Discovery of tetrahydrotetramethylnaphthalene analogs as adult T-cell leukemia cell-selective proliferation inhibitors in a small chemical library constructed based on multi-template hypothesis

Article abstract of DOI:10.1016/j.bmc.2009.04.044

Adult T cell leukemia (ATL), caused by infection of human T-lymphotropic virus type 1 (HTLV-1), has a poor prognosis and curative therapy is unavailable, so it is important to find or design superior lead compounds for the drug treatment of ATL. We used our micro-reversed fragment-based drug design hypothesis and multi-template hypothesis to extract the tetrahydrotetramethylnaphthalene (TMN) skeleton from tamibarotene, a useful medicament for the treatment of acute promyelocytic leukemia (APL). Structural development of TMN yielded highly ATL cell-selective growth inhibitors, including 2-acetyl-3-hydroxy-5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalene (6). Structure-activity relationship analysis suggests the existence of a specific target molecule for ATL cell-selective inhibition of proliferation through G2 arrest.

Full text of DOI:10.1016/j.bmc.2009.04.044

Bioorganic & Medicinal Chemistry 17 (2009) 4740–4746
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Bioorganic & Medicinal Chemistry
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Discovery of tetrahydrotetramethylnaphthalene analogs as adult T-cell
leukemia cell-selective proliferation inhibitors in a small chemical library
constructed based on multi-template hypothesis
Masahiko Nakamura a, , Takayuki Hamasaki b, , Maiko Tokitou b, Masanori Baba b,
,
*
Yuichi Hashimoto a, Hiroshi Aoyama a,
*
a Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
b Division of Antiviral Chemotherapy, Center for Chronic Viral Diseases, Graduate School of Medical and Dental Sciences,
Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Adult T cell leukemia (ATL), caused by infection of human T-lymphotropic virus type 1 (HTLV-1), has a
poor prognosis and curative therapy is unavailable, so it is important to find or design superior lead com-
pounds for the drug treatment of ATL. We used our micro-reversed fragment-based drug design hypoth-
esis and multi-template hypothesis to extract the tetrahydrotetramethylnaphthalene (TMN) skeleton
from tamibarotene, a useful medicament for the treatment of acute promyelocytic leukemia (APL). Struc-
tural development of TMN yielded highly ATL cell-selective growth inhibitors, including 2-acetyl-3-
hydroxy-5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalene (6). Structure–activity relationship analysis
suggests the existence of a specific target molecule for ATL cell-selective inhibition of proliferation
through G2 arrest.
Received 8 April 2009
Revised 21 April 2009
Accepted 22 April 2009
Available online 3 May 2009
Keywords:
Tetrahydrotetramethylnaphthalene
ATL
HTLV-1, tamibarotene
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
suggesting that a molecular target(s) for inhibition of ATL cell-
selective proliferation might exist.
Adult T cell leukemia (ATL) is an intractable disease caused by
infection of human T-lymphotropic virus type 1 (HTLV-1) and in-
volves the expansion of leukemic cells and the development of
immunodeficiency.1,2 The geographic distribution of HTLV-1 has
been well defined; it is highly prevalent in Japan, Africa, the Carib-
bean islands, and South America.3 In Japan, the number of HTLV-1
carriers is estimated to be 1.2 million, and more than 700 cases of
ATL are diagnosed every year.4 Since conventional anticancer che-
motherapy active against other lymphoid malignancies proved to
be ineffective for treating aggressive types of ATL, it seems manda-
tory to find or design superior lead compounds for the develop-
ment of drugs to treat this fatal disease.5–7 HTLV-1 infection is
the cause of ATL, and monoclonal expansion of HTLV-1-infected T
cells is the reason for the malignancy of the disease. However,
ATL cells generally do not express HTLV-1 gene. Therefore, it would
be expected that an altered specific gene expression pattern caused
by HTLV-1 infection resulted in the transformation of normal cells,
Only a few medicaments which elicit their pharmacological ef-
fects at the gene expression level by targeting a specific mole-
cule(s) are known. Tamibarotene (Am80), a synthetic retinoid
derived from all trans-retinoic acid (ATRA), is one example
(Fig. 1).8–10 Tamibarotene has been clinically used to treat acute
promyelocytic leukemia (APL), and its mechanism of action is con-
sidered to be the regulation of specific gene expression mediated
by binding to aberrant nuclear retinoic acid receptor [PML-RAR
fused protein resulting from chromosomal translocation
t(15;17)] and/or normal nuclear retinoic acid receptor (RAR).
Although tamibarotene inhibits ATL cell proliferation,11,12 it also
inhibits proliferation of other HTLV-1-negative malignant
cells.8,13,14 In our assay system, tamibarotene elicited almost
non-selective (actually slightly selective for HL-60 cells) anti-pro-
liferative activity against all of the following cell lines examined:
S1T (a cell line established from an ATL patient,7 IC50 = 15.9
HL60 cells (IC50 = 6 M), Jurkat cells (IC50 = 17.3 M), U937 cells
(IC50 = 20.2 M) and MOLT-4 cells (IC50 = 19.5 M). The amide
lM),
l
l
l
l
bond isomer of tamibarotene, Am580, is also a superior ligand
for both PML-RAR and RAR, like ATRA.8,13 The three-dimensional
structures of complexes formed by various ligands and the ligand
binding domain (LBD) of RAR, as well as the structural require-
ment of ligands for high-affinity binding to RAR(LBD), have been
* Corresponding authors. Tel.: +81 99 275 5930, fax: +81 99 275 5932 (M.B.), tel.:
+81 3 5841 7848; fax: +81 3 5841 8495 (H.A.).
E-mail addresses: m-baba@vanilla.ocn.ne.jp (M. Baba), aoyama@iam.u-to
kyo.ac.jp (H. Aoyama).
The first two authors contributed equally.
0968-0896/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2009.04.044

M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
4741
Figure 1. Molecular anatomy of tamibarotene.
well characterized by X-ray analysis, docking studies and struc-
2. Results and discussion
ture–activity relationship analysis (Fig. 1).15–17
The required interactions for the formation of stable ligand/
RAR(LBD) complexes have been established to be ionic and hydro-
phobic interactions.14–16 The former type of interaction is a point-
to-point interaction which is specific for the amino acid sequence
(or perhaps more precisely, for the chemical nature of the amino
acid residues in the sequence) of RAR(LBD). On the other hand,
the latter interaction can be regarded as more environmental in
nature, that is, the fold structure of the hydrophobic pocket into
which the tetrahydrotetramethylnaphthyl (TMN) moiety of tami-
barotene (Am80) and/or Am580 fits (indicated by the blue band
in Fig. 1) is an important factor. There is an enormous number of
proteins (perhaps 50,000–70,000 in humans) from the standpoint
of amino acid sequences, but it is thought that the three-dimen-
sional spatial structures (i.e., fold structures) of proteins are far
more highly conserved in evolution than are the amino acid se-
quences.17,18 The number of fold structure types that comprise
all the domains occurring in human proteins is thought to be as
few as approximately 1000.18–20 Therefore, one might expect that
many proteins would contain a fold structure similar to that of the
hydrophobic pocket of RAR(LBD) mentioned above, into which the
TMN skeleton fits; this is the multi-template hypothesis. In addi-
tion, it might be expected that similar folds exhibit similar roles
from the standpoint of biological responses to the corresponding
ligands. On this basis,21 we expected that the TMN skeleton might
act as a multi-template for ATL cell-selective proliferation inhibi-
tors, and so we prepared the TMN analogs listed in Figure 1 (com-
pounds 1–18).
2.1. Screening for ATL cell-selective proliferation inhibitors:
structure–activity relationships
Compounds 1–18 were prepared by usual organic synthetic
methods as shown in Scheme 1 (see Section 4). Briefly, compounds
containing the 5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalene
skeleton, including (1), were prepared by Friedel–Crafts alkylation
as previously described.8 Introduction of acyl groups was per-
formed by Friedel–Crafts acylation catalyzed by AlCl3 (compounds
2–4 and 6–8), except for the pivaloyl group (9) and benzoyl group
(5). Introduction of the pivaloyl group was smoothly achieved by
the use of TiCl4 as a catalyst instead of AlCl3 to give compound 9.
Formyl and carboxylic acid derivatives (12 and 13, respectively)
were obtained by selective oxidation of 2-methyl-5,6,7,8-tetrahy-
dro-5,5,8,8-tetramethylnaphthalene using CAN and KMnO4,
respectively.
For screening of ATL cell-selective inhibitors, two cell lines were
adopted, that is, S1T established from acute-type ATL7,22 and
MOLT-4 established from HTLV-1-negative T-cell leukemia. Chem-
ical(s) which inhibits S1T cell proliferation, but not MOLT-4 cell
proliferation might be suitable lead compound(s) for the develop-
ment of drugs to treat ATL. The effects of compounds 1–18 on the
growth and viability of S1T and MOLT-4 cells were examined. S1T
and MOLT-4 cells were incubated in the absence or presence of
various concentrations of test compounds for 4 days, viable cell
number was determined by the MTT method, and IC50 values were
calculated. The results are shown in Table 1.
In this paper, we describe our structural development study of
TMN analogs as ATL cell-selective proliferation inhibitors. We also
present preliminary data concerning their mechanism of action at
the cellular level.
The most simple hydrophobic skeleton, 5,6,7,8-tetrahydro-
5,5,8,8-tetramethylnaphthalene (TMN: 1) did not show apparent
growth-inhibitory activity toward S1T cells or MOLT-4 cells. How-
ever, introduction of an acetyl group into the 2-position of TMN,

4742
M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
Scheme 1. Synthesis of TMN derivatives.
Table 1
of 2, that is, the formyl derivative 12, caused decreased activity to-
ward S1T cells with retention of moderate activity toward MOLT-4
cells, resulting in loss of the cell type selectivity (SI value of 0.75:
slightly MOLT-4 selective). Reduction of a carbonyl group on the
acetyl moiety of 2, that is, compound 11, also caused decreased
activity toward S1T cells with retention of moderate activity to-
ward MOLT-4 cells, resulting in loss of the cell type selectivity.
Among alkylcarbonyl derivatives (2–4), the activity toward S1T
cells decreased in the order of 4 (isopropyl) > 3 (ethyl) > 2 (methyl),
while the order for MOLT-4 cells was 3 (ethyl) > 4 (isopropyl) > 2
(methyl). The phenylcarbonyl derivative (5) showed about the
same activity toward S1T cells as 2, but the SI value was far lower
than that of 2 (SI = 1.7). Overall, the acetyl group seemed to be the
best substituent for further structural development from the
standpoints of both S1T cell growth-inhibitory activity and cell
type selectivity.
The effect of introduction of a hydroxyl group into the alkylcar-
bonyl derivatives, that is, compounds 6–10, was also investigated.
Comparison of corresponding compounds with and without a hy-
droxyl group, that is, 2 versus 6, 3 versus 7, and 4 versus 8, indi-
cates that introduction of a hydroxyl group had little apparent
effect on the activity. But, there seems to be some indication that
the introduction of a hydroxyl group produced a very slight de-
crease of the activity toward MOLT-4 cells, because compound 6
possesses the highest SI value (12.4) among the compounds inves-
tigated. Introduction of a hydroxyl group into the phenylcarbonyl
derivative (5), that is, compound 10, potentiated the activity to-
ward both S1T and MOLT-4 cells. The tertiary-butylcarbonyl analog
(9) possessed moderate cell growth-inhibitory activity towards
both S1T and MOLT-4 cells, but it showed almost no cell type
selectivity.
Cell type-selective proliferation inhibitory activity of tetrahydrotetramethylnaphtha-
lene derivatives.
Compds.
IC50 values (
l
M)
SI valuesa
S1T cells
MOLT-4 cells
1
2
3
4
5
6
7
8
>100
6.9
4.7
3.8
7.0
6.7
4.7
6.0
41.5
15.2
393
33.0
>100
29.7
6.9
7.0
37.0
12.6
>100
66.0
21.5
34.6
11.8
82.9
32.3
31.9
43.2
28.3
34.4
24.8
61.1
44.4
36.4
11.9
39.4
9.9
—
9.6
4.6
9.l
1.7
12.4
6.9
5.3
1.0
1.9
0.87
0.75
—
1.5
5.3
1.7
1.1
0.8
9
10
11
12
13
14
15
16
17
18
a
IC50 for MOLT-4 cells/IC50 for SIT cells.
that is, compound 2, resulted in appearance of the activity. Inter-
estingly, compound 2 showed S1T cell-selective proliferation-
inhibitory activity with a selectivity index (SI: IC50 value for
MOLT-4 cells/IC50 value for S1T cells) value of 9.6, that is, S1T cells
are one magnitude of order more sensitive to 2 than MOLT-4 cells.
Further introduction of one and two methyl groups at the aliphatic
b-carbon of the carbonyl moiety, that is, ethylcarbonyl (3) and iso-
propylcarbonyl (4) derivatives, respectively, caused enhancement
of the growth-inhibitory activity towards both S1T and MOLT-4
cells with retention of S1T selectivity (SI values of 4.6 and 9.1,
respectively). Deletion of the methyl group on the acetyl moiety
The tetramethylcyclohexane moiety of the above-mentioned
compounds seems to be essential for the activity, because the dem-
ethyl analog of 6, that is, compound 19, and its oxa-analogs (20 and
21), and dimethyl analogs of acetophenone (compounds 22–24)

M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
4743
Table 2
Effect of compound 6 (20
lM) on S1T/MOLT-4 cell cycle (2-1) and apoptosis induction
(2-2)
Cell population (%)
Phase
SIT cells
MOLT-4 cells
2-1
Non-treated
G0/G1
G2/M
S
41.39
18.08
40.53
40.27
12.42
47.31
Chart 1.
were inactive (IC50 values of these compounds toward both S1T
Treated for 24 h
G0/G1
G2/M
S
37.0
23.0
39.95
42.14
11.10
46.76
and MOLT-4 cells were larger than 100
lM) (Chart 1). Some other
analogs 12–18 were also prepared and their activity was investi-
gated. Although the thiocarbonyl analog of 6, that is, compound
15, showed almost the same potency toward S1T cells as 6, its
activity toward MOLT-4 cells was increased (IC50 value changed
Apoptosis (%)
S1T cells
+ compd 6
MOLT-4 cells
None
None
+ compd 6
to 36.4 lM from 82.9 lM), resulting in S1T cell-selectivity with
an SI value of 5.3. Other compounds were found to be almost
non-selective with SI values of 0.75–1.7. Compound 16 is an analog
of 6 in which the phenolic hydroxyl group is methylated, and the
two compounds showed almost the same activity toward S1T cells,
but the activity toward MOLT-4 cells of 16 was much more potent
than that of 6, resulting in loss of cell type selectivity. Compound
17 is an amide analog of 2, whose activity toward S1T cells was
much lower than that of 2, while its activity toward MOLT-4 cells
was more potent than that of 2.
2-2
Treated for 24 h
Treated for 48 h
7.9
4.9
10.1
10.1
6.9
4.0
7.0
4.0
least two molecular bases for the cell proliferation-inhibiting activ-
ity elicited by our TMN derivatives, of which one is common to
both S1T and MOLT-4 cells and the other is specific to S1T cells,
(ii) there may be a specific target molecule in S1T cells which rec-
ognizes the structure shown as the Markush structure in Figure 2.
The requirement of at least one hydrogen atom at the a-carbon of
the carbonyl moiety might suggest that the active form is an enol-
like form of the compounds.
2.2. Correlation analysis
The correlation of the cell proliferation-inhibitory activities of
the prepared compounds toward S1T cells and MOLT-4 cells was
analyzed by plotting the IC50 values for S1T cells (vertical scale)
and those for MOLT-4 cells (horizontal scale) (Fig. 2).
As shown in Figure 2, the active compounds whose IC50 values
for S1T/MOLT-4 cells are less than 100 lM (2–12 and 14–18) could
apparently be divided into two groups, that is, one group is the
compounds with no cell type-selective activity (compounds 5, 9–
12, 14, and 16–18: these compounds were located around the line
defined by IC50/S1T cells = IC50/MOLT-4 cells in Fig. 2), and the
other group is the compounds with S1T cell-selective toxicity
[compounds 2–4, 6–8, and 15: all of these possess IC50 values of
2.3. Cell level analysis
Among the compounds prepared, compound 6 showed superior
activity with the highest SI value of 12.4 (Table 1). Cell cycle and
apoptosis analyses were performed by fluorescence flow cytome-
try (Table 2). As shown in Table 2-1, treatment of S1T cells with
20 lM compound 6 for 24 h resulted in increase of the population
of G2 M stage cells and decrease of the population in both G0/G1
and S-phase, indicating that 6 induced G2-arrest of S1T cells. By
contrast, treatment of MOLT-4 cells with 6 had no apparent effect
on the cell cycle. Similarly, as shown in Table 2-2, treatment of S1T
cells with compound 6 for 24 and 48 h induced increased apoptotic
cell death [the ratio of apoptosis (%) in S1T cells untreated and
treated with 6 for 24 or 48 h was 1.3 or 2.1, respectively], while
24 and 48 h treatment of MOLT-4 cells had no effect on the ratio
of apoptosis. These results suggest that 6 selectively induces G2-ar-
rest and apoptosis of S1T cells. The selectivity of 6 for ATL cells was
confirmed by the use of several HTLV-1-positive and negative cell
lines (unpublished observations). The target molecule(s) of 6 and
related compounds and the molecular mechanism of G2-arrest/
apoptosis elicited by 6 remain to be elucidated.
3.8–6.9
lM toward S1T cells with various IC50 values (21.5–
82.9 M) toward MOLT-4 cells, and they are located inside the dot-
l
ted square in Fig. 2]. The apparent common structural feature of
the compounds of the latter group is illustrated as a Markush
structure in Figure 2. Among the compounds we prepared, all of
the compounds which fitted the Markush structure (Fig. 2) were
grouped into the latter group without exception. In other words,
compounds with no hydrogen at the a-carbon of the carbonyl moi-
ety are non-selective. The results suggests that (i) there exist at
3. Conclusion
In conclusion, we extracted the TMN skeleton from our synthetic
retinoids based on the multi-template hypothesis and micro-re-
versed fragment-based drug design hypothesis (molecular anatomy
to extract small protopharmacophore skeletons which are applica-
ble as multi-templates).18 Preparation and screening of TMN deriv-
atives resulted in discovery of ATL cell-selective proliferation
inhibitors,
including
2-acetyl-3-hydroxy-5,6,7,8-tetrahydro-
5,5,8,8-tetramethylnaphthalene (6) which selectively induced G2-
arrest/apoptosis in S1T cells. Structure–activity relationship analy-
sis of the TMN derivatives suggested the existence of a specific target
molecule(s) for eliciting S1T cell-selective growth-inhibitory activ-
ity. Studiestoidentifytheputativetarget molecule(s) andthemolec-
ular mechanism are under way.
Figure 2. Correlation of S1T and MOLT-4 cells inhibitory activities of TMN
derivatives towards S1T and MOLT-4 cells.

4744
M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
and extracted with ethyl acetate. The extract successively washed
4. Experimental
4.1. Cells
with water, saturated aqueous NaHCO3 and brine and then dried
over MgSO4. The solvent was evaporated, and the residue was puri-
fied by silica gel column chromatography (hexane/CH2Cl2 = 10/1)
to give 2 (359 mg, 78%) as a colorless oil. 1H NMR (500 MHz, CDCl3)
d 7.92 (d, 1H, J = 1.9 Hz), 7.70 (dd, 1H, J = 8.0, 1.9 Hz), 7.38 (d, 1H,
J = 8.0 Hz), 2.55 (s, 3H), 1.69 (s, 4H), 1.30 (s, 6H), 1.28 (s, 6H); HRMS
(FAB) calcd for C16H23O 231.1749; found: 231.1780 (M+H)+.
4.1.1. Cell culture
The HTLV-1 carrying T-cell line S1T was established from the
peripheral blood mononuclear cells of an ATL patient, as described
previously.7,22 The HTLV-1-negative T-cell line MOLT-4 was also
used.7 These cell lines were maintained in RPMI1640 medium sup-
plemented with 10% v/v heat-inactivated fetal bovine serum, 100
4.2.4. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl ethyl
ketone (3)
U/ml penicillin G, and 100 lg/ml streptomycin.
27% (colorless oil); 1H NMR (500 MHz, CDCl3) d 7.94 (d, 1H,
J = 2.0 Hz), 7.70 (dd, 1H, J = 8.0, 2.0 Hz), 7.38 (d, 1H, J = 8.0 Hz),
2.97 (q, 2H, J = 7.3 Hz), 1.70 (s, 4H), 1.31 (s, 6H), 1.29 (s, 6H), 1.22
(t, 3H, J = 7.3 Hz); HRMS (FAB) calcd for C17H25O 245.1905; found:
245.1924 (M+H)+.
4.1.2. Cell cycle analysis
Cells were seeded at a density of 1 Â 106 cells per ml in 24-well
plate and incubated in the absence or the presence of 2-acetyl-3-
hydroxy-5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalene (6) at
a concentration of 20 lM. After 24 h, cells were washed with phos-
4.2.5. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl
isopropyl ketone (4)
phate buffered saline (PBS), fixed with 1% paraformaldehyde, per-
meabilized with 70% ethanol and incubated with propidium
iodide/RNA staining buffer (BD Biosciences, San Diego, CA) for
15 min. The stained cells were analyzed by FACS Calibur (Becton
Dickinson, San Jose, CA). The distribution of cell cycle phase was
analyzed by MODFIT software.
38% (pale yellow oil); 1H NMR (500 MHz, CDCl3) d 7.95 (d, 1H,
J = 1.8 Hz), 7.70 (dd, 1H, J = 8.0, 1.8 Hz), 7.38 (d, 2H, J = 8.0 Hz),
3.54 (septet, 1H, J = 7.0 Hz), 1.70 (s, 4H), 1.31 (s, 6H), 1.29 (s, 6H),
1.21 (d, 6H, J = 7.0 Hz); HRMS (FAB) calcd for C18H27O 259.2062;
found: 259.2047 (M+H)+.
4.1.3. Assays for apoptosis
Cells were seeded at a density of 1 Â 106 cells per ml in 24-well
plate and incubated in the absence or the presence of 2-acetyl-3-
hydroxy-5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalene (6) at
4.2.6. 2-Acetyl-3-hydroxy-5,6,7,8-tetrahydro-5,5,8,8-
tetramethylnaphthalene (5,6,7,8-Tetrahydro-3-hydroxy-5,5,
8,8-tetramethyl-2-naphthyl methyl ketone) (6)24
Pale yellow solid; 1H NMR (500 MHz, CDCl3) d 11.85 (s, 1H),
7.63 (s, 1H), 6.88 (s, 1H), 2.59 (s, 3H), 1.66 (s, 4H), 1.27 (s, 6H),
1.25 (s, 6H); HRMS (FAB) calcd for C16H23O2 247.1698; found:
247.1705 (M+H)+.
a concentration of 20 lM. After 24 or 48 h, cells were washed with
PBS and incubated with fluorescein isothiocyanate-conjugated An-
nexin V (Invitrogen, Eugene, OR) in annexin-binding buffer (10 mM
HEPES, 140 mM NaCl, and 2.5 mM CaCl2, pH 7.4) for 15 min. After
washing, the stained cells were analyzed by FACS Calibur (Becton
Dickinson).
4.2.7. 5,6,7,8-Tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2-nap-
hthyl ethyl ketone (7)
45% (white solid); 1H NMR (500 MHz, CDCl3) d 11.96 (s, 1H),
7.68 (s, 1H), 6.90 (s, 1H), 3.03 (q, 2H, J = 7.3 Hz), 1.68 (s, 4H), 1.28
(s, 6H), 1.27 (s, 6H), 1.25 (t, 3H, J = 7.3 Hz); Anal. Calcd for
C17H24O2: C, 78.42; H, 9.29; O, 12.29. Found: C, 78.19; H, 9.23; O,
12.58.
4.2. Chemistry
4.2.1. General
1H NMR spectra were recorded on
a JEOL JNM-GX500
(500 MHz) spectrometer. Chemical shifts are expressed in parts
per million relative to tetramethylsilane. Mass spectra were re-
corded on a JEOL JMS-DX303 spectrometer.
4.2.8. 5,6,7,8-Tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2-nap-
hthyl isopropyl ketone (8)
47% (colorless oil); 1H NMR (500 MHz, CDCl3) d 12.11 (s, 1H),
7.71 (s, 1H), 6.91 (s, 1H), 3.60 (septet, 1H, J = 7.0 Hz), 1.68 (s, 4H),
1.29 (s, 6H), 1.27 (s, 6H), 1.24 (d, 6H, J = 7.0 Hz); HRMS (FAB) calcd
for C18H27O2 275.2011; found: 275.2032 (M+H)+.
4.2.2. 5,6,7,8-Tetrahydro-2-hydroxy-5,5,8,8-
tetramethylnaphthalene23
Toasolutionofphenol(1.02 g, 10.8 mmol)in CH2Cl2 (5.0 mL)was
added aluminum chloride (144 mg, 10.8 mmol) and 2,5-dichloro-
2,5-dimethylhexane (2.18 g, 11.9 mmol) at room temperature, and
the mixture was stirred at the same temperature for 19 h. The reac-
tion mixture was poured into ice-water and extracted with ethyl
acetate. The extract successively washed with water, saturated
aqueous NaHCO3 and brine and then dried over MgSO4. The solvent
was evaporated, and the residue was purified by recrystallization
from hexane to give the title compound (1.83 g, 83%) as a white solid.
FAB-MS m/z: 204 (M+H)+; 1H NMR (500 MHz, CDCl3) d 7.17 (d, 1H,
J = 8.5 Hz), 6.75 (d, 1H, J = 3.0 Hz), 6.62 (dd, 1H, J = 8.5, 3.0 Hz), 4.49
(s, 1H), 1.66 (s, 4H), 1.25 (s, 6H), 1.24 (s, 6H).
4.2.9. 5,6,7,8-Tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2-nap-
hthyl tert-butyl ketone (9)
9% (yellow oil); 1H NMR (500 MHz, CDCl3) d 12.30 (s, 1H), 7.97
(s, 1H), 6.92 (s, 1H), 2.05 (s, 1H), 1.68 (s, 4H), 1.45 (s, 9H), 1.29 (s,
6H), 1.27 (s, 6H); HRMS (FAB) calcd for C19H29O2 289.2168; found:
289.2135 (M+H)+.
4.2.10. 5,6,7,8-Tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2-
nap-hthyl phenyl ketone (10)
9% (pale yellow oil); 1H NMR (500 MHz, CDCl3) d 11.63 (s, 1H),
7.69 (s, 1H), 7.67 (s, 1H), 7.61–7.58 (m, 2H), 7.55–7.49 (m, 3H), 6.99
(s, 1H), 2.05 (s, 1H), 1.70–1.65 (m, 4H), 1.30 (s, 6H), 1.17 (s, 6H);
HRMS (FAB) calcd for C21H25O2 309.1855; found: 309.1863 (M+H)+.
4.2.3. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl
methyl ketone (2): General procedure for the synthesis of
compounds 2–4, 6–10
To a solution of 5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphtha-
lene (1)8 (377 mg, 2.00 mmol) in CH2Cl2 (3.0 mL) was added alumi-
num chloride (296 mg, 2.22 mmol) and acetyl chloride (155 lL,
4.2.11. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-methylnaph-
thalene8
2.18 mmol) at room temperature, and the mixture was stirred at
50 °C for 2 h. The reaction mixture was poured into ice-water
To a suspension of aluminum chloride (200 mg, 1.50 mmol) in
toluene (10 mL) was added 2,5-dichloro-2,5-dimethylhexane

M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
4745
(4.70 g, 25.7 mmol) at room temperature, and the mixture was
stirred at the same temperature for 24 h. The reaction mixture
was poured into ice-water and extracted with ethyl acetate. The
extract was successively washed with water, saturated aqueous
NaHCO3 and brine and then dried over MgSO4. The solvent was
evaporated to give the title compound (4.90 g, 94%) as a pale yel-
low oil. This crude product was used for the next step without fur-
duced pressure. The residue was dissolved in CH2Cl2 (10 mL),
and to this was added N-methoxy-N-methylamine hydrochloride
(116 mg, 1.20 mmol) and triethylamine (4.0 mL, 28.7 mmol). The
mixture was stirred at room temperature for 17 h. The solvent
was removed under reduced pressure and the residue was diluted
with ethyl acetate. The organic solution successively washed with
diluted HCl, water, saturated aqueous NaHCO3 and brine, and then
dried over MgSO4. The solvent was evaporated, and the residue
was purified by silica gel column chromatography (hexane/ethyl
acetate = = 10/1) to give 18 (139 mg, 50%) as a white solid. 1H
NMR (500 MHz, CDCl3) d 7.34 (d, 1H, J = 1.8 Hz), 7.30 (d, 1H,
J = 8.0 Hz), 7.16 (dd, 1H, J = 8.0, 1.8 Hz), 3.10 (br s, 1H), 3.00 (br
s, 1H), 1.68 (s, 4H), 1.29 (s, 6H), 1.28 (s, 6H); HRMS (FAB) calcd
for C17H26NO2 276.1964; found: 276.1991 (M+H)+.
ther purification. 1H NMR (500 MHz, CDCl3)
d 7.20 (d, 1H,
J = 8.0 Hz), 7.10 (d, 1H, J = 1.2 Hz), 6.95 (dd, 1H, J = 8.0, 1.2 Hz),
2.29 (s, 3H), 1.67 (s, 4H), 1.28 (s, 6H), 1.26 (s, 6H).
4.2.12. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthaldehyde
(12)
To a solution of 5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-meth-
ylnaphthalene (202 mg, 1.00 mmol) in AcOH (8.2 mL) was added
cerium ammonium nitrate (2.40 g, 4.37 mmol) at room tempera-
ture and the mixture was stirred at 100 °C for 1 h. The reaction
mixture was poured into ice-water and extracted with ethyl ace-
tate. The extract was successively washed with water, saturated
aqueous NaHCO3 and brine and then dried over MgSO4. The sol-
vent was evaporated, and the residue was purified by silica gel
column chromatography (hexane/ethyl acetate = 15/1) to give 12
(106 mg, 49%) as a pale yellow solid. 1H NMR (500 MHz, CDCl3)
d 9.95 (s, 1H), 7.83 (d, 1H, J = 2.0 Hz), 7.62 (dd, 1H, J = 8.0,
2.0 Hz), 7.46 (d, 1H, J = 8.0 Hz), 1.72 (s, 4H), 1.32 (s, 6H), 1.31 (s,
6H); HRMS (FAB) calcd for C15H21O 217.1592; found: 217.1619
(M+H)+.
4.2.16. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl
phenyl ketone (5)
To a solution of 18 (55.0 mg, 200 mmol) in diethyl ether
(2.0 mL) was added phenylmagnesium bromide (prepared from
bromobenzene and magnesium in THF) at room temperature,
and the mixture was stirred at the same temperature for 22 h.
The reaction mixture was poured into saturated aqueous NH4Cl
and extracted with ethyl acetate. The extract was successively
washed with water, saturated aqueous NaHCO3 and brine and
then dried over MgSO4. The solvent was evaporated, and the res-
idue was purified by silica gel column chromatography (hexane/
ethyl acetate = 2/1) to give 5 (14.9 mg, 25%) as a colorless oil. 1H
NMR (500 MHz, CDCl3) d 7.80 (d, 1H, J = 7.3 Hz), 7.79 (s, 1H),
7.57 (t, 1H, J = 7.3 Hz), 7.55 (dd, 1H, J = 8.0, 1.8 Hz), 7.47 (t, 1H,
J = 8.0 Hz), 7.39 (d, 1H, J = 8.0 Hz), 1.72 (s, 4H), 1.31 (s, 6H), 1.29
4.2.13. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthoic acid
(13)
To a solution of 5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-meth-
ylnaphthalene (3.52 g, 17.4 mmol) in pyridine (12 mL) was added
KMnO4 (6.70 g, 42.4 mmol) and sodium hydroxide (1.00 g,
25.0 mmol) at room temperature, and the mixture was stirred at
95 °C for 5 h. The reaction mixture was filtered through a Celite
pad and the filtrate was added to diluted HCl to acidify it. The mix-
ture was extracted with ethyl acetate and then dried over MgSO4.
The solvent was evaporated, and the residue was purified by silica
gel column chromatography (hexane/ethyl acetate = 4/1) to give
13 (142 mg, 3.0%) as a colorless solid. 1H NMR (500 MHz, CDCl3)
d 8.05 (d, 1H, J = 1.8 Hz), 7.82 (dd, 1H, J = 8.0, 1.8 Hz), 7.40 (d, 1H,
J = 8.0 Hz), 1.71 (s, 4H), 1.32 (s, 6H), 1.30 (s, 6H); HRMS (FAB) calcd
for C15H21O2 233.1542; found: 233.1563 (M+H)+.
(s, 6H); HRMS (FAB) calcd for C21H25
O 293.1905; found:
293.1882 (M+H)+.
4.2.17. rac-1-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-
naphthyl)ethanol (11)
To a solution of 2 (50.0 mg, 217
lmol) in MeOH (1.0 mL) was
added NaBH4 (10.0 mg, 264 mol) at room temperature, and the
l
mixture was stirred at the same temperature for 30 min. The reac-
tion mixture was poured into water and extracted with ethyl ace-
tate. The extract was successively washed with water, saturated
aqueous NaHCO3 and brine and then dried over MgSO4. The solvent
was removed in vacuo to give 11 as a colorless oil (47.9 mg, 95%).
1H NMR (500 MHz, CDCl3) d 7.30 (s, 1H), 7.29 (d, 1H, J = 6.0 Hz),
7.14 (dd, 1H, J = 6.0, 2.0 Hz), 4.85 (q, 1H, J = 6.7 Hz), 1.68 (s, 4H),
1.50 (d, 3H, J = 6.7 Hz), 1.29 (s, 6H), 1.27 (s, 6H); HRMS (FAB) calcd
for C16H25O 233.1905; found 233.1930 (M+H)+.
4.2.14. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthylamide
(17)
To a solution of 13 (465 mg, 2.00 mmol) in CH2Cl2 (5.0 mL) was
added oxalyl chloride (250 lL, 2.95 mmol) and DMF (3 drops) at
4.2.18. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-3-hydroxy-2-
naphthoic acid (14)
0 °C, and the mixture was stirred at the same temperature. After
1 h, to this was added 25% aqueous ammonia and the mixture
was stirred at room temperature for 15 h. The reaction was
quenched by adding water and extracted with CH2Cl2. The extract
was successively washed with water and brine, and then dried over
MgSO4. The solvent was evaporated, and the residue was purified
by recrystallization from ethyl acetate to give 17 (453 mg, 98%)
as a white solid. 1H NMR (500 MHz, CDCl3) d 7.81 (d, 1H,
J = 2.0 Hz), 7.49 (dd, 1H, J = 8.0, 2.0 Hz), 7.37 (d, 1H, J = 8.0 Hz),
1.70 (s, 4H), 1.31 (s, 6H), 1.29 (s, 6H); HRMS (FAB) calcd for
C15H22NO 232.1701; found: 232.1718 (M+H)+.
To a solution of 624 (98.5 mg, 400
lmol) in EtOH (2.0 mL) was
added aqueous NaOCl solution (active chlorine concentration: 5%,
3 mL) at room temperature, and the mixture was stirred at 70 °C
for 3 h. To this was added NaOH (300 mg, 7.50 mmol) and the mix-
ture was stirred at the same temperature. After 1 h, to this was
added I2 (305 mg, 1.20 mmol) and the mixture was stirred at the
same temperature for 3 h. After the reaction mixture had cooled
to room temperature, the mixture was back-extracted with CH2Cl2.
The aqueous layer was acidified by the addition of 2 N HCl, ex-
tracted with CH2Cl2, and then dried over MgSO4. The solvent was
evaporated, and the residue was purified by silica gel column chro-
matography (CH2Cl2/MeOH = 9/1) to give 14 (8.0 mg, 8.1%) as a
pale yellow solid. 1H NMR (500 MHz, DMSO-d6) d 13.73 (br s,
1H), 10.84 (br s, 1H), 7.69 (s, 1H), 6.85 (s, 1H), 1.58–1.64 (m, 4H),
1.22 (s, 6H), 1.20 (s, 6H); HRMS (FAB) calcd for C15H21O3
249.1491; found: 249.1522 (M+H)+.
4.2.15. 5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthyl-N-
methoxy-N-methylamide (18)
To a solution of 13 (232 mg, 1.00 mmol) in CH2Cl2 (10 mL) was
added oxalyl chloride (294 mg, 2.40 mmol) and DMF (1 drop) at
room temperature, and the mixture was stirred at the same tem-
perature. After 5 h, the volatile material was removed under re-

4746
M. Nakamura et al. / Bioorg. Med. Chem. 17 (2009) 4740–4746
4.2.19. 1-(5,6,7,8-Tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2-
naphthyl)ethanethione (15)
References and notes
To a solution of 624 (13.3 mg, 53.9
lmol) in toluene (1.0 mL)
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was added Lawesson’s reagent (32 mg, 80.9 mol) at room temper-
l
ature, and the mixture was stirred at 120 °C for 24 h. The reaction
mixture was poured into water and extracted with CH2Cl2. The sol-
vent was evaporated, and the residue was purified by silica gel col-
umn chromatography (hexane/ethyl acetate = 12/1) to give 15 as a
yellow solid (4.2 mg, 30%). 1H NMR (500 MHz, CDCl3) d 12.99 (s,
1H), 7.82 (s, 1H), 6.99 (s, 1H), 3.12 (s, 3H), 1.69 (s, 4H), 1.30 (s,
6H), 1.29 (s, 6H); HRMS (FAB) calcd for C16H23OS 263.1470; found:
263.1446 (M+H)+.
3. Proietti, F. A.; Carneiro-Proietti, A. B.; Catalan-Soares, B. C.; Murphy, E. L.
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4.2.20. 5,6,7,8-Tetrahydro-3-methoxy-5,5,8,8-tetramethyl-2-
naphthyl methyl ketone (16)
To a solution of 624 (123 mg, 500
lmol) in acetone (2.0 mL)
was added K2CO3 (138 mg, 1.00 mmol) and MeI (400 L,
l
6.42 mmol) at room temperature, and the mixture was stirred
at 70 °C for 10 h. The reaction mixture was filtered, washed with
acetone, and evaporated. The residue was purified by silica gel
column chromatography (hexane/ethyl acetate = 20/1) to give 16
(92.4 mg, 71%) as a white solid. 1H NMR (500 MHz, CDCl3) d
7.71 (s, 1H), 6.82 (s, 1H), 3.87 (s, 3H), 2.57 (s, 3H), 1.69–1.62
(m, 4H), 1.28 (s, 6H), 1.25 (s, 6H); HRMS calcd for C17H25O2:
261.1855; found: 261.1893 (M+H)+.
Acknowledgments
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The work described in this paper was partially supported by
Grants-in-Aid for Scientific Research from The Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan, and the Japan
Society for the Promotion of Science.