Quinoline-4-carboxyhc acid

PUtzing erReaction. Quinoline-4-carboxyhc acids are easily prepared by the condensation of isatin [91-56-5] (16) with carbonyl compounds (50). The products may be decarboxylated to the corresponding quinolines. The reaction of isatin with cycHc ketones has been reported, eg, the addition of cyclohexanone gives the tricycHc intermediate (17) [38186-54-8] which upon oxidation produces quinoline-2,3,4-tricarboxyhc acid [16880-83-4] (51). 

In the alkaline medium, isatin is cleaved at the amide bond and converted to the salt 82 of isatinic acid, which undergoes aldol condensation with a-methylene ketones and cyclization with H2O elimination affording quinoline-4-carboxyhc acids (83). Notably, N-acetylisatins (84), after base-induced ring-opening (— -85), undergo an intramolecular aldol condensation giving rise to 2-quinolone-4-carboxylic acids (86). 

Alkylation a.ndAryla.tion, The direct introduction of carbon—carbon bonds in quinoline rings takes place in low yield and with Htde selectivity. The most promising report involves carboxyHc acids with ammonium persulfate and silver nitrate (31). 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

ZN(C)153, 00ZN(C)323, 00ZN(C)857, 01MI2, 01MIP4, 01TL5849). 5-Amino-8 3)-d i hyd roxy-2,3-d i hydro-1 //-py nmido[l,2-<2]quinoline-3-carboxyHc acid moiety 4 was also identified as a chromophoric moiety of certain... 

There are two basic approaches which are commonly used for the synthesis of quinolin-4-one-3-carboxyhc acids [4,14]. The first one is based on use of fluorinated anilines (1, A=CH, CF) or 2-aminopyridmes (1, A=N) as starting materials and involves their condensation with ethoxymethylene derivative of nudonate, cyanoace-tate or acetoacetate to form enamines 2. The intramolecular cyclization of compounds 2 with polyphosphoric acid (PPA) (the Gould-Jacobs reaction) affords the corresponding fluoroquinolones (3, A=CH, CF) or naphthyridones (3, A=N) (Scheme 2). 

Beyond those often-used hnkage strategies, some more seldom carboxyhc acid-forming variations should be mentioned. A quinoline linker system cleavable via two mild reactions was developed for peptide synthesis in 1999. 

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