Steroselective synthesis of some steroidal oxazolines, as novel potential inhibitors of 17alpha-hydroxylase-C17,20-lyase

From electrochemistry to enzyme kinetics of cytochrome P450

This review is an attempt to describe advancements in the electrochemistry of cytochrome P450 enzymes (EC 1.14.14.1) and to study molecular aspects and catalytic behavior of enzymatic electrocatalysis. Electroanalysis of cytochrome P450 demonstrates how to translate theoretical laws and equations of classical electrochemistry for the calculation of the kinetic parameters of enzymatic reactions and then translation of kinetic parameters to interpretation of drug-drug interactions. The functional significance of cytochrome P450s (CYPs) includes the metabolism of drugs, foreign chemicals, and endogenic compounds. The pharmaceutical industry needs sensitive and cost-effective systems for screening new drugs and investigation of drug-drug interactions. The development of different types of CYP-based biosensors is now in great demand. This review also highlights the characteristics of electrode processes and electrode properties for optimization of the cytochrome P450 electroanalysis. Electrochemical cytochrome P450-biosensors are the most studied. In this review, we analyzed electrode/cytochrome P450 systems in terms of the mechanisms underlying P450-catalyzed reactions. Screening of potential substrates or inhibitors of cytochromes P450 by means of electrodes were described.

Synthesis of novel 17-triazolyl-androst-5-en-3-ol epimers via Cu(I)-catalyzed azide-alkyne cycloaddition and their inhibitory effect on 17α-hydroxylase/C17,20-lyase

The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 17α- and 17β-azidoandrost-5-en-3β-ol epimers (3b and 5b) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-k and 9a-k). For the preparation of 5'-iodo-1',2',3'-triazoles (8m-n and 9m-n), an improved method was developed, directly from steroidal azides and terminal alkynes, in reaction mediated by CuI and ICl as iodinating agents. Acetolysis and subsequent hydrolysis of 8n and 9n yielded 5'-hydroxy-1',2',3'-triazoles 8o and 9o. The inhibitory effect of 8a-o, 9a-o, 3, and 5 on rat testicular C_17,20-lyase was investigated by means of an in vitro radioincubation technique. The results revealed that the C-17 epimers of steroidal triazoles influence the C_17,20-lyase effect. Inhibitors were found only in the 17α-triazolyl series (8a-o), whereas in the C-17 azide pair the 17β compound (5b) was more potent.

Synthesis of unprecedented steroidal spiro heterocycles as potential antiproliferative drugs

Herein we report the straightforward preparation of novel conformationally-restricted steroids from trans-androsterone and estrone, decorated with spiranic oxazolidin-2-one or 2-aminooxazoline motifs at C-17 as potential antiproliferative agents. Such unprecedented pharmacophores were accessed using an aminomethylalcohol derivative at C-17 as the key intermediate; reaction of such functionality with triphosgene, or conversion into N-substituted thioureas, followed by an intramolecular cyclodesulfurization reaction promoted by yellow HgO, furnished such spirocycles in excellent yields. Title compounds were tested in vitro against a panel of six human tumor cell lines, named A549 (non-small cell lung), HBL-100 (breast), HeLa (cervix), SW1573 (non-small cell lung), T-47D (breast) and WiDr (colon), and the results were compared with steroidal chemotherapeutic agents (abiraterone and galeterone); the A-ring of the steroidal backbone, the nature of the heterocycle and the N-substituents proved to be essential motifs for establishing structure-activity relationships concerning not only the potency but also the selectivity against tumor cell lines. Estrone derivatives, particularly those bearing a spiranic 2-aminooxazoline scaffold were found to be the most active compounds, with GI₅₀ values ranging from the low micromolar to the submicromolar level (0.34-1.5 μM). Noteworthy, the lead compounds showed a remarkable increase in activity against the resistant cancer cell lines (T-47D and WiDr) compared to the anticancer reference drugs (up to 120-fold).

Synthesis of novel 17-(5'-iodo)triazolyl-3-methoxyestrane epimers via Cu(I)-catalyzed azide-alkyne cycloadditon, and an evaluation of their cytotoxic activity in vitro

The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 3-methoxyestrane 17α- and 17β-azide epimers (3 and 5) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-f and 11a-f). If the Ph3P in the classical CuAAC process was replaced by Et3N, the formation of small quantities of 5-iodotriazoles (9a-f and 11a-f) was observed. For the preparation of 5-iodo-1,2,3-triazoles (9a-f and 11a-f), an improved method was developed, directly from steroidal azides and terminal alkynes, in reactions mediated by CuI and ICl as iodinating agents. The antiproliferative activities of the structurally related triazoles were determined in vitro with the microculture tetrazolium assay on six malignant human cell lines of gynecological origin (HeLa, A2780, MCF7, MDA-MB-231, MDA-MB-361 and T47D). X-ray analysis revealed the presence of the iodo substituent on the 1,2,3-triazole ring.

Design and synthesis of new dihydrotestosterone derivative with positive inotropic activity

There are several reports which indicate that some steroid derivatives have inotropic activity; nevertheless, the cellular site and mechanism of action of steroid derivatives at cardiovascular level is very confusing. In order, to clarify these phenomena in this study, two dihydrotestosterone derivatives (compounds 5 and 10) were synthesized with the objective of to evaluate its biological activity on left ventricular pressure and characterize their molecular mechanism. In the first stage, the Langendorff technique was used to measure changes on perfusion pressure and coronary resistance in an isolated rat heart model in absence or presence of the steroid derivatives. Additionally, to characterize the molecular mechanism involved in the inotropic activity induced by the compound 5 was evaluated by measuring left ventricular pressure in absence or presence of following compounds; nifedipine, flutamide, indomethacin, prazosin, isoproterenol, propranolol and metoprolol. The results showed that the compound 5 significantly increased the perfusion pressure and coronary resistance in comparison with dihydrotestosterone, compound 10 and the control conditions. Other data indicate that 5 increase left ventricular pressure in a dose-dependent manner (0.001-100 nM); nevertheless, this phenomenon was significantly inhibited only by propranolol or metoprolol at a dose of 1 nM. These data suggest that positive inotropic activity induced by the compound 5 is through β1-adrenergic receptor however, this effect was independent of cAMP levels. This phenomenon is a particularly interesting because the positive inotropic activity induced by this steroid derivative involves a molecular mechanism different in comparison with other positive inotropic drugs.

Steroidal pyrazolines and pyrazoles as potential 5α-reductase inhibitors: synthesis and biological evaluation

Taking pregnenolone as the starting material, two series of pyrazolinyl and pyrazolyl pregnenolones were synthesized through different routes. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of pyrazolinyl pregnenolones is the heterocyclization of benzylidine derivatives (3) in presence of hydrazine hydrate, it is the condensation of 3β-hydroxy-21-hydroxymethylidenepregn-5-en-3β-ol-20-one (5) with phenylhydrazine in the synthesis of pyrazolyl derivatives. Compounds of both the series were tested for their 5α-reductase inhibitory activities. Amongst all the compounds screened for their 5α-reductase inhibitory activities, compound 4b, 4c and 6b were found to be the most active.

Novel oxazolinyl derivatives of pregna-5,17(20)-diene as 17α-hydroxylase/17,20-lyase (CYP17A1) inhibitors

New oxazolinyl derivatives of [17(20)E]-pregna-5,17(20)-diene: 2'-{[(E)-3β-hydroxyandrost-5-en-17-ylidene]methyl}-4',5'-dihydro-1',3'-oxazole 1 and 2'-{[(E)-3β-hydroxyandrost-5-en-17-ylidene]methyl}-4',4'-dimethyl-4',5'-dihydro-1',3'-oxazole 2 were evaluated as potential CYP17A1 inhibitors in comparison with 17-(pyridin-3-yl)androsta-5,16-dien-3β-ol 3 (abiraterone). Differential absorption spectra of human recombinant CYP17A1 in the presence of compound 1 (λmax=422 nm, λmin=386 nm) and compound 2 (λmax=416 nm) indicated significant differences in enzyme/inhibitors complexes. CYP17A1 activity was measured using electrochemical methods. Inhibitory activity of compound 1 was comparable with abiraterone 3 (IC50=0.9±0.1 μM, and IC50=1.3±0.1 μM, for compounds 1 and 3, respectively), while compound 2 was found to be weaker inhibitor (IC50=13±1 μM). Docking of aforementioned compounds to CYP17A1 revealed that steroid fragments of compound 1 and abiraterone 3 occupied close positions; oxazoline cycle of compound 1 was coordinated with heme iron similarly to pyridine cycle of abiraterone 3. Configuration of substituents at 17(20) double bond in preferred docked position corresponded to Z-isomers of compounds 1 and 2. Presence of 4'-substituents in oxazoline ring of compound 2 prevents coordination of oxazoline nitrogen with heme iron and worsens its docking score in comparison with compound 1. These data indicate that oxazolinyl derivative of [17(20)E]-pregna-5,17(20)-diene 1 (rather than 4',4'-dimethyl derivative 2) may be considered as potential CYP17A1 inhibitor and template for development of new compounds affecting growth and proliferation of prostate cancer cells.

Design and synthesis of D-ring steroidal isoxazolines and oxazolines as potential antiproliferative agents against LNCaP, PC-3 and DU-145 cells

Two series of novel steroidal isoxazolines and oxazolines were synthesized through different routes from dehydroepiandrosterone acetate and pregnenolone acetate, respectively. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of former is the cycloaddition of aromatic nitrile oxides across α,β-unsaturated olefins, it is the condensation of α,β-azidoalcohols with aromatic aldehydes in the later. Compounds of both the series were tested for their cytotoxic activities against LNCaP, PC-3 and DU-145 prostate cancer cell lines. Amongst all the compounds of both the series screened for their prostate cancer activity, compound 6a, 6e and 12a are the most active especially against LNCaP and DU-145 cancer cell lines.

Steroidal 5α-reductase and 17α-hydroxylase/17,20-lyase (CYP17) inhibitors useful in the treatment of prostatic diseases

The role of steroidal inhibitors of androgen biosynthesis as potential weapons in the treatment of prostatic diseases, such as benign prostatic hyperplasia and prostatic cancer will be reviewed. Two enzymes have been targeted in the development of inhibitors that potentially could be useful in the management of such conditions. 5α-Reductase is primarily of interest in benign prostatic disease, though some role in the chemoprevention of prostatic carcinoma have been considered, whereas the 17α-hydroxylase/17,20-lyase (CYP17) enzyme is of interest in the treatment of malignant disease. An overview of the main achievements obtained during the past years will be presented, however special focus will be made on steroidal molecules that reached clinical trials or have been commercially launched. Relevant examples of such drugs are finasteride, dutasteride, abiraterone acetate and galeterone (TOK-001, formerly known as VN/124-1). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Synthesis of sex hormone-derived modified steroids possessing antiproliferative activity

During recent years intensive research has been focused on the synthesis of structurally modified steroid hormones in order to obtain compounds with beneficial biological activity such as cell-growth inhibition. Experimental results have revealed that some steroidal derivatives possess direct cytostatic effect on cancer cells in a hormone receptor-independent manner. After a brief account on the most important biological function and characteristics of the naturally occurring sex hormones in physiological and pathological conditions, structural modifications of estrane and androstane scaffolds are discussed in detail. The review covers literature publications (from 2002 to 2012) relating to the synthesis and antiproliferative activity of semisynthetic sex hormone-derived molecules containing simple or heterocyclic substituents. The compounds reviewed are divided into three main categories according to their sterane framework and the nature of substitution. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Synthesis and molecular modeling of (4'R)- and (4'S)- 4'-substituted 2'-{[(E)-androst-5-en-17-ylidene]-methyl}oxazolines

Synthesis of four novel (4'R)- and (4'S)- 2'-{[(E)-3β-hydroxyandrost-5-en-17-ylidene]-methyl} oxazolines, comprising 4'-hydroxymethyl (1 and 2) and 4'-methoxycarbonyl (3 and 4) substituents is presented. Reaction of 17α-bromo-21-iodo-3β-acetoxypregn-5-en-20-one with either (L)-serine methyl ester, or (D)-serine methyl ester resulted in methyl N-[3β-acetoxy-21-oxopregna-5,17(20)-dien-21-yl]-(L)-serinate and methyl N-[3β-acetoxy-21-oxopregna-5,17(20)-dien-21-yl]-(D)-serinate (as mixtures of related [17(20)E]- and [17(20)Z]-isomers). Cyclization of obtained amides led to methyl 2'-{[(E)-3β-acetoxyandrost-5-en-17-ylidene]methyl}-(4'S)-4',5'-dihydro-1',3'-oxazole-4'-carboxylate and methyl 2'-{[(E)-3β-acetoxyandrost-5-en-17-ylidene]methyl}-(4'R)-4',5'-dihydro-1',3'-oxazole-4'-carboxylate which were transformed to titled compounds 1-4. The molecular docking of compounds 1-4 to ligand binding site of nuclear receptor LXRβ revealed significant differences due to stereochemical configuration of 4' atom and structure of 4'-substituent.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

Synthesis, characterization and biological evaluation of some novel 17-isoxazoles in the estrone series

Regioselective 1,3-dipolar cycloadditions of different aryl nitrile oxides to mestranol were carried out to furnish novel steroidal 17α-isoxazoles in good to excellent yields. Copper(I) was found to be an efficient catalyst, accelerating the intermolecular ring-closures and leading exclusively to 3,5-disubstituted isoxazoles. The yields of the cycloadducts, however, were influenced by the substituents on the aromatic moiety of the 1,3-dipoles. Moreover, dehydration of the primary products resulted in the corresponding Δ(16,17)exo-heterocyclic derivatives. All the synthesized compounds were subjected to in vitro pharmacological studies of their antiproliferative effects relative to three human malignant cell lines (HeLa, MCF7 and A2780).

Novel series of 17β-pyrazolylandrosta-5,16-diene derivatives and their inhibitory effect on 17α-hydroxylase/C(17,20)-lyase

The Claisen condensation of 3β-acetoxypregna-5,16-dien-20-one (1) with ethyl formate in the presence of sodium methylate in pyridine is known to lead to 3β-hydroxy-21-hydroxymethylidenepregna-5,16-dien-20-one (2) in good yield. With the methods described for the preparation of the saturated D-ring pyrazolyl series, the reactions of 2 with phenylhydrazine and its p-substituted derivatives in acetic acid resulted in mixtures of two steroidal regioisomers, the 1'-aryl-3'-pyrazolyl-(4a-e) and 1'-aryl-5'-pyrazolyl (5a-e) steroids. Compounds 4a-e are unknown in the literature. The arylpyrazoles produced were tested against 17α-hydroxylase/C(17,20)-lyase (P450(17α)) in vitro and neither of the regioisomers exerted efficient inhibition.

Synthesis of D-ring-substituted (5'R)- and (5'S)-17β-pyrazolinylandrostene epimers and comparison of their potential anticancer activities

Various steroidal benzylidenes were synthetized from pregnenolone with benzaldehyde and p-substituted benzaldehydes. The resulting 17β-chalconyl derivatives of pregnenolone were reacted with hydrazine hydrate in acetic acid solution. Regardless of the starting material, the ring-closure reaction afforded (in contrast with the literature data) a mixture of two steroidal pyrazoline epimers. The epimers were critical isomer pairs, which could be separated only in their acetylated form; their structures were investigated by NMR techniques. The in vitro inhibition of rat testicular C(17,20)-lyase activity and the antiproliferative effects on four human cancer cell lines were measured, and the results obtained from the two epimer series were compared.

Synthesis of 21-nitrogen substituted pregna-5,17(20)-dienes from pregnenolone

The facile synthesis of six [17(20)Z]- and [17(20)E]-isomeric 3β-hydroxy-pregna-5,17(20)-dien-21-oyl amides and three [17(20)E]-3β-hydroxy-2-[prergna-5,17(20)-dien-20-yl]-oxazolines from pregnenolone is presented. The synthetic scheme consists of transformation of pregnenolone into the known 17α-bromo-21-iodo-3β-acetoxypregn-5-en-20-one followed by reaction with ethanolamine, 2-methyl-2-aminopropanol, and (1-aminocyclohexyl)methanol resulted in mixture of [17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-(2-hydroxy)-oyl amides; separation of [17(20)E]- and [17(20)Z]-isomers; their cyclization into [17(20)E]-oxazolines under action of POCl(3) in pyridine, and removal of acetate protecting groups. Significantly different orientation of nitrogen containing substituents in [17(20)Z]- and [17(20)E]-isomers regarding to steroid backbone enables their configuration to be easily identified by NMR spectroscopy. All synthesized compounds did not exhibit marked toxic effects in three cell lines (MCF-7, Hep G2, and LNCaP). In androgen-sensitive LNCaP cells all testing compounds at concentrations of 50 nM potently stimulated proliferation.

Synthesis of novel steroidal 17α-triazolyl derivatives via Cu(I)-catalyzed azide-alkyne cycloaddition, and an evaluation of their cytotoxic activity in vitro

Regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of steroidal 17α-azides with different terminal alkynes afforded novel 1,4-disubstituted triazolyl derivatives in good yields in both the estrone and the androstane series. The antiproliferative activities of the structurally related triazoles were determined in vitro on three malignant human cell lines (HeLa, MCF7 and A431), with the microculture tetrazolium assay.

Synthesis and in vitro antiproliferative activity of novel androst-5-ene triazolyl and tetrazolyl derivatives

A straightforward and reliable method for the regioselective synthesis of steroidal 1,4-disubstituted triazoles and 1,5-disubstituted tetrazoles via copper(I)-catalyzed cycloadditions is reported. Heterocycle moieties were efficiently introduced onto the starting azide compound 3β-acetoxy-16β-azidomethylandrost-5-en-17β-ol through use of the “click” chemistry approach. The antiproliferative activities of the newly-synthesized triazoles were determined in vitro on three human gynecological cell lines (HeLa, MCF7 and A2780) using the microculture tetrazolium assay.

Determination of rat 5alpha-reductase type 1 isozyme activity and its inhibition by novel steroidal oxazolines

The 5alpha-reductase type 1 isozyme is a key enzyme in the metabolism of the androgen steroid hormones and inhibitors of this enzyme represent a new pharmacological treatment for several androgen dependent diseases. We developed a radiosubstrate in vitro incubation method for the determination of 5alpha-reductase type 1 activity using rat liver microsomes as an enzyme source. With this method we have studied the inhibiting activity of novel (5' S)-17beta-(4,5-dihydrooxazol-5-yl)androst-5-en-3-one compounds containing various derivatized phenyl substituents coupled to the exo -heterocyclic moiety. Tests revealed moderate inhibitory actions compared to finasteride, nevertheless, results provide interesting structure-activity relationship data.

Synthesis of regioisomeric 17beta-N-phenylpyrazolyl steroid derivatives and their inhibitory effect on 17alpha-hydroxylase/C(17,20)-lyase

The reaction of 3beta-hydroxy-21-hydroxymethylidenepregn-5-en-3beta-ol-20-one (1) with phenylhydrazine (2a) affords two regioisomers, 17beta-(1-phenyl-3-pyrazolyl)androst-3-en-3beta-ol (5a) and 17beta-(1-phenyl-5-pyrazolyl)androst-5-en-3beta-ol (6a). The direction of the ring-closure reactions of 1 with p-substituted phenylhydrazines (2b-e) depends strongly on the electronic features of the substituents. Oppenauer oxidation of 3beta-hydroxy-17beta-exo-heterocyclic steroids 5a-e and 6a-e yielded the corresponding Delta(4)-3-ketosteroids 9a-e and 10a-e. The inhibitory effects (IC(50)) of these compounds on rat testicular C(17,20)-lyase were investigated by means of an in vitro radioligand incubation technique.