Synthesis of transition-metal steroid derivatives

Advancements in steroidal Pt(II) & Pt(IV) derivatives for targeted chemotherapy (2000-2023)

One of the key strategies in chemotherapy involves crosslinking the DNA strands of cancer cells to impede their replication, with platinum (Pt) coordination compounds being a prominent class and cisplatin being its major representative. Steroidal ligands tethered to DNA interactive Pt core act as drug carriers for targeted therapy. While crosslinking of nuclear or mitochondrial DNA strands using coordination complexes has been studied for years, there remains a lack of comprehensive reviews addressing the advancements made in steroidal-Pt derivatives. This review specifically focuses on advancements made in steroid-tethered structural derivatives of Pt(II) or prodrug Pt(IV) for targeted chemotherapy, synthesized between 2000 and 2023. This period was deliberately chosen due to the widespread use of computational techniques for more accurate structure-based drug-design in last two decades. This review discusses the strategy behind tethering steroidal ligands such as testosterone, estrogen, bile acids, and cholesterol to the central DNA interactive Pt core through specific linker groups. The steroidal ligands function as drug delivery vehicles of DNA interactive Pt core and bind with their respective target receptors or proteins that are often overexpressed in cancer cells, thus enabling targeted delivery of Pt moiety to interact with DNA. We discussed structural features such as the location of the linker group on the steroid, the mono, bi, and tridentate configuration of the chelating arm in coordination with Pt, and the rigidity and flexibility of the linker group. The comparative in vitro, in vivo activities, and relative binding affinities of the designed compounds against standard Pt drugs are also discussed. We also provided a critique of observed trends and shortcomings. Our review will provide insights into future molecular designing of targeted DNA crosslinkers and their structural optimization to achieve desired drug properties. From this analysis, we proposed further research directions leading to the future of targeted chemotherapy.

Steroids Bearing Heteroatom as Potential Drugs for Medicine

Heteroatom steroids, a diverse class of organic compounds, have attracted significant attention in the field of medicinal chemistry and drug discovery. The biological profiles of heteroatom steroids are of considerable interest to chemists, biologists, pharmacologists, and the pharmaceutical industry. These compounds have shown promise as potential therapeutic agents in the treatment of various diseases, such as cancer, infectious diseases, cardiovascular disorders, and neurodegenerative conditions. Moreover, the incorporation of heteroatoms has led to the development of targeted drug delivery systems, prodrugs, and other innovative pharmaceutical approaches. Heteroatom steroids represent a fascinating area of research, bridging the fields of organic chemistry, medicinal chemistry, and pharmacology. The exploration of their chemical diversity and biological activities holds promise for the discovery of novel drug candidates and the development of more effective and targeted treatments.

Solvent-Driven Transformation of Zn/Cd2+-Deoxycholate Assemblies

Deoxycholic acid (DOC) is a unique, biologically derived surfactant with facial amphiphilicity that has been exploited, albeit minimally, in supramolecular assembly of materials. Here, we present the synthesis and structural characterization of three hybrid metal (Zn²⁺ and Cd²⁺)-DOC compounds. Analysis by single-crystal X-ray diffraction reveals the many interactions that are possible between these facial surfactants and the influence of solvent molecules that drive the assembly of materials. These structures are the first metal-DOC complexes besides those obtained from alkali and alkaline earth metals. We isolated polymeric chains of both Cd and Zn (Zn_poly-DOC and Cd_poly-DOC) from water. Major interactions between DOC molecules in these phases are hydrophobic in nature. Cd_poly-DOC exhibits unique P1 symmetry, with complete interdigitation of the amphiphiles between neighboring polymeric chains. Zn₄-DOC, obtained from methanol dissolution of Zn_poly-DOC, features the OZn₄ tetrahedron, widely known in basic zinc acetate and MOF-5 (metal organic framework). We document a solvent-driven, room-temperature transition between Zn_poly-DOC and Zn₄-DOC (in both directions) by scanning and transmission electron microscopies in addition to small-angle X-ray scattering, powder X-ray diffraction, and infrared spectroscopy. These studies show the methanol-driven transition of Zn_poly-DOC to Zn₄-DOC occurs via an intermediate with no long-range order of the Zn₄ clusters, indicating the strongest interactions driving assembly are intramolecular. On the contrary, water-driven solid-to-solid transformation from Zn₄-DOC to Zn_poly-DOC exhibits crystal-to-crystal transformation. Zn_poly-DOC is robust, easy to synthesize, and comprised of biologically benign components, so we demonstrate dye absorption as a proxy for water treatment applications. It favors absorption of positively charged dyes. These studies advance molecular level knowledge of the supramolecular assembly of facial surfactants that can be exploited in the design of organic-inorganic hybrid materials. This work also highlights the potential of solvent for tuning supramolecular assembly processes, leading to new hybrid materials featuring facial surfactants.

Reactivity of steroidal 1-azadienes toward enamines: an approach to novel chiral penta- and hexacyclic steroids

The chemical behavior of steroidal N-sulfonyl-1-azadienes toward carbonyl compounds, in the presence of pyrrolidine, is described. With aldehydes, these azadienes participate in hetero-Diels-Alder reactions with the in situ generated enamines. The stereoselectivity results from the approach of the dienophiles from the less hindered α-face of the steroid, with the pyrrolidine moiety endo and retention of the enamine trans geometry. This diastereoselective synthetic methodology led to a new class of chiral pentacyclic steroids. Interestingly, the studied steroidal scaffolds follow a different mechanistic pathway with cyclic ketones. They undergo a diastereoselective annulation reaction, under enamine catalysis, affording chiral hexacyclic steroids.

Novel d-Annulated Pentacyclic Steroids: Regioselective Synthesis and Biological Evaluation in Breast Cancer Cells

The acid-catalyzed cyclization of benzylidenes based on 16-dehydropregnenolone acetate (16-DPA) was studied. It was found that these compounds readily undergo regioselective interrupted Nazarov cyclization with trapping chloride ion and an efficient method of the synthesis of d-annulated pentacyclic steroids based on this reaction was proposed. The structures of the synthesized pentacyclic steroids were determined by NMR and X-ray diffraction. It was found that the reaction affords a single diastereomer, but the latter can crystallize as two conformers depending on the structure. Antiproliferative activity of synthesized compounds was evaluated against two breast cancer cell lines: MCF-7 and MDA-MB-231. All tested compounds showed relatively high antiproliferative activity. The synthetic potential of the protocol developed was illustrated by the gram-scale experiment.

Antibacterial activity of Mn(I) and Re(I) tricarbonyl complexes conjugated to a bile acid carrier molecule

A bifunctional cholic acid-bis(2-pyridylmethyl)amine (bpa) ligand featuring an amide linker was coordinated to a manganese(i) or rhenium(i) tricarbonyl moiety to give [M(bpacholamide)(CO)3] with M = Mn, Re in good yield and very high purity. Strong antibacterial activity was observed against four strains of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus, with minimum inhibitory concentrations (MICs) in the range of 2-3.5 μM. No difference in response was observed for the MSSA vs. MRSA strains. Activity was also independent of the nature of the metal center, as the Mn and Re complexes showed essentially identical MIC values. In contrast to some other metal carbonyl complexes, the activity seems to be unrelated to the release of carbon monoxide, as photoactivation of the Mn complex reduced the potency by a factor of 2-8. Both metal complexes were non-toxic in Galleria mellonella larvae at concentrations of up to 100× the MIC value. In vivo testing in Galleria larvae infected with MRSA/MSSA demonstrated a significant increase in overall survival rates from 46% in the control to 88% in the group treated with the metal complexes. ICP-MS analysis showed that the Mn and Re cholamide complexes are efficiently internalized by E. coli cells and do not interfere with membrane integrity, as evident from a lack of release of intracellular ATP. An increased sensitivity was observed in acrB, acrD, and mdt mutants that are defective in multidrug exporters, indicating that the compounds have an intracellular mechanism of action. Furthermore, E. coli mntP mutants defective in the gene encoding an Mn exporter were more sensitive than the wildtype, while inactivation of the regulator that controls expression of the Mn uptake proteins MntP and MntH slightly increased sensitivity to the compound. Single knockout mutants defective in genes linked to bile salt and oxidative stress response (dinF, yiaH, sodA, katE, and soxS) did not show increased sensitivity relative to the wild type. Overall, neither the cholic acid moiety nor the metal-carbonyl fragment alone appear to be responsible for the biological activity observed and thus the search for the primary intracellular target continues.

Development and characterization of a 99m Tc-labeled Neuropeptide Y short analog with potential application in breast cancer imaging

The aim of this work was to develop and evaluate a ^99m Tc-labeled neuropeptide Y derivative with affinity toward Y1-receptor. The selected amino acid sequence included nine amino acids derived from the C-terminal portion of the NPY complemented with the addition of one cysteine-mercaptoacetic acid moiety to bind the radiometal. Labeling was achieved through the preparation of a 3 + 1 nitrido complex. Physicochemical evaluation, cell uptake, internalization and externalization studies, and competitive assays were performed. Biodistribution experiments were carried out in normal and tumor-bearing mice. A single product with radiochemical purity >90% and high stability was obtained. In vitro analysis showed specific cellular uptake, IC₅₀ of 73.2 nM, and a high internalization rate (80%). Biodistribution studies showed low blood and renal uptake and combined hepatobiliary and urinary elimination. Preliminary studies in mice bearing induced breast tumors rendered promising uptake values.

C-12 vs C-3 substituted bile salts: An example of the effects of substituent position and orientation on the self-assembly of steroid surfactant isomers

Biomolecule derivatives are transversally used in nanotechnology. Deciphering their aggregation behavior is a crucial issue for the rational design of functional materials. To this end, it is necessary to build libraries of selectively functionalized analogues and infer general rules. In this work we enrich the highly applicative oriented collection of steroid derivatives, by reporting a rare example of C-12 selectively modified bile salt. While nature often exploits such position to encode functions, it is unusual and not trivial to prepare similar analogues in the laboratory. The introduction of a tert-butyl phenyl residue at C-12 provided a molecule with a self-assembly that remarkably switched from rigid pole-like structures to twisted ribbons at a biologically relevant critical temperature (∼25 °C). The system was characterized by microscopy and spectroscopy techniques and compared with the C-3 functionalized analogue. The twisted ribbons generate samples with a gel texture and a viscoelastic response. The parallel analysis of the two systems suggested that the observed thermoresponsive self-assemblies occur at similar critical temperatures and are probably dictated by the nature of the substituent, but involve aggregates with different structures depending on position and orientation of the substituent. This study highlights the self-assembly properties of two appealing thermoresponsive systems. Moreover, it adds fundamental insights hereto missing in the investigations of the relation between self-assembly and structure of synthetic steroids, which are valuable for the rational design of steroidal amphiphiles.

Development and evaluation of a 99mTc(V)-nitrido complex derived from estradiol for breast cancer imaging

Estrogen receptors are overexpressed in 70% of breast cancer and identification of their presence is important to select the appropriate treatment. This work proposes the preparation and evaluation of an estradiol derived as potential ER imaging agent. Ethinylestradiol was derivatized to introduce a dithiocarbamate function for Tc coordination. Labeling was achieved through the formation of a symmetric Tc(V)-nitrido complex with a radiochemical purity (RCP) > 95%. Physicochemical evaluation, cell uptake, biodistribution in normal animals and in nude mice bearing induced ER + breast tumors showed promising results.

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.

Synthesis of steroidal 1,2- and 1,3-diamines as ligands for transition metal ion complexation

Two series of cholestane-based diamines (1,2 and 1,3) were synthesized using simple and efficient procedures. The convenient substrates for these syntheses were cholesteryl mesylate and tosylate, which were converted to appropriate amines via easily obtained azides. The final diamines were prepared using a substitution reaction with bromoacetonitrile (in the case of 1,2-diamines) or condensation with acrylonitrile (in the case of 1,3-diamines), followed by the reduction of intermediate aminonitriles. Furthermore, the other two amines were synthesized from 16-dehydropregnenolone acetate using aza-Michael addition as a key step. Some of the diamines were subjected to complexation reactions with K₂PtCl₄ to form steroidal analogs of cisplatin. The synthetic methods tested in this work will allow us to prepare other cisplatin derivatives based on steroids showing anticancer properties themselves.

Hexafluoroisopropanol-Mediated Domino Reaction for the Synthesis of Thiazolo-androstenones: Potent Anticancer Agents

A cascade reaction of thioamides with 6β-bromoandrostenedione in hexafluoroisopropanol formed substituted thiazolo-androstenones. This is a simple and mild protocol to synthesize novel molecules by using readily available reagents and substrates. Feasibility of the reaction has been rationalized by density functional theory calculations. Moreover, these compounds are potent growth inhibitors of colon, central nervous system, melanoma, ovarian, and renal cancer cell lines with 50% growth inhibition values as low as 1.04 μM.

Benign Synthesis of Thiazolo-androstenone Derivatives as Potent Anticancer Agents

An unprecedented reaction of thiourea derivatives with 6β-bromoandrostenedione has been discovered for the formation of aminothiazolo-androstenones via a simple, safer, cascade protocol that enables the syntheses of novel molecules by using readily available reagents. The reaction mechanism of product formation has been rationalized by density functional theory calculations. This benign methodology accentuates a domino protocol deploying a renewable solvent, ethanol, while generating novel compounds that display potent growth inhibitory effects in in vitro studies for several cancer cell lines at submicromolar concentrations.

Development and characterization of a 99m Tc-tricarbonyl-labelled estradiol derivative obtained by "Click Chemistry" with potential application in estrogen receptors imaging

Assessment of the presence of estrogen receptors in breast cancer is crucial for treatment planning. With the objective to develop a potential agent for estrogen receptors imaging, we present the development and characterization of a ^99m Tc-tricarbonyl-labelled estradiol derivative. Using ethinylestradiol as starting material, an estradiol derivative bearing a 1,4-disubstituted 1,2,3-triazole-containing tridentate ligand system was synthesized by "Click Chemistry" and fully characterized. Labelling with high yield and radiochemical purity was achieved through the formation of a ^99m Tc-tricarbonyl complex. The radiolabelled compound was stable, exhibited moderate binding to plasma protein (approximately 33%) and lipophilicity in the adequate range (logP 1.3 ± 0.1 at pH 7.4). Studies in MCF7 showed promising uptake values (approximately 2%). However, more than 50% of the activity is quickly released from the cell. Biodistribution experiments in normal rats confirmed the expected "in vivo" stability of the radiotracer but showed very high gastrointestinal and liver activity, which is inconvenient for in vivo applications. Taking into consideration the well-documented influence of the chelating system in the physicochemical and biological behaviour of technetium-labelled small biomolecules, research will be continued using the same pharmacophore but different complexation modalities of technetium.

Synthesis of novel 13α-18-norandrostane-ferrocene conjugates via homogeneous catalytic methods and their investigation on TRPV1 receptor activation

13α-Steroid-ferrocene derivatives were synthesized via two reaction pathways starting from an unnatural 16-keto-18-nor-13α-steroid. The unnatural steroid was converted to ferrocene derivatives via copper-catalyzed azide-alkyne cycloaddition or palladium-catalyzed aminocarbonylation. 16-Azido- and 16-N-(prop-2-ynyl)-carboxamido-steroids were synthesized as starting materials for azide-alkyne cycloaddition with the appropriate ferrocene derivatives. Based on our earlier work, aminocarbonylation of 16-iodo-16-ene and 16-iodo-15-ene derivatives was studied with ferrocenylmethylamine. The new products were obtained in moderate to good yields and were characterized by (1)H and (13)C NMR, IR and MS. The solid state structure of the starting material 13α-18-norandrostan-16-one and two carboxamide products were determined by X-ray crystallography. Evidences were provided that the N-propargyl-carboxamide compound as well as its ferrocenylmethyltriazole derivative are able to decrease the activation of TRPV1 receptor on TRG neurons.