| abstract |
wherein R1 to R5 are independently hydrogen, an optionally substituted alkyl, an optionally substituted aryl, an optionally substituted alkoxy, an optionally substituted alkanoyloxy, a carboxy, an optionally substituted alkoxycarbonyl, a hydroxy, a halo, a nitro, a cyano, or wherein two of these adjacent substituents represented by R1 to R5, together form a methylene dioxy group. |