Quinoline, Acridine, and Benzodiazepine Alkaloids

The following ring systems are the fundamental structures of the above mentioned groups of alkaloids  

In the compounds found in nature these ring systems are hydroxylated, methylated, prenylated and iV-methylated. They may carry aliphatic or aromatic side chains and in the case of quinoline alkaloids may be condensed with a furane or dihydrofurane ring. 

Quinoline, acridine and benzodiazepine alkaloids are formed in microorganisms, e.g., pseudans in Pseudomonas and benzodiazepines in Penicillium as well as in higher plants, e.g., Rutaceae and Compositae. 

Quinoline and Furoquinoline Alkaloids (Fig. 151). (Activated ) anthranilic acid reacts with (activated ) acetic acid to 2,4-dihydroxyquinoline. Probably 2-aminobenzoyl acetic acid, which is in a pH-dependent equilibrium with 2,4-dihydroxy quinoline, or an activated derivative of this compound is an intermediate. On the one hand 2,4-dihydroxy quinoline is transformed to echinorine. On the other hand it is a precursor of 3-prenylated chinoline alkaloids, isopropyl-dihydrofuroquinolines and furoquinolines. 

2-n Alkylquinolones (Pseudans) and 2-Phenylquinolones Fig, 152). Anthranoyl CoA may react with activated / -keto acids to 2-n-alkylated quinolones (aliphatic -keto acids) or 2-benzyl quinolones (benzoyl acetic acid). Intermediates are probably 3-carboxylated quinolones. 

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Quinoline, acridine and benzodiazepine alkaloids (D 8.4.2) Nonprotein amino acids (D 9.1)... 

Dehydroquinic acid, shikimic acid, and chorismic acid are carboxylated compounds containing a six-membered carbocyclic ring with one or two double bonds (Fig. 143). The secondary products derived from these substances either still contain the ring and the C -side chain of the acids (see the structure of the benzoic acid derivatives, of anthranilic and 3-hydroxyanthranilic esters, D 8, D 8.2, D 8.4 and D 8.4.1) or have additional rings (see the formulae of naphthoquinones and anthraquinones, D 8.1, of quinoline, acridine, and benzodiazepine alkaloids, D 8.3.2). The carbon skeletons may be substituted by isoprenoid side chains (see the structure of ubiquinones, D 8.3) and may carry different functional groups, e.g., hydroxy, carboxy, methoxy, and amino groups. 

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