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).
Saeed
Aamer
A
Department of Chemistry, Quaid-I-Azam University, Islamabad, Pakistan. aamersaeed@yahoo.com
D020902:Hypericum / Q000737:chemistry; D049934:Isocoumarins / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D013237:Stereoisomerism
C549261:6-O-methylannulatomarin; C549262:7-demethylannulatomarin; D049934:Isocoumarins; C525227:annulatomarin