S. Paula et al. / Bioorg. Med. Chem. 17 (2009) 6613–6619
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M3, if residues 250 and 254 are involved) and prevent their relative
movement, which is necessary for the catalytic cycle to continue.
2-(4-Methoxybenzyl)hydroquinone (2c). Solvent: DMI. Purifi-
cation by silica gel column chromatography (hexanes–ethyl ace-
tate, 7:3) yielded a tan solid (734 mg, 36%). Mp 128–130 °C. 1H
NMR (DMSO-d6): d 3.70 (s, 3H), 3.71 (s, 2H), 6.38–6.42 (m, 2H),
6.59 (d, J = 8.3 Hz, 1H), 6.82 (m, 2H), 7.11 (m, 2H), 8.51 (s, 1H,
exchangeable with D2O), 8.61 (s, 1H, exchangeable with D2O). 13C
NMR (DMSO-d6): d 34.92, 55.54, 113.74, 114.18, 116.09, 117.21,
129.10, 130.25, 133.73, 147.81, 150.26, 157.93. HRMS (EI):
230.0942 (calcd for C14H14O3: 230.0943).
2-(2-Furanylmethyl)hydroquinone (2d). Solvent: pyridine.
Purification by column chromatography (hexanes–ethyl acetate,
3:1) gave 560 mg (33%) of a pale yellow solid. Mp 57–60 °C.33 1H
NMR (DMSO-d6): d 3.79 (s, 2H), 6.04 (br s, 1H), 6.35–6.46 (m,
3H), 6.60 (d, J = 8 Hz, 1H), 7.51 (s, 1H), 8.58 (s, 1H, exchangeable
with D2O), 8.70 (s, 1H, exchangeable with D2O). 13C NMR (DMSO-
d6): d 28.3, 106.7, 110.9, 114.3, 116.1, 116.9, 125.5, 142.0, 147.8,
150.2, 154.7.
2.4. Conclusion and future directions
In this study, we utilized several synthetic routes for the prep-
aration of hydroquinone-based SERCA inhibitors. We demon-
strated that these routes afford access to novel compounds with
good inhibitory potencies. In comparison to the preparation of
TG analogues, the presented synthetic approaches are straightfor-
ward and economical because they involve no more than two steps
and require only inexpensive, commercially available starting
materials. Future efforts will be directed at a more comprehensive
exploitation of the outlined synthetic routes for the refinement and
expansion of existing SARs for SERCA inhibition by hydroquinones.
Finally, the preparation of inhibitors tethered to a second molecu-
lar entity will be explored further.
General procedure for synthesis of unsymmetrically disub-
stituted hydroquinones. A mixture of 4-nitrobenzylhydroquinone
(200 mg, 0.8 mmol) and the appropriate alcohol (1 mL) was placed
in a round bottom flask, cooled in an ice bath, and concentrated
sulfuric acid (0.5 mL) was added dropwise with stirring, followed
by the addition of glacial acetic acid (1 mL). A brown solid precip-
itated within 10 min. After 1 h, the reaction was quenched with
water and the crude product was taken up in ethyl acetate, washed
with water, and dried with sodium sulfate. The organic layer was
then concentrated to a crude oil by rotary evaporation.
2-(4-Nitrobenzyl)-5-tert-amylhydroquinone (3a). Purified by
silica gel column chromatography (hexanes–ethyl acetate, 7:3).
The obtained oil was triturated with hexanes to give a yellow pow-
der (40 mg, 15%). Mp 108–112 °C. 1H NMR (CDCl3): d 0.66 (t,
J = 7.8 Hz, 3H), 1.31 (s, 6H), 1.82 (qr, J = 7.8 Hz, 2H), 3.97 (s, 2H),
6.36 (s, 1H), 6.63 (s, 1H), 7.38 (m, 2H), 8.14 (m, 2H). 13C NMR
(CDCl3): d 9.61, 27.67, 29.58, 35.53, 38.10, 114.90, 116.20, 118.56,
123.76, 129.66, 134.64, 146.52, 146.75, 148.18, 148.58. HRMS
(ES): 338.1385 (calcd for C18H21NO4Na: 338.1368).
2-(4-Nitrobenzyl)-5-(3-methyl-3-pentyl)hydroquinone (3b).
Purified by silica gel column chromatography (hexanes–ethyl ace-
tate, 6:4). The obtained oil was triturated with hexanes to give a
yellow solid (70 mg, 26%). Mp 84–87 °C. 1H NMR (CDCl3): d 0.65
(t, J = 7.4 Hz, 6H), 1.23 (s, 3H), 1.51 (m, 2H), 2.07 (m, 2H), 3.96 (s,
2H), 6.35 (s, 1H), 6.59 (s, 1H), 7.34 (m, 2H), 8.09 (m, 2H). 13C
NMR (CDCl3): d 9.22, 23.59, 32.35, 35.53, 41.93, 117.44, 118.41,
123.64, 123.74, 129.67, 132.87, 146.45, 146.71, 148.23, 148.72.
HRMS (ES): 330.1704 (calcd for C19H24NO4 (MH+): 330.1705).
2,5-Di-tert-amylhydroquinone (5a). A mixture of hydroqui-
none (4, 2.0 g, 18 mmol), tert-amyl alcohol (3.22 g, 36.5 mmol),
and acetic acid (10 mL) was added to a round bottom flask, fol-
lowed by the dropwise addition of concentrated sulfuric acid
(2 mL). The contents of the flask were stirred for 7 h at room tem-
perature. The reaction was then quenched with ice water and the
precipitate was collected by suction filtration and washed with
water. Purification by recrystallization from benzene yielded a
white solid (3.55 g, 78%). Mp 178–180 °C. 1H NMR (CDCl3): d 0.66
(t, J = 7.8 Hz, 6H), 1.31 (s, 12H), 1.80 (qr, J = 7.8 Hz, 4H), 4.32 (br
s, 2H, exchangeable with D2O), 6.49 (s, 2H). 13C NMR (CDCl3): d
9.60, 27.61, 33.37, 37.67, 116.90, 132.61, 147.31. HRMS (EI):
250.1932 (calcd for C16H26O2: 250.1933).
3. Experimental
3.1. Organic synthesis
Chemistry. All reagents were purchased from Sigma–Aldrich
(St. Louis, MO) or Fisher Scientific (Pittsburgh, PA) and were used
without further purification. Reactions were carried out under an
argon atmosphere. Melting points were measured with a Thomas
Hoover melting point apparatus and are uncorrected. Thin layer
chromatography (TLC) was performed using Baker-flex silica gel
sheets and detection of spots was made by UV light and/or iodine
vapors. Column chromatography was performed using silica gel
70–230-mesh. Proton (500 MHz) and carbon (125.7 MHz) NMR
spectra were obtained on a JEOL Eclipse 500 spectrometer (Pea-
body, MA). Chemical shifts are reported as parts per million
(ppm) relative to TMS in CDCl3 or DMSO-d6. For all compounds
not previously characterized in the literature, high resolution mass
spectra (HRMS) using either electron impact (EI) or electrospray
(ESI) techniques were obtained using the facilities at the Mass
Spectrometry Laboratory at the University of Illinois at Urbana.
General procedure for synthesis of monosubstituted hydro-
quinones (2a–d). Following the procedure of Ozaki et al.,33 1,4-
cyclohexanedione (1 g, 8.9 mmol), the appropriate aldehyde
(8.9 mmol), and LiCl (380 mg, 8.9 mmol) were dissolved in 5 mL
of either 1,3-dimethyl-2-imidazolidinone (DMI) or pyridine. The
mixture was stirred for 1 h at 160–170 °C or, if pyridine was the
solvent, refluxed for 1 h. Then, the reaction mixture was diluted
with ethyl ether, washed twice with water, and dried with anhy-
drous sodium sulfate. The crude product was purified by silica
gel column chromatography.
2-Benzylhydroquinone (2a). Solvent: pyridine. Purification by
column chromatography (hexanes–ethyl acetate, 3:1) followed
by recrystallization from benzene–hexane gave an off-white solid
(786 mg, 44%). Mp 105–106.5 °C, literature value: 101–103 °C.47
1H NMR (DMSO-d6): d 3.78 (s, 2H), 6.42 (m, 2H), 6.60 (m, 1H),
7.12–7.29 (m, 5H), 8.54 (s, 1H, exchangeable with D2O), and 8.66
(s, 1H, exchangeable with D2O). 13C NMR (DMSO-d6): d 35.8,
113.9, 116.1, 117.3, 126.2, 128.6, 128.7, 129.3, 141.9, 147.9, 150.3.
2-(4-Nitrobenzyl)hydroquinone (2b). Solvent: DMI. Purifica-
tion by silica gel column chromatography (hexanes–ethyl acetate,
6:4) gave a yellow solid (286 mg, 13%). Mp 152–154 °C. 1H NMR
(DMSO-d6): d 3.92 (s, 2H), 6.45–6.49 (m, 2H), 6.62 (d, J = 8.7 Hz,
1H), 7.46 (d, J = 8.7 Hz, 2H), 8.14 (d, J = 8.7 Hz, 2H), 8.62 (s, 1H,
exchangeable with D2O), 8.77 (s, 1H, exchangeable with D2O). 13C
NMR (DMSO-d6): d 39.76, 114.56, 116.36, 117.51, 123.95, 127.03,
130.32, 146.29, 147.97, 150.41. HRMS (EI): 245.0690 (calcd for
C13H11NO4: 245.0688).
2,5-Di-(3-methyl-3-pentyl)hydroquinone (5b). To a mixture
of hydroquinone (4, 1.0 g, 9 mmol) and 3-methyl-3-pentanol
(1.98 g, 19 mmol), sulfuric acid (70% aqueous solution, 15 mL)
was added dropwise at room temperature. During the addition, a
white precipitate formed. After 1 h, the reaction was quenched
with ice water. The precipitate was collected by suction filtration
and washed with water. Purification by recrystallization (metha-
nol/water) yielded a white crystalline product (1.46 g, 58 %). Mp