Improved Synthesis and Molecular Modeling of 4.BETA.,19-Dihydroxyandrost-5-en-17-one, an Excellent Inhibitor of Aromatase.

Abstract

Aromatase is a cytochrome P-450 enzyme complex responsible for the conversion of the 4-en-3-one androgens, androst-4-ene-3,17-dione (AD) and testosterone, into estrogens, estrone and estradiol. [1][2][3] Aromatization of the androgens is thought to proceed through three sequential oxygenations at the C-19 position, respectively. [4][5][6] In the third step, the angular methyl group at C-19 and 1b,2b-hydrogens are eliminated to result in the aromatization of the A-ring of the androgen molecule to form estrogen. Inhibitors of aromatase are valuable as therapeutic agents in the treatment of the advance breast cancer. 7)Structure-activity studies on aromatase inhibitors [8][9][10][11][12][13][14] and a recent structural prediction of aromatase by modeling 15,16) indicated the existence of a hydrophobic binding pocket extending roughly in the plane of substrate AD from the position that would be occupied by its C 4 , 8,9) C 6 10,11) and C 7 -14) atoms. On the other hand, in the course of studies on structure-activity relationships of series of 3-deoxy androgens, androst-4-en-17-one (1) 17) and its 5-ene isomer 4, 18) and their 19-hydroxy analogs 2 19) and 5, 18) we found that 4b,19-dihydroxy-5-ene steroid 6 20) is one of the most powerful competitive inhibitor of aromatase among the steroidal compounds reported so far (Fig. 1). This finding indicates that the polar 4b,19-diol moiety of 3-deoxy compound 6 can be torelated in the pocket of the active site of aromatase. Thus, diol 6 would play an important role in not only the development of a powerful aromatase inhibitor but also understanding the spacial and electronical nature of the active site. 12Compound 6 was previously synthesized from 4b-acetoxyandrost-5-en-17-one (7) in four steps through hypoiodite oxidation of 5a-bromo-6b-ol intermediate, giving 5a-bromo-6b,19-epoxide, as a key reaction. 21) We report here the alternate, improved synthesis of diol 6 suitable for a gram-order scale synthesis along with molecular modeling of this compound with the PM3 method for understanding its three dimensional structure. Results and DesucussionSynthetic sequence employed in this study involves an acid-catalyzed trans-diaxial cleavage of an epoxy moiety of 4,5-epoxy steroids 9 and 10 as a key reaction for the introduction of a 4b-hydroxy group to a steroid nucleus (Chart 1). Treatment of 19-(tert-butyldimethylsilyloxy)androst-4-en-17-one (8), previously synthesized, 19) with m-chloroperbenzoic acid (MCPBA) in CH 2 Cl 2 gave a 1.4 : 1 mixture of 4a,5a-epoxide 9 and its 4b,5b-isomer 10 in 90% yield. The configuration of the epoxy ring was established according to the 1 H-NMR spectroscopic data of 4a,5a-and 4b,5b-epoxy steroids having a 19-methyl group 22) ; lower chemical shifts of one of 19-CH 2 (d 3.76 ppm) and 4a-H (d 2.97 ppm) of 4a,5a-epoxide 9, compared to the corresponding C-19 and C-4 protons (d 3.51 and 2.87 ppm) of the 4b,5b-epoxide 10. Irradiation of the 4-H signal of compound 9 or 10 produced no significant nuclear overhauser effect (NOE) enhancement of the ...

Efficient Chemoenzymatic Synthesis, Cytotoxic Evaluation, and SAR of Epoxysterols

“…They are essential in the synthesis of important drugs such as (S)-timolol, a -adrenergic blocking agent, indinavir, a HIV protease inhibitor, and diltiazem, a calcium channel blocker. In the steroid field, several 4,5-epoxysteroids are intermediates in the synthesis of biologically active compounds like aromatase inhibitors 18,19 and anti-HIV agents 20,21 among others. 22 Furthermore, ringopening of 5R,6R-epoxysteroids gives access to contraceptives, anti-inflammatory agents, and enzymatic inhibitors.…”

6β-Azido-7α-hydroxy-17-oxo-5α-androstan-3β-yl acetate

“…Most of the steroids which have been studied as aromatase inhibitors are analogues of androstenedione, with substituents at C4, C6, C7 and C19 (Numazawa et al, 2002). Several 6-and 7-substituted analogues of androstenedione are powerful inhibitors of human placental aromatase (Njar et al, 1995).…”

17-Oxo-5α-androst-6-en-3β-yl acetate

“…The 5 steroids are¯at, whereas the 5 epimers are bent at the A/B ring junctions. Structure±activity relationships and recent aromatase modelling studies have revealed the existence of a hydrophobic binding pocket with a limited accessible volume in the region corresponding to the side, rather than the side, of the C4, C6 and C7 positions of the androstenedione substrate (Numazawa et al, 2002).…”