Quinolones derivatization

The same methodology was also used starting from the ethyl 6-amino-7-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate, prepared by reduction of the nitro derivative. The requisite nitro derivative was prepared by nitration of ethyl 7-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate. A second isomer was prepared from 4-chloro-3-nitroaniline by reaction with diethyl ethoxymethylene-malonate, subsequent thermal cyclization, and further ethylation because of low solubility of the formed quinolone. After separation and reduction, the ethyl 7-amino-6-chloro-l-ethyl-4-oxo-l,4-dihydroquinoline-3-carboxylate 32 was obtained. The ort/io-chloroaminoquinolones 32,33 were cyclized to the corresponding 2-substituted thiazoloquinolines 34 and 35, and the latter were derivatized (Scheme 19) (74JAP(K)4, 79CPB1). 

A direct spectrometric method for screening nalidixic acid in chicken tissues (189, 190) has been reported. This method was based on fluorometric detection after derivatization of the analyte with sulfuric acid. The major drawback of this method is tliat it cannot differentiate among the various quinolones, it is less sensitive than the screening tests usually employed for regulatory purposes, and it is complicated by the necessity for derivatization. 

In liquid chromatographic analysis of quinolone antibacterials, most popular is the fluorometric detector due to the inherent fluorescence of these drugs and the advantages in terms of selectivity and sensitivity that this detector offers (Table 29.6). Fluorometric detection after postcolumn derivatization with sulfuric acid has also been reported (203). However, quinolones exhibit also remarkable ultraviolet absorption and are therefore ideal for direct determination without derivatization. Detection can be performed in the wavelength range of 254-295 nm. 

Ozonolyses of tetrahydro-lH-pyrido-[4,3-fe]-indoles resulted in the formation of a nine-membered keto-lactam, which could either be isolated or in situ cyclized to dihydropyrrolo[3,2-( ]quinolones, which can be derivatized by electrophilic aromatic substitution, selectively on the pyrrole moiety. In the ozonolysis reaction, alkyl cin-noline betaines were formed as side products, most likely via Cl side products. ... 

---