Chemistry and neurotrophic activity of seco-prezizaane- and anislactone-type sesquiterpenes from Illicium species

This review focuses mainly on our findings of chemistry and neurotrophic activity of the seco-prezizaane- and anislactone-type sesquiterpenes. The genus Illicium is the only member of the family Illiciaceae. From a chemical and biological point of view, the Illicium species are known to be rich in biosynthetically unique seco-prezizaane-type sesquiterpenes, some of which have been known to exhibit neurotoxic activity. Our continuing chemical studies of the Illicium species such as Illicium anisatum, I. tashiroi, I. merrillianum and I. jiadifengpi have resulted in the isolation of a number of sesquiterpenes, most of which belong to both of seco-prezizaane- and anislactone-type sesquiterpenes. Chemical studies on unique sesquiterpenes, such as illicinolide, tashironin, merrilactone A, and jiadifenin isolated from the above plants, allow us to further categorize seco-prezizaane-type sesquiterpenes into six sub-groups according to their carbon skeletons: anisatin-subtype, pseudoanisatin-subtype, majucin-subtype, minwanensin-subtype, cycloparvifloralone-subtype, and allo-cedrane-type. On the basis of chemical correlation of these subtypes, plausible biosynthetic pathway for all the subtypes of seco-prezizaane-type and anislactone-type sesquiterpenes is discussed. In addition, some sesquiterpenes such as merrilactone A, 11-debenzoyltashironin and jiadifenin are shown to have potent neurite outgrowth promoting activity in primary cultured rat cortical neurons.