Efficient synthesis and structure–activity relationship of honokiol, a neurotrophic biphenyl-type neolignan

Honokiol, a biphenyl-type neolignan, which shows the remarkable neurotrophic effect in primary cultured rat cortical neurons, has been effectively synthesized in 21% yield over 14 steps starting from 5-bromosalicylic acid and p-hydroxybenzoic acid by utilizing Pd-catalyzed Suzuki–Miyaura coupling reaction as a key step. Additionally, the structure–activity relationship between neurite outgrowth-promoting activity and its O-methylated and/or its hydrogenated analogues was examined in the primary cultures of fetal rat cortical neurons, suggesting that 5-allyl and 4′-hydroxyl groups are essential for affecting the neurotrophic activity of honokiol.