Fusidane steroidal antibiotics

Helvolic acid (5.145) was the first of the steroidal fusidane antibiotics to be isolated. It was obtained from Aspergillus fumigatus var helvola in 1943 by Chain and Florey. Cephalosporin Pi (5.146) was deseribed by Abraham as a metabolite of the same Brotzu strain of Cephalosporium acremonium as that 

Evidence for the relative and absolute stereochemistry, which was reported in 1965, was based on a more detailed analysis of the NMR spectra and on the signs of the circular dichroism curves of various ketones when compared to steroid models. The stereochemistry was finally confirmed by X-ray crystallography. 

Fusidic acid and helvolic acid were interrelated by an interesting microbiological strategy that has potentially wider applications. The fungus 

The biosynthesis of these antibiotics has attracted interest because of their protolanosterol structure. Thus, fusidic acid was shown to incorporate [2- C]-and (47 )-[2- C,4- H]mevalonic acid (5.151) as well as squalene in accordance with a pathway in which the final backbone rearrangement of lanosterol biosynthesis has not taken place. 

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