Journal of Medicinal Chemistry
Article
1H), 6.79 (dd, 1H), 6.86−6.89 (m, 1H). ESI-MS (M + Na+)
calculated, 220.30; found, 220.10.
preliminary pharmacophore model is proposed based on the
structure−activity relationships. Molecules with in vitro activity
showed promising in vivo efficacy in a mouse model of diabetic
neuropathy. Our findings support the development of a novel
class of drugs to treat diabetic neuropathy.
(2R)-3-(2-Methoxyphenoxy)propane-1,2-diol ((R)-1). A sus-
pension of NaOH (298 mg, 7.45 mmol) in anhydrous DMF (2 mL)
was mixed with guaiacol (616 mg, 4.96 mmol) and (R)-(−)-α-
monochlorohydrine (822 mg, 7.44 mmol) in a microwave vessel. The
reaction vessel was placed in the microwave and was irradiated at 210
°C for 15 min. The reaction mixture was then diluted with EtOAc (30
mL), washed with H2O (15 mL), brine (15 mL), and dried (Na2SO4).
Evaporation of the solvent and purification of the crude by silica gel
column chromatography (6% MeOH in CH2Cl2) yielded compound
(R)-1 (630 mg, 64%) as a white powder which was then recrystallized
EXPERIMENTAL PROCEDURES
■
Synthesis. General. All chemicals including reagents with
stereocenters including (R)-(−)-α-monoclhorhydrine, (S)-(−)-α-
monochlorohydrine, and (R)-epichlorohydrin were purchased from
commercial suppliers and were used without further purification. DMF
and triethylamine were dried over 4 Å molecular sieves. Microwave
reactions were carried out in a Biotage Initiator microwave equipped
with a robotic arm for four consecutive reactions. Reactions were
monitored by thin layer chromatography (TLC) performed on
precoated silica gel aluminum sheets (F254, 60 Å, Merck). Column
chromatography was performed using silica gel (230−400 Å mesh,
1
from EtOAc. H NMR (CDCl3) δ 3.78−3.79 (m, 2H), 3.81 (s, 3H),
4.04−4.06 (m, 1H), 4.13 (d, 2H), 6.90−6.91 (m, 4H). 13C NMR
(CDCl3) δ 56.1, 64.2, 70.3, 72.6, 112.2, 115.2, 121.4, 122.6, 148.3,
150.0. ESI-MS (M + Na+) calculated, 221.32; found, 221.0. [α]2D3.6
−7.14° (c 1.12, MeOH).
(2S)-3-(2-Methoxyphenoxy) propane-1,2-diol ((S)-1). Com-
pound (S)-1 was synthesized using the same reaction conditions as for
compound (R)-1 but in presence of (S)-(+)-α-monochlorohydrine,
and the product was isolated as a white solid (64%). 1H NMR
(CDCl3) δ 3.78−3.79 (m, 2H), 3.81 (s, 3H), 4.04−4.06 (m, 1H), 4.13
(d, 2H), 6.90−6.91 (m, 4H). ESI-MS (M + Na+) calculated, 221.32;
found, 221.0. [α]2D3.6 +7.5° (c 1.2, MeOH).
(R)-2-((2-Methoxyphenoxy)methyl)oxirane (10). To a stirring
mixture of NaOH (363 mg, 9.09 mmol), K2CO3 (2.5 g, 18.28 mmol),
guaiacol (1.12 g, 9.09 mmol), and tetra-n-butylammonium bromide
(295 mg, 0.91 mmol) was added (R)-epichlorohydrin (1.26g, 13.61
mmol), and the mixture was placed in the microwave vessel. The
reaction vessel was heated at 110 °C for 5 min using microwave
irradiation. After cooling, the reaction mixture was diluted with H2O
(15 mL), extracted with EtOAc (60 mL), washed with brine (15 mL),
and dried (Na2SO4). The organic layer was concentrated and then
purified by silica gel column chromatography (10% EtOAc/hexanes)
to yield compound 10 (530 mg). 1H NMR (CDCl3) δ 2.73−2.74 (dd,
1H), 2.88−2.90 (dd, 1H), 3.80−3.90 (m, 1H), 3.86 (s, 3H), 4.02−4.06
(dd, 1H), 4.21−4.25 (dd, 1H), 6.89−6.95 (m, 4H). 13C NMR
(CDCl3) δ 44.7, 49.9, 55.6, 69.9, 111.7, 114.0, 120.6, 121.7, 147.7,
149.4.
1
EMD Chemicals). The 13C and H NMR spectra were recorded on a
1
Joel (JEOL) spectrometer (500 MHz for H, 125 MHz for 13C) or a
Bruker spectrometer (400 MHz for 1H, 100 MHz for 13C). The
chemical shifts for 1H NMR spectra are reported in ppm (δ) relative to
tetramethylsilane. Mass spectra (ESI) were recorded on a Waters
UPLC/MS instrument with a Waters 3100 mass detector. Specific
rotations of synthesized enantiomers were obtained using Interscience
AA-55 polarimeter in methanol at 23 °C. Purity of the synthesized
compounds was determined by a Waters HPLC system (Delta 600)
and/or LC−MS system (Waters 2545 binary gradient module)
equipped with a PDA. The purity of compound (R/S)-1 was found to
be 97.03% and that of compound (S)-11 was 90.07% by HPLC, and
the purity of all other compounds reported was positively established
by elemental analyses criteria. Mass spectra (ESI) were recorded on a
Waters MS system equipped with a Waters 3100 mass detector.
General Procedures for the Synthesis of Compounds (R/S)-1
and 6−8. Appropriate ortho substituted phenol or aniline (1.0 equiv)
in the presence of sodium hydroxide (0.9−2.5 equiv) was reacted with
1,2-dihydoxy-3-chloropropane (0.9−2.5 equiv) in DMF (2 mL) in a
Biotage Initiator microwave. The reaction mixture was irradiated at
210 °C for 15 min to obtain the phenol derivatives (R/S)-1, 6, 7 and at
150 °C for 5 min to obtain the aniline derivative 8. The reaction
mixture was then diluted with EtOAc (10 mL) and washed with H2O
(10 mL). The organic phase was separated, and the aqueous phase was
extracted with EtOAc (3 × 50 mL). The combined organic layers were
washed with H2O (2 × 50 mL) followed by brine and dried (Na2SO4).
The solvents were removed under reduced pressure, and the resulting
crude was purified by silica gel flash chromatography using a gradient
of 1−5% MeOH in CHCl3.
(S)-1-Fluoro-3-(2-methoxyphenoxy)propan-2-ol (11). To a
stirring solution of compound 10 (50 mg, 0.27 mmol) in toluene (1
mL) was added tetra-n-butylammonium fluoride (1.0 M, 1.7 mL), and
the mixture was heated to 80 °C for 3 h. The reaction mixture was
diluted with H2O (15 mL) and then extracted with EtOAc (60 mL).
The organic layer was washed with brine (15 mL), dried (Na2SO4),
and concentrated. It was further purified by silica gel column
chromatography (5% MeOH/CHCl3) to give compound 11 (23
1
(R/S)-3-(2-Methoxyphenoxy)-1,2-propanediol ((R/S)-1)). The
product was obtained as a white solid (149 mg, 75%). Mp 79−80 °C.
1H NMR (CDCl3) δ 2.60 (t, 1H), 3.39 (d, 1H), 3.75−3.84 (m, 2H),
mg, 41%). H NMR (CDCl3) δ 3.86 (s, 3H), 4.06−4.14 (m, 2H),
4.21−4.27 (dd, 2H), 4.48−4.67 (dd, 2H), 6.89−7.01 (m 4H). 13C
NMR (CDCl3) δ 55.9, 69.0 (d, JC−F = 20.45 Hz, 1C), 70.6, (d, JC−F
=
6.59 Hz, 1C), 83.7 (d, JC−F = 170.04 Hz, 1C). ESI-MS (M + Na+):
calculated, 223.30; found, 223.0. [α]2D3.6 +20.51° (c 1.95, DCM).
Bioassays for (R/S)-1 and (R)-1. Assay protocol using plasma
samples included the following procedure: A 50 μM solution of (R/S)-
3-(2-trifluoromethoxyphenoxy)-1,2-propanediol in water was used as
an internal standard (IS). IS response was variable and was not used in
quantification. Working standard solutions for either R-guaifenesin or
R-guaifenesin toluyl ester were 20, 50, 200, 500, 2000, 5000, 20 000,
50 000, 100 000 nM in water. All plasma samples in the Eppendorf
tubes were capped and vortexed for 2 min followed by centrifugation
at 3500 rpm for 5 min. The aqueous layer was frozen in dry ice−
methanol bath, and the organic layer was transferred into 16 × 100
mm culture tubes (catalog no. 47729-576). Organic solvent was dried
under N2 stream (10 psi) at room temperature for 30 min. Each
sample was then reconstituted in 100 μL of 0.2% TFA in MeOH/
water, 20:80, and transferred into 96-well plates for LC−MS/MS
analysis.
3.86 (s, 3H), 4.04−4.12 (m, 2H), 4.13−4.20 (m, 1H), 6.88−6.95 (m,
3H), 6.96−7.01 (m, 1H). 13C NMR (CDCl3) δ 55.9, 64.0, 70.1, 72.5,
111.9, 115.0, 121.2, 122.4, 148.1, 149.8. ESI-MS (M + Na+) calculated,
221.19; found, 221.0.
(R/S)-3-(2-Methylphenoxy)-1,2-propanediol (6). Product was
obtained as a white solid (171 mg, 94%). Mp 68 °C. 1H NMR
(CDCl3) δ 2.15 (t, 1H), 2.23 (s, 3H), 2.66 (d, 1H), 3.76−3.82 (m,
1H), 3.84−3.91 (m, 1H), 4.06 (d, 2H), 4.11−4.17 (m, 1H), 6.83 (d,
1H), 6.89 (t, 1H), 7.16 (t, 2H). ESI-MS (m/z) calculated, 182.22;
found, 182.10.
(R/S)-3-(2-Ethylphenoxy)-1,2-propanediol (7). Product was
obtained as a white solid (175 mg, 89%). Mp 53 °C. 1H NMR
(CDCl3) δ 1.20 (t, 3H), 2.08−2.18 (br, 1H), 2.64 (q, 2H), 3.76−3.83
(m, 1H), 3.85−3.91 (m, 1H), 4.06 (d, 2H), 4.11−4.18 (m, 1H), 6.84
(d, 1H), 6.91 (t, 1H), 7.14−7.21 (m, 2H). ESI-MS (m/z) calculated,
196.24; found, 196.10.
(R/S)-3-(2-Methoxyphenylamino)-1,2-propanediol (8). Prod-
1
uct was obtained as a light brown solid (315 mg, 26%). H NMR
Assessment of Neurite Outgrowth in Vitro. DRG from adult
male Sprague−Dawley rats were dissociated using a previously
described method.20,31,32 Neurons were cultured in defined Hams
(CDCl3) δ 3.24 (dd, 1H), 3.30 (dd, 1H), 3.66 (dd, 1H), 3.80 (dd,
1H), 3.896 (s, 3H), 3.98−4.02 (m, 1H), 6.67 (dd, 1H), 6.70−6.74 (m,
F
dx.doi.org/10.1021/jm400401y | J. Med. Chem. XXXX, XXX, XXX−XXX