6- Amino-indole-4,7-quinones

NENITZESCU Indole Synthesis Indole synthesis trom quinones and amino crotonates... 

The Nenitzescu reaction generally occurs under relatively mild reaction conditions. Moreover mono-, di-, and tri-substituted quinones react with equal facility. Many enamines including p-aminoacrylonitriles, p-aminoacrylamides, and p-amino-a,p-unsaturated ketones react with quinones to form indole nuclei as well. The mild reaction conditions and the availability of the starting material render it attractive even in those instances where the yield of the product is low. ... 

Bacteria overall > 410 Groom, 1992 Scarce diversification between land and sea. ALKAL. indole, phenazine, pyperazine, pyrrole, polypyrrole. PEPT. various classes, including siderophores. POLYKET. lactones, macrolides, quinones. CARBOH. (amino)glycoside, terpenoids hi hi ... 

Some synthetically useful reactions not covered in the above sections should be mentioned. An unusual heterocyclization to form indole derivatives is found in the aminomercuration of allylenaminones (equation 130).261 Palladium(II)-catalyzed cyclizations of o-allyl- and -vinyl-anilines and amino-quinones are discussed elsewhere.30 Other electrophiles used to form dihydroindole derivatives include phenylselenenyl chloride216 and methyl(bismethylthio)sulfonium salts.231... 

The formation of indole rings during the polymerization of quinones and amino compounds has been proposed by Rinderknecht and Jurd (1958) who report that the reaction of phloroglucinol with glycine results in the formation of 3-hydroxyindole (Fig. 13). 

NENITZESCU Indole Synthesis Indole synthesis from quinones and amino croto nates... 

General name for antitumor antibiotics with benzo-quinone and aziridine structural units from cultures of streptomycetes (e. g., Streptomyces lavendulae, S. ver-ticillatus, S. caespitosus). There are more than 15 natural variants containing a pyrrolo) 1,2-a)indole system and differing in R and R, with OH in place of OCHj at C-9a, and different stereochemistries at C-9. The violet to blue-violet, optically active M. crystallize readily and are soluble in water, methanol, and acetone. A cluster of 47 bacterial genes that control biosynthesis of M. C has been characterised. The biosynthetic building block of the benzoquinone (C7N) unit is 3-amino-5-hydroxybenzoic acid, several total syntheses have been repotted. 

Hundreds of applications have been mentioned in the Zweig (1968) review acids, alkaloids, amino acids, antibiotics, antioxidants, food and feed additives, bases and amines, bile acids, carbonyls, dyes, enzymes, lipids, hydrocarbons, hormones, indoles, natural products, peptides, proteins, pesticides, plant growth regulators, pharmaceutical products, phenols, pigments (chlorophylls, xanthophylls, porphyrins, melanin, pterins, pteridines, anthocyanins, ilavonoids, etc.), polymers, purine and pyrimidine derivatives, quinones, RNA, DNA, organic sulfur compounds, steroids, sugars, toxins, vitamins, inorganic ions, and others. 

This reaction was first reported by Nenitzescu in 1929. It is the synthesis of a 5-hydroxyindoie derivative involving the condensation between a 1,4-benzoquinone and a /3-amino-a ,/3-unsaturated compound and subsequent cyclization. Therefore, this reaction is generally known as the Nenitzescu indole synthesis, Nenitzescu reaction, j or Nenitzescu synthesis.Occasionally, it is also referred to as the Nenitzescu cyclization, Nenitzescu condensation, s.2i qj. Nenitzescu process. It should be pointed out that the synthesized indole derivatives by this reaction are restricted to those with an electron-withdrawing group at position 3, such as an ester or a carbonyl group. In addition, the completion of this reaction requires an appropriate oxidizing agent to convert the initial adduct into the indole derivative. i From monosubstituted quinone, 4-, 6- and 7-substituted 5-hydroxyindole derivatives all are possible products, but 6-substituted isomer is the one normally obtained. ... 

An intriguing synthesis of pyrroloquinohne quinone (80), a cofactor of quinoproteins (1995NPR45) (also considered by some to be a vitamin) involves first, constmction of a coumarin (79) and then its conversion into the tricychc pyrroloquinohne 82 via the indole 80. The amino group was then utilized for quinoHne ring formation giving tricycle 81 (Scheme 7) (1993HCA988). 

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