Formaldehyde emerges as a cornerstone in multicomponent reactions, mainly prized for its robust reactivity. Yet, alongside these beneficial traits, this highly reactive C1-building block raises concerns, primarily regarding its toxicity. One notable issue is the challenge of controlling the formation of undesired byproducts during its reactions. This review explores alternative C1-building blocks that serve as surrogates for formaldehyde, aiming to mitigate some of the challenges associated with its use in multicomponent reactions. By identifying these alternatives, toxicity concerns and improved reaction control can be addressed, paving the way for more efficient and sustainable synthetic methodologies.

The discovery of bioactive compounds is a complex endeavor that frequently involves investigation of natural products (NPs). However, inherent difficulties associated with the extraction and synthesis of NPs have prompted the development of alternative methods. In this context, pseudo-natural products (pNPs) - synthetic compounds that resemble the structural intricacy of NPs - emerge as a useful source of bioactive chemical entities. The simplicity of the design principles for pNPs allows for a vast diversity of libraries to be envisioned, which is limited only by creativity and the synthetic tools available for generating them. In this study, we employed a combination of fragment- and reaction-based de novo designs to create pNPs that mimic the structural complexity of NPs while exploring uncharted chemical spaces. The library of pNPs synthesized via multicomponent reactions was subjected to phenotypic biological assays to evaluate their bioactivity. Among the tested compounds, two exhibited significant antiviral properties. Notably, one of these compounds demonstrated potent activity against both Zika virus (ZIKV) and SARS-CoV2, highlighting its potential as a broad-spectrum antiviral agent. Further investigation revealed that the antiviral activity of this compound might be associated with modulation of host cell lipid droplets, a novel mechanism of action that warrants further exploration.

A facile photochemical preparation of 4‐chromanone fused to estrone has successfully been achieved upon direct irradiation with light of 254 nm under a nitrogen atmosphere employing 3‐(2′‐alkenoyl)estrone and 3‐(2′‐alkenoyl)‐17‐ nor estrone derivatives as optimal substrates. The two‐phase acid‐ and base‐catalyzed method relies upon two consecutive pathways in a one‐pot fashion, involving the photo‐Fries rearrangement reaction and a catalyzed intramolecular oxa ‐Michael addition to afford the desired 4‐chromanone fused products in good yields.

The fusion of privileged heterocyclic scaffolds with biologically relevant structures represents a powerful strategy for developing novel hybrid molecules with enhanced properties. In this work, we report the preparation of flavone- and aurone-fused estrone derivatives via a sequential photo-Fries rearrangement and intramolecular annulation approach. The photo-Fries reaction of estrone 3-phenylpropiolate ester efficiently afforded ortho-hydroxyaryl phenylethynyl ketones, which were further cyclized under basic conditions. The selective formation of flavone (6-endo-dig) or aurone (5-exo-dig) derivatives could be tuned by varying the base strength and solvent conditions. Moreover, the aurone-fused estrone compounds exhibited visible-light-responsive photoisomerization, opening new possibilities for their application as photoswitchable steroidal systems. This photochemical strategy offers a versatile and efficient method to access functionalized steroidal derivatives with potential in chemical biology and material sciences. A comparative investigation on the preparation of chromenones and aurones fused to estrone has been developed applying two distinct approaches, viz. a two sequential steps and a one-pot two-step sequence. Both methods involve the photo-Fries rearrangement and the thermal intramolecular oxa-Michael cyclization reactions. The last step was found to depend on the strength of the chosen base, such as KOH or K2CO3, to promote the 6-endo-dig or 5-exo-dig cyclization, providing the desired products in good yields.

Steroid hormones are essential for the biological processes of eukaryotic organisms. The steroid endocrine system of C. elegans, which includes dafachronic acids (DA) and the nuclear receptor ceDAF-12, provides a simple model for exploring the role of steroid hormone signaling pathways in animals. In this study, we show for the first time the feasibility of designing synthetic steroids that can modulate different physiological processes, such as development, reproduction and ageing, in relation to ceDAF-12. Our results not only confirm the conclusions derived from genetic studies linking these processes but also provide new chemical tools to selectively manipulate them, as we found that different compounds produce different phenotypic results. The structures of these compounds are much more diverse than those of endogenous hormones and analogues previously described by other researchers, allowing further development of the chemical modulation of the steroid endocrine system in C. elegans and related nematodes.

The mitochondrial cysteine desulfurase NFS1 is an essential PLP-dependent enzyme involved in iron-sulfur cluster assembly. The enzyme catalyzes the desulfurization of the l-Cys substrate, producing a persulfide and l-Ala as products. In this study, we set the measurement of the product l-Ala by NMR in vitro by means of 1H NMR spectra acquisition. This methodology provided us with the possibility of monitoring the reaction in both fixed-time and real-time experiments, with high sensitivity and accuracy. By studying I452A, W454A, Q456A, and H457A NFS1 variants, we found that the C-terminal stretch (CTS) of the enzyme is critical for function. Specifically, mutation of the extremely conserved position W454 resulted in highly decreased activity. Additionally, we worked on two singular variants: "GGG" and C158A. In the former, the catalytic Cys-loop was altered by including two Gly residues to increase the flexibility of this loop. This variant had significantly impaired activity, indicating that the Cys-loop motions are fine-tuned in the wild-type enzyme. In turn, for C158A, we found an unanticipated increase in l-Cys desulfurase activity. Furthermore, we carried out molecular dynamics simulations of the supercomplex dedicated to iron-sulfur cluster biosynthesis, which includes NFS1, ACP, ISD11, ISCU2, and FXN subunits. We identified CTS as a key element that established interactions with ISCU2 and FXN concurrently; we found specific interactions that are established when FXN is present, reinforcing the idea that FXN not only forms part of the iron-sulfur cluster assembly site but also modulates the internal motions of ISCU2.

A protocol involving the irradiation of some 3-(2-alkenyl)estrone and 3-(2-alkenyl)-17-norestrone derivatives under a nitrogen atmosphere in organic solvents (both hexane and MeOH) followed by base-mediated intramolecular oxa-Michael cyclization reaction was investigated under steady-state conditions. The solvent effect and nature of the acyl group on the preparative photoreaction were studied and the multiplicity of the excited state was also demonstrated. The ortho-regioisomers were obtained in modest to good yields. Intramolecular based-mediate cyclization reaction of these synthons led to the formation of a set of novel substituted 4-chromanone moieties fused to estrone (and 17-norestrone) in good yields. This two-step sequential procedure involving a photochemical/intramolecular thermal cyclization strategy will be useful for the preparation of wide heterocyclic-fused-steroid compounds.

Mitochondrial adrenodoxins (ADXs) are small iron-sulfur proteins with electron transfer properties. In animals, ADXs transfer electrons between an adrenodoxin reductase (ADXR) and mitochondrial P450s, which is crucial for steroidogenesis. Here we show that a plant mitochondrial steroidogenic pathway, dependent on an ADXR-ADX-P450 shuttle, is essential for female gametogenesis and early embryogenesis through a maternal effect. The steroid profile of maternal and gametophytic tissues of wild-type (WT) and adxr ovules revealed that homocastasterone is the main steroid present in WT gametophytes and that its levels are reduced in the mutant ovules. The application of exogenous homocastasterone partially rescued adxr and P450 mutant phenotypes, indicating that gametophytic homocastasterone biosynthesis is affected in the mutants and that a deficiency of this hormone causes the phenotypic alterations observed. These findings also suggest not only a remarkable similarity between steroid biosynthetic pathways in plants and animals but also a common function during sexual reproduction.

Computer-aided drug discovery methods play a major role in the development of therapeutically important small molecules, but their performance needs to be improved. Molecular dynamics simulations in mixed solvents are useful in understanding protein-ligand recognition and improving molecular docking predictions. In this work, we used ethanol as a cosolvent to find relevant interactions for ligands toward protein kinase G, an essential protein of Mycobacterium tuberculosis (Mtb). We validated the hot spots by screening a database of fragment-like compounds and another one of known kinase inhibitors. Next, we performed a pharmacophore-guided docking simulation and found three low micromolar inhibitors, including one with a novel chemical scaffold that we expanded to four derivative compounds. Binding affinities were characterized by intrinsic fluorescence quenching assays, isothermal titration calorimetry, and the analysis of melting curves. The predicted binding mode was confirmed by X-ray crystallography. Finally, the compounds significantly inhibited the viability of Mtb in infected THP-1 macrophages.

The photochemical reaction of sulfonate steroids in a sustainable environment was carried out successfully under steady-state conditions. Significant selectivity in photoproduct formation was also observed.

Evolution of metabolism is a longstanding yet unresolved question, andseveral hypotheses were proposed to address this complex process from aDarwinian point of view. Modern statistical bioinformatic approaches targeted to the comparativeanalysis of genomes are being used to detect signatures of natural selection atthe gene and population level, as an attempt to understand the origin ofprimordial metabolism and its expansion. These studies, however, are still mainlycentered on genes and the proteins they encode, somehow neglecting the smallorganic chemicals that support life processes. In this work, we selectedsteroids as an ancient family of metaboliteswidely distributed in all eukaryotes and applied unsupervised machine learning techniques to reveal the traits that natural selection hasimprinted on molecular properties throughout the evolutionary process. Ourresults clearly show that sterols, the primal steroids that first appeared,have more conserved properties and that, from then on, more complex compoundswith increasingly diverse properties have emerged, suggesting that chemical diversificationparallels the expansion of biological complexity. In a wider context, thesefindings highlight the worth of chemoinformatic approaches to a better understanding the evolution ofmetabolism.

In this study, we carried out preparative and mechanistic studies on the photochemical reaction of a series of 3-acylestrone derivatives in confined and sustainable micellar environment under steady-state conditions and the results were compared with those obtained in cyclohexane solution. The aim of this work is mainly focused to show whether the nature of the surfactant (cationic, neutral and anionic) leads to noticeable selectivity in the photoproduct formation. The 3-acylestrone derivatives underwent the photo-Fries rearrangement, with concomitant homolytic fragmentation of the ester group and [1;3]-acyl migration. This pathway afforded the ortho-acyl estrone derivatives, the main photoproducts together with estrone. However, epimerization of the ortho regioisomer 2-acetylestrone and estrone through Norrish Type I photoreaction occurred involving the fragmentation of the C-α at the carbonyl group (C-17) of the steroid. UV-visible and 2D-NMR (NOESY) spectroscopies have been employed to measure the binding constant Kb and the location of the steroids within the hydrophobic core of the micelle.

The delta-amino acid 5-aminolevulinic acid (ALA), is the precursor of the endogenous photosensitiser Protoporphyrin IX (PpIX), and is currently approved for Photodynamic Therapy (PDT) of certain superficial cancers. However, ALA-PDT is not very effective in diseases in which T-cells play a significant role. Cutaneous T-cell lymphomas (CTCL) is a group of non-Hodgkin malignant diseases, which includes mycosis fungoides (MF) and Sézary syndrome (SS). In previous work, we have designed new ALA esters synthesised by three-component Passerini reactions, and some of them showed higher performance as compared to ALA. This work aimed to determine the efficacy as pro-photosensitisers of five new ALA esters of 2-hydroxy-N-arylacetamides (1f, 1 g, 1 h, 1i and 1 k) of higher lipophilicity than ALA in Myla cells of MF and HuT-78 cells of SS. We have also tested its effectiveness against ALA and the already marketed ALA methyl ester (Me-ALA) and ALA hexyl ester (He-ALA). Both cell Myla and SS cells were effectively and equally photoinactivated by ALA-PDT. Besides, the concentration of ALA required to induce half the maximal porphyrin synthesis was 209 μM for Myla and 169 μM for HuT-78 cells. As a criterion of efficacy, we calculated the concentration of the ALA derivatives necessary to induce half the plateau porphyrin values obtained from ALA. These values were achieved at concentrations 4 and 12 times lower compared to ALA, according to the derivative used. For He-ALA, concentrations were 24 to 25 times lower than required for ALA for inducing comparable porphyrin synthesis in both CTCL cells. The light doses for inducing 50% of cell death (LD50) for He-ALA, 1f, 1 g, 1 h and 1i were around 18 and 25 J/cm2 for Myla and HuT-78 cells respectively, after exposure to 0.05 mM concentrations of the compounds. On the other hand, the LD50s for the compound 1 k were 40 and 57 J/cm2 for Myla and HuT-78, respectively. In contrast, 0.05 mM of ALA and Me-ALA did not provoke photokilling since the concentration employed was far below the porphyrin saturation point for these compounds. Our results suggest the potential use of ALA derivatives for topical application in PDT treatment of MF and extracorporeal PDT for the depletion of activated T-cells in SS.

In this work, we describe how stereochemically complex polycyclic compounds can be generated by applying a synthetic sequence comprising an intramolecular Ugi reaction followed by a Pictet-Spengler cyclization on steroid-derived scaffolds. The resulting compounds, which combine a fragment derived from a natural product and a scaffold not found in nature. are both structurally distinct and globally similar to natural products at the same time, and interrogate an alternative region of the chemical space. One of the new compounds showed significant antiproliferative activity on HepG2 cells through a caspase-independent cell-death mechanism, an appealing feature when new antitumor compounds are searched.

Rac1 (Ras-related C3 botulinum toxin substrate1), is a member of the family of Rho GTPases involved in the dynamic control ofcytoskeleton reorganization and other fundamental cellular functions includinggrowth, motility and survival. Aberrant activity of Rac1 and its regulators iscommon in human cancer. In particular, deregulated expression/activity of RacGuanine nucleotide Exchange Factors (GEFs), responsible for Rac activation, hasbeen largely associated to a metastatic phenotype and drug resistance. Thus, the development of novel Rac1-GEF interactioninhibitors is a promising strategy for finding new preclinical candidates. Inthis work, we have studied structure-activity relationships within a new familyof N,N’-disubstituted guanidine as Rac1-GEF protein-protein interactioninhibitors, starting from our first developed member 1A-116. We found that newanalogue 1D-142, bearing a pyridine ring instead of benzene ring, presentsimproved antiproliferative activity in human cancer cell lines and higherpotency as Rac1-GEF interaction inhibitor in vitro. In addition, 1D-142 reducesTNFα-induced NF-κB nuclear translocation, a mechanisms mediated by Rac1 duringcell proliferation and migration in NSCLC. Notably, 1D-142 was used to show forthe first time the application of a Rac1 inhibitor in a lung cancer animalmodel.

TheUgi-Smiles multicomponent reaction is a powerful tool for obtaining N-arylaminesfrom acidic phenols and has been widely used for gaining access to structurallydiverse scaffolds. In this work we demonstrate that this isocyanide-based couplingcan be used for the straightforward and efficient synthesis of N,N-disubstituted3-aminoestrones, steroidal derivatives that usually show interesting biologicalactivities. In this sense, we analyzed the scope and limitations of thereaction when applied to aromatic nitrosteroids and found that the outcome is highly influenced by the stericeffects imposed by the steroidal skeleton. After optimization of the reactionconditions a set of thirteen N-substituted 3-aminoestromes were obtained, some ofthem with interesting antiproliferative and antiviral activities.

Fil: Arbeitman, C.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biociencias, Biotecnologia y Biologia Traslacional; Argentina

Herein, the synthesis and characterization of the first family of multipodal ligands with a Tröger's base framework designed for the preparation of luminescent lanthanide(III) complexes are reported. Eight ligands were designed and synthesized using different strategies, including alkylation reactions, amide couplings, and Ugi multicomponent reactions. All the ligands bear carboxylate groups for the coordination of the lanthanide(III) ions, with the lanthanide(III)-sensitizing units consisting of the Tröger's base framework itself or attached benzamides. Upon irradiation of the chromophoric ligands, green terbium(III) emission was efficiently generated, whereas europium(III) emission was negligible. The geometry and substitution pattern of the ligands allow control of the stoichiometry of the species formed and the TbIII luminescence sensitization efficiency, showing that para-substitution patterns are more efficient than meta substitution for the formation of coordination compounds with lower TbIII /ligand ratio. We propose that the species formed are self-assembled 2:2 or 2:4 metallosupramolecular structures.

Direct irradiation of estrone aryl and methyl sulfonates in different organic solvents under nitrogen atmosphere was investigated under steady-state conditions. The estrone derivatives reacted efficiently through the photo-Fries rearrangement reaction involving [1;3]-sulfonyl migration providing the ortho-sulfonyl estrone derivatives and estrone as the photoproducts. In addition, estrone and 2-arylsulfonyl estrone derivatives were epimerized involving a Norrish Type-I reaction. Chemical quenching and photosensitization experiments on the photoreaction have been also carried out to establish the photoreactive excited state. Likewise, the solvent effect and the nature of the sulfonyl group on the photoreactions have been also studied.