合成路线1

Condensation of o-nitroacetophenone (I) with aldehyde (II) in the presence of piperidine acetate afforded the chalcone (III). Both the double bond and the nitro group of (III) were reduced by catalytic hydrogenation over PtO2 to give (IV). 5-Bromopiperonal (VI) was prepared by treatment of 5-bromo-3,4-dihydroxybenzaldehyde (V) with dibromomethane. Reductive condensation of aldehyde (V) with amine (IV) by means of sodium cyanoborohydride produced the secondary amine (VII), which was condensed with ethyl oxalyl chloride (VIII) to produce amide (IX). Cyclization of (IX) to the corresponding quinolone (X) was achieved by treatment with K2CO3 in EtOH. The ethyl group of the target compound was introduced by Stille coupling of bromide (X) with vinyl tributyltin, followed by catalytic hydrogenation of the resulting ethylene derivative (XI) to give (XII). Finally, saponification of diester (XII) with KOH furnished the title dipotassium salt.