Synlett 2006(4): 0621-0623  
DOI: 10.1055/s-2006-926248
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Pyranonaphthoquinone Antibiotics Involving the Phthalide Annulation Strategy

Sven Claessensa, Dashnie Naidoob, Dulcie Mulhollandb, Luc Verschaevec, Johannes van Stadend, Norbert De Kimpe*a
a Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
Fax: +32(9)2646243; e-Mail: norbert.dekimpe@UGent.be;
b School of Chemistry, University of KwaZulu-Natal, Howard College Campus, 4041 Durban, South Africa
c Department of Environmental Toxicology, Vito (Flemish Institute for Technological Research), Boeretang 200, 2400 Mol, Belgium
d Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal, Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
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Publikationsverlauf

Received 24 November 2005
Publikationsdatum:
20. Februar 2006 (online)

Abstract

The synthesis of the pyranonaphthoquinone antibiotic pentalongin was performed using the phthalide annulation strategy. Annulation of the cyanophthalide onto 6H-pyran-3-one resulted in a hongconin analogue, which upon further elaboration was converted into the natural product.

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Van Puyvelde, L.; Hakizayezu, D.; Brioen, P.; De Kimpe, N.; De Vroey, C.; Bogaerts, J.; Hakizamungu, E., presented at International Congress on Natural Products Research, July 31 to August 4, 1994; Halifax, Canada, 1994.

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De Kimpe, N.; Kesteleyn, B.; Nguyen, Van T.; Van Puyvelde, L. 18th International Congress of Heterocyclic Chemistry, July 29 to August 3, 2001; Yokohama, Japan, 2001, 120.

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5,10-Dimethoxy-1 H -benzo[ g ]isochromene-4-one ( 13): yellowish oil; 1H NMR (acetone-d 6): δ = 3.90 (3 H, s, OCH3), 4.01 (3 H, s, OCH3), 4.30 (2 H, s, CH2C=O), 5.06 (2 H, s, CH2O), 7.62 (1 H, ddd, J = 8.4, 7.0, 1.4 Hz, CH-7), 7.73 (1 H, ddd, J = 8.4, 7.0, 1.4 Hz, CH-8), 8.11 (1 H, dd, J = 8.4, 1.4 Hz, CH-9), 8.34 (1 H, dd, J = 8.4, 1.4 Hz, CH-6). 13C NMR (acetone-d 6): δ = 62.13 (OCH3), 63.14 (OCH3), 64.46 (CH2O), 74.50 (CH2OC=O), 118.30 (Cquat), 122.01 (CH-9), 125.05 (CH-6), 126.84 (CH-7), 127.45 (Cquat), 129.08 (Cquat), 129.74 (CH-8), 131.74 (Cquat), 146.43 (Cquat), 155.64 (Cquat), 193.47 (C=O). IR (KBr): νmax 1689 (C=O) cm-1. MS (ES+): m/z = 258 [M+].

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4-Hydroxy-3,4-dihydro-1 H -benzo[ g ]isochromene-5,10-dione ( 6): 1H NMR (CDCl3): δ = 3.86 (1 H, dd, J = 12.2, 3.8 Hz, CHCH a Hb), 4.03 (1 H, dd, J = 12.2, 3.5 Hz, CHCHa H b ), 4.49 (1 H, dd, J = 18.9, 1.65 Hz, OCH a Hb), 4.76 (1 H, dd, J = 18.9, 0.6 Hz, OCHa H b ), 4.82 (1 H, m, CHOH), 7.76 (2 H, m, CH7-CH8), 8.09 (2 H, m, CH6-CH9). 13C NMR (CDCl3): δ = 60.18 (CH2O), 63.23 (CHOH), 69.51 (CH2), 126.38 (C-6 or C-9), 126.63 (C-9 or C-6), 131.83 (2 × Cquat), 134.28 (C-7 and C-8), 140.58 (Cquat), 143.74 (Cquat), 183.84 (C=O), 184.59 (C=O). IR (KBr): νmax = 3468 (OH), 1661 (C=O) cm-1. MS (ES+): m/z (%) = 231 (15) [M + H+], 213 (100) [M+ - H2O].