Icilio Guareschi and his amazing "1897 reaction".

Organic chemistry honors Icilio Guareschi (1847-1918) with three eponymic reactions, the best known ones being the Guareschi synthesis of pyridones and the Guareschi-Lustgarten reaction. A third Guareschi reaction, the so-called "Guareschi 1897 reaction", is one of the most unusual reactions in organic chemistry, involving the radical-mediated paradoxical aerobic generation of hydrocarbons in near-neutral water solution. A discussion of the mechanism of this amazing reaction, the only metal-free process that generates hydrocarbons, and the implications of the approach in biology and geosciences mirrors the multifaceted scientific personality of the discoverer. Thus, Guareschi's eclectic range of activities spans a surprising variety of topics, overcoming the boundaries of the traditional partition of chemistry into organic, inorganic, and analytical branches and systematically crosses the divide between pure and applied science as well as between the history of chemistry and the personal contributions to its development.

A multicomponent approach in the discovery of indoleamine 2,3-dioxygenase 1 inhibitors: Synthesis, biological investigation and docking studies.

Indoleamine 2,3-dioxygenase plays a crucial role in immune tolerance and has emerged as an attractive target for cancer immunotherapy. In this study, the Passerini and Ugi multicomponent reactions have been employed to assemble a small library of imidazothiazoles that target IDO1. While the p-bromophenyl and the imidazothiazole moieties have been kept fixed, a full SAR study has been performed on the side-chain, leading to the discovery of nine compounds with sub-micromolar IC50 values in the enzyme-based assay. Compound 7d, displaying a α-acyloxyamide substructure, is the most potent compound, with an IC50 value of 0.20 µM, but a low activity in a cell-based assay. Compound 6o, containing a α-acylaminoamide moiety, shows an IC50 value of 0.81 µM in the IDO1-based assay, a full biocompatibility at 10 µM, together with a modest inhibitory activity in A375 cells. Molecular docking studies show that both 7d and 6o display a unique binding mode in the IDO1 active site, with the side-chain protruding in an additional pocket C, where a crucial hydrogen bond is formed with Lys238. Overall, this work describes an isocyanide based-multicomponent approach as a straightforward and versatile tool to rapidly access IDO1 inhibitors, providing a new direction for their future design and development.

The Guareschi Pyridine Scaffold as a Valuable Platform for the Identification of Selective PI3K Inhibitors.

A novel series of 4-aryl-3-cyano-2-(3-hydroxyphenyl)-6-morpholino-pyridines have been designed as potential phosphatidylinositol-3-kinase (PI3K) inhibitors. The compounds have been synthesized using the Guareschi reaction to prepare the key 4-aryl-3-cyano-2,6-dihydroxypyridine intermediate. A different selectivity according to the nature of the aryl group has been observed. Compound 9b is a selective inhibitor against the PI3Kα isoform, maintaining a good inhibitory activity. Docking studies were also performed in order to rationalize its profile of selectivity.

ZINClick: a database of 16 million novel, patentable, and readily synthesizable 1,4-disubstituted triazoles.

Since Professors Sharpless, Finn, and Kolb first introduced the concept of "click reactions" in 2001 as powerful tools in drug discovery, 1,4-disubstituted-1,2,3-triazoles have become important in medicinal chemistry due to the simultaneous discovery by Sharpless, Fokin, and Meldal of a perfect click 1,3-dipolar cycloaddition reaction between azides and alkynes catalyzed by copper salts. Because of their chemical features, these triazoles are proposed to be aggressive pharmacophores that participate in drug-receptor interactions while maintaining an excellent chemical and metabolic profile. Surprisingly, no virtual libraries of 1,4-disubstituted-1,2,3-triazoles have been generated for the systematic investigation of the click-chemical space. In this manuscript, a database of triazoles called ZINClick is generated from literature-reported alkynes and azides that can be synthesized within three steps from commercially available products. This combinatorial database contains over 16 million 1,4-disubstituted-1,2,3-triazoles that are easily synthesizable, new, and patentable! The structural diversity of ZINClick ( http://www.symech.it/ZINClick ) will be explored. ZINClick will also be compared to other available databases, and its application during the design of novel bioactive molecules containing triazole nuclei will be discussed.

De novo computer-aided design of novel antiviral agents.

Computer-aided drug design techniques have become an integral part of the drug discovery process. In particular, de novo methodologies can be useful to identify putative ligands for a specific target relying only on the structural information of the target itself. Here we discuss the basic de novo approaches available and their application in antiviral drug design.:

Replacement of the double bond of antitubulin chalcones with triazoles and tetrazoles: Synthesis and biological evaluation.

In the chalcone scaffold, it is thought that the double bond is an important structural linker but it is likely not essential for the interaction with tubulin. Yet, it may be a potential site of metabolic degradation and interaction with biological nucleophiles. In this letter, we have replaced this olefinic portion of chalcones with two metabolically stable and chemically inert heterocyclic rings, namely triazole or tetrazole. Yet, our biologic data suggest that, unlike in other antitubulinic structures, the olephinic ring might not be merely a structural linker.

Groebke multicomponent reaction and subsequent nucleophilic aromatic substitution for a convenient synthesis of 3,8-diaminoimidazo[1,2-a]pyrazines as potential kinase inhibitors.

In a program aimed at discovering novel protein kinase inhibitors, a convenient synthesis of 3,8-diaminoimidazo[1,2-a]pyrazines has been developed exploiting the isocyanide-based multicomponent Blackburn reaction, followed by a nucleophilic aromatic substitution with ammonia or primary and secondary amines. The potential of the reported scaffold is strengthened by the inhibition of STAT5-dependent transcription displayed by four of the synthesized compounds.

Solution-phase parallel synthesis and biological evaluation of combretatriazoles.

Combretastatin A-4 is an antitumoral and antitubulin agent that is active only in its cis configuration. In the present manuscript, we have synthesized cis-locked combretastatins containing a triazole ring (combretatriazoles). To achieve this, we have developed a column chromatography-free parallel solution-phase synthesis that exploits the reaction between azides and alpha-keto phosphorus ylids, which is known to regioselectively generate the 1,5-disubstituted triazoles. The prepared compounds were screened as antitubulinic agents, allowing us to identify three new compounds with high potency, two of which show a new mechanism of action that induces cells to appear multinucleated and display a high number of mitotic spindles.

Targeting Transient Receptor Potential Vanilloid 1 (TRPV1) Channel Softly: The Discovery of Passerini Adducts as a Topical Treatment for Inflammatory Skin Disorders.

Despite being an old molecule, capsaicin is still a hot topic in the scientific community, and the development of new capsaicinoids is a promising pharmacological approach in the management of skin disorders related to inflammation and pruritus. Here we report the synthesis and the evaluation of capsaicin soft drugs that undergo deactivation by the hydrolyzing activity of skin esterases. The implanting of an ester group in the lipophilic moiety of capsaicinoids by the Passerini multicomponent reaction affords both agonists and antagonists that retain transient receptor potential vanilloid 1 channel (TRPV1) modulating activity and, at the same time, are susceptible to hydrolysis. The most promising antagonist identified shows in vivo anti-nociceptive activity on pruritus and hyperalgesia without producing hyperthermia, thus validating it as novel treatment for dermatological conditions that implicate TRPV1 channel dysfunction.

Pyrtriazoles, a Novel Class of Store-Operated Calcium Entry Modulators: Discovery, Biological Profiling, and in Vivo Proof-of-Concept Efficacy in Acute Pancreatitis.

In recent years, channels that mediate store-operated calcium entry (SOCE, i.e., the ability of cells to sense a decrease in endoplasmic reticulum luminal calcium and induce calcium entry across the plasma membrane) have been associated with a number of disorders, spanning from immune disorders to acute pancreatitis and have been suggested to be druggable targets. In the present contribution, we exploited the click chemistry approach to synthesize a class of SOCE modulators where the arylamide substructure that characterizes most inhibitors so far described is substituted by a 1,4-disubstituted 1,2,3-triazole ring. Within this series, inhibitors of SOCE were identified and the best compound proved effective in an animal model of acute pancreatitis, a disease characterized by a hyperactivation of SOCE. Strikingly, two enhancers of the process were discovered, affording invaluable research tools to further explore the (patho)physiological role of capacitative calcium entry.

Identification of a Potent Phosphoinositide 3-Kinase Pan Inhibitor Displaying a Strategic Carboxylic Acid Group and Development of Its Prodrugs.

Activation of the phosphoinositide 3-kinase (PI3K) pathway is a key signaling event in cancer, inflammation, and other proliferative diseases. PI3K inhibitors are already approved for some specific clinical indications, but their systemic on-target toxicity limits their larger use. In particular, whereas toxicity is tolerable in acute treatment of life-threatening diseases, this is less acceptable in chronic conditions. In the past, the strategy to overcome this drawback was to block selected isoforms mainly expressed in leukocytes, but redundancy within the PI3K family members challenges the effectiveness of this approach. On the other hand, decreasing exposure to selected target cells represents a so-far unexplored alternative to circumvent systemic toxicity. In this manuscript, we describe the generation of a library of triazolylquinolones and the development of the first prodrug pan-PI3K inhibitor.

Identification of Novel Triazole-Based Nicotinamide Phosphoribosyltransferase (NAMPT) Inhibitors Endowed with Antiproliferative and Antiinflammatory Activity.

Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme involved in the recycling of nicotinamide to maintain adequate NAD levels inside the cells. It has been postulated to be a pharmacological target, as it is overexpressed in cancer cells as well as in inflammatory diseases. We describe the synthesis and characterization of a novel class of one-digit nanomolar NAMPT inhibitors based on in vitro characterization. The most active compound tested, 30c, displayed activity in xenograft and allograft models, strengthening the potential of NAMPT inhibitors as antitumoral drugs. Furthermore, in the present contribution we describe the ability of 30c to significantly improve the outcome of colitis in mice. Given that this is the first report of an effect of NAMPT inhibitors in colitis, this result paves the way for novel applications for this class of compounds.

Rapid synthesis of triazole-modified resveratrol analogues via click chemistry.

Resveratrol is a phytoalexin able to display an array of biological activities. We decided to replace the double bond with a triazole ring using the archetypical click reaction: the Huisgen [3 + 2] cycloaddition. Seventy-two triazole derivatives were synthesized via a parallel combinatorial approach. Preliminary data suggest that this procedure can lead to the synthesis of compounds that display some, but not all, of resveratrol's actions with increased potency.

Synthesis and cytotoxic evaluation of combretafurans, potential scaffolds for dual-action antitumoral agents.

We have synthesized rigid analogues of combretastatin bearing a furan ring in place of the olefinic bridge. These compounds are cytotoxic at nanomolar concentrations in neuroblastoma cells, display a similar structure-activity relationship compared to combretastatin A4, and inhibit tubulin polymerization. We also show that the furan ring can be further functionalized. Thus, it is possible that combretafurans could act as scaffolds for the development of dual-action antitumoral agents.

Synthesis and cytotoxic evaluation of combretafurazans.

Combretastatin A-4 is an antitumoral and antitubulin agent that is active only in its cis configuration. In the present manuscript, we have synthesized cis-locked combretastatins embodying a furazan ring (combretafurazans). To achieve this, we have developed a new strategy that exploits the dehydration of vicinal dioximes using the Mitsunobu reaction. Among the advantages of following such a strategy are the mild conditions used for the construction of the diarylfurazan derivatives, allowing for the presence of highly functionalized substrates and deactivated aromatic rings. Combretafurazans are more potent in vitro cytotoxic compounds compared to combretastatins in neuroblastoma cells, yet maintaining similar structure-activity relationship and pharmacodynamic profiles.

Synthesis and antimalarial activities of some furoxan sulfones and related furazans.

Furoxan derivatives bearing a sulfone moiety at position 3 or 4 were synthesized and tested for their antimalarial action on the chloroquine-sensitive D10 and the chloroquine-resistant W2 strains of Plasmodium falciparum. The furazan analogues were considered for comparison. The most active compounds were the products in which the -SO2R groups are at the 3-position of the furoxan system. These latter substances displayed an antimalarial activity in the microM range, possibly related in part to their ability to release NO.

Design, synthesis, and biological evaluation of combretabenzodiazepines: a novel class of anti-tubulin agents.

In the present manuscript, starting from the 1,4-benzodiazepin-2-one nucleus, a privileged structure in medicinal chemistry, we have synthesized a novel class of cis-locked combretastatins named combreatabenzodiazepines. They show similar cytotoxic and antitubulin activity compared to combretastatin A-4 in neuroblastoma cells, showing a better pharmacokinetic profile. This class of compounds has therefore the potential for further development as antitubulin agents.

A new class of NO-donor H3-antagonists.

Synthesis and pharmacological characterisation of a series of compounds obtained by joining, through appropriate spacers, NO-donor furoxan and nitrooxy moieties to the imidazole ring, as well as their structurally related analogues devoid of NO-donating properties are described. All the products were studied for their capacity to interact with H3-receptors present on the guinea-pig ileum and with H2-receptors present on guinea-pig right atrium. The whole series of products displayed reversible H3-antagonistic activity. No activity on H2-receptors was observed when the products were tested at 10 microM concentration. Many of the products were also able to induce partial relaxation when added to the bath after electrical contraction of the guinea-pig ileum during the study of their H3-antagonism. This phenomenon seems to be dependent on various factors; for some compounds it proved to be dependent on NO-mediated sGC activation, for other products it could be due to their weak M3-antagonism. The investigation of the lipophilic-hydrophilic balance of all the products indicates, for many of them, an ideal value to cross the blood-brain barrier.

Are 1,4- and 1,5-disubstituted 1,2,3-triazoles good pharmacophoric groups?

Over the last decade, 1,2,3-triazoles have received increasing attention in medicinal chemistry thanks to the discovery of the highly useful and widely applicable 1,3-dipolar cycloaddition reaction between azides and alkynes (click chemistry) catalyzed by copper salts and ruthenium complexes. After a decade of medicinal chemistry research on 1,2,3-triazoles, we feel that the time is ripe to demonstrate the real ability of this heterocycle to participate in important and pivotal binding interactions with biological targets while maintaining a good pharmacokinetic profile. In this study, we retrieved and analyzed X-ray crystal structures of complexes between 1,2,3-triazoles and either proteins or DNA to understand the pharmacophoric role of the triazole. Furthermore, the metabolic stability, the capacity to inhibit cytochromes, and the contribution of 1,2,3-triazoles to the overall aqueous solubility of compounds containing them have been analyzed. This information should furnish fresh insight for medicinal chemists in the design of novel bioactive molecules that contain the triazole nucleus.