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DOI: 10.1055/s-2008-1078280
Synthesis of Isofagomine and a New C6 Pyrrolidine Azasugar with Potential Biological Activity
Publikationsverlauf
Publikationsdatum:
22. August 2008 (online)
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Abstract
An efficient asymmetric synthesis of isofagomine, based on a precursor containing three differentiated hydroxyl functions, is described. The side product in the key alkylation step is converted into (2S,3R,4R)-2,4-bis(hydroxymethyl)-3-hydroxypyrrolidine, a new C6 pyrrolidine azasugar, which inhibits α-glucosidase from yeast.
Keywords
asymmetric synthesis - azasugars - glycosidase inhibitors - hydroboration - ring-closing metathesis
- 1
Stütz AE. Iminosugars as Glycosidase Inhibitors Wiley-VCH; Weinheim: 1999. - 2
Compain P.Martin OR. Iminosugars Wiley; Chichester: 2007. - 3
Dong W.Jespersen T.Bols M.Skrydstrup T.Sierks MR. Biochemistry 1996, 35: 2788 - 4
Ouchi H.Mihara Y.Takahata H. J. Org. Chem. 2005, 70: 5207 - 6
Schaus S.Brandes B.Larrow J.Tokunaga M.Hansen K.Gould A.Furrow M.Jacobsen E. J. Am. Chem. Soc. 2002, 124: 1307 - 9 For a recent related approach towards
racemic isofagomine (rac-1),
see:
Imahori T.Ojima H.Tateyama H.Mihara Y.Takahata H. Tetrahedron Lett. 2008, 49: 265 - 10
Jautelat M,Artl D, andWieland H. inventors; Eur Patent, EP 0110245. - 11
Friedrich M.Savchenko A.Wächtler A.de Meijere A. Eur. J. Org. Chem. 2003, 11: 2138 -
16a
Negishi E.Brown HC. Synthesis 1974, 77 -
16b
Freshly prepared (according to the Aldrich Technical Bulletin AL-109) 0.5 M solution of thexylborane in THF.
-
18a
When 19 was submitted to the same hydrogenolysis conditions, the TBDMS protecting group remained intact.
-
18b
Ikawa T.Sajiki H.Hirota K. Tetrahedron 2004, 60: 6189 -
18c
Hattori K.Sajiki H.Hirota K. Tetrahedron 2001, 57: 2109 - 19
Jespersen T.Bols M.Sierks MR.Skrydstrup T. Tetrahedron 1994, 50: 13449 - 21
Zhao H.Thurkauf A. Synlett 1999, 1280
References and Notes
[α]D +20 (c = 1, pentane).
7Chiral HPLC analysis: Chiralcel OD-H; n-hexane-EtOH, 99:1 (isocratic); T = 35 ˚C; UV (λ = 214 nm).
8Incomplete stereoselective epoxidation [4] and incomplete regioselective epoxide opening with vinyl cuprate [4] both yielded an inseparable mixture of product and starting material.
12
Selected Experimental
Details:
O-Benzylation and Staudinger
Reduction of 14: To an ice-cooled solution of 14 (12.17
g, 107.6 mmol, colorless oil) in anhyd DMF (180 mL) was added NaH
(6.45 g, 60% dispersion on mineral oil, 161.3 mmol). After
stirring for 30 min at 0 ˚C, benzyl bromide (25.6 mL, 214
mmol) was added at 0 ˚C and the reaction was stirred overnight
(0 ˚C → r.t.). NaOH (60 mL, 2 M aq solution) was
added and the mixture was stirred at 80 ˚C during 1 h.
The reaction mixture was diluted with H2O (1 L) and extracted
with Et2O (3 × 1 L). The organic phase was washed
with brine (1 L) and dried (Na2SO4). The drying
agent was filtered and the resulting clear solution was evaporated
under reduced pressure. The oil was filtered over silica gel (n-hexane-EtOAc, 9:1) and after
evaporation, the crude residue was dissolved in anhyd THF (570 mL).
Ph3P (56.4 g, 215.2 mmol) was added and the mixture was
stirred overnight at r.t. NaOH (190 mL, 2 M aq solution) was added
and the mixture was refluxed for 1 h. The mixture was diluted with
H2O (1 L) and extracted with CH2Cl2 (3 × 1
L). The organic phase was washed once with brine (0.6 L) and dried
(MgSO4). The drying agent was filtered and the resulting
clear solution was evaporated under reduced pressure. After flash
column chromatography on silica gel and purification (EtOAc-CH2Cl2,
8:2 + 5% Et3N), 2-benzyloxymethylallylamine
(8; 15 g, 84.63 mmol, 78%) was
isolated as a colorless oil.
8: ¹H
NMR (300 MHz, CDCl3): δ = 7.18-7.30
(m, 5 H), 5.03 (d, 2 H), 4.43 (s, 2 H), 3.97 (s, 2 H), 3.28 (s,
2 H), 1.21 (s, 2 H). ¹³C NMR (75 MHz,
CDCl3): δ = 147.6 (C), 138.3 (C), 128.4
(CH), 127.7 (CH), 127.7 (CH), 111.3 (CH2), 72.1 (CH2),
72.1 (CH2), 44.8 (CH2). HRMS (ES): m/z [M + H]+ calcd
for C11H15NO: 178.12263; found: 178.12260.
Alkylation of 2-Benzyloxymethylallylamine (8) with (
S
)-Vinyloxirane [(
S
)-4]:
2-Benzyloxymethylallylamine (8; 5.24 g,
29.56 mmol) was mixed with H2O (132 µL, 7.33 mmol)
in a pressure tube at 0 ˚C. (S)-Vinyloxirane [(S)-4; 0.8 mL,
9.93 mmol] was slowly added at 0 ˚C and the reaction
vessel was sealed, heated and stirred for 6 h at 100 ˚C.
The reaction mixture was transferred to a 100-mL round-bottomed
flask and dissolved in H2O (5.8 mL), dioxane (35 mL)
and NaOH (23 mL, 1 M in H2O). Boc2O (9.7 g,
44.44 mmol) was added at r.t. and the reaction mixture was stirred overnight
at r.t. The mixture was evaporated under reduced pressure, diluted
with Et2O (500 mL), subsequently washed with H2O
(200 mL), citric acid (200 mL, 20%) and brine (200 mL).
The pooled aqueous phases were extracted with Et2O (3 × 250
mL). The organic phases were dried (MgSO4). The drying
agent was filtered and the resulting clear solution was evaporated
under reduced pressure. The residue (13 g) was purified by flash
column chromatography on silica gel (gradient elution: n-hexane-EtOAc, 85:15 → 6:4)
to furnish 15 (2.21 g, 6.35 mmol, 64%)
and 16 (558 mg, 1.61 mmol, 16%)
as colorless oils.
15: [α]D 0
(c = 1, CHCl3). ¹H
NMR (300 MHz, CDCl3): δ = 7.18-7.30
(m, 5 H), 5.75 (ddd, J = 5.6,
10.5, 17.1 Hz, 1 H), 5.25 (d, J = 17.1
Hz, 1 H), 5.08 (m, 2 H), 4.94 (s, 1 H), 4.42 (s, 2 H), 4.26 (m,
1 H), 3.87 (m, 4 H), 3.58 (br s, 1 H), 3.21 (m, 2 H), 1.36 (s, 9
H). ¹³C NMR (75 MHz, CDCl3): δ = 157.5
(C), 141.9 (C), 138.4 (CH), 138.0 (C), 128.4 (CH), 127.7 (CH), 115.7
(CH2), 113.4 (CH2), 80.6 (C), 72.7 (CH), 72.2
(CH2), 71.3 (CH2), 53.7 (CH2),
51.5 (CH2), 28.3 (Me). HRMS (ES): m/z [M + Na]+ calcd
for C20H29NO4: 370.19889; found:
370.19967.
16: [α]D +9.1
(c = 1, CHCl3). ¹H
NMR (300 MHz, CDCl3): δ = 7.18-7.30
(m, 5 H), 5.78 (m, 1 H), 5.04-5.15 (m, 4 H), 4.43 (s, 2
H), 4.26 (m, 1 H), 3.93 (m, 2 H), 3.80 (m, 2 H), 3.70 (m, 2 H),
1.37 (s, 9 H). ¹³C NMR (75 MHz, CDCl3): δ = 156.3
(C), 143.0 (C), 137.9 (C), 133.9 (CH), 128.4 (CH), 127.8 (CH), 117.5
(CH2), 113.9 (CH2), 80.4 (C), 72.3 (CH2), 71.7
(CH2), 63.5 (CH2), 62.0 (CH), 48.7 (CH2),
28.4 (Me). HRMS (ES): m/z [M + Na]+ calcd
for C20H29NO4: 370.19889; found:
370.19897.
Ring-Closing
Metathesis of 15: To a solution of 15 (1.89
g, 5.44 mmol) in anhyd and degassed CH2Cl2 (170
mL) was added the Grubbs second generation catalyst (150 mg, 0.177 mmol)
at r.t. under an argon atmosphere and the solution was stirred for
48 h. The solvent was evaporated and purified by flash column chromatography
on silica gel (n-hexane-EtOAc,
2:1; silica gel saturated with Et3N) to furnish 9 (1.60 g, 5 mmol, 92%) as a brown
solid.
9: [α]D +52.2
(c = 1.01, CHCl3). ¹H
NMR (300 MHz, CDCl3): δ = 7.19-7.30
(m, 5 H), 5.84 (m, 1 H), 4.43 (s, 2 H), 4.16 (br s, 1 H), 3.93 (d, J = 18.0 Hz, 1 H), 3.89 (s,
2 H), 3.73 (d, J = 18.1 Hz,
1 H), 3.46 (br s, 2 H), 1.40 (s, 9 H). ¹³C
NMR (75 MHz, CDCl3): δ = 155.2 (C),
137.9 (C), 136.6 (C), 128.5 (CH), 127.8 (CH), 127.8 (CH), 125.4
(CH), 80.2 (C), 72.4 (CH2), 71.5 (CH2), 63.7
(CH), 47.7 (CH2), 44.0 (CH2), 28.4 (Me). HRMS
(ES): m/z [M +
Na]+ calcd for C18H25NO4: 342.16759;
found: 342.16788.
Hydroboration of
18: Compound 18 (500 mg, 1.15 mmol) was
dissolved in anhyd THF (2 mL) and a freshly prepared solution of
thexylborane (20;
[¹6]
5.77
mmol, 11.5 mL, 0.5 M in THF) was added at 0 ˚C and the
reaction was stirred for 48 h (0 ˚C → r.t.). The
reaction was quenched by adding 30% H2O2-2
M NaOH (1:1; 8 mL) at 0 ˚C and the mixture was then stirred
for 2 h at 0 ˚C. The reaction was diluted with brine (100
mL) and extracted with CH2Cl2 (3 × 100
mL). After drying (Na2SO4), filtration and
evaporation of the solvent, the residue was purified by flash chromatography
on silica gel (n-hexane-EtOAc,
4:1), affording 19 (488 mg, 1.08 mmol,
93%) as a clear colorless oil.
19: [α]D -5
(c = 0.97, CHCl3). ¹H
NMR (300 MHz, CDCl3): δ = 7.20-7.30
(m, 5 H), 4.45 (s, 2 H), 4.06 (m, 2 H), 3.53 (br s, 2 H), 3.34 (m,
2 H), 2.54 (m, 3 H), 1.76 (m, 1 H), 1.39 (s, 9 H), 0.84 (s, 9 H),
0.06 (s, 6 H). ¹³C NMR (75 MHz, CDCl3): δ = 154.6
(C), 138.2 (C), 128.4 (CH), 127.6 (CH), 127.5 (CH), 80.0 (C), 75.7
(CH), 73.3 (CH2), 73.1 (CH), 69.4 (CH2), 48.8
(CH2), 45.1 (CH2), 41.6 (CH), 28.4 (Me), 25.8
(Me), 18.1 (C), -4.4 (Me). HRMS (ES): m/z [M + Na]+ calcd
for C24H41NO5Si: 452.28265; found:
452.28284
Reported yields are isolated yields. The ratio of 15/16 was determined by RP-HPLC: 30% → 65% MeCN in H2O in 60 min; Phenomenex Luna C18 (2), 5 µ, 250 × 4.6 mm.
14RCM can also be accomplished by the Grubbs-Hoveyda catalyst, however, not by the Grubbs first generation catalyst.
15Solutions of Boc-protected 17, 21, 22 and 23 consisted of rotamers complicating interpretation of NMR data.
1724: [α]D -4.0 (c = 0.72, H2O). ¹H NMR (700 MHz, D2O): δ = 4.09 (app. t, J 2,3 = J 3,4 = 8.0 Hz, 1 H, H-3), 3.98 (dd, J 2,6a = 3.6 Hz, J 6a,6b = 12.6 Hz, 1 H, H-6a), 3.86 (dd, J 2,6b = 6.4 Hz, J 6a,6b = 12.6 Hz, 1 H, H-6b), 3.82 (dd, J 4,7a = 4.6 Hz, J 7a,7b = 11.6 Hz, 1 H, H-7a), 3.73 (dd, J 4,7b = 6.3 Hz, J 7a,7b = 11.6 Hz, 1 H, H-7b), 3.66 (dd, J 4,5a = 8.7 Hz, J 5a,5b = 12.2 Hz, 1 H, H-5a), 3.58 (ddd, J 2,6a = 3.6 Hz, J 2,6b = 6.4 Hz, J 2,3 = 8.0 Hz, 1 H, H-2), 3.25 (dd, J 4,5b = 9.3 Hz, J 5a,5b = 12.2 Hz, 1 H, H-5b), 2.48 (m, 1 H, H-4). ¹³C NMR (75 MHz, D2O): δ = 70.9 (C-3), 65.3 (C-2), 59.5 (C-7), 57.8 (C-6), 46.2 (C-4), 45.3 (C-5). IR (HATR): 3304, 2930, 2749, 1595, 1400, 1346, 1055, 1021, 956, 820, 640 cm-¹. HRMS (ES): m/z [M + H]+ calcd for C6H13NO3: 148.09681; found: 148.09671.
2025: ¹H NMR (700 MHz, CDCl3): δ = 7.18-7.30 (m, 5 H, Ph), 4.46 (s, 2 H, OBn), 4.41 (dd, J = 7.4, 9.2 Hz, 1 H, H-1b), 4.27 (dd, J = 2.5, 9.2 Hz, 1 H, H-1a), 3.75 (m, 2 H, H-2, H-3), 3.62 (dd, J = 5.2, 9.0 Hz, 1 H, H-6b), 3.40 (m, 2 H, H-5a, H-6a), 3.22 (dd, J = 8.2, 11.7 Hz, 1 H, H-5b), 2.70 (br s, 1 H, OH), 2.45 (m, 1 H, H-4). ¹³C NMR (75 MHz, CDCl3): δ = 161.4 (C), 137.4 (C), 128.7 (CH), 128.1 (CH), 127.8 (CH), 78.9 (CH), 73.7 (CH2), 71.5 (CH2), 66.3 (CH2), 64.1 (CH), 47.2 (CH), 46.7 (CH2).
22The inhibition constants (K
i) were determined using
four inhibitor concentrations within a limited range around the K
i value.
Inhibition of β-Glucosidase (Almond): K
i was determined at 37 ˚C
using a NaH2PO4-Na2HPO4 buffer
(pH 6.5; 100 mM) and 2-chloro-4-nitrophenyl-β-d-glucoside as substrate. The release of
2-chloro-4-nitrophenol was monitored continuously by measuring absorbance
at λ = 405 nm. The K
i values
were determined by Dixon plots.
Inhibition
of α-Glucosidase (Yeast): K
i was
determined at 37 ˚C using a NaH2PO4-Na2HPO4 buffer
(pH 5.6; 100 mM) and 4-nitrophenyl-α-d-glucoside
as substrate. The release of 4-nitrophenol was monitored by measuring
absorbance at λ = 405 nm after
addition of 10% Na2CO3 to samples
of the reaction mixture at regular time intervals. The K
i values were determined
by Dixon plots.
Inhibition of α-Mannosidase
(Jack Bean): Reactions were performed at 37 ˚C using
a HOAc-NaOAc buffer (pH 4.5; 100 mM) containing ZnCl2 (2
mM) and 4-nitrophenyl-α-d-mannoside
as substrate, and were monitored analogously to the α-glucosidase
assay above.
No significant inhibition of the glycolysis of 4-nitrophenyl-α-d-mannoside was observed at a concentration of 1.9 mM in the presence of 24 or rac-24 (1 mM).