) cmꢃ1: 3417 (OH), 1724 (C=O). H-
NMR ꢂH (CDCl3): 2.20 (3H, s, Ar-Me), 2.32 (3H, s, Ar-
Me), 3.86 (3H, s, OMe), 3.93 (3H, s, OMe), 5.36 (1H,
br. s, OH), 5.49 (1H, br. s, OH), 6.26 (1H, s, ArH), 6.60
(1H, s, ArH), 7.00 (1H, d, J ¼ 2:3 Hz, ArH), 7.38 (1H,
d, J ¼ 2:3 Hz, ArH). 13C-NMR ꢂC (CDCl3): 19.3, 20.9,
52.5, 52.8, 111.7, 112.0, 112.5, 116.3, 122.9, 129.9,
130.5, 132.8, 138.1, 142.5, 145.0, 157.3, 166.0, 169.6.
Anal. Found: C, 62.51; H, 5.42%. Calcd. for C18H18O7:
C, 62.42; H, 5.24%.
3-Methyl-5-(2,2,6-trimethyl-1,3-benzodioxol-4-yloxy)-
phthalic acid (20). To a stirred solution of 18 (115 mg,
0.298 mmol) in THF (2.3 ml) and MeOH (0.7 ml) was
.
added a solution of LiOH H2O (71.0 mg, 1.69 mmol) in
5-(2,3-Dihydroxy-5-methylphenoxy)-2-methoxycarbon-
yl-3-methylbenzoic acid (4). In the same manner as that
described for deprotecting 13 to gerfelin (1), 19 (30.5
mg, 0.0819 mmol) afforded 26.7 mg (98%) of 4 as a
white solid. Recrystallization from ethyl acetate–ben-
zene afforded an analytical sample. Mp 145–147 ꢁC. IR
water (1.8 ml). This mixture was stirred at 60 ꢁC for
75 h, before being diluted with water (8 ml), neutralized,
carefully acidified to pH 5–6 with 0.5 N HCl, and then
quickly extracted with EtOAc. The extract was dried
over anhydrous MgSO4, filtered and concentrated in
vacuo. Purification by silica gel column chromatogra-
phy, using ethyl acetate–hexane (1:1 to 1:0) as the
eluent, afforded 81.6 mg (77%) of 20 as a white solid
and 9.2 mg (8.3%) of 19. Recrystallization from ethyl
acetate–hexane afforded colorless prisms for analysis.
Mp 182–183 ꢁC. IR ꢁmax (nujol) cmꢃ1: 3200–2400
(OH), 1705 (C=O). 1H-NMR ꢂH (CD3OD): 1.59 (6H, s,
Me2), 2.25 (3H, s, Ar-Me), 2.34 (3H, s, Ar-Me), 6.42
(1H, s, ArH), 6.51 (1H, s, ArH), 7.03 (1H, d, J ¼ 2:6 Hz,
ArH) and 7.25 (1H, d, J ¼ 2:6 Hz, ArH). 13C-NMR ꢂC
(CD3OD): 19.4, 21.2, 25.8, 107.5, 115.5, 115.7, 120.3,
122.6, 131.4, 131.9, 133.5, 137.1, 137.9, 138.3, 150.9,
158.6, 168.5, 173.4. ESI-HRMS: calcd. for C19H18O7Na
½M þ Naꢄþ, 381.0950; found, 381.0941.
1
ꢁmax (nujol) cmꢃ1: 3200–2500 (OH), 1714 (C=O). H-
NMR ꢂH (CD3OD): 2.18 (3H, s, Ar-Me), 2.26 (3H, s,
Ar-Me), 3.84 (3H, s, OMe), 6.30 (1H, d, J ¼ 1:8 Hz,
ArH), 6.53 (1H, d, J ¼ 1:8 Hz, ArH), 6.96 (1H, d, J ¼
2:4 Hz, ArH) and 7.26 (1H, d, J ¼ 2:4 Hz, ArH). 13C-
NMR ꢂC (CD3OD): 19.3, 20.9, 52.8, 113.9, 114.2, 116.1,
122.5, 130.1, 130.6, 132.0, 136.4, 138.7, 143.8, 148.2,
160.1, 168.7, 171.8. ESI-HRMS: calcd. for C17H16O7Na
½M þ Naꢄþ, 355.0794; found, 355.0824.
5-(2,3-Dihydroxy-5-methylphenoxy)-3-methylphthalic
acid (5). In the same manner as that described for
deprotecting 13 to gerfelin (1), 20 (48.0 mg, 0.134
mmol) afforded 42.2 mg (99% yield) of 5 as a white
solid. Recrystallization from ethyl acetate afforded an
analytical sample. Mp 178–180 ꢁC. IR ꢁmax (nujol)
cmꢃ1: 3600–2500 (OH), 1715 (C=O). 1H-NMR ꢂH
(CD3OD): 2.18 (3H, s, Ar-Me), 2.33 (3H, s, Ar-Me),
2-Methoxycarbonyl-6-methyl-4-(2,2,6-trimethylbenzo-
1,3-dioxol-4-yloxy)benzoic acid (21). A mixture of 20
(208 mg, 0.580 mmol) and 16 ml of Ac2O was stirred at

2528
Md. S. ISLAM et al.
2) Zenitani, S., Tashiro, S., Shindo, K., Nagai, K., Suzuki,
K., and Imoto, M., Gerfelin, a novel inhibitor of
geranylgeranyl diphosphate synthase from Beauveria
felina QN22047. II. Structural elucidation. J. Antibiotics,
56, 658–660 (2003).
6.29 (1H, dd, J ¼ 1:9, 0.6 Hz, ArH), 6.52 (1H, dd, J ¼
1:9, 0.6 Hz, ArH), 6.96 (1H, d, J ¼ 2:4, Hz, ArH) and
7.26 (1H, d, J ¼ 2:4, Hz, ArH). ESI-HRMS: calcd. for
C16H14O7Na ½M þ Naꢄþ, 341.0637; found, 341.0598.
´
3) Nicolaou, K. C., Rodrıguez, R. M., Mitchel, H. J., Suzuki,
4-(2,3-Dihydroxy-5-methylphenoxy)-2-methoxycarbon-
yl-6-methylbenzoic acid (6). In the same manner as that
described for deprotecting 13 to gerfelin (1), 21 (94 mg,
0.25 mmol) afforded 56.7 mg (68% yield) of 6 as a white
solid. Recrystallization from ethyl acetate afforded
an analytical sample. Mp 163–164 ꢁC. IR ꢁmax (nujol)
cmꢃ1: 3503 (OH), 3332 (OH) 1718 (C=O), 1700
(C=O). 1H-NMR ꢂH (CD3OD): 2.18 (3H, s, Ar-Me),
2.34 (3H, s, Ar-Me), 3.82 (3H, s, OMe), 6.29 (1H, dd,
J ¼ 1:8, 0.6 Hz, ArH), 6.53 (1H, dd, J ¼ 1:8, 0.6 Hz,
ArH), 6.98 (1H, dd, J ¼ 2:4, 0.6 Hz, ArH), 7.18 (1H,
dd, J ¼ 2:4, 0.6 Hz, ArH). ESI-HRMS: calcd. for
C17H16O7Na ½M þ Naꢄþ, 355.0794; found, 355.0806.
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6) Aranyos, A., Old, D. W., Kiyomori, A., Wolfe, J. P.,
Sadighi, J. P., and Buchwald, S. L., Novel electron-rich
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