Special Topic Biological Synthesis of Aromatic Rings Phenylalanine

15 Special Topic Biological Synthesis of Aromatic Rings Phenylalanine 

Some of the amino acids from which our tissues are constructed contain benzene rings, and so nature must have a way of making them. You might actually set yourself that problem right now you have at your disposal the means to generate benzene from simple hydrocarbon precursors. 

Here is how the process works for phenylalanine, one of your amino acids. A sugar is transformed enzymatically into dehydroquinate (A), which undergoes an elimination reaction, also enzjme mediated, to give dehydroshikimate (B) (Fig. 14.115). 

FIGURE 14.115 In the biosynthesis of phenylalanine, enzymes transform a sugar into dehydroquinate (A) and then dehydroshikimate (B). 

The carbon-oxygen double bond in B is reduced and phosphorylated to give shikimate-3P (C) (Fig. 14.116). Another enzyme adds a three-carbon fragment to one of the hydroxyl groups (you ll see why this is critical in a moment) to give D, which undergoes a second elimination to place the second double bond in the ring 

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