Solid-phase synthesis and spectral properties of 2-alkylthio-6H-pyrano[2,3-f]benzimidazole-6-ones: a combinatorial approach for 2-alkylthioimidazocoumarins |
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Authors: | Song Aimin Zhang Jinhua Lebrilla Carlito B Lam Kit S |
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Institution: | Division of Hematology and Oncology, Department of Internal Medicine, University of California Davis Cancer Center, 4501 X Street, Sacramento, California 95817, USA. |
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Abstract: | The solid-phase synthesis of 2-alkylthio-6H-pyrano2,3-f]benzimidazole-6-ones (2-alkylthioimidazocoumarins) is described. 7-Fluoro-4-methyl-6-nitro-2-oxo-2H-1-benzopyran-3-carboxylic acid was coupled to Rink amide resin via its carboxyl group. The resin-bound scaffold then underwent aromatic nucleophilic substitution with primary amines, followed by reduction of the nitro group with tin (II) chloride. Subsequent cyclization of the o-dianilino intermediates with thiocarbonyldiimidazole (TCD) afforded resin-bound 1,3-dihydro-2-thioxo-6H-pyrano2,3-f]benzimidazole-6-ones, which were then S-alkylated with alkyl halides in the presence of N,N-diisopropylethylamine (DIEA). The desired products were obtained in good yield with high purity after trifluoroacetic acid cleavage. The unique spectral properties of 2-alkylthioimidazocoumarins indicate that they may be useful in photodynamic therapy. |
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