Abstract
The lipase-mediated kinetic resolution of racemic scopoline [(±)-4] and 6-hydroxytropinone [(±)-7] is reported. Whereas (±)-4 is difficult to resolve due to steric hindrance of the hydroxy function, the resolution of (±)-7 with vinyl acetate as acyl donor gave alcohol (+)-7 and the corresponding acetate (-)-9 with high enantiomeric excess. In case of the optimal result of 99% ee for (+)-7 and 80% ee for (-)-9, an E-value of 35 was calculated. The preparative lipase-catalyzed resolution of (±)-7 resulted in almost enantiopure alcohol (+)-7 with >99% ee after one recrystallization.
Key words
enantioselectivity - lipase - resolution - tropinone
References
1a
Singh S.
Chem. Rev.
2000,
100:
925
1b
O’Hagan D.
Nat. Prod. Rep.
2000,
17:
435
1c
Hemscheidt T.
Top. Curr. Chem.
2000,
209:
175
1d
Newman AH.
Agoston GE.
Curr. Med. Chem.
1998,
5:
305
1e
Fodor G. In Rodd’s Chemistry of Carbon Compounds
2nd ed., Vol.:
Sainsbury M.
Elsevier;
Amsterdam:
1997.
p.4251-4276
1f
Lounasmaa M.
Tamminen T.
Alkaloids
1993,
44:
1
Some recent examples:
2a
Airaksinen AJ.
Lipsonen J.
Ahlgren M.
Vainiotalo P.
Bergstrom KA.
Laatikainen R.
Vepsäläinen J.
Tetrahedron
2003,
59:
377
2b
Lazny R.
Nodzewska A.
Tetrahedron Lett.
2003,
44:
2441
2c
Airaksinen AJ.
Ahlgren M.
Vepsäläinen J.
J. Org. Chem.
2002,
67:
5019
2d
Cheng J.
Moore Z.
Stevens ED.
Trudell ML.
J. Org. Chem.
2002,
67:
5433
2e
Armstrong A.
Ahmed G.
Dominguez-Fernandez B.
Hayter BR.
Wailes JS.
J. Org. Chem.
2002,
67:
8610
2f
Zhao L.
Johnson KM.
Zhang M.
Flippen-Anderson J.
Kozikowski AP.
J. Med. Chem.
2000,
43:
3283
2g
Petrović G.
Saičić RN.
Čeković Z.
Synlett
1999,
635
2h
Bremner JB.
Smith RJ.
Tarrant GJ.
Tetrahedron Lett.
1996,
37:
97
2i
Justice DE.
Malpass JR.
Tetrahedron Lett.
1995,
36:
4689
3a
Node M.
Nakamura S.
Nakamura D.
Katoh T.
Nishide K.
Tetrahedron Lett.
1999,
40:
5357
3b
Johnson CR.
Bis SJ.
J. Org. Chem.
1995,
60:
615
3c
Werner G.
Arzneim.-Forsch.
1967,
17:
1467
4
Katoh T.
Kakiya K.
Nakai T.
Nakamura S.
Nishida K.
Node M.
Tetrahedron: Asymmetry
2002,
13:
2351
5
Cramer N.
Laschat S.
Baro A.
Frey W.
Synlett
2003,
in press:
6
Zeile K.
Heusner A.
Chem. Ber.
1957,
90:
2809
7a
Chen C.-S.
Sih CJ.
Angew. Chem., Int. Ed. Engl.
1989,
28:
695 ; Angew. Chem. 1989, 101, 711
7b
Baumann M.
Hauer BH.
Bornscheuer UT.
Tetrahedron: Asymmetry
2000,
11:
4781
8
Screening Procedure for the Lipase-catalyzed Resolution. To a solution of the racemic substrate 4 or 7 (0.1 mmol) in the respective solvent was added vinyl acetate (13 µL, 0.30 mmol), molecular sieves 4 Å (4 pellets) and the respective enzyme (2000-10000 U; units according to the manufacturer’s information, respective 2-15 mg). The reaction mixture was shaken at 40 °C for 1 h. After sedimentation of the enzyme, an aliquot of 50 µL was taken from the supernatant, filtered through a plug of cotton wool, diluted with CH2Cl2 (300 µL) and directly analyzed by capillary GC. This procedure was repeated in time intervals from 0.5 to 4 h depending on the reaction rate (TLC control). The reaction was stopped after 48 h.
9 Capillary GC: Bondex unβ (20 m × 2.5 mm), carrier gas H2 (0.4 bar), temperature program: 3 min at 100 °C, then 2.5 °C min-1 gradient to 150 °C, tR[(+)-8] = 15.09 min.
10 A solution of (±)-4 (230 mg, 1.49 mmol), vinyl acetate (300 µL), molecular sieves 4 Å (50 pellets) and Chirazyme l-1 (120 mg) in i-Pr2O (25 mL) was shaken at 40 °C for 2.5 h. After filtration, the filtrate was concentrated and chromatographed on Al2O3 with a gradient of EtOAc to MeOH to yield (-)-4 (62 mg, 27%) and (+)-8 (161 mg, 51%). [α]D
20 -9.3 (c 1.00, CHCl3), 33% ee for (-)-4 and [α]D
20 +48.7 (c 1.00, CHCl3), 60% ee for (+)-8.
11 Capillary GC: Bondex unβ (20 m × 2.5 mm), carrier gas H2 (0.4 bar), temperature program: 3 min at 80 °C, then 2.5 °C min-1 gradient to 150 °C, tR[(+)-7] = 28.66 min, tR[(-)-9] = 25.29 min.
12 A solution of (±)-7 (180 mg, 1.16 mmol), vinyl acetate (250 µL), molecular sieves 4 Å (50 pellets) and Chirazyme l-6 (178 mg) in acetone (17 mL) was shaken at 40 °C for 90 min. After filtration, the filtrate was concentrated, taken up in CH2Cl2 and chromatographed on basic Al2O3 with EtOAc to EtOAc/MeOH (1:1) to give (+)-7 (63 mg, 35% after recrystallization from i-Pr2O) and (-)-9 (89 mg, 39%). [α]D
20 +24.8 (c 1.00, CHCl3), 99% ee for (+)-7 and [α]20 -13.3
(c 1.00, CHCl3), 80% ee for (-)-9.
13
Chen C.-S.
Fujimoto Y.
Girdaukas G.
Sih CJ.
J. Am. Chem. Soc.
1982,
104:
7294