Isotetracene antibiotics

Among all the isotetracene antibiotics, tetrangomycin (32a), obtained from S. rimosus, possesses the simplest structure, and is the first antibiotic to be isolated [162, 163]. Compound (32a) differs from (31) only by the presence of a double bond (instead of a diol) between C-4a and C-12b. Base treatment of (32a) does not cause a skeletal rearrangement, but readily aromatizes it to the benz[a]anthraquinone derivative, tetrangulol (33a). The latter is an antibiotic per se, since it can also be isolated from the culture filtrates of S. rimosus without any alkaline treatment [162]. A related antibiotic rabelomycin (32b)... 

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