Steroids and related products. XLVII. Cardiotonic steroids. VII. The 14β-hydroxylation of 17β-substituted steroids. Part II

The most efficient method for introducing a 14β-hydroxy group into a steroid with a 17β-side chain is reported. It can be used in the presence of an unsaturated lactone ring.     

Proton magnetic resonance spectra of 17ξ-Hydroxy-17ξ-methyl-5ξ-androstane C-3 ketone and c-3ξ alcohol isomers in chloroform-d and pyridine-d5

17α-Hydroxy-17β-methyl-5β-androstan-3-one, 17μ-methyl-5α-androstane-3α, 17α-diol, 17β-methyl-5α-androstane-3β, 17α-diol, 17α-methyl-5β-androstane-3β, 17β-diol, 17β-methyl-5β-androstane-3α, 17α-diol and 17β-methy1–5β-androstane-3β, 17α-diol were synthesized for the first time. ¹H NMR spectra of all four 17ξ-hydroxy/17ξ-methyl C-3 ketones and all eight C-3 alcohols were recorded in chloroform-d and pyridine-d₅. Pyridine-induced chemical shifts are discussed. Thin-layer Chromatographic data are given.     

Synthesis of 5α-Androstane-3α,16α,17β-triol from 3β-hydroxy-5-androsten-17-one

5α-Androstane-3α, 16α 17β-triol was synthesized from 3β-hy-droxy-5-androsten-17-one. The procedure Involved catalytic hydrogenation of 3β-hydroxy-5-androsten-17-one to 3β-hydroxy-5α-androstan-17-one. This was followed by conversion of the 3β-hydroxy group to 3α-benzoyloxy group by the Mitsunobu reaction. Further treatment with isopropenyl acetate yielded 5α-androsten-16-ene-3α, 17-diol 3-benzoate 17-acetate. This was then converted to 3α, 17-dihydroxy-5α-androstan-16-one 3-benzoate 17-acetate via the unstable epoxide intermediate after treatment with $\text{m}$-cloroperoxybenzoic acid. LiAlH₄ reduction of this compound formed 5α-androstane-3α, 16α, 17β-trlol. ¹H and ¹³C NMR of various steroids are presented to confirm the structure of this compound.     

Intramolecular catalysis. VII: The nature of side chain shielding of the 12alpha-hydroxyl group of steroids

A series of 12α-hydroxy steroids with varying side chains was prepared, and their 24-hour acetylation yields were compared, l2α-Hydroxy-5β-pregnan-20-one ($\text{lb}$) was prepared from 3α, 12α-diacetoxy-5β~pregnan-20-one ($\text{2}$) and also by side chain degradation of 12α-acetoxy-5β-cholanoic acid ($\text{5d}$). 21-Benzyl-5β-pregnan-12α-ol ($\text{1g}$) was synthesized by hydrogenation of the 21-benzylidine derivative of ketone $\text{1b}$. 23-Pheny1-5β-norcholan-12α-ol ($\text{1k}$) was obtained by the Grignard reaction of 2-phenyl-ethylmagnesium bromide and ketone $\text{1b}$, dehydration, hydrogenation and hydride reduction; a similar sequence produced 20-methyl-5β-pregnan-12α-ol ($\text{lm}$). The acetylation results (Table 11) imply that branching at C-20 may be more significant for 12α-hydroxyl reactivity than side chain length or type. An additional compound with an unbranched side chain, 21-nor-5β-cholan-12α-ol ($\text{14}$), was synthesized by a Grignard reaction on the 21-bromo intermediate $\text{11b}$. Acetylation rates determined by glc indicate (Table 111) That compounds with unbranched side chains have 12α-hydroxyl groups about ten times as reactive as their analogs with 20-methyl groups.     

Properties of antisera to progesterone and to 17-hydroxy-progesterone elicited by immunization with the steroids attached to protein through position 7

Antibodies to progesterone (P) and to 17-hydroxyprogesterone (17-OHP) were raised by immunization of rabbits with progesterone-7α-carboxyethyl thioether--bovine serum albumin (P-7—BSA) or with 17-OHP-7α-carboxyethyl thioether--BSA (17-OHP-7--BSA). The antisera produced were of high affinity: K_a towards the homologous hapten was 3. 7 × 10¹⁰ 1./mol for the anti-P serum and 5. 9 × 10⁹ 1/mol for the anti-17-OHP serum. The antiserum to P-7—BSA displayed little or no cross reaction (?= 2%) with the 20α-, 20β- or 5β-dihydro-derivatives of progesterone, moderate cross-reaction with pregnenolone (4%), but considerable cross-reaction with 11-deoxycorticosterone (7%), 5α-dihydro-progesterone (11%) and 17-OHP (15%). The antiserum to 17-OHP-7--BSA showed very little cross-reaction (?= 2%) with progesterone and other steroids lacking a 17α-hydroxyl group, such as pregnenolone or 11-deoxycorticosterone, but reacted significantly with 17α, 21-dihydroxy-4-pregnene-3, 20-dione (8%) and 3β, 17-dihydroxy-5-pregnen-20-one (13%). None of the sera reacted with testosterone, cortisol or estradiol-17β. It appears that conjugation of progesterone to protein through carbon-7 affords antisera comparable in specificity to those raised with 11α-conjugates and superior to those raised with 3-, 6- and 20-conjugates. The antiserum to 17-hydroxyprogesterone described is the first one that specifically recognizes this metabolite.     

The catalytic activity of mycelial fungi towards 7-oxo-DHEA – an endogenous derivative of steroidal hormone dehydroepiandrosterone

Seventeen species of fungi belonging to thirteen genera were screened for the ability to carry out the transformation of 7-oxo-DHEA (7-oxo-dehydroepiandrosterone). Some strains expressed new patterns of catalytic activity towards the substrate, namely 16β-hydroxylation (Laetiporus sulphureus AM498), Baeyer–Villiger oxidation of ketone in D-ring to lactone (Fusicoccum amygdali AM258) and esterification of the 3β-hydroxy group (Spicaria divaricata AM423). The majority of examined strains were able to reduce the 17-oxo group of the substrate to form 3β,17β-dihydroxy-androst-5-en-7-one. The highest activity was reached with Armillaria mellea AM296 and Ascosphaera apis AM496 for which complete conversion of the starting material was achieved, and the resulting 17β-alcohol was the sole reaction product. Two strains of tested fungi were also capable of stereospecific reduction of the conjugated 7-keto group leading to 7β-hydroxy-DHEA (Inonotus radiatus AM70) or a mixture of 3β,7α,17β-trihydroxy-androst-5-ene and 3β,7β,17β-trihydroxy-androst-5-ene (Piptoporus betulinus AM39). The structures of new metabolites were confirmed by MS and NMR analysis. They were also examined for their cholinesterase inhibitory activity in an enzymatic-based assay in vitro test.     

Application of α- and β-naphthoflavones as monooxygenase inhibitors of Absidia coerulea KCh 93, Syncephalastrum racemosum KCh 105 and Chaetomium sp. KCh 6651 in transformation of 17α-methyltestosterone

In this work, 17α-methyltestosterone was effectively hydroxylated by Absidia coerulea KCh 93, Syncephalastrum racemosum KCh 105 and Chaetomium sp. KCh 6651. A. coerulea KCh 93 afforded 6β-, 12β-, 7α-, 11α-, 15α-hydroxy derivatives with 44%, 29%, 6%, 5% and 9% yields, respectively. S. racemosum KCh 105 afforded 7α-, 15α- and 11α-hydroxy derivatives with yields of 45%, 19% and 17%, respectively. Chaetomium sp. KCh 6651 afforded 15α-, 11α-, 7α-, 6β-, 9α-, 14α-hydroxy and 6β,14α-dihydroxy derivatives with yields of 31%, 20%, 16%, 7%, 5%, 7% and 4%, respectively. 14α-Hydroxy and 6β,14α-dihydroxy derivatives were determined as new compounds. Effect of various sources of nitrogen and carbon in the media on biotransformations were tested, however did not affect the degree of substrate conversion or the composition of the products formed. The addition of α- or β-naphthoflavones inhibited 17α-methyltestosterone hydroxylation but did not change the percentage composition of the resulting products.     

The aromatization of (7 -3H) androstenedione by human placental mitochondria

A metabolite of 2,3-dihydroxyestra-1,3,5(10)-trien-17-one-6, 7-³H isolated from rat bile, was partially characterized by mass spectrometry as a methyl ether of 2,3,16-trihydroxyestra-1,3,5(10)-trien-17-one. The α configuration of the 16-hydroxy function was established by chromatographic comparison of the sodium borohydride reduced metabolite with synthetic 2-methoxy-estra-1, 3,5(10)-triene-3,16α,17β-triol and 2-methoxy-estra-1, 3,5(10)-triene-3,16β,17β-triol. The methyl group was located on the C-2 position by comparison with authentic 2- and 3- monomethyl ethers of 2,3-dihydroxy-estra-1, 3,5(10)-trien-17-one following pyrolytic removal of the 16α-hydroxyl group.3,16α-dihydroxy-2-methoxyestra-1,3,5(10)-trien-17-one was found to constitute 2% and 15% of the biliary radioactivity following administration of estrone-6,7-³H and 2,3-dihydroxyestra-1,3,5(10)-trien-17-one-6,7-³H respectively.     

The syntheses of 3-substituted perfluoroalkyl steroids

The syntheses of three classes of C-3 perfluoroalkyl substituted steroids are described. They are the 3β-hydroxy-3α-perfluoroalkylandrost-4-en-17-ones (5a-c), 3-perfluoroalkylandrosta-3,5-dien-3-ones (8a-c) and 3β-hydroxy-3α-perfluoroalkylandrost-5-en-17-ones (12a-c). Addition of a series of perfluroalkylorganometallic reagents (R_FLi; R_F = C₂F₅, C₃F₇, or C₄F₉) to the 3 position of silylated testosterone 2b afforded Δ⁴ perfluoroalkyl carbinols 3. In Scheme 1, deprotection with HF and oxidation at the C-17 carbon with PCC produced Δ⁴ ketones 5. In Scheme 2 dehydration of 3 with 1,2-phenylenephosphorochloridite and iodine afforded Δ^3,5 dienes 6 which were deprotected and oxidized as above to the C-17 ketones 8. In Scheme 3 isomerization of the double bond of 3 from the C-4 to the C-5 position using the allylic halogenation followed by treatment with lithium aluminum hydride led to the synthesis of the double bond isomer series 12. A new method for dehydration was developed. On average and within experimental error, 3β-hydroxy-3α-perfluoroalkylandrost-5-en-17 ones (12a-c) were better than the 3-perfluoroalkylandrosta-3,5-dien-17-ones (8a-c) and 3β-hydroxy-3α-perfluoroalkylandrost-4-en-17-ones (5a-c) at inhibiting glucose-6-phosphate dehydrogenase.     

齐墩果酸氧化产物的成分研究

以齐墩果酸为原料,分别用高锰酸钾和SeO2/H2O2(30%)进行氧化。从产物中分离得到3个化合物,经1H NMR、13C NMR、2D-NMR、MS等波谱分析,分别鉴定为3,11-二羰基-12,17-二烯-28-去甲基齐墩果烷(1)、3β-羟基-11-烯-13,28-内酯-齐墩果烷(2)和3α,12β,13α-三羟基-28-羧基齐墩果烷(3),收率依次是4.5%、6.4%、2%,其中化合物1和3为新化合物。     

Neuroactive steroids with perfluorobenzoyl group

During an initial study in searching for the alternative derivatives suitable for photolabeling of neuroactive steroids, perfluorobenzoates and perfluorobenzamides in position 17 of 5β-androstan-3α-ol were synthesized from the corresponding 17-hydroxy and 17-amino derivatives. After transformation into glutamates or sulfates, 17α-epimers had comparable inhibitory activity at NMDA receptors to the natural neurosteroid (20-oxo-5β-pregnan-3β-yl sulfate), however, were more potent (2- to 36-fold) than their 17β-substituted analogs. In one case, fluorine in position 4' of perfluorobenzoate group was substituted with azide and activity of the final glutamate was retained comparing with the corresponding perfluorobenzoate. The series was expanded with perfluorobenzoyl derivatives of pregnanolone: Perfluorobenzamide of glutamate and perfluorobenzoate of 11α-hydroxy pregnanolone were prepared and tested. From nine tested compounds, four of them exhibit very good inhibition activity and can serve as promising leads for photolabeling experiments.     

Effect of defolliculation and 17α-hydroxy, 20β-dihydroprogesterone on cyclic AMP level in full-grown oocytes of the rainbow trout,Salmo gairdneri

The changes in cAMP were followed in trout oocytes incubated in vitro after defolliculation performed by either enzymatic or manual dissection. Both defolliculation methods induced a highly significant rise in oocyte cAMP level (4.5 times the basal level of control [follicle-enclosed oocytes], after 6 h). Treatment of defolliculated oocytes with 17α-hydroxy,20β-dihydroprogesterone (17α,20β-OH-P) (10^?6 M), which induced oocyte maturation (germinal vesicle breakdown [GVBD]) was able, first, to interrupt the increase of oocyte cAMP level promoted by defolliculation and then to lower this level significantly down to values that still remained higher than folliculated controls. Very low concentrations of 17α,20β-OH-P (1.38–55.6 10^?9 M), or physiological doses of testosterone (0.35 10^?6 M, in the range found in vivo before ovulation) were able to induce a similar decrease of oocyte cAMP level without inducing GVBD. Under the same experimental conditions estradiol (0.35 10^?6 M) exhibited no action. These results suggest that some factor(s) originating in the follicle (FIF), inhibit the oocytes' tendency to accumulate cAMP before the final surge of 17α,20β-OH-P. This factor might be a follicular steroid such as testosterone or nonmaturing concentrations of 17α,20β-OH-P. Moreover our data favour the hypothesis that the final surge of 17α,20β-OH-P could induce distinct intraoocyte mechanisms: the first induces an irreversible blockage of cAMP level before the inhibitory action of the FIF is suppressed by ovulation, and the second mechanism leads to GVBD.     

Identification of drostanolone and 17-methyldrostanolone metabolites produced by cryopreserved human hepatocytes

Methyldrostanolone (2α,17α-dimethyl-17β-hydroxy-5α-androstan-3-one) was synthesized from drostanolone (17β-hydroxy-2α-methyl-5α-androstan-3-one) and identified in commercial products. Cultures of cryopreserved human hepatocytes were used to study the biotransformation of drostanolone and its 17-methylated derivative. For both steroids, the common 3α- (major) and 3β-reduced metabolites were identified by GC-MS analysis of the extracted culture medium and the stereochemistry confirmed by incubation with 3α-hydroxysteroid dehydrogenase. Structures corresponding to hydroxylated metabolites in C-12 (minor) and C-16 were proposed for other metabolites based upon the evaluation of the mass spectra of the pertrimethylsilyl (TMS-d₀ and TMS-d₉) derivatives. Finally, on the basis of the GC-MS and ¹H NMR data and through chemical synthesis of the 17-methylated model compounds, structures could be proposed for metabolites hydroxylated in C-2. All the metabolites extracted from hepatocyte culture medium were present although in different relative amounts in urines collected following the administration to a human volunteer, therefore confirming the suitability of the cryopreserved hepatocytes to generate characteristic metabolites and study biotransformation of new steroids.     

Synthesis and stereochemistry of C-3- and C-7-linked (O-carboxymethyl)-oximino- and hemisuccinamido derivatives of 5 alpha-dihydrotestosterone.

The 3-(O-carboxymethyl)oximino derivative of 17β-hydroxy-5α-androstan-3-one (5α-dihydrotestosterone) was prepared. Thin-layer chromatography of the corresponding methyl ester showed the presence of two syn (60%) and anti (40%) geometrical isomers of the oxime chain to the C-4 position, which were characterized by ¹³C nmr. The 3β-hemisuccinami-do-5α-androstan-17β-ol was obtained after selective saponification with potassium carbonate of the 17β-hemisuccinate group of the 3,17-dihemi-succinoylated derivative of the previously described 3β-amino-5α-androstan-17β-ol. This 3β-hemisuccinamide was purified as the corresponding methyl ester-17β-acetate and was regenerated after saponification. The 3,3'-ethylenedioxy-7-oxo-5α-androstan-17β-yl acetate was obtained in quantitative yield by catalytic hydrogenation over 10% palladium-oncharcoal of the Δ⁵-7-oxo precursor in a dioxane-ethanol mixture containing traces of pyridine. The exclusive 5α-configuration of this hydrogenated product was established from nmr data and was confirmed by the synthesis of methyl 3,3'-ethylenedioxy-7-oxo-5β-cholan-24-oate as 5β-H-reference compound. The preceding 5α-H-7-ketone was converted into the 7-(O-carboxymethyl)oximino derivative (syn isomer to the C-6 position, exclusively) which was esterified into the corresponding methyl ester. The selective hydrolysis of the 3-ethyleneketal group was achieved by a short treatment with a formic acid-ether 1:1 (v/v) mixture at 20°C. Saponification of the latter reaction product with ethanolic potassium hydroxide gave the 7-(O-carboxymethyl)oximino-17β-hydroxy-5α-androstan-3-one derivative, which was characterized as the corresponding methyl ester. The reduction of the oxime of the 5α-H-7-ketone with sodium in ethanol or with lithium-aluminium hydride gave respectively the 7β-amine or the 7α-amine as the major product. The 7β- and 7α-configurations were established from nmr spectra of the corresponding 7-acetamido derivatives. The 7β- and 7α-hemisuccinamido derivatives were prepared from the mixture of 7β- and 7α-amines, as described above for 3-derivatives and were isolated after thin-layer chromatography of the methyl esters, followed by saponification of the corresponding 17β-acetates.     

Microbial transformations of steroids

The preparation ofΔ ^{1, 4} , 17-dione fromΔ ⁴ , 17-dione with the aid ofFusarium lateritium 403 is described, the yield being 80%, referred to the original steroid. The undesirable 1-dehydrotestololactone is formed under the given conditions only in traces. If progesterone was used as the starting steroid the yield of the undesirable 1-dehydrotestololactone is 40%, referred to the progesterone used. Dehydroepiandrosterone was not transformed by theFusarium lateritium strain to steroid metabolites. During the preparation of 1-dehydrotestosterone fromΔ ⁴ -androstene-3, 17-dione, using two successive microbial procedures (dehydrogenation of the A ring in position 1–2 and reduction of the keto group at C₁₇ giving rise to the corresponding 17β-hydroxy derivative), the isolation yield was 55–60%, referred to the starting steroid.     

Microbial hydroxylation of 17β-estradiol by Penicillium brevicompactum

Microbial hydroxylation of 17β-estradiol (1) with Penicillium brevicompactum, a fungal species not used in biotransformation so far, yielded four metabolites: 1, 3, 5-estratriene-3, 15α-diol-17-one (2); 1, 3, 5-estratriene-3, 6α, 17β-triol (3); 1, 3, 5-estratriene-3, 15α, 17β-triol (4); and 1, 3, 5-estratriene-3, 6α, 15α-triol-17-one (5). All the products were determined by ¹H NMR, ¹³C NMR, two-dimensional NMR, and HRMS techniques. Compounds 3, 4, and 5 are reported for the first time via microbial transformation, and 5 is a new compound as far as we know. Possible metabolic pathway of 17β-estradiol via Penicillium brevicompactum was also proposed.     

Steroid modification by filamentous fungus Drechslera sp.: Focus on 7-hydroxylase and 17β-hydroxysteroid dehydrogenase activities

Fungal strain Drechslera sp. Ph F-34 was shown to modify 3-oxo- and 3-hydroxy steroids of androstane series to form the corresponding allylic 7-alcohols and 17β-reduced derivatives thus evidencing the presence of 7α-, 7β-hydroxylase and 17β-hydroxysteroid dehydrogenase (17β-HSD) activities. The growing mycelium predominantly hydroxylated androsta-1,4-diene-3,17-dione (ADD) at the 7β-position, while much lower 7α-hydroxylation was observed. Along with 7β-hydroxy-ADD and its corresponding 7α-isomer, their respective 17β-alcohols were produced.In this study, transformation of ADD, androst-4-en-17β-ol-3-one (testosterone, TS) and 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone, DHEA) by resting mycelium of Drechslera sp. have been estimated in different conditions with regard to the inducibility and functionality of the 17β-HSD and 7-hydroxylase enzyme systems. Steroids of androstane, pregnane and cholane series were evaluated as inducers. The inhibitory analysis was provided using cycloheximide (CHX). Steroids were assayed using TLC and HPLC methods, and the structures were confirmed by mass-spectrometry, ¹H and ¹³C NMR spectroscopy data.17β-HSD of the mycelium constitutively reduced 17-carbonyl group of ADD and DHEA to form the corresponding 17β-alcohols, namely, androsta-1,4-diene-17β-ol-3-one (1-dehydro-TS), and androst-5-ene-3β,17β-diol. Production of the 7α- and 7β-hydroxylated derivatives depended on the induction conditions. The inducer effect relied on the steroid structure and decreased in the order: DHEA > pregnenolone > lithocholic acid. β-Sitosterol did not induce hydroxylase activity in Drechslera sp. CHX fully inhibited the synthesis of 7-hydroxylase in Drechslera mycelium thus providing selective 17-keto reduction.Results contribute to the diversity of steroid modifying enzymes in fungi and can be used at the development of novel biocatalysts for production of valuable steroid 7(α/β)- and 17β-alcohols.     

Transformation of some 3α-substituted steroids by Aspergillus tamarii KITA reveals stereochemical restriction of steroid binding orientation in the minor hydroxylation pathway

Aspergillus tamarii contains an endogenous lactonization pathway which can transform progesterone to testololactone in high yield through a sequential four step enzymatic pathway. In this pathway testosterone is formed which primarily undergoes oxidation of the C-17β-alcohol to a C-17 ketone but, can also enter a minor hydroxylation pathway where 11β-hydroxytestosterone is produced. It was recently demonstrated that this hydroxylase could monohydroxylate 3β-hydroxy substituted saturated steroidal lactones in all four possible binding orientations (normal, reverse, inverted normal, inverted reverse) on rings B and C of the steroid nucleus. It was therefore of interest to determine the fate of a series of 3α-substituted steroidal analogues to determine stereochemical effect on transformation. Hydroxylation on the central rings was found to be restricted to the 11β-position (normal binding), indicating that the 3α-stereochemistry removes freedom of binding orientation within the hydroxylase. The only other hydroxylation observed was at the 1β-position. Interestingly the presence of this functional group did not prevent lactonization of the C-17 ketone. In contrast the presence of the 11β-hydroxyl completely inhibited Baeyer–Villiger oxidation, a result which again demonstrates that single functional groups can exert significant control over metabolic handling of steroids in this organism. This may also explain why lactonization of 11β-hydroxytestosterone does not occur. Lactonization of the C-17 ketone was not significantly affected by the 3α-alcohol with significant yields achieved (53%). Interestingly a time course experiment demonstrated that the presence of the 3α-acetate inhibited the Baeyer–Villiger monooxygenase with its activity being observed 24 h later than non-acetate containing analogues. Apart from oxidative transformations observed a minor reductive pathway was revealed with the C-17 ketone being reduced to a C-17β-alcohol for the first time in this organism.     

Acetylation and hydroxylation of 5alpha-androstane-3beta,17beta-diol by prostate and epididymis

An unknown radiometabolite, formed in the canine prostate and epididymis after intra-arterial infusion of testosterone-4-¹⁴C in physiologic saline and extraction of the organs with ethyl acetate-acetone, was identified as the 3-monoacetate of 5α-androstane-3β, 17β-diol (3β-diol). Transformation of 3β-diol-¹⁴C to its identified 3-monoacetate derivative could also be demonstrated, if the incubation of the radiosubstrate with minced canine prostate was terminated by ethyl acetate extraction. The formation of polar products in high yield was noted. Whereas minced canine prostate actively converted 5α-androstane-3α,17β-diol-¹⁴C to 17β-hydroxy-5α-androstan-3-one-¹⁴C, the same preparation hydroxylated 3β-diol-¹⁴C predominantly at the 7ξ- and, to a lesser extent, at the 6ξ-positions. Partial identification of the hydroxylated radiometabolites was by crystallization of the CrO₃-oxidation products 5α-androstane-3,6,17-trione-¹⁴C and 5α-androstane-3,7,17-trione-¹⁴C to constant SA and by GLC/MS of the latter derivative. NADPH-supplementation of the preparation enhanced the yield of hydroxylated products derived from 3β-diol-¹⁴C in a 1 hr incubation from 22% to 41%. Analogous supplemented incubations of benign hyperplastic human prostate and canine epididymis produced polar metabolites (in 12.5% and 76% yields, respectively) which gave rise to similar proportions of the same androstanetrione epimers on CrO₃-oxidation.     

Exploring new chemical functionalities to improve aromatase inhibition of steroids

In this work, new potent steroidal aromatase inhibitors both in microsomes and in breast cancer cells have been found. The synthesis of the 3,4-(ethylenedioxy)androsta-3,5-dien-17-one (12), a new steroid containing a heterocycle dioxene fused in the A-ring, led to the discovery of a new reaction for which a mechanism is proposed. New structure–activity relationships were established. Some 5β-steroids, such as compound 4β,5β-epoxyandrostan-17-one (9), showed aromatase inhibitory activity, because they adopt a similar A-ring conformation as those of androstenedione, the natural substrate of aromatase. Moreover, new chemical features to increase planarity were disclosed, specifically the 3α,4α-cyclopropane ring, as in 3α,4α-methylen-5α-androstan-17-one (5) (IC₅₀ = 0.11 μM), and the Δ^9–11 double bond in the C-ring, as in androsta-4,9(11)-diene-3,17-dione (13) (IC₅₀ = 0.25 μM). In addition, induced-fit docking (IFD) simulations and site of metabolism (SoM) predictions helped to explain the recognition of new potent steroidal aromatase inhibitors within the enzyme. These insights can be valuable tools for the understanding of the molecular recognition process by the aromatase and for the future design of new steroidal inhibitors.