7-alkoxyquinolines: New fluorescent substrates for cytochrome p450 monooxygenases

A series of 7-alkoxyquinolines was synthesized and tested as substrates with hepatic microsomes prepared from male Wistar rats. Microsomal O-dealkylation rates and kinetic constants were determined for the 7-alkoxyquinolines with microsomes from control, 3-methylcholanthrene (MC)-pretreated, and phenobarbitone (PB)-pretreated rats. Structure-activity relationship studies indicated that the 7-benzyloxyquinoline was the most rapidly metabolized substrate for control microsomes and those from PB-pretreated rats, whereas the 7-ethoxy- and 7-propoxyquinolines were O-dealkylated more rapidly by microsomes of MC-pretreated animals. Differences in activities occurred in V max and apparent K m values; however, there does not appear to be a correlation between these two values for the different quinoline substrates. Apparent K m and V max values for the 7-alkoxyquinolines were: control microsomes, K m = 71−773 μM, V max = 0.37–8.4 nmol 7-quinolinol/min/mg protein; MC microsomes, K m = 0.5–14 μmm, V max = 0.29–2.7 nmol 7-quinolinol/min/mg protein; PB microsomes, K m = 2.8–46 μM, V max = 0.9–12 nmol 7-quinolinol/min/mg protein. All of the quinoline substrates gave Type I binding spectra with control and MC microsomes. With PB microsomes. Type I, Reverse Type I, and a mixture of the two types of binding spectra were observed. Comparisons of the structure-activity relationships, levels of induction, and kinetic constants were made with 7-alkoxycoumarin and 7alkoxyphenoxazone analogs. In addition, three new coumarin substrates (7-pentoxy-, 7-hexoxy-, and 7benzyloxycoumarin) are described.