Electrophilic aromatic substitution biological example

The structural theory of organic chemistry was developed in the last half of the nineteenth century. It led to the concept that chemical, physical and biological properties of all kinds must be a function of structural change. The earliest structure-property relationships (SPR) were qualitative. Examples are the directional effect of substituents on the benzene ring with respect to electrophilic aromatic substitution and orientation in... 

Electrophilic aromatic substitution (SeAt) of lH,4H-2,3-dione precursors has also been demonstrated. For example, intermediate 202 prepared by Komberg and co-workers (see previous section) was converted to nitro derivative 203 through SgAr chemistry, which was subsequently used to prepare a library of derivatives for biological testing, including the synthetically useful dichloro derivative 204 <99JHC1271>. 

An example of a biological electrophilic aromatic substitution occurs during the biosynthesis of phylloquinone, or vitamin Kj, the human bloodclotting factor. Phylloquinone is formed by reaction of 1,4-dihydroxy-naphthoic acid with phytyl diphosphate. Phytyl diphosphate first dissociates to a resonance-stabilized allylic carbocation, which then substitutes onto the aromatic ring in the typical way. Several further transformations lead to phylloquinone (Figure 9.15). 

There is, for example, no end-of-text chapter entitled Heterocyclic Compounds. Rather, heteroatoms are defined in Chapter 1 and nonaromatic heterocyclic compounds introduced in Chapter 3 heterocyclic aromatic compounds are included in Chapter 11, and their electrophilic and nucleophilic aromatic substitution reactions described in Chapters 12 and 23, respectively. Heterocyclic compounds appear in numerous ways throughout the text and the biological role of two classes of them—the purines and pyrimidines—features prominently in the discussion of nucleic acids in Chapter 27. 

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