Recent advances in azasteroids chemistry

An efficient regioconvergent synthesis of 3-aza-obeticholic acid

Bile acids (BAs) are steroidal molecules that play important roles in nutrient absorption, distribution, and excretion. They also act on specific receptors implicated in various metabolic and inflammatory diseases demonstrating their importance as potential drug candidates. Accordingly, there has been a concerted effort to develop new BA derivatives to probe structure-activity relationships with the goal of discovering BA analogues with enhanced pharmacological properties. Among the many steroidal derivatisations reported, the formation of endocyclic azasteroids appeals due to their potential to deliver altered biological responses with minimal change to the steroidal superstructure. Here, we report the synthesis of 3-aza-obeticholic acid (6) via a regioconvergent route. Ammoniolysis of lactones, formed from an m-CPBA-mediated Baeyer-Villiger reaction on a 3-keto-OCA derivative, furnished protected intermediate amido-alcohols which were separately elaborated to amino-alcohols via Hofmann degradation with BAIB. Upon individual N-Boc-protection, these underwent annulation to the 3-aza-A-ring when subjected to either mesylation or a Dess-Martin oxidation/hydrogenation sequence. Global deprotection of the 3-aza-intermediate delivered 3-aza-OCA in ten steps and an overall yield of up to 19 %.

Iridium Acylnitrenoid-Initiated Biomimetic Cascade Cyclizations: Stereodefined Access to Polycyclic δ-Lactams

Ring-fused azacyclic compounds are important building units in the synthesis of biorelevant natural products, pharmaceutical agents, and molecular materials. Herein, we present a new approach to these condensed azacycles by a biomimetic cascade cyclization of arylalkenyl dioxazolones. This cascade reaction was found to proceed with excellent stereoselectivity and a high functional group tolerance. The substrate scope of arylalkenyl dioxazolones turned out to be highly flexible and extendable to additional terminating subunits, such as heteroaryl and alkynyl moieties. This biomimetic cyclization was elucidated to be initiated by an intramolecular transfer of the in situ generated electrophilic Ir-acylnitrenoid to the tethered olefinic double bond, leading to a key N-acylaziridine intermediate, which is in turn reacted with pendant (hetero)arenes or alkynes in a highly regio- and stereoselective manner to produce ring-fused azacyclic compounds.

Azasteroids from diosgenin: Synthesis and evaluation of their antiproliferative activity

In this work, we report the synthesis of two new azasteroids through the modification of the A and B rings of diosgenin 1. The 4-azasteroid derivative 12 was prepared in three steps using the α,β-insaturated-3-keto compound 11 as a precursor, which was first oxidized with KMnO4/KIO4 followed by an oxidative cleavage of ring A, and subsequently cyclized with an ammonium salt, under focused microwave irradiation for a short time of 3 min. A second azasteroid was synthesized, for which the key step was the Beckmann rearrangement of ring B of the oxime 16, affording the lactam-type enamide 17 in good yield. The methodologies developed for the synthesis of the precursors derivatives 10 and 11 contribute to improved yields, compared to those reported in the literature. The biological activity of the azasteroidal compounds 12 and 17 and their precursors has been evaluated in cervical cancer cells (HeLa), colon (HCT-15), and triple negative breast cancer (MDA-MB-231) lines.

Microwave-Induced Ugi-Four Component Reactions: Synthesis of New Hetero- Steroid-Amino Acid Conjugates

BACKGROUND

Aza-steroids are an important class of compounds because of their numerous biological activities. The hetero steroids have different hydrogen bonding ability and hydrophobicity in comparison to steroids.

MATERIALS AND METHODS

Microwave-induced synthesis of a novel type of hybrid hetero-steroid amine conjugates, following Ugi-four component reactions of steroidal amines with alanine and valine methyl esters as amino acid residues is described. Specifically, hetero-steroid-amino acid conjugate based on D-ring fused hetero steroidal amine, hetero-steroid-amino acid conjugate based on A-ring hetero steroidal amine, and hetero-steroidamino acid conjugate based on B-ring hetero steroidal amine are synthesized.

RESULTS AND DISCUSSION

The yield of the products under microwave-induced process was considerably higher than that obtained by the conventional method. In contrast to the conventional method for the synthesis of these molecules, microwave-induced method has several advantages.

CONCLUSION

These include rapid reaction, a superior yield of the product, minimum side reaction, and economical microwave-induced process.

Discovery and development of azasteroids as anticancer agents

Cancer is the second leading cause of death worldwide following cardiovascular diseases. Cancer can be treated by a variety of techniques including surgery, radiation therapy, immunotherapy, and chemotherapy. Choice of the method can be made based on type, physiologic location and the stage of disease progression. Among chemical methods, steroids find broad applications. Azasteroids have N- substitutions in steroidal rings. This structural modification renders azasteroids advantageous in increased effectiveness and reduced side effects. Numerous accounts of cancer efficacy of this family of compounds are available in literature. The progress made in the discovery, synthetic efforts and development of azasteroids as anticancer agents is broadly outlined in this review.

A general strategy for diversifying complex natural products to polycyclic scaffolds with medium-sized rings

The interrogation of complex biological pathways demands diverse small molecule tool compounds, which can often lead to important therapeutics for the treatment of human diseases. Since natural products are the most valuable source for the discovery of therapeutics, the derivatization of natural products has been extensively investigated to generate molecules for biological screenings. However, most previous approaches only modified a limited number of functional groups, which resulted in a limited number of skeleta. Here we show a general strategy for the preparation of a library of complex small molecules by combining state-of-the-art chemistry – the site-selective oxidation of C-H bonds - with reactions that expand rigid, small rings in polycyclic steroids to medium-sized rings. This library occupies a unique chemical space compared to selected diverse reference compounds. The diversification strategy developed herein for steroids can also be expanded to other types of natural products.

Derivatization of natural products is a powerful approach to generate new molecules for biological screenings. Here, the authors employ C-H oxidation and ring expansion methods for the preparation of a library of medium-sized ring skeleta, which occupy a unique chemical space based on chemoinformatic analysis.

Novel steroidal 1,3,4-thiadiazines: Synthesis and biological evaluation in androgen receptor-positive prostate cancer 22Rv1 cells

A flexible approach to previously unknown spirofused and linked 1,3,4-thiadiazine derivatives of steroids with selective control of heterocyclization patterns is disclosed. (N-Arylcarbamoyl)spiroandrostene-17,6' [1,3,4]thiadiazines and (N-arylcarbamoyl)17-[1',3',4']thiadiazine-substituted androstenes, novel types of heterosteroids, were prepared from 16β,17β-epoxypregnenolone and 21-bromopregna-5,16-dien-20-one in good to high yields by the treatment with oxamic acid thiohydrazides. The synthesized compounds were screened for antiproliferative activity against the human androgen receptor-positive prostate cancer cell line 22Rv1. Most of (N-arylcarbamoyl)17-[1',3',4']thiadiazine-substituted androstenes exhibit better antiproliferative potency (IC₅₀ = 2.1-6.6 µM) than the antiandrogen bicalutamide. Compounds 7d with IC₅₀ = 3.0 μM and 7j with IC₅₀ = 2.1 μM proved to be the most active in the series under study. Lead synthesized compound 7j downregulates AR expression and activity in 22Rv1 cells. NF-κB activity is also blocked in 7j-treated 22Rv1 cells. Apoptosis is considered as a possible mechanism of 7j-induced cell death.

Reagent-controlled regiodivergent ring expansions of steroids

Ring expansion provides a powerful way of introducing a heteroatom substituent into a carbocyclic framework. However, such reactions are often limited by the tendency of a given substrate to afford only one of the two rearrangement products or fail to achieve high selectivity at all. These limitations are particularly acute when seeking to carry out late-stage functionalization of natural products as starting points in drug discovery. In this work, we present a stereoelectronically controlled ring expansion sequence towards selective and flexible access to complementary ring systems derived from common steroidal substrates. Chemical diversification of the reaction intermediate affords over 100 isomerically pure analogs with spatial and functional diversity. This regiodivergent rearrangement, and the concept of using chiral reagents to affect regiocontrol in chiral natural products, should be broadly applicable to late-stage natural product diversification programs.

Late-stage diversification of natural products is an important starting point for drug discovery. Here, the authors use chiral reagents to perform the regiocontrolled ring expansion of steroid precursors and achieve more than 100 isomerically pure analogs with spatial and functional diversity.

Synthesis and biological activity of two pregnane derivatives with a triazole or imidazole ring at C-21

Pregnane derivatives are studied as agents for the treatment of different hormone-dependent diseases. The biological importance of these steroids is based on their potential use against cancer. In this study, we report the synthesis, characterization and biological activity of two pregnane derivatives with a triazole (3β-hydroxy-21-(1H-1,2,4-triazol-1-yl)pregna-5,16-dien-20-one; T-OH) or imidazole (3β-hydroxy-21-(1H-imidazol-1-yl)pregna-5,16-dien-20-one; I-OH) moieties at C-21. These derivatives were synthesized from 16-dehydropregnenolone acetate. The activity on cell proliferation of the compounds was measured on three human cancer cells lines: prostate cancer (PC-3), breast cancer (MCF7) and lung cancer (SK-LU-1). The cytotoxic and antiproliferative effects of T-OH and I-OH were assessed by using SBR and XTT methods, respectively. The gene expressions were evaluated by real time PCR. In addition, results were complemented by docking studies and transactivation assays using an expression vector to progesterone and androgen receptor. Results show that the two compounds inhibited the three cell lines proliferation in a dose-dependent manner. Compound I-OH downregulated the gene expression of the cyclins D1 and E1 in PC-3 and MFC7 cells; however, effect upon Ki-67, EAG1, BIM or survivin genes was not observed. Docking studies show poor interaction with the steroid receptors. Nevertheless, the transactivation assays show a weak antagonist effect of I-OH on progesterone receptor but not androgenic or antiandrogenic actions. In conclusion, the synthesized compounds inhibited cell proliferation as well as genes key to cell cycle of PC-3 and MCF7 cell lines. Therefore, these compounds could be considered a good starting point for the development of novel therapeutic alternatives to treat cancer.

Concise synthesis of 12a-methyl-11-aryl-1,2-dihydrobenzo[f]pyrrolo[1,2-a]quinolin-3(12aH)-ones as racemic 14-azaestrogen analogs

A concise method for the synthesis of 14-azasteroid analogs with angular methyl group at C-13 of the steroidal nucleus has been reported in this paper. We have developed an interesting cascade reaction of arylacetylenes and N-(naphthalen-2-yl)pent-4-ynamides under gold (III)-catalysis to produce novel tetracyclic 12a-methyl-11-aryl-1,2-dihydrobenzo[f]pyrrolo[1,2-a]quinolin-3(12aH)-ones which may be viewed as 14-azaestrogen analogs.

Synthesis and antibacterial activity evaluation of two androgen derivatives

In this study two androgen derivatives were synthesized using several strategies; the first stage an aza-steroid derivative (3) was developed by the reaction of a testosterone derivative (1) with thiourea (2) in presence of hydrogen chloride. The second step, involves the synthesis of an amino-steroid derivative (4) by the reaction of 1 with 2 using boric acid as catalyst. The third stage was achieved by the preparation of an aminoaza-androgen derivative (6) by the reaction of 3 with ethylenediamine using boric acid as catalyst. In addition, the compound 6 was made reacting with dihydrotestosterone to form a new androgen derivative (7) in presence of boric acid. The following step was achieved by the reaction of 7 with chloroacetyl chloride to synthesize an azetidinone-androgen derivative (8) using triethylamine as catalyst. Additionally, a thiourea-androgen derivative (9) was synthetized by the reaction of 4 with dihydrotestosterone using boric acid as catalyst. Finally, the compound 9 was made reacting with chloroacetyl chloride in presence of triethylamine to synthesize a new azetidinone-androgen derivative (10). On the other hand, antibacterial activity of compounds synthesized was evaluated on Gram negative (Escherichia coli and Vibrio cholerae) and Gram positive (Staphylococos aureus) bacteria. The results indicate that only the compound 3 and 8 decrease the growth bacterial of E. coli and V. cholerae. Nevertheless, growth bacterial of S. aureus was not inhibited by these compounds. These data indicate that antibacterial activity exerted by the compounds 3 and 8 depend of their structure chemical in comparison with the controls and other androgen derivatives that are involved in this study.

Advances in the detection of designer steroids in anti-doping

The abuse of unknown designer androgenic anabolic steroids (AAS) is considered to be an issue of significant importance, as AAS are the choice of doping preference according to World Anti-doping Agency statistics. In addition, unknown designer AAS are preferred since the World Anti-doping Agency mass spectrometric identification criteria cannot be applied to unknown molecules. Consequently, cheating athletes have a strong motive to use designer AAS in order to both achieve performance enhancement and to escape from testing positive in anti-doping tests. To face the problem, a synergy is required between the anti-doping analytical science and sports anti-doping regulations. This Review examines various aspects of the designer AAS. First, the structural modifications of the already known AAS to create new designer molecules are explained. A list of the designer synthetic and endogenous AAS is then presented. Second, we discuss progress in the detection of designer AAS using: mass spectrometry and bioassays; analytical data processing of the unknown designer AAS; metabolite synthesis; and, long-term storage of urine and blood samples. Finally, the introduction of regulations from sports authorities as preventive measures for long-term storage and reprocessing of samples, initially reported as negatives, is discussed.

C-H functionalization of sp(3) centers with aluminum: a computational and mechanistic study of the Baddeley reaction of decalin

Decalin undergoes reaction with aluminum trichloride and acetyl chloride to form a tricyclic enol ether in good yield, as first reported by Baddeley. This eye-catching transformation, which may be considered to be an aliphatic Friedel-Crafts reaction, has not previously been studied mechanistically. Here we report experimental and computational studies to elucidate the mechanism of this reaction. We give supporting evidence for the proposition that, in the absence of unsaturation, an acylium ion acts as a hydride acceptor, forming a tertiary carbocation. Loss of a proton introduces an alkene, which reacts with a further acylium ion. A concerted 1,2-hydride shift/oxonium formation, followed by elimination, leads to formation of the observed product.

Synthesis and evaluation of some new aza-B-homocholestane derivatives as anticancer agents

Using analogues of some marine steroidal oximes as precursors, a series of aza-B-homocholestane derivatives possessing different substituted groups at the 3-position of the steroidal nucleus were synthesized. Their biological activity against cancer cell proliferation was determined with multiple cancer cell lines. Aza-B-homocholestane derivatives possessing 3-hydroxyl, 3-hydroximino and 3-thiosemicarbazone groups displayed remarkable cytotoxicity to cancer cells via apoptosis inducing mechanism. Compounds 5, 10, 12, 15 and 18 exhibited better potency to inhibit cancer cell proliferation. In addition, compound 15 was further evaluated with three dimensional (3D) multicellular spheroids assay to determine its potency against spheroid growth. The structure-activity relationship (SAR) generated in the studies is valuable for the design of novel chemotherapeutic agents.

Synthesis and cytotoxic activity of some 4,6-diaza-A,B-dihomo-steroid bilactams

Using cholesterol, stigmasterol and sitosterol as starting materials, some 4,6-diaza-A,B-dihomo-steroid bilactams were synthesized via two different synthetic routes by oxidation, reduction, oximation, Beckman rearrangement, etc. The cytotoxic activity of the synthesized compounds against SGC 7901 (human ventriculi carcinoma), Bel-7404 (human liver carcinoma), HeLa (human cervical carcinoma) and HT-29 (colonic carcinoma) cancer cells were investigated. The results showed that compounds 2 and 7b displayed a good cytotoxic activity to the SGC 7901, Bel 7404 and HeLa tumor cell lines with the IC50 values of 11.6, 16.4, 13.9 and 13.1, 21.8, 13.1 μmol/L, respectively. Their cytotoxic activity is almost same as cisplatin to these cells. The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs.

Synthesis of novel estrone analogs by incorporation of thiophenols via conjugate addition to an enone side chain

Functionalized estrogen analogs have received interest due to their unique and differing biological activity compared to their parent compounds. The synthesis of a new class of 3-methoxyestrone analogs functionalized at the C17 position possessing both alkyl and aryl substituted α,β-unsaturated ketones is described, along with their thiophenol conjugate addition products.

Synthesis of 6-azaprogesterone and 19-hydroxy-6-azasteroids

19-Hydroxy-6-azapregnanes were obtained from pregnenolone via a 7-azido-5-oxo-6-nor-5,7-secopregnane intermediate. The 6-azapregnane core was built in good yield in a straightforward way from the secosteroid, by means of a Staudinger (aza-Wittig) reaction. Finally the 19-hydroxy-6-azapregnane was transformed into 19-hydroxy-6-azaprogesterone (that cyclized spontaneously to the 19→3 hemiketal) and 6-azaprogesterone. The 6-azapregnanes lacked agonistic/antagonistic activity on the progesterone receptor.

Synthesis of 12-oxa, 12-aza and 12-thia cholanetriols

An efficient synthesis of 12-hetero steroids was achieved via a Baeyer-Villiger oxidation and a photolysis as the key steps. We set out to describe in this paper the first synthesis of 12-aza steroids. The characteristic (1)H and (13)C NMR spectroscopic features of the synthesized compounds are reported.

Structural characteristics of anabolic androgenic steroids contributing to binding to the androgen receptor and to their anabolic and androgenic activities. Applied modifications in the steroidal structure

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone introduced for therapeutic purposes providing enhanced anabolic potency with reduced androgenic effects. Androgens mediate their action through their binding to the androgen receptor (AR) which is mainly expressed in androgen target tissues, such as the prostate, skeletal muscle, liver and central nervous system. This paper reviews some of the wide spectrum of testosterone and synthetic AAS structure modifications related to the intended enhancement in anabolic activity. The structural features of steroids necessary for effective binding to the AR and those which contribute to the stipulation of the androgenic and anabolic activities are also presented.