Inactivation of delta 5-3-oxo steroid isomerase with active-site-directed acetylenic steroids

Several steroid analogues containing conjugated acetylenic ketone groups as part of a seco-ring structure or as substituents on the intact steroid system are irreversible inhibitors of delta 5-3-oxo steroid isomerase (EC 5.3.3.1) from Pseudomonas testosteroni. Thus 10 beta-(1-oxoprop-2-ynyl)oestr-4-ene-3,17-dione (I), 5,10-seco-oestr-4-yne-3,10,17-trione (II), 17 beta-hydroxy-5,10-seco-oestr-4-yne-3,10-dione (III) and 17 beta-(1-oxoprop-2-ynyl)androst-4-en-3-one (IV) irreversibly inactivate isomerase in a time-dependent manner. In all cases saturation kinetics are observed. Protection against inactivation is afforded by the powerful competitive inhibitor 19-nortestosterone. The inhibition constants (Ki) for 19-nortestosterone obtained from such experiments are in good agreement with those determined from conventional competitive-inhibition studies of enzyme activity. These compounds thus appear to be active-site directed. In every case the inactivated enzyme could be dialysed without return of activity, indicating that a stable covalent bond probably had formed between the steroid and enzyme. Compound (I) is a very potent inhibitor of isomerase [Ki = 66.0 microM and k+2 = 12.5 x 10(-3) s-1 (where Ki is the dissociation constant of the reversible enzyme-inhibitor complex and k+2 is the rate constant for the inactivation reaction of the enzyme-inhibitor complex)] giving half-lives of inactivation of 30-45 s at saturation. It is argued that the basic-amino-acid residue that abstracts the intramolecularly transferred 4 beta-proton in the reaction mechanism could form a Michael-addition product with compound (I). In contrast, although compound (IV) has a lower inhibition constant (Ki = 14.5 microM), it is a relatively poor alkylating agent (k+2 = 0.13 x 10(-3) s-1). If the conjugated acetylenic ketone groups are replaced by alpha-hydroxyacetylene groups, the resultant analogues of steroids (I)-(IV) are reversible competitive inhibitors with Ki values in the range 27-350 microM. The enzyme binds steroids in the C19 series with functionalized acetylenic substituents at C-17 in preference to steroids in the C18 series bearing similar groups in the ring structure or as C-10 substituents. In the 5,10-seco-steroid series the presence of hydroxy groups at both C-3 and C-17 is deleterious to binding by the enzyme.

Study of 3 alpha, 20 beta-hydroxysteroid dehydrogenase with an enzyme-generated affinity alkylator: dual enzyme activity at a single active site

The substrate 17 beta-[(1S)-1-hydroxy-2-propynyl]-androst-4-en-3-one (beta-HPA) and its enzyme-generated alkylating product 17 beta-(1-oxo-2-propynyl)androst-4-en-3-one (OPA) were synthesized to investigate the relationship between the 3 alpha and 20 beta activities observed in commercially available cortisone reductase (EC 1.1.1.53) from Streptomyces hydrogenans. beta-HPA, a substrate [apparent Km = 145 microM; Vmax = 63 nmol (min microgram)-1], when enzymatically oxidized by cortisone reductase of OPA, inactivates simultaneously the 3 alpha and 20 beta activities in a time-dependent and irreversible manner following pseudo-first-order kinetics. OPA alone, an affinity alkylating steroid (KI = 40.5 microM; k3 = 1.8 X 10(-2) S-1), simultaneously inactivates 3 alpha and 20 beta activities in a time-dependent and irreversible manner. At pH 7, the t 1/2 of enzyme inactivation for beta-HPA (10 h) or OPA (41 min) is slower than at pH 9.2 (beta-HPA, 16 min, and OPA, 3.3 min). Substrates (progesterone, 20 beta-hydroxypregn-4-en-3-one, and 5 alpha-dihydrotestosterone), but not all steroids (20 al]ha-delta 4-pregn-4-en-3-one and 17 beta-estradiol), protect against loss of both enzyme activities by beta-HPA and OPA. The alpha isomer of HPA is not enzymatically oxidized and therefore does not cause inactivation of either 3 alpha or 20 alpha activity. Thus, beta-HPA functions as a substrate for the enzymatic generation of a powerful affinity alkylator of cortisone reductase. Second, the identical change in both the 3 alpha and 20 beta activities in all experimental conditions clearly results from dual enzyme activity at a single enzyme active site.

The addition of hypobromous acid to 3 beta, 17 beta-diacetoxy-4-estrene and an equilibration study involving neighboring group participation by the A-ring acetoxy group

The reaction of 3 beta, 17 beta-diacetoxy-4-estrene with N-bromoacetamide in a two phase ether/water solvent mixture gave 5-bromo-4 beta, 17 beta-diacetoxy-5 alpha-estran-3 beta-ol as the major product (75%). Four minor products were also isolated and identified. These were: 4 alpha-bromo-3 beta, 17 beta-diacetoxy-5 alpha-estran-5-ol (5%), 5-bromo-3 beta, 17 beta-diacetoxy-5 alpha-estran-4 beta-ol (6%), 5-bromo-4 alpha, 17 beta-diacetoxy-5 alpha-estran-3 beta-ol (3%), and 4 beta-bromo-3 beta, 17 beta-diacetoxy-5 alpha-estran-5-ol (4%). The 5-bromo-4 beta, 17 beta-diacetoxy-5 alpha-estran-3 beta-ol was equilibrated by heating with oxalic acid in refluxing benzene for ca. 16 h to give a mixture of it and 5-bromo-3 beta, 17 beta-diacetoxy-5 alpha-estran-4 beta-ol in the ratio of 16:84 respectively. A similar equilibration mixture (14:86) was obtained under identical conditions when 5-bromo-3 beta, 17 beta-diacetoxy-5 alpha-estran-4 beta-ol was the starting material.

Synthesis of 17 beta-[(1S)-1-hydroxy-2-propynyl]- and 17 beta-[(1R)-1-hydroxy-2-propynyl]androst-4-en-3-one. Potential suicide substrates of 20 alpha- and 20 beta-hydroxysteroid dehydrogenases

The title compounds have been synthesized for evaluation as potential suicide substrates of 20 alpha- and 20 beta-hydroxysteroid dehydrogenases. Synthesis was achieved by the following route. Acetylenedimagnesium bromide was reacted with 3 beta-hydroxyandrost-4-ene-17 beta-carboxaldehyde to give 17 beta-[(1R,S)-1-hydroxy-2-propynyl] androst-4-en-3 beta-ol. Separation of the R and S diols was achieved by HPLC (high pressure liquid chromatography). Selective oxidation of the 3 beta-hydroxyl group with Jones reagent at 0 degrees gave the title compounds. Further oxidation with Jones reagent converted each acetylenic alcohol to the conjugated acetylenic ketone, 17 beta-(1-oxo-2-propynyl)androst-4-en-3-one.

Inhibition of testosterone 5 alpha-reductase by and antiandrogenicity of allenic 3-keto-5,10-secosteroids

(4R)-5,10-seco-19-norpregna-4,5-diene-3,10,20-trione(II), A 3-keto-5,10-secosteroid which is an irreversible inhibitor of delta 5-3-ketosteroid isomerase was tested for its possible antiandrogenicity in the hamster flank organ test. The organs of female animals topically treated with 4 microgram of testosterone propionate (TP) for 4 weeks enlarged in size and showed pigmentation resembling adult males. When compound II was applied concomitantly with TP, androgenic stimulation was completely blocked and the flank organs remained small like those of female animals. These results suggest that compound II may be a useful anti-androgen when applied topically. It may well act mainly by inhibition of the formation of 5alphs-reduced metabolites was markedly inhibited.

Effects of novel acetylenic and allenic steroids on the rat prostate

Novel acetylenic and allenic steroid analogs previously have been synthesized in this laboratory and were shown to be potent irreversible inhibitors of delta5-3-ketosteroid isomerase from P. Testosteroni. This bacterial enzyme catalyzes the conversion of delta5-3-ketosteroids to the corresponding delta4-3-ketosteroids. These isomerizations are key steps in the mammalian biosynthesis of steroid hormones, and it was hoped that the acetylenic and allenic steroid analogs migh inhibit androgen biosynthesis. We have now shown that these compounds cause a significant and dose-dependent decrease in the wet weight of both ventral and dorsal lateral prostate in the mature male rat.