Page - (000033) - in Biomedical Chemistry: Current Trends and Developments

Scheme 1.1.12: Mechanism of an electrophilic aromatic substitution reaction. The reactivity of the aromatic ring is enhanced if electron donating (hydroxyl, amino and alkoxyl) groups are attached to the ring, increasing the electron density and making the attack to the electrophile easier. 1.1.4.3.2 Nucleophilic Aromatic Substitutions Nucleophilic aromatic substitutions are also possible when electron withdrawing groups are attached to the ring (e.g. nitro group and carbonyl moieties) allowing it to accommodate a carbanion, even though aromatic rings are already dense in electrons. The leaving group also needs to be quite electronegative to leave easily and drive the reaction forward (Scheme 1.1.13). The exact mechanism varies dependently on the leaving group having some parallels to normal nucleophilic substitution. Scheme 1.1.13: General reaction of a nucleophilic aromatic substitution. 1.4.3.3 Hallucinogen Synthesis ‒ Aromatic Substitution on Fungi Ergot fungi produce a variety of alkaloids often with strong hallucinogenic effects upon consumption. The first pathway-specific step in their synthesis is the alkylation of tryptophan by dimethylallyl diphosphate obtaining the dimethylallyl tryptophan (DMAT) (Scheme