Lignans Syringaresinol

On the other hand, biosynthetic pathways that do not involve the conversion from coniferyl alcohol to matairesinol have been proposed for lignans composed of two syringyl (3,5-dimethoxy-4-hydroxyphenyl) groups (+)-syringaresinol formation in Liriodendron tulipifera [50] and (H-)-lyoniresinol biosynthesis in Lyonia ovalifolia var. elliptica [51]. Enantioselective coupling of two sinapyl alcohol units was proposed for the selective formation of (H-)-syringaresinol [50], On the other hand, a non-enantioselective dimerization of sinapyl alcohol was proposed for (+)-lyoniresinol biosynthesis and the enantioselectivity in the biosynthesis was ascribed... 

Only one specie, H. lawsoniae has been found to contain lignans. Novel sesquilignans named as hedyotol A, -B, -C and -D (66-69) [16] and their acetyl derivatives, (+)-pinoresinol, (+) medioresinol, (+)-syringaresinol, (-)-dehydrodiconiferyl alcohol, (70-73) as well as the novel dilignans, hedyotisol A, -B and -C (74-76) have been isolated from this plant (Table 7) [17]. 

The EtOH extracts of the wood of S. sachalinensis was fractionated with diethyl ether and the solubles subjected to silica-gel column and preparative thin-layer chromatographies to give (+)-syringaresinol and two lignan esters 23 and 24. 

The lignans (+)-pinoresinol 20a and (-)-matairesinol 36b, isolated from Forsythia species inhibit cAMP phosphodiesterase which catalyses the breakdown of the second messenger, cAMP, inside the cells (99). Cis-hinokiresinol 102 and oxy-c/.y-hinokiresinol 103 from Anemarrhena asphodeloides (100), and (+)-syringaresinol-di-0-P-D-glucopyranoside 104 and (+)-hydroxypinoresinol 4, 4"-di-0-p-D-glucopyranoside 105 from Eucommia ulmoides (Eucommiaceae) bark (101) are also inhibitors of this phosphodiesterase. 

The cardiovascular effects of lignans are also worthy of mention. It has been known for some time that certain plants, such as Siberian ginseng (Acanthopomax senticosus), have an ability to sustain cardiovascular activity during prolonged exercise (see Ref. (107)), and this effect was recently attributed to (+)-syringaresinol di-O-P-D-glucoside 104 (108). 

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