STEREOISOMERS OF KETOCONAZOLE - PREPARATION AND BIOLOGICAL-ACTIVITY

The four stereoisomers of the antifungal agent ketoconazole (1) were prepared and evaluated for their selectivity in inhibiting a number of cytochrome P-450 enzymes. Large differences in selectivity among the isomers were observed for inhibition of the cytochromes P-450 involved in steroid biosynthesis, whereas little difference was observed for inhibition of those associated with hepatic drug metabolism. The cis-(2S,4R) isomer 2 was the most effective against rat lanosterol 14-alpha-demethylase, (2S,4R)-2 > (2R,4S)-4 >> (2R,4R)-3 = (2S,4S)-5, and progesterone 17-alpha,20-lyase, (2S,4R)-2 >> (2S,4S)-5 > (2R,4R)-3 = (2R,4S)-4, whereas the cis-(2R,4S) isomer 4 was more effective against cholesterol 7-alpha-hydroxylase, (2R,4S)-4 > (2S,4S)-5 > (2R,4R)-3 > (2S,4R)-2, and the trans-(2S,4S) isomer 5 was the most effective against aromatase, (2S,4R)-5 >> (2R,4R)-3 = (2R,4S)-4 > (2S,4R)-2. The cis-(2S,4R) and trans-(2R,4R) isomers 2 and 3 are equipotent in inhibiting corticoid 11-beta-hydroxylase and much more effective than their antipodes. Little selectivity was observed for inhibition of cholesterol side chain cleavage or xenobiotic hydroxylases. These data indicate that the affinity of azoles for cytochrome P-450 enzymes involved in steroid synthesis is highly dependent on the stereochemistry of the entire molecule, whereas binding to drug metabolizing enzymes is a less selective process.