Microwave‐Assisted Synthesis of cAMP Phosphodiesterase Inhibitor 8‐Hydroxy‐6,7‐dimethoxy‐3‐hydroxymethylisocoumarin

Synthesis and antibacterial evaluation of typharin analog: 6,8-dihydroxy-7-methyl-3-styryl-3,4-dihydroisocoumarin

Synthesis of the 6-hydroxy-7-methyl analog of typharin (8-dihydroxy-3-styryl-3,4-dihydroisocoumarin) isolated from the rhizomes of Typha capensis has been described. Direct condensation of 3,5-dimethoxy-4-methylhomophthalic acid (1) with cinnamoyl chloride at elevated temperature under inert conditions afforded 6,8-dihydroxy-7-methyl-3-styrylisocoumarin (2). Hydrolysis of isocoumarin to keto acid (3) followed by reduction and cyclodehydration of hydroxy acid analog (4) afforded ( ± )-6,8-dimethoxy-3-(4-methoxyphenyl)-3,4-dihydroisocoumarin (5). Demethylation of the latter using anhydrous aluminum chloride/ethane thiol furnished the title isocoumarin (6). Compounds (1-6) were screened for in vitro antibacterial activity against a representative panel of Gram-positive and Gram-negative bacteria using levofloxacin as the reference drug.

Synthesis of 5-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin

The synthesis of title isocoumarin, the 5-chloro analog of naturally occurring 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, isolated from Tessmannia densiflora is described. Chlorination of ethyl 2-(2-ethoxy-2-oxoethyl)-4,6-dimethoxybenzoate (2) afforded 3-chloro ester (3) followed by hydrolysis to furnish the 2-(carboxymethyl)-3-chloro-4,6-dimethoxybenzoic acid (4) that was converted to corresponding anhydride (5). Condensation of the latter with hexanoyl chloride in the presence of tetramethylguanidine and triethyl amine afforded 5-chloro-6,8-dimethoxy-3-pentylisocoumarin (6) which upon regioselective demethylation yielded the title isocoumarin (1).

Synthesis of (+/-)-6-O-methyl and 7-demethylannulatomarin

Synthesis of 6-O-methyl and 7-demethyl derivatives of annulatomarin (1) (6,8-dihydroxy-7-methoxy-3-phenyl-3,4-dihydroisocoumarin) isolated from the aerial parts of Hypericum annulatum is described. The key step involves an efficient, microwave-accelerated solvent and catalyst-free condensation of methyl benzoate with 3,4,5-trimethoxyhomophthalic acid (2) to afford 6,7,8-trimethoxy-3-phenylisocoumarin (3). Saponification of the latter to keto acid (4) followed reduction to furnish 6,7,8-trimethoxy-3-phenyl-3,4-dihydroisocoumarin (5), which was either regioselectively demethylated to ( +/- )-6-O-methylannulatomarin (6) or completely demethylated to ( +/- )-7-demethylannulatomarin (7).