Synthesis and evaluation of a new series of mechanism-based aromatase inhibitors

Abstract

A series of new 4-(alkylthio)-substituted androstenedione analogues was designed as potential suicide inhibitors of aromatase on the basis of mechanistic considerations on the mode of action of the enzyme. Their synthesis and biological evaluation are described. Among the most interesting are the 4-[(difluoromethyl)thio]-, 4-[(fluoromethyl)thio]-, and 4-[(chloromethyl)thio]androstenediones 12, 13, and 14 with respective IC50's of 2.7, 0.8, and 0.94 microM. Compound 12 was a reversible inhibitor of aromatase while compounds 13 and 14 displayed time-dependent kinetics of inhibition with respective KI's and half-times of inactivation of 30 nM and 3.75 min for 13 and 30 nM and 3 min for 14. The inhibition of aromatase by 14 was NADPH-dependent, and was protected by the presence of substrate (0.5-1 microM), while beta-mercaptoethanol (0.5 mM) failed to protect the enzyme from inactivation. Dialysis failed to reactivate aromatase previously inactivated by 14. The mechanistic implications of these findings are discussed.

Biochemical Significance of 19-Hydroxytestosterone in the Process of Aromatization in Human Corpus Luteum.

“…Using placental aromatase [11], 4-OHA exhibited an apparent Ki of 15.0 nM which with testosterone as the substrate it was reported that 4-OHA inhibits the first oxidative step as a suicide aromatase inhibitor [13]. In this study, considering the inhibiLion of estradiol formation from 19-OHT as well as testosterone by 4-OHA, 4-OHA may be expected to inhibit at the first step in oxidation from each substrate.…”

Enzymatic Baeyer–Villiger oxidation of steroids with cyclopentadecanone monooxygenase

“…Instead, estrogen 12, bearing a 16␣-hydroxy group, gave the usual lactone 12a in 20% yield. Steroid 13 was synthesized as a mixture of ␤ and ␣ epoxide [16] and, when subjected to enzymatic BV oxidation, yielded only trace amounts of products, which prevented their complete characterization. The ESI mass spectrum revealed ions at m/z 319 [M+H] + and 341 [M+Na] + , which is in agreement with the insertion of an oxygen atom in 13.…”

“…For 3-keto-5␤ steroids, two regioisomers with different ratios depending on the nature of the oxidant, were obtained [17]. Table 1 depicts the structures of the 3-ketosteroids studied by us (14)(15)(16)(17). With androstanolone (14) the enzymatic BV reaction gave the 3-one-4-oxa-4a-homo lactone 14a as the only regioisomer (24% yield).…”

New trends in the chemistry of α-fluorinated ethers, thioethers, amines and phosphines

“…Although previously several electrophilic monofluoromethylations of oxygen-, sulphur-, nitrogen-, and carbon nucleophiles have been reported with CH 2 FI [49][50][51], CH 2 FBr [52][53][54][55][56][57][58], CH 2 FCl [56,[59][60][61], or CH 2 FOSO 2 R (R = CF 3 , CH 3 , tolyl) [55,62] as monofluoromethylating agents, their use was restricted to 18 F-labelling.…”