Development of a Scalable Synthesis of Tofogliflozin

Article abstract of DOI:10.1021/acs.joc.5b02734

An efficient and scalable synthesis of an antidiabetic drug, tofogliflozin (1), which was identified as a highly selective sodium glucose cotransporter 2 (SGLT2) inhibitor, is described. A key factor in the synthesis of 1 was the selection of the purpose-designed protecting group, which plays a strategic role in protection, chemoselective activation, and crystalline purification. The developed and optimized method made it possible to prepare 1 on a multidecagram scale without any column chromatography.

Full text of DOI:10.1021/acs.joc.5b02734

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Note
Development of a Scalable Synthesis of Tofogliflozin
Yoshihito Ohtake, Takashi Emura, Masahiro Nishimoto, Koji Takano, Keisuke
Yamamoto, Satoshi Tsuchiya, Sang-Yong Yeu, Yasushi Kito, Nobuaki Kimura,
Sunao Takeda, Masao Tsukazaki, Masatoshi Murakata, and Tsutomu Sato
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b02734 • Publication Date (Web): 12 Feb 2016
Downloaded from http://pubs.acs.org on February 16, 2016
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Development of a Scalable Synthesis of
Tofogliflozin
Yoshihito Ohtake,†* Takashi Emura,† Masahiro Nishimoto,† Koji Takano,† Keisuke Yamamoto,†
Satoshi Tsuchiya,† Sang-Yong Yeu,† Yasushi Kito,‡ Nobuaki Kimura,§ Sunao Takeda, § Masao
Tsukazaki,‡ Masatoshi Murakata,§ and Tsutomu Sato†
† Research Division, Chugai Pharmaceutical Co., Ltd., 1-135 Komakado, Gotemba, Shizuoka
412-8513, Japan
‡ Research Division, Chugai Pharmaceutical Co., Ltd., 200 Kajiwara, Kamakura, Kanagawa 247-
8530, Japan
§ Pharmaceutical Technology Division, Chugai Pharmaceutical Co., Ltd., 5-5-1 Ukima, Kita-ku,
Tokyo 115-8543, Japan
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Abstract
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An efficient and scalable synthesis of an antidiabetic drug, tofogliflozin (1), which was identified
as a highly selective sodium glucose cotransporter 2 (SGLT2) inhibitor, is described. One of the
keys for the synthesis of 1 was the selection of the purpose-designed protecting group, which plays
a strategic role in protection, chemoselective activation, and crystalline purification. The
developed and optimized method made it possible to prepare 1 on a multi-decagram scale without
any column chromatography.
Tofogliflozin (1), (1S,3'R,4'S,5'S,6'R)-6-[(4-ethylphenyl)methyl]-6'-(hydroxymethyl)-3',4',5',6'-
tetrahydro-3H-spiro[2-benzofuran-1,2'-pyran]-3',4',5'-triol, is a highly selective SGLT2 inhibitor
and it was launched in Japan as a new antidiabetic drug.1 In the process of our research and
development plan, a large amount of 1 was required for in vivo pharmacological and toxicological
studies. Therefore, we undertook research to investigate a scalable synthetic route, and herein we
wish to report a newly established synthetic route of 1.
In the analysis of the medicinal chemistry route (Scheme 1),2 which had been established in
reference to the methods of the synthetic intermediates of antibiotic papulacandins,3 it had a
difficulty for large scale synthesis. All the intermediates with benzyl protections (7, 8, 9, and 10)
tended to be gummy and were difficult to isolate as solids by filtration, which forced us to use
cost- and time-inefficient column chromatography purification in most steps.
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Initially, a retrosynthesis was outlined as shown in Figure 1. Our key concept was to set
compound 15 as a key intermediate for the following reasons: (1) to allow the use of easily
accessible aglycone 3 and D-gluconolactone 11 with the same chiral centers as D-glucose in order
to synthesize 15, (2) to permit the distinction between the two hydroxy groups of 3 by
intramolecular spirocyclization reaction, (3) to facilitate easy quality control of the product 15 after
C-C bond formation, because 15 is crystalline, and (4) to allow only the benzyl part to be involved
in a Suzuki-type reaction to introduce the 4-ethylphenyl group after full esterification of 15. Also,
17 needs to be crystalline as a precursor of 1 for easy quality control of the product after the
Suzuki- type reaction. Therefore, we screened the protecting groups of 1 in order to find crystalline
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intermediates. Both tetra-acetylated compound 17a and tetra-methoxylcarbonylated compound
17b were prepared from 1 (Scheme 2). As a result, fortunately, 17b was obtained as a crystalline
solid.
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After obtaining crystalline intermediate 17b, synthesis of the spirocyclized intermediate 15 was
investigated. One of the keys for the synthesis of 15 was selecting the protecting groups for 3 and
11. The addition reaction of protected 3 with protected 11 was supposed to proceed under a
strongly basic condition, whereas the spiroketal cyclization could be conducted after deprotection
under an acidic condition. From many base-tolerant and acid-removable protecting groups of the
sugar part, we selected the trimethylsilyl (TMS) groups. TMS-protected gluconolactone 124 was
synthesized as described in the literatures.5 Compound 12 had an oily and moisture-sensitive
nature, but it could be used in the next addition reaction without further purifications after the
extraction procedure. A diol 3 was protected with the 1-methoxy-1-methylethyl group, which is
also base-tolerant and acid-removable. Actually, 3 was reacted with 2-methoxypropene by using
a catalytic amount of pyridinium p-toluenesulfonate (PPTS) to obtain the oily compound 13, which
was also used in the next addition reaction without further purification after the extraction
procedure.
Di-protected 13 in anhydrous toluene was halogen–metal exchanged with n-BuLi and reacted
with 12 to give the coupled intermediate 14. Removal of all the protecting groups of the crude 14
under acidic condition, followed by stereospecific spirocyclization, resulted in producing the key
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intermediate 15 as a single isomer.6 Interestingly, β-isomer of 15 was not observed at all. It was
supposed that this spirocyclization proceeded stereoselectively by the anomeric effect. Finally,
pure 15 was obtained by trituration with MTBE as a stable crystal.
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Next, we investigated the methoxycarbonylation reaction. Permethoxycarbonylation of five
hydroxy groups of 15 was achieved by use of stoichiometric DMAP and methyl chloroformate in
CH2Cl2. The use of Et3N with or without a catalytic amount of DMAP resulted in insufficient
reaction conversion because of competitive decomposition of ClCO2Me. Compound 16 obtained
by the extraction work-up procedure was used in the coupling reaction without further purification.
Then, we investigated Suzuki-type coupling reaction conditions of 16 with 4-ethylphenylboronic
acid in order to prepare 17b, following Kuwano’s report.7 It described the importance of the ligand
bite angle, which influenced the reaction rate in the reaction. Therefore, we first evaluated some
phosphine ligands (10 mol%) in the presence of 16 (1.0 equivalent), 4-ethylphenylboronic acid
(1.5 equivalents), [Pd(η3-C3H5)Cl]2 (APC, 10 mol%), and K2CO3 (3.0 equivalents) in DMF (0.2M)
(Table 1). As a result, bidentate phosphine ligands and APC afforded some satisfactory results,
being in close agreement with Kuwano’s results (Entries 1-6). A bidentate ligand 1,1’-
bis(diphenylphosphino)ferrocene (DPPF), which has high availability and economy, was also
acceptable as the same as 1,4-bis(diphenylphosphino)butane (DPPB) (Entry 7). Moreover, we
optimized the reaction condition by using DPPF, focusing on the Pd source, amount of the base,
reaction concentration, and solvent. The reaction conversion rate was slightly decreased with
Pd(OAc)2, which is an absolutely low cost catalyst precursor (Entry 8), but it was improved by
higher reaction concentration (Entry 9). The amount of carbonate-hydrolyzed products was
reduced by using 1.0 equivalent base (Entry 10). Under high concentration with 1 equivalent of
base, 16 completely disappeared to give 17b in 77% isolated yield (Entry 11). In addition, solvent
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screening was conducted in order to diminish the hydrolysis products. Toluene, 1,4-dioxane, and
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DME resulted in reduction of the hydrolysis products (Entries 12‒14), suggesting that the
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hydrolysis can be avoided by using nonpolar solvents. We selected DME, since an easy work-up
procedure was achieved, as described below.
Pd coupling reaction to introduce the distal phenyl group was successfully performed under the
condition in Entry 14 of Table 1 on a hundred gram scale. The residual Pd was precipitated by
adding 20 mol% of N-acetyl-L-cysteine (NAC) to the reaction mixture, and it was efficiently
removed by filtration. In addition, treatment of the crude mixture with EtOH and water containing
20 mol% of NAC afforded the crystalline 17b with >99 area% of purity and <1 ppm of residual
Pd in 88% yield.
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Permethoxylcarbonylated compound 17b was hydrolyzed with aqueous sodium hydroxide
solution in DME. Under the condition, the reaction mixture was heterogeneous and temperature
elevation was observed, which suggests a difficulty in controlling the reaction initiation. Thus,
MeOH was used as a co-solvent, which made the reaction mixture homogenous and the reaction
controllable by modifying the addition rate of sodium hydroxide. Finally, 1 with >99% purity was
obtained by extraction and concentration in quantitative yield as a colorless amorphous solid. This
early process route is summarized in Scheme 3.8 This newly-developed method achieved a higher
overall yield compared to the previous one (Scheme 1).
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According to the established method, we also synthesized a major human metabolite of 1, a
carboxylic acid 19, into which the ethyl moiety of 1 was oxidized by CYPs (Scheme 4).9
Pentamethoxycarbonylated 16 was reacted with the corresponding boronic acid reagent (purchased
from Combi-Blocks Inc.) under our best reaction condition (Table 1, Entry 14) to afford the
coupled product 18 in 82% yield, and then the highly-hydrophilic metabolite 19 was obtained in
96% yield after hydrolysis.
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In conclusion, we have successfully constructed an effective and scalable synthetic route for the
antidiabetic drug, tofogliflozin 1, that does not use column chromatography purification, and by
which several decagrams of 1 can be supplied for in vivo pharmacological and toxicological studies.
Our key success factor was selecting the optimal protecting groups for the purpose of
chemoselective activation and crystalline purification, which indicates that they play critical roles
in the establishment of the early process. Moreover, we demonstrated that this method was utilized
to synthesize a human metabolite 19.
Experimental Section
All reactions were carried out under an argon or a nitrogen atmosphere. All solvents and reagents
were purchased from commercial sources without further drying. Melting points (mp) were
determined by using differential scanning calorimetry (DSC). Optical rotations were measured
with a polarimeter at the sodium D line (589 nm). 1H NMR spectra were recorded on 400 MHz
spectrometers. Chemical shifts were reported in parts per million (δ) downfield from
tetramethylsilane (δH 0.00) as an internal standard. Data are presented as follows: chemical shift
(δ, ppm), integration, multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet, and
m = multiplet) and coupling constant. 13C NMR spectra were recorded on 100 MHz spectrometers.
The following internal reference was used (DMSO-d6; 39.5, CD3OD; δ 49.0, CDCl3; δ 77.0). Mass
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spectra (MS) were measured using ESI mode. High resonance mass (HRMS) analysis were
recorded using EI mode or ESI mode by Q-TOF.
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2,3,4,6-Tetrakis-O-trimethylsilyl-D-glucono-1,5-lactone (12). This titled compound was
synthesized from D-gluconolactone (11) according to the literature.5
(2-Bromo-4-hydroxymethylphenyl)methanol (3).2 To a solution of commercially available 2-
bromoterephthalic acid (2) (575 g, 2.34 mol) in THF (5.75 L), a THF solution of BH3 (1.0 M, 5.86
L) was added at 0 °C dropwise for 2.5 h and the mixture was stirred for 1 h at 0 ºC. The mixture
was gradually warmed up to 35 ºC over 3.5 h. The reaction mixture was cooled to 0 ºC and
quenched by dropwise addition of MeOH (1.15 L) over 30 min. Then, the mixture was
concentrated in vacuo. The residue was dissolved in MeOH (1.72 L), and then water (10.3 L) was
added and the mixture was stirred at 0 ºC for 30 min. The off-white solid was filtered and washed
with water (1.15 L x 3) and heptanes (2.30 L) to obtain 3 (426 g, 84%) as a white crystal; mp 108–
109 ºC; 1H NMR (400 MHz, DMSO-d6) δ: 4.47 (2H, d, J = 5.6 Hz), 4.49 (2H, d, J = 5.4 Hz), 5.29
(1H, t, J = 5.6 Hz), 5.39 (1H, t, J = 5.4 Hz), 7.31 (1H, d, J = 7.8 Hz), 7.47 (1H, d, J = 7.8 Hz),
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7.48–7.49 (1H, m); C NMR (100 MHz, DMSO-d6) δ: 61.9, 62.5, 120.8, 125.5, 127.9, 129.7,
139.1, 143.4; HRMS (EI) calcd for C8H9BrO2 [M]+ 215.9786, found 215.9787.
(1S,3’S,4’S,5’S,6’R)-3’,4’,5’,6’-tetrahydro-6,6’-bis(hydroxymethyl)-spiro[2-benzofuran-
1(3H),2-[2H]pyran]-3’, 4’, 5’-triol (15). To a solution of 3 (800 g, 3.69 mol) in THF (4.00 L),
PPTS (46.3 g, 0.18 mol) was added at rt and the mixture was cooled to 0 ºC. 2-Methoxypropene
(797 g, 11.1 mol) was dropwise added to this solution at the same temperature. After stirring at
10 ºC for 2 h, the reaction was quenched by dropwise addition of saturated K2CO3 aq. solution
(4.00 L) and water (4.00 L) at 10 ºC. The resulting mixture was extracted with heptane (4.00 L).
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The organic layer was washed with brine (4.00 L), and dried over anhydrous Na2SO4 (200 g). The
mixture was concentrated in vacuo to obtain crude 13 (1.27 kg) as a yellow oil.
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To a solution of crude 13 (630 g, 1.74 mol) in anhydrous toluene (3.78 L), 2.67 M n-BuLi in
hexane solution (650 mL, 1.74 mol) was added dropwise over 45 min at 5 °C under a nitrogen
atmosphere and the resultant mixture was stirred under the same condition for 20 min. After this
solution was cooled at −70 ºC, a solution of prepared 12 (810 g, 1.74 mol) in anhydrous toluene
(1.89 L) was added to the resultant mixture dropwise over 2 h below −60 ºC. After stirring at this
temperature for 30 min, satd. NH4Cl (3.78 L) and water (1.89 L) were added thereto. After the
resultant mixture was warmed up to rt, the mixture was separated. The resultant organic layer was
washed with satd. NH4Cl (3.78 L), and then dried over anhydrous Na2SO4 (158 g). The mixture
was then concentrated in vacuo to obtain the crude 14 (1.30 kg) as an orange oil. This reaction was
carried out one more time on the same scale to afford another 1.30 kg batch of crude intermediate
14.
All the obtained 14 (2.61 kg, 3.49 mol) was dissolved in THF (5.23 L) and MeOH (2.61 L), and
p-toluenesulfonic acid hydrate (133 g, 700 mmol) was added at rt. The mixture was stirred at rt for
2 h, and then cooled at 0 ºC. MTBE (2.61 L) was added to the mixture, and the mixture was stirred
at 0 ºC for 1 h. The precipitate was collected by filtration. The obtained solid was dried in vacuo
to obtain 15 (663 g, 60% from 3) as a white crystal; mp 193–194 ºC; [α]D25 +43.8º (c 1.07, H2O);
1H NMR (400 MHz, CD3OD) δ: 3.46–3.49 (1H, m), 3.63–3.69 (1H, m), 3.75–3.85 (4H, m), 4.64
(2H, s), 5.10 (1H, d, J = 12.5 Hz), 5.15 (1H, d, J = 12.5 Hz), 7.23–7.27 (1H, m), 7.30–7.37 (2H,
m); 13C NMR (100 MHz, CD3OD) δ: 62.8, 65.0, 71.9, 73.5, 74.9, 76.2, 76.3, 111.6, 121.8, 121.9,
129.2, 140.2, 141.2, 142.5; MS (ESI) m/z: 299 [M+H]+; HRMS (ESI) calcd for C14H19O7 [M+H]+
299.1125, found 299.1119.
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(1S,3’R,4’S,5’S,6’R)-6-[(methoxycarbonyloxy)methyl]-3’,4’,5’,6’-tetrahydro-3’,4’,5’-
tris(methoxycarbonyloxy)-6’-[(methoxycarbonyloxy)methyl]-spiro[2-benzofuran-1(3H),2-
[2H]pyran] (16). To a solution of 15 (600.0 g, 2.01 mol) and DMAP (1.55 kg, 12.7 mol) in
anhydrous CH2Cl2 (6.00 L), methyl chloroformate (933 mL, 12.1 mol) was added dropwise over
70 min at −10 °C. The reaction mixture was stirred for 30 min at 0 ºC and for 3 h at rt. 10% KHSO4
aq. solution (6.00 L) was added to the mixture, and the resultant mixture was separated. The
resultant organic layer was washed with 10% KHSO4 aq. solution (6.00 L x 2) and satd. NaHCO3
(6.00 L), and then dried over anhydrous Na2SO4 (600 g). The mixture was concentrated in vacuo
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to obtain crude 16 (1.16 kg, 98%) as a light-yellow amorphous solid; [α]D +9.29 º (c 1.01,
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CHCl3); H NMR (400 MHz, CDCl3) δ: 3.55 (3H, s), 3.78 (6H, s), 3.81 (6H, s), 4.23 (1H, dd, J =
2.7, 11.7 Hz), 4.33 (1H, dd, J = 4.2, 11.7 Hz), 4.36–4.41 (1H, m), 5.11–5.24 (5H, m), 5.41 (1H, d,
J = 10.3 Hz), 5.51 (1H, t, J = 9.6 Hz), 7.24–7.26 (1H, m), 7.41–7.45 (2H, m); 13C-NMR (100 MHz,
CDCl3) δ: 54.9, 55.0, 55.1, 55.3, 55.4, 65.5, 68.9, 69.5, 72.5, 73.1, 74.5, 75.5, 108.3, 121.2, 122.7,
130.2, 135.4, 135.5, 140.6, 154.4, 154.7, 154.9, 155.3, 155.5; MS (ESI) m/z: 589 [M+H]+; HRMS
(ESI) calcd for C24H29O17 [M+H]+ 589.1399, found 589.1399.
(1S,3’R,4’S,5’S,6’R)-6-[(4-ethylphenyl)methyl]-3’,4’,5’,6’-tetrahydro-3’,4’,5’-
tris(methoxycarbonyloxy)-6’-[(methoxycarbonyloxy)methyl]-spiro[2-benzofuran-1(3H),2-
[2H]pyran] (17b). In a round flask, 16 (104 g, 177 mmol), potassium carbonate (24.4 g, 177
mmol), 4-ethylphenylboronic acid (37.1 g, 247 mmol), Pd(OAc)2 (3.97 g, 17.7 mmol), and DPPF
(11.8 g, 21.2 mmol) were added. DME (200 mL) was added and the reaction mixture was heated
at 85 ºC for 3.5 h. After cooling, AcOEt (50.0 mL) and N–acetyl–L–cysteine (5.50 g) were added
to the mixture. The resultant mixture was stirred for 1 h at a water-bath temperature. The resultant
mixture was filtered by Celite and washed with AcOEt. The filtrate was concentrated in vacuo,
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and the obtained residue was recrystallized from EtOH (400 mL) and H2O (40.0 mL) with N-
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acetyl-L-cysteine (5.50 g) to obtain 17b (96.1 g, 88%) as a white crystal; mp 128–129 ºC; [α]D
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+29.3 º (c 1.18, CHCl3); 1H NMR (400 MHz, CDCl3) δ: 1.20 (3H, t, J = 7.7 Hz), 2.60 (2H, q, J =
7.7 Hz), 3.50 (3H, s), 3.76 (3H, s), 3.77 (3H, s), 3.81 (3H, s), 3.96 (2H, s), 4.23 (1H, dd, J = 2.8,
12.0 Hz), 4.33 (1H, dd, J = 4.5, 12.0 Hz), 4.36–4.40 (1H, m), 5.11–5.20 (3H, m), 5.41 (1H, d, J =
10.0 Hz), 5.51 (1H, t, J = 10.0 Hz), 7.07–7.14 (4H, m), 7.14 (1H, d, J = 7.8 Hz), 7.19 (1H, dd, J =
1.5, 7.8 Hz), 7.31 (1H, d, J = 1.5 Hz); 13C-NMR (100 MHz, CDCl3) δ: 15.6, 28.4, 41.3, 55.0, 55.0,
55.2, 55.4, 65.6, 69.5, 72.6, 73.2, 74.6, 75.6, 108.4, 121.0, 123.3, 127.9, 128.7, 131.1, 135.2, 137.9,
138.0, 141.4, 142.0, 154.5, 154.7, 155.0, 155.4; MS (ESI) m/z: 619 [M+H]+; HRMS (ESI) calcd
for C30H35O14 [M+H]+ 619.2021, found 619.2025.
(1S,3'R,4'S,5'S,6'R)-6-[(4-ethylphenyl)methyl]-6'-(hydroxymethyl)-3',4',5',6'-tetrahydro-
3H-spiro[2-benzofuran-1,2'-pyran]-3',4',5'-triol (1, tofogliflozin).2 To a solution of 17b (89.9
g, 145 mmol) in DME (653 mL) and MeOH (73.0 mL), 2N NaOH aq. solution (726 mL, 1.45 mol)
was added dropwise for 1 hr at water-bath temperature. After stirring at rt for 1 h, 2N H2SO4 aq.
solution (436 mL) was added slowly to the mixture. Water (700 mL) was added to the mixture and
the resultant mixture was extracted with AcOEt (500 mL x 2). The resultant organic layer was
washed with brine (1.00 L), and then dried over anhydrous Na2SO4 (250 g). The mixture was
concentrated in vacuo to obtain 1 (57.3 g, quant) as a colorless amorphous solid; [α]D26 +24.2º (c
1.02, MeOH); 1H NMR (400 MHz, CD3OD) δ: 1.19 (3H, t, J = 7.6 Hz), 2.58 (2H, q, J = 7.6 Hz),
3.42–3.47 (1H, m), 3.63–3.67 (1H, m), 3.75–3.88 (4H, m), 3.95 (2H, s), 5.06 (1H, d, J = 12.5 Hz),
5.12 (1H, d, J = 12.5 Hz), 7.07–7.14 (4H, m), 7.17–7.23 (3H, m); 13C NMR (100 MHz, CD3OD)
δ: 16.3, 29.4, 42.3, 62.8, 71.9, 73.4, 74.9, 76.2, 76.4, 111.6, 121.8, 123.6, 128.9, 129.9, 131.1,
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139.7, 139.9, 140.2, 142.6, 143.2; MS (ESI) m/z: 387 [M+H]+; HRMS (ESI) calcd for C22H27O6
[M+H]+ 387.1802, found 387.1801.
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[(2'R,3S,4'S,5'R)-3',4',5'-Triacetoxy-5-[(4-ethylphenyl)methyl]spiro[1H-isobenzofuran-
3,6'-tetrahydropyran]-2'-yl]methyl acetate (17a) for crystalline investigation (Scheme 2). To
a solution of 1 (200 mg, 518 µmol) and DMAP (348 mg, 2.85 mmol) in anhydrous CH2Cl2 (2.00
mL), acetyl chloride (185 µL, 2.59 mmol) was added at 0 °C. The reaction mixture was stirred for
10 min at 0 ºC and for 20 h at rt. 2N HCl aq. solution was added to the mixture, and the resultant
mixture was extracted with CH2Cl2. The resultant organic layer was washed with brine, and then
dried over anhydrous Na2SO4. The mixture was concentrated in vacuo and the residue was purified
by reverse-phase column chromatography (ODS, 0.1% formic acid in H2O / 0.1% formic acid in
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MeCN) to obtain 17a (264 mg, 92%) as a colorless amorphous solid; [α]D +22.6 º (c 1.04,
CHCl3); 1H NMR (400 MHz, CDCl3) δ: 1.22 (3H, t, J = 7.6 Hz), 1.71 (3H, s), 2.00 (3H, s), 2.05
(3H, s), 2.07 (3H, s), 2.61 (2H, q, J = 7.6 Hz), 3.97 (2H, s), 4.05 (1H, dd, J = 2.2, 12.2 Hz), 4.27
(1H, dd, J = 3.9, 12.2 Hz), 4.33 (1H, ddd, J = 2.2, 3.9, 10.3 Hz), 5.11 (1H, d, J = 12.5 Hz), 5.20
(1H, d, J = 12.5 Hz), 5.27–5.32 (1H, m), 5.57–5.65 (2H, m), 7.06–7.08 (2H, m), 7.10–7.15 (3H,
m), 7.18 (1H, dd, J = 1.2, 7.8 Hz), 7.26 (1H, d, J = 1.5 Hz); 13C-NMR (100 MHz, CDCl3) δ: 15.6,
20.3, 20.7, 20.7, 20.8, 28.4, 41.3, 62.1, 68.6, 70.0, 71.0, 71.9, 73.0, 108.8, 120.9, 123.1, 128.0,
128.8, 130.9, 135.9, 137.9, 137.9, 141.6, 142.1, 169.3, 169.6, 170.2, 170.8; MS (ESI) m/z: 555
[M+H]+; HRMS (ESI) calcd for C30H34O10Na [M+Na]+ 577.2050, found 577.2050.
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Ethyl
2-[4-[[(3S,3'R,4'S,5'R,6'R)-3',4',5'-tris(methoxycarbonyloxy)-6'-
(methoxycarbonyloxymethyl)spiro[1H-2-benzofuran-3,2'-oxane]-5-
yl]methyl]phenyl]acetate (18). In a sealed tube, 16 (200 mg, 340 µmol), potassium carbonate
(47.0 mg, 340 µmol), [4-(2-ethoxy-2-oxoethyl)phenyl]boronic acid (99.0 mg, 476 µmol),
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Pd(OAc)2 (3.80 mg, 17.0 µmol), and DPPF (11.3 mg, 20.0 µmol) were added. DME (340 μL) was
added and the reaction mixture was heated at 85 ºC for 6 h. After cooling, formic acid (100 μL)
was added to the mixture. The resultant mixture was purified by reverse-phase chromatgraphy
(ODS, 0.1% formic acid in H2O / 0.1% formic acid in MeCN) to afford roughly purified compound
18. The obtained residue was recrystallized from MeOH (1.40 mL) with N-acetyl-L-cysteine (2.77
mg) to obtain 18 (189 mg, 82%) as a white crystal; mp 90–91 ºC; [α]D19 +23.7 º (c 1.02, CHCl3);
1H NMR (400 MHz, CDCl3) δ: 1.24 (3H, t, J = 7.3 Hz), 3.50 (3H, s), 3.56 (2H, s), 3.76 (3H, s),
3.77 (3H, s), 3.81 (3H, s), 3.97 (2H, s), 4.13 (2H, q, J = 7.3 Hz), 4.23 (1H, dd, J = 2.6, 11.9 Hz),
4.31–4.40 (2H, m), 5.10–5.21 (3H, m), 5.40 (1H, d, J = 10.0 Hz), 5.51 (1H, t, J = 9.7 Hz), 7.10–
7.15 (3H, m), 7.17–7.20 (3H, m), 7.31 (1H, s); 13C-NMR (100 MHz, CDCl3) δ: 14.1, 41.0, 41.3,
55.0, 55.1, 55.2, 55.4, 60.8, 65.6, 69.5, 72.6, 73.2, 74.6, 75.6, 108.4, 121.0, 123.4, 129.0, 129.3,
131.1, 131.9, 135.3, 138.1, 139.5, 141.0, 154.5, 154.7, 155.0, 155.4, 171.6; MS (ESI) m/z: 694
[M+H2O]+; HRMS (ESI) calcd for C32H36O16Na [M+Na]+ 699.1901, found 699.1910.
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2-[4-[[(3S,3'R,4'S,5'S,6'R)-3',4',5'-trihydroxy-6'-(hydroxymethyl)spiro[1H-2-benzofuran-
3,2'-oxane]-5-yl]methyl]phenyl]acetic acid (19). To a solution of 18 (486 mg, 718 µmol) in
MTBE (2.43 mL) and MeOH (3.65 mL), 10N NaOH aq. solution (718 µL, 7.18 mmol) was added
dropwise over 5 min at 60 ºC. After stirring at 60 ºC for 2 hr, the reaction mixture was cooled to
rt, and formic acid (500 μL) was added. The resultant mixture was purified by reverse-phase
chromatography (ODS, 0.1% formic acid in H2O / 0.1% formic acid in MeCN) to afford the desired
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compound 19 (286 mg, 96%) as a colorless amorphous solid by lyophilization.; [α]D +17.7º (c
1.03, MeOH); 1H NMR (400 MHz, CD3OD) δ: 3.41–3.48 (1H, m), 3.54 (2H, s), 3.65 (1H, dd, J =
5.6, 12.0 Hz), 3.74–3.83 (4H, m), 3.98 (2H, s), 5.07 (1H, d, J = 12.5 Hz), 5.13 (1H, d, J = 12.5
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Hz), 7.07–7.14 (4H, m), 7.17–7.23 (3H, m); C NMR (100 MHz, CD3OD) δ: 41.7, 42.2, 62.8,
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71.8, 73.4, 74.9, 76.2, 76.4, 111.6, 121.9, 123.7, 130.0, 130.5, 131.2, 133.9, 140.0, 140.2, 141.1,
142.3, 175.9; MS (ESI) m/z: 415 [M‒H]‒; HRMS (ESI) calcd for C22H23O8 [M‒H]‒ 415.1393,
found 415.1397.
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ASSOCIATED CONTENT
Supporting Information. 1H-NMR and 13C-NMR spectra of all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: ohtakeysh@chugai-pharm.co.jp
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We are very grateful to Professor emeritus of Tohoku University Kunio Ogasawara (formerly a
scientific advisor in our company) for many scientific and constructive suggestions. We thank Ms.
Hitomi Suda, Mr. Yuichiro Ishiguro, and Ms. Masako Arai for mass spectrometry measurements,
Dr. Noriyuki Takata for X-ray structure analysis, and Mr. Satoshi Tanida for DSC measurements.
We also thank Editing Services at Chugai Pharmaceutical Co., Ltd for assistance with English
usage.
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REFERENCES
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1. (a) Suzuki, M.; Honda, K.; Fukazawa, M.; Ozawa, K.; Hagita, H.; Kawai, T.; Takeda, M.; Yata,
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Exp. Ther. 2012, 341, 692–701. (b) Ikeda, S.; Takano, Y.; Cynshi, O.; Tanaka, R.; Christ, A.
D.; Boerlin, V.; Beyer, U.; Beck, A.; Ciorciaro, C.; Meyer, M.; Kadowaki, T. Diabetes,
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2. Ohtake, Y.; Sato, T.; Kobayashi, T.; Nishimoto, M.; Taka, N.; Takano, K.; Yamamoto, K.;
Ohmori, M.; Yamaguchi, M.; Takami, K.; Yeu, S.-H.; Ahn. K.-H.; Matsuoka, H.; Morikawa,
K.; Suzuki, M.; Hagita, H.; Ozawa, K.; Yamaguchi, K.; Kato, M.; Ikeda, S. J. Med. Chem.
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Hagan, D. L.; Morgan, N.; Taylor, J. R.; Obermeier, M. T.; Humphreys, W. G.; Khanna, A.;
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P.; Whaley, J. M.; Washburn, W. N. J. Med. Chem. 2008, 51, 1145–1149. (b) Deshpande, P.
P.; Singh, J.; Pullockaran, A.; Kissick, T.; Ellsworth, B. A.; Gougoutas, J. Z.; Dimarco, J.;
Fakes, M.; Reyes, M.; Lai, C.; Lobinger, H.; Denzel, T.; Ermann, P.; Crispino, G.; Randazzo,
M.; Gao, Z.; Randazzo, R.; Lindrud, M.; Rosso, V.; Buono, F.; Doubleday, W. W.;
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6. We have reported the configuration of the anomeric carbon of 1 is alpha-anomer from X-ray
analysis of mono-acetylated tofogliflozin (ref. 2). Compound 1 prepared at that time was
synthesized by the alternative scheme proposed here, but compound 15 obtained by
spirocyclization was also converted into 1 as shown in this manuscript, and it was identified
as the same compound by 1H-NMR data. In conclusion, we determined that the stereo
configuration of the anomeric carbon of 15 was alpha-anomer.
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7. Kuwano, R.; Yokogi, M. Org. Lett. 2005, 7, 945–947.
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Takano, K.; Nishimoto, M.; Ohtake, Y.; Emura, T.; Kito, Y. PCT Int. Appl. WO2011074675,
2011; Chem. Abstr. 2011, 155, 785683.
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Hagita, H.; Kuhlmann, O.; Opirier, A.; Fowler, S.; Funk, C.; Simon, S.; Aso, Y.; Ikeda, S.;
Ishigai, M. Xenobiotica 2015, 45, 230–238.
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