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Synlett 2005(20): 3126-3130  
DOI: 10.1055/s-2005-922748
LETTER
© Georg Thieme Verlag Stuttgart · New York

O-Heterocycles via Laccase-Catalyzed Domino Reactions with O2 as the Oxidant

Heiko Leutbecher, Jürgen Conrad, Iris Klaiber, Uwe Beifuss*
Bioorganische Chemie, Institut für Chemie, Universität Hohenheim, Garbenstraße 30, 70599 Stuttgart, Germany
Fax: +49(711)4592951; e-Mail: ubeifuss@uni-hohenheim.de ;
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Publication History

Received 24 August 2005
Publication Date:
28 November 2005 (online)

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Abstract

Laccase-catalyzed domino reactions of 4-hydroxy-6-­methyl-2H-pyran-2-one or substituted 4-hydroxy-2H-chromen-2-ones with catechols using molecular oxygen as an oxidant afford coumestans and related O-heterocycles with yields ranging from 51% to 99%.

Key words

enzymes - catalysis - oxygen - heterocycles - domino ­reactions

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General Procedure for Laccase-Catalyzed Domino Reactions. 4-Hydroxy-2H-pyran-2-one (1, 1 equiv, 3.0 mmol), 4-hydroxy-2H-chromen-2-one (6, 1 equiv, 3.0 mmol), and catechol 2 (1.1 equiv, 3.4 mmol) were dissolved in 200 mL acetate buffer (pH 4.37, 0.2 M) and vigorously stirred under air at r.t. in the presence of 25 mg laccase (19 U/mg) of Trametes versicolor until the substrates had been fully consumed, as judged by TLC. The reaction mixture was saturated with NaCl and filtered on a Buchner funnel. The filter cake was washed with a solution of 200 mL 15% NaCl and 10 mL H2O. The crude products obtained after drying exhibited a purity of 90-95% (NMR). Analytically pure products could be obtained by recrystallization. Trans-formations with laccase (320 U/mg) of Agaricus bisporus were performed in a phosphate buffer (pH 6.0, 0.2 M).

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Selected data for 4e: IR (ATR): 3405, 3119, 1703, 1440, 1296, 1220, 1050, 839 cm-1. UV (MeCN): λmax (lg ε) = 233 (4.28), 335 nm (4.18). 1H NMR (300 MHz, DMSO-d 6): δ = 2.36 (s, 3 H, CH3), 3.83 (s, 3 H, OCH3), 6.95 (s, 1 H, 4-H), 7.20 (s, 1 H, 6-H), 9.51 (br s, 2 H, 7-OH, 8-OH). 13C NMR (75 MHz, DMSO-d 6): δ = 20.51 (CH3), 52.44 (OCH3), 96.36 (C-4), 100.04 (C-6), 103.02 (C-9b), 110.94 (C-9a), 114.45 (C-9), 142.02, 146.40, 148.43 (C-5a, C-7 or C-8), 158.72 (C-1), 162.76 (C-3), 164.31 (C-4a), 166.73 (C=O). MS (EI, 70 eV): m/z (%) = 290 (20) [M+], 258 (100) [M+ - CH4O], 229 (4), 202 (16), 174 (11), 69 (7), 43 (19). HRMS: m/z calcd for C14H10O7: 290.04266; found: 290.04251.

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Selected data for 5: IR (ATR): 3440, 3092, 2500, 1693, 1636, 1273, 1252, 1046, 832 cm-1. UV (MeCN): λmax (lg ε) = 225 (4.00), 244 (4.08), 347 nm (4.04). 1H NMR (300 MHz, acetone-d 6): δ = 2.42 (s, 3 H, CH3), 6.53 (s, 1 H, 4-H), 7.49 (d, 3 J 9-H, 10-H = 8.7 Hz, 1 H, 9-H or 10-H), 8.39 (d, 3 J 10-H, 9-H = 8.7 Hz, 1 H, 9-H or 10-H), 8.74 (br s, 1 H, OH), 10.87 (br s, 1 H, OH). 13C NMR (75 MHz, acetone-d 6): δ = 19.27 (CH3), 98.95 (C-4), 99.72 (C-10b), 106.14 (C-6a or C-10a), 116.58 (C-9 or C-10), 124.46 (C-9 or C-10), 124.50 (C-6a or
C-10a), 145.42 (C-7 or C-8), 149.31 (C-7 or C-8), 160.13 (C-1, C-4a or C-6), 160.15 (C-1, C-4a or C-6), 163.15 (C-3), 164.33 (C-1 or C-6). MS (EI, 70 eV): m/z (%) = 260 (100) [M+], 245 (4) [M+ - CH3], 232 (4), 189 (5), 176 (11), 161 (6), 120 (15), 43 (25). HRMS: m/z calcd for C13H8O6: 260.03207; found: 260.03162.

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Selected data for 7f: IR (ATR): 3504, 3207, 1685, 1459, 1318, 1254, 1085, 848, 817 cm-1. UV (MeCN): λmax (lg ε) = 215 (4.57), 250 (4.14), 343 nm (4.21). 1H NMR (300 MHz, DMSO-d 6): δ = 2.43 (s, 3 H, CH3), 4.11 (s, 3 H, OCH3), 7.06 (s, 1 H, 7-H), 7.44 (s, 2 H, 3-H, 4-H), 7.82 (s, 1 H, 1-H), 9.38 (br s, 2 H, 8-OH, 9-OH). 13C NMR (75 MHz, DMSO-d 6): δ = 21.01 (CH3), 61.35 (OCH3), 100.04 (C-7), 106.12 (C-6a or C-6b), 112.66 (C-11b), 115.01 (C-6a or C-6b), 117.49 (C-3 or C-4), 121.51 (C-1), 133.05 (C-3 or C-4), 134.16 (C-10), 135.16 (C-2), 138.16, 142.41, 146.55 (C-8, C-9 or C-10a), 151.32 (C-4a), 158.29 (C-6 or C-11a), 158.67 (C-6 or C-11a). MS (EI, 70 eV): m/z (%) = 312 (100) [M+], 297 (45) [M+ - CH3], 269 (17), 185 (7), 156 (9), 139 (11), 128 (16), 77 (12). Anal. Calcd for C17H12O6 (312.27): C, 65.39; H, 3.87. Found: C, 65.11; H, 4.10.