1-Alkyl analogues of aminoglutethimide. Comparative inhibition of cholesterol side chain cleavage and aromatase and metabolism of the 1-propyl derivative, a highly selective inhibitor of aromatase

Some 1-, and 3-substituted 3-(4'-aminophenyl)pyrrolidine-2,5-diones as selective inhibitors of aromatase

1-Alkyl-3-(4'aminophenyl)pyrrolidine-2,5-diones (7,R = C3H7-C7H15) are potent inhibitors of aromatase in vitro, the 1-hexyl (Ki = 62nM) being about 100-fold more potent than aminoglutethimide (AG), and more selective in their ratio of aromatase:CSCC inhibitory potency. The 1-pentyl, 1-hexyl and 1-heptyl derivatives are more stable to liver microsomal metabolism in vitro than AG possibly due to inhibition of the liver cytochrome P450s. 1,3-Dialkyl-3(4'-aminophenyl)pyrrolidine-2,5-diones (9) have been synthesised by a novel method. Although the higher homologues (di-pentyl and di-hexyl) are more potent in vitro as inhibitors of aromatase than AG, they are less active than their 1-alkyl counterparts with the same alkyl substituent.

Inhibition and time-dependent inactivation of human placental aromatase by 3-oxo-17 beta-carboxamido steroids

Several N,N-dialkyl-3-oxo-4-aza-17 beta-carboxamido steroids were found to be competitive inhibitors versus androstenedione (AND) and time-dependent inactivators of aromatase activity from human term placental microsomes. Inhibition constants (Kis) from dead-end inhibition analyses indicated interactions between these compounds and the enzyme over a 0.8-7 microM inhibitor concentration range. The affinity of these compounds for aromatase leading to the time-dependent loss of enzyme activity was several fold higher than that estimated by the steady-state kinetics, with rate constants of inactivation of 0.025-0.033 min-1. 3-Oxo-4-aza steroids lacking a 17 beta-carboxamide were found to be competitive inhibitors of AND for aromatase, but did not inactivate enzyme activity in a time-dependent manner. Steroids which did not contain a 4-aza substituent, but retained the 17 beta-carbamoyl functionality, were both inhibitors and inactivators of aromatase activity in the microsomes. The time-dependent loss of aromatase activity induced by these compounds was shown to require reducing equivalents as provided by NADPH. Hence, it is suggested that the inactivation of aromatase by compounds in this series is dependent on enzymatic activation in the presence of the N,N-dialkyl-17 beta-carbamoyl substituent.