Ergosterol biosynthesis scheme

Figure 7-12 outlines the terminal steps in the complex sequence of both the biosynthesis of cholesterol and ergosterol. The synthesis, starting with acetate, leads to the common steroid precursor lanosterol.9 Thus, in the case of cholesterol, the scheme involves steps for the reduction of the A24 double bond, and the oxidation and removal of the 14a methyl group and of both methyls at C-4. This is followed by isomerization of the A8 double bond of the resultant zygmosterol to the A5 position, affording desmesterol, and finally cholesterol. 

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