Time-Dependent Inactivation of Human Placental Aromatase by Bromoacetoxy 4-Androsten-3-ones in the Presence of Reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH)

6-Bromoacetoxyandrostenediones (1 and 2) and 17β-bromoacetoxy-4-androsten-3-one having a 6β-bromo (3), 6-keto (4), 6β-methoxyl (5) substituent were evaluated as mechanism-based inactivators of human placental aromatase. All of these compounds except the 6α-bromoacetate 1 showed a time-dependent, pseudo-first-order inactivation of aromatase in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) with apparent Ki's of 40, 50, 30, and 34 μM and kinact's of 0.048, 0.364, 0.267, and 0.040 min-1, respectively, for compounds 2, 3, 4, and 5. The enzyme inactivation with compounds 3 and 4 was blocked by the addition of the substrate androstenedione to the incubates, and NADPH and oxygen were required for their effective time-dependent inactivation.