Claisen condensation reaction biological example

An example of Claisen reaction is provided by the first step in the biosynthesis of cholesterol and terpenes, which starts from acetyl-CoA. Similar to the Claisen condensation, 2equiv of acetyl-CoA couple to acetoacetyl-CoA, which represents a biological analog of acetoacetate. Following the pattern of an aldol reaction, acetoacetyl-CoA reacts with another equivalent of acetyl-CoA as a carbon nucleophile to give p-hydroxy-p-methylglutaryl-CoA (Figure 1.20). 

We know of a demonstrated example "in vitro" of the biological Claisen-type reaction to B-diketones, that of the condensation of... 

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