Beyond Pseudo-natural Products: Sequential Ugi/Pictet-Spengler Reactions Leading to Steroidal Pyrazinoisoquinolines That Trigger Caspase-Independent Death in HepG2 Cells.

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.

Exploring lectin-like activity of the S-layer protein of Lactobacillus acidophilus ATCC 4356.

The surface layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling, proteinaceous subunits non-covalently bound to the outmost bacterial cell wall envelope and is involved in the adherence of bacteria to host cells. We have previously described that the S-layer protein of L. acidophilus possesses anti-viral and anti-bacterial properties. In this work, we extracted and purified S-layer proteins from L. acidophilus ATCC 4356 cells to study their interaction with cell wall components from prokaryotic (i.e., peptidoglycan and lipoteichoic acids) and eukaryotic origin (i.e., mucin and chitin), as well as with viruses, bacteria, yeast, and blood cells. Using chimeric S-layer fused to green fluorescent protein (GFP) from different parts of the protein, we analyzed their binding capacity. Our results show that the C-terminal part of the S-layer protein presents lectin-like activity, interacting with different glycoepitopes. We further demonstrate that lipoteichoic acid (LTA) serves as an anchor for the S-layer protein. Finally, a structure for the C-terminal part of S-layer and possible binding sites were predicted by a homology-based model.

A Minimalist Approach to the Design of Complexity-Enriched Bioactive Small Molecules: Discovery of Phenanthrenoid Mimics as Antiproliferative Agents.

Over the last decades, much effort has been devoted to the design of the "ideal" library for screening, the most promising strategies being those which draw inspiration from biogenic compounds, as the aim is to add biological relevance to such libraries. On the other hand, there is a growing understanding of the role that molecular complexity plays in the discovery of new bioactive small molecules. Nevertheless, the introduction of molecular complexity must be balanced with synthetic accessibility. In this work, we show that both concepts can be efficiently merged-in a minimalist way-by using very simple guidelines during the design process along with the application of multicomponent reactions as key steps in the synthetic process. Natural phenanthrenoids, a class of plant aromatic metabolites, served as inspiration for the synthesis of a library in which complexity-enhancing features were introduced in few steps using multicomponent reactions. These resulting chemical entities were not only more complex than the parent natural products, but also interrogated an alternative region of the chemical space, which led to an outstanding hit rate in an antiproliferative assay: four out of twenty-six compounds showed in vitro activity, one of them being more potent than the clinically useful drug 5-fluorouracil.

Multicomponent synthesis of 4,4-dimethyl sterol analogues and their effect on eukaryotic cells.

Most sterols, such as cholesterol and ergosterol, become functional only after the removal of the two methyl groups at C-4 from their biosynthetic precursors. Nevertheless, some findings suggest that 4,4-dimethyl sterols might be involved in specific physiological processes. In this paper we present the synthesis of a collection of analogues of 4,4-dimethyl sterols with a diamide side chain and a preliminary analysis of their in vitro activity on selected biological systems. The key step for the synthesis involves an Ugi condensation, a versatile multicomponent reaction. Some of the new compounds showed antifungal and cytotoxic activity.

Sterol analogues with diamide side chains interfere with the intracellular localization of viral glycoproteins.

The need to develop novel antiviral agents encouraged us to assess the antiviral activity of synthetic sterol analogues with a diamide side chains. Cytotoxicity and antiviral activity of a family of azasterol previously synthesized was evaluated against herpes simplex virus 1 (HSV-1) (KOS and B2006) and vesicular stomatitis virus (VSV). This family of compounds was extended by the synthesis of novel analogs using an Ugi multicomponent reaction and their ability to inhibit viral multiplication was also evaluated. The results show that some of the compounds tested exert an antiviral activity. Besides, the effect of the azasterols on the intracellular localization of viral glycoproteins was examined. Strikingly, alteration on the glycoprotein D (gD) of HSV-1 fluorescence pattern was observed with both the antiherpetic compounds and the inactive azasterols.

1-Cinnamoyl-3,11-dihydroxymeliacarpin delays glycoprotein transport restraining virus multiplication without cytotoxicity.

The 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), isolated from extracts of Melia azedarach L., displays antiviral and immunomodulating properties. CDM is the first reported tetranortriterpenoid responsible for the alkalinization of intracellular compartments affecting both, viral endocytic and exocytic pathways. Considering that viral glycoprotein synthesis is completely dependent upon cellular membrane trafficking, we questioned whether CDM might also interfere with the normal transport of cellular glycoproteins. This study demonstrates that CDM promoted a transient block in the transport of two cellular glycoproteins, the transferrin receptor (TfR) and TNF-alpha. Nevertheless, CDM did not affect the transferrin binding ability of TfR and did not impede the TNF-alpha secretion. On the other hand, CDM disturbed the intracellular localization of capsid, glycoprotein and tegument proteins simultaneously in the same HSV-1 infected cells. Besides, we show that concanamycin A and monensin provoke a permanent blockage of viral and cellular glycoproteins, in contrast to the delay observed after CDM treatment. Thus, the delay on glycoprotein transport caused by CDM would account for the strong inhibition on virus multiplication without interfering with the bioactivity of cellular glycoproteins.

A natural tetranortriterpenoid with immunomodulating properties as a potential anti-HSV agent.

Meliacine (MA), an antiviral principle present in partially purified leaf extracts of Melia azedarach L., prevents the development of herpetic stromal keratitis (HSK) in mice by diminishing the viral load in the eye and the severity of lesions caused by a virus-induced immunopathological reaction. The tetranortriterpenoid 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), obtained from MA purification, displays anti-herpetic activity and impedes nuclear factor kappaB (NF-kappaB) activation in HSV-1 infected conjunctival cells. To extend our understanding about CDM biological properties, we investigated its anti-HSV-1 activity as well as the effect on NF-kappaB activation and cytokine secretion induced by viral (HSV-1) and no-viral (LPS) stimuli, in corneal cells and macrophages. CDM exerted a potent anti-HSV-1 effect on corneal cells and inhibited NF-kappaB translocation to the nucleus, leading to a decrease in IL-6 production. Besides, CDM seemed to modulate IL-6 and TNF-alpha responses in macrophages, whether they were infected with HSV-1 or stimulated with LPS. However, CDM did not affect NF-kappaB activation in these cells, suggesting that an alternative NF-kappaB cell signaling pathway would be involved in the modulation of cytokine production. We conclude that, in addition to its antiviral effect, CDM would be acting as an immunomodulating compound which would be responsible for the improvement of murine HSK already reported.

1-Cinnamoyl-3,11-dihydroxymeliacarpin is a natural bioactive compound with antiviral and nuclear factor-kappaB modulating properties.

We have reported the isolation of the tetranortriterpenoid 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM) from partially purified leaf extracts of Melia azedarach L. (MA) that reduced both, vesicular stomatitis virus (VSV) and Herpes simplex virus type 1 (HSV-1) multiplication. CDM blocks VSV entry and the intracellular transport of VSV-G protein, confining it to the Golgi apparatus, by pre- or post-treatment, respectively. Here, we report that HSV-1 glycoproteins were also confined to the Golgi apparatus independently of the nature of the host cell. Considering that MA could be acting as an immunomodulator preventing the development of herpetic stromal keratitis in mice, we also examined an eventual effect of CDM on NF-kappaB signaling pathway. CDM is able to impede NF-kappaB activation in HSV-1-infected conjunctival cells and leads to the accumulation of p65 NF-kappaB subunit in the cytoplasm of uninfected treated Vero cells. In conclusion, CDM is a pleiotropic agent that not only inhibits the multiplication of DNA and RNA viruses by the same mechanism of action but also modulates the NF-kappaB signaling pathway.

Block of vesicular stomatitis virus endocytic and exocytic pathways by 1-cinnamoyl-3,11-dihydroxymeliacarpin, a tetranortriterpenoid of natural origin.

Previously, it has been shown that 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), a natural compound isolated from leaf extracts of Melia azedarach L., inhibits the vesicular stomatitis virus (VSV) multiplication cycle when added before or after infection. Here, we have established that the lack of VSV protein synthesis in CDM pre-treated Vero cells is ascribed to the inhibition of an initial step during virus multiplication, although indirect immunofluorescence (IFI) studies confirmed that the binding and uptake of [(35)S]methionine-labelled VSV was not affected by CDM pre-treatment. Instead, our findings revealed that this compound impedes the uncoating of VSV nucleocapsids in pre-treated Vero cells, since the antiviral action of CDM was partially reversed by inducing VSV direct fusion at the plasma membrane, and VSV M protein fluorescence was confined to the endosomes, even 2 h post-internalization. Furthermore, CDM induced cytoplasmic alkalinization, as shown by acridine orange staining, consistent with the inhibition of virus uncoating. Although VSV proteins are synthesized when CDM is added after infection, IFI studies revealed that G protein was absent from the surface of infected cells and co-localized with a Golgi marker. Therefore, CDM inhibits the transport of G protein to the plasma membrane. Taken together, these findings indicate that CDM exerts its antiviral action on the endocytic and exocytic pathways of VSV by pre- or post-treatment, respectively.

An antiviral principle present in a purified fraction from Melia azedarach L. leaf aqueous extract restrains herpes simplex virus type 1 propagation.

Meliacine (MA), an antiviral principle isolated from leaves of Melia azedarach L., exhibits potent antiviral activity against herpes simplex virus type 1 (HSV-1) by inhibiting specific infected-cell polypeptides (ICPs) produced late in infection. Some of these are involved in DNA synthesis and in the assembly of nucleocapsids. The present report provides additional evidence to elucidate the mode of action of MA against HSV-1. Time-of-addition experiments confirmed that MA affects a late event in the multiplication cycle of HSV-1. We showed that MA diminished the synthesis of viral DNA and inhibited the spread of infectious viral particles when HSV-1 that expresses beta-galactosidase activity was used. In addition, the lack of a protein with an apparent MW of 55 KD was detected in MA-treated cell extracts. Ultrastructural analysis of infected cells showed that, in the case of MA treatment, a large number of unenveloped nucleocapsids accumulated in the cytoplasm and a minor proportion of mature virus was found in cytoplasmic vesicles.These findings suggest that MA exerts an antiviral action on both the synthesis of viral DNA and the maturation and egress of HSV-1 during the infection of Vero cells.