Luteolin, a compound with adenosine A(1) receptor-binding activity, and chromone and dihydronaphthalenone constituents from Senna siamea

Activity-guided fractionation led to the isolation of luteolin (1) from the leaves of Senna siamea (syn. Cassia siamea). This compound was found to be an antagonist at the adenosine Al receptor with a K-i, value in the low mi cromolar range. Four additional nonactive compounds (2-5) were also isolate d, and their structures were elucidated. One compound was identified as cas sia chromone (5-acetonyl-7-hydroxy-2-methylchromone) (2). Three other compo unds are new, and they were identified as 5-acetonyl-7-hydroxy-2-hydroxymet hyl-chromone (3), 4-(trans)-acetyl-3,6,8-trihydroxy-3-methyldihydronaphthal enone (4), and 4-(cis)-acetyl-3,6,8-trihydroxy-3-methyldihydronaphthalenone (5).