Synthesis of Coumarins in Search of Better Nonpeptidic HIV Protease Inhibitors

Department of Chemistry, University of Calcutta, 92, Acharya Prafulla Chandra Road, Calcutta-700 009

Manuscript received 7 August 1998

3-Substituted-4-hydroxycoumarins have been recently identified as active nonpeptidic HIV protease inhibitors. In order to get more potent inhibitors, synthesis of a number of 3-substituted-4-hydroxycoumarins have been designed. Nucleophilicity of C-3 in 4- hydroxycoum arin is exploited by reacting with an electrophile 3-carbethoxycoumarin to achieve a new C-3 substituted-4-hydroxycoumarin. But the product identified is a benzopyranodicoumarin (2), which is also obtained by the reaction of 4-hydroxycoumarin with salicylaldehyde. However, the reaction of 4-hydroxycoumarin with a number of 2-oxygenated aldehydes 4b-e affords dicoumarols (5a-d) only. On the contrary, with 2,4,5-trim ethoxybenza ldehyde (4f), a benzopyranodicoumarin (6a) is formed. The reaction of 4-hydroxycoumarin with 6- bromo-3,4-methylenedioxybenzaldehyde (4g) and 6-bromo-3,4-dimethoxybenzaldehyde (4h), when treated separately, furnishes benzopyranodicoumarin (6b) and benzopyranocoumarin (7) respectively. In both the cases, unusual nucleophilic aromatic substitution of bromine occurs in electron-rich aromatic systems without any catalyst.