TERPENOIDS 247 



Either C-1 or C-7 may be derived from formate, and C-9 may 

 be provided from a one-carbon pool representing carbon- 1 of glucose, 

 not however from sodium formate directly. Based on admittedly in- 

 complete evidence, Ferretti and Richards speculated that head-to-tail 

 condensation of three acetyl CoA units occurs followed by the 

 acquisition of appropriate carbon side chains. These authors then 

 postulate an oxidative ring enlargement of the six-membered ring to 

 yield the tropolone. This work involved mold tropolones. 



If this general scheme is correct, the metabolism of tropolones 

 is related to that of benzenoid compounds rather than terpenoid, as 

 suggested by Erdtman. It is possible that tropolone metabolism in 

 gymnosperms bears no relationship at all to that of the mold species. 

 There is no comparable information on the biosynthesis of the 

 gymnosperm tropolones, but such would be of very great interest. 

 Since there is hardly any doubt as to the independent origin of these 

 pathways, a comparative study of biochemical routes and enzymology 

 would be illuminating. This situation represents, theoretically at 

 least, one suited to the study of questions of enzyme homology such 

 as were mentioned in an earlier section. 



If the mechanism for the formation of the basic tropolone 

 nucleus is eventually estabhshed to be that proposed by Ferretti and 

 Richards, and further, if it applies to the gymnosperm tropolones as 

 well as to mold tropolones, then the critical step in tropolone syn- 

 thesis, as it pertains to biochemical systematics, is the oxidative ring 

 enlargement. The acetate condensation is one of major significance to 

 a great majority of vascular plants, but this type of ring enlargement 

 is quite rare. 



The only family of higher plants known to produce tropolones, 

 the family Cupressaceae, is represented by about fifteen genera and 

 about 140 species. It is found throughout the world. Although rela- 

 tively few species have been studied intensively, among those genera 

 which are known to include some tropolone-containing species are 

 Juniperus, Chamaecyparis, Cupressus, Libocedrus, Thuja, Thujopsis, 

 and Biota. Biota orientales, which has been classified with Thuja, 

 does not apparently produce tropolones. Individual species of Thuja 

 contain different tropolones. Erdtman believes that the Thuja, 

 Thujopsis, Biota group might be an excellent prospect for an inten- 

 sive comparative biochemical study of tropolones, sesquiterpenes, and 



flavonoids. 



The presence of tropolones in both Chamaecyparis and 

 Cupressus is not surprising in view of the morphological similarity of 

 the two genera. However, individual species vary in their tropolone 

 and terpene constituents. On this basis Erdtman (1955b) states. 



