13 



Tetracycline, Analogues and Related Sub- 

 stances 



The tetracycline antibiotics display features indicative of an 

 acetate origin. The oxygenation pattern is generally consistent 

 as are the points of occurrence of methyl groups and halogen 

 atoms. There is also at least a superficial resemblance to 

 proved acetate derivatives such as the anthraquinones. So far 

 the experimental evidence published concerning the biosyn- 

 thetic origin of the tetracyclines has been limited, and some in- 

 teresting obscurities remain. 



The general concept of an acetate-derived precursor in the 

 sense of a polyketomethylene chain is, in the case of oxytetra- 

 cycline as follows: 



./ 



C, lO] 



C C 



/ 



[O] 



\ 



Ci 



10]C 



/ 



c 



/ \ 



o o o o 



loi 



A 6-demethyltetracychne has been isolated from a fermentation 

 broth, and tetracycline itself is a 5-deoxyoxytetracychne as well 

 as a 7-dechlorochlortetracycUne; so sometimes some of the steps 

 in the biosynthetic scheme are omitted. 



