Chemostructural requirement for centrally acting muscle relaxant effect of magnolol and honokiol, neolignane derivatives.

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Abstract
Effects of some diphenyl and monophenyl compounds on grip strength in mice and spinal reflexes in young chicks were investigated in order to study structure-activity relationships between muscle relaxant activity and neolignane compounds, magnolol and honokiol extracted from Magnolia officinalis. Diphenyl produced a long-lasting suppression in the spinal reflex and relatively weak inhibition in the grip strength. Introduction of a hydroxyl into 2-position of diphenyl, o-phenylphenol, increased the muscle relaxant activity and accelerated the onset, although the duration was still long. In the spinal reflex preparation, the duration of action became short. The introduction of 2 hydroxyls into 2- and 2''-position of diphenyl,2,2''-dihdroxydiphenyl, further strengthened the activity and shortened the duration of the inhibitory effect on the grip strength and the spinal reflex. When 2 allyls are introduced into 5,5''-position of 2,2''-dihydroxydiphenyl, it corresponds to magnolol Magnolol, 5,5''-diallyl-2,2''-dihydroxydiphenyl, produced potent inhibitory effects of gradual onset and of long duration on the 2 test preparations. Position of allyls and hydroxyls in honokiol, 5,3''-diallyl-2,4''-dihydroxydiphenyl, is different from magnolol, although the pharmacological characteristics are quite similar to magnolol. Evidently, a hydroxyl accelerates the onset and shortens the muscle relaxant activity of diphenyl and an allyl influences the activity in the opposite direction. Both radicals appear to intensify the activity.