TERPENOIDS 



265 



Table 13-5. Distribution of sesquiterpene lactones according to sections of the 

 genus Helenium and related genera. 



Tribe Helenieae (As Classically Constituted) 



Helenium 



Sect. Helenium (One species examined) Sect. Tetrodus (Seven species examined) 



helenalin helenalin 



Sect. Leptopoda (Four species examined) mexicanin 



brevilin tenulin 



flexuostn 



helenalin 



pinnatifidin 



Tribe Heliantheae (As Classically Constituted) 



A ctinospermum 

 helenalin 



Balduina 

 balduilui 



Two types of lactones derived from sesquiterpenes are to be 

 found among Artemisia species. Neither type is identical with the 

 sesquiterpene lactones of Helenium, but both types are closely related 

 on structural grounds. The helenalin type (I) is illustrated again for 

 purposes of comparison with arborescin (II) and a-santonin (III). 



CH 



H3C Q 



H,C 



III 



Both helenalin (I) and arborescin (II) are sesquiterpenes of 

 the guajol type. They differ in their mode of lactone formation. To 

 the writer's knowledge Type I is not found in Anthemideae. However, 

 both II and III are found in the Anthemideae (in Artemisia species) 

 but not the Helenieae (although tenuHn may be interpreted as a 

 lactone of type I to which a two-carbon unit adds to form an acetal). 

 Three eudesmol type sesquiterpene lactones related to a-santonin 

 (alantolactone, isoalanto-lactone, and dihydroisoalantolactone) occur 

 in Inula helenium. Eudesmol, a non-lactone, is obtained from Balsa- 

 morhiza, and ivahn, a lactone of the eudesmol type, is found in Iva. 



