Synthesis of 28a-homoselenolupanes and 28a-homoselenolupane saponins

Selective transformations of friedelanes isolated from cork smoker wash solids

Friedelin (1) and 3-acetoxyfriedel-3-en-2-one (4), commonly known as friedelane triterpenoids, have been isolated from cork smoker wash solids (also known as black wax) on a multi-gram scale. These compounds are valuable starting materials for the synthesis of new friedelane derivatives. Stereoselective reduction of friedelin by treatment with LiAlH4, sodium, or catalytic hydrogenation results in the formation of both isomers of friedelinol (5 and 7) in excellent yields. Similarly, the reduction of 3-acetoxyfriedel-3-en-2-one gave epi-cerin (14) and a series of isomeric 2,3-diols or α-hydroxyketones. These transformations provide the most straightforward and convenient methods for the synthesis of A-ring functionalised friedelane derivatives using easily accessible starting materials.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Small molecule selenium-containing compounds: Recent development and therapeutic applications

Selenium (Se) is an essential micronutrient of organism and has important function. It participates in the functions of selenoprotein in several manners. In recent years, Se has attracted much attention because of its therapeutic potential against several diseases. Many natural and synthetic organic Se-containing compounds were studied and explored for the treatment of cancer and other diseases. Studies have showed that incorporation of Se atom into small molecules significantly enhanced their bioactivities. In this paper, according to different applications and structural characteristics, the research progress and therapeutic application of Se-containing compounds are reviewed, and more than 110 Se-containing compounds were selected as representatives which showed potent activities such as anticancer, antioxidant, antifibrolytic, antiparasitic, antibacterial, antiviral, antifungal and central nervous system related effects. This review is expected to provide a basis for further study of new promising Se-containing compounds.

Oxidative Functionalization of Trinor-18α-olean-17(22)-ene Derivatives. Annulation of the E-Ring by an Intramolecular Aldol Reaction

cis-Dihydroxylation of trinor-18α-olean-17(22)-ene 2 with osmium tetroxide led to diol 9. Its cleavage with lead tetraacetate gave tetracyclic ketoaldehyde 10. By comparison, the ozonation of trinor-18α-olean-17(22)-ene 2 in the presence of p-toluenesulfonic acid gave the corresponding ketoacetal 12. Both products were subjected to an intramolecular aldol reaction under the acidic conditions and yielded unusual triterpenes bearing a bicyclo[4.3.1]decane fragment (22). Further manipulation of the protective groups afforded compounds useful in triterpene synthesis, especially in the preparation of potentially biologically active saponins based on a tetracyclic terpene core.

On-water synthesis of glycosyl selenocyanate derivatives and their application in the metal free organocatalytic preparation of nonglycosidic selenium linked pseudodisaccharide derivatives

Glycosyl selenocyanate derivatives were prepared in very good yield by the treatment of glycosyl halide or triflate derivatives with potassium selenocyanate in water. A variety of selenium linked pseudodisaccharide derivatives were prepared in excellent yield using glycosyl selenocyanates as stable building blocks in the presence of hydrazine hydrate under metal-free organocatalytic reaction conditions.

Rearrangements of the Betulin Core. Synthesis of Terpenoids Possessing the Bicyclo[3.3.1]nonane Fragment by Rearrangement of Lupane-Type Epoxides

The rearrangements of dihydrobetulin, dihydrobetulinic acid, and abeo-lupane epoxides under acidic conditions (HCl, montmorillonite K10, and BF₃·Et₂O) were studied. The treatment of dihydrobetulin with HCl or K10 produced abeo-lupane olefins. Their epoxidation afforded epoxides, which, in the presence of protic or Lewis acids, rearranged to dienes or lupanes bearing a bicyclo[3.3.1]nonane fragment. The structure of final products depended on the nature of the catalyst. The HCl promoted 1,4-elimination of water, whereas in the presence of BF₃·Et₂O bond migration took place preferentially. Montmorillonite K10 favored cyclization to bicyclononane.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Room-Temperature Pd-Catalyzed Synthesis of 1-(Hetero)aryl Selenoglycosides

A general protocol for functionalization of an anomeric selonate anion at room temperature has been reported. By using the PdG3 XantPhos catalyst, the cross-coupling between the in situ-generated glycosyl selenolate and a broad range of (hetero)aryl and alkenyl iodides furnished a series of functionalized selenoglycosides in excellent yields with perfect control of the anomeric configuration.

New lupane bidesmosides exhibiting strong cytotoxic activities in vitro

Triterpene bidesmosides are considered as highly cytotoxic saponins, usually less toxic against normal cells than monodesmosides, and less haemolytic. Biological activity of the betulin-type bidesmosides, rarely found in Nature, and seldom prepared due to serious synthetic problems, is poorly recognized. We report herein a protocol for the preparation of disubstituted lupane saponins (betulin bidesmosides) by treatment of their benzoates with potassium carbonate in dichloromethane / methanol solution. Cytotoxicity of all compounds was tested in vitro for a series of cancer cell lines, as well as normal human skin BJ fibroblasts. Presence of l-rhamnose moiety is crucial for cytotoxicity of betulin bidesmosides. On the other hand, l-arabinose fragment connected to lupane C-3 carbon atom significantly decreases activity. Presented results clearly show that betulin bidesmosides have significant clinical potential as anticancer agents.

Selenium and selenoproteins: it's role in regulation of inflammation

Abstract

Selenium is an essential immunonutrient which holds the human’s metabolic activity with its chemical bonds. The organic forms of selenium naturally present in human body are selenocysteine and selenoproteins. These forms have a unique way of synthesis and translational coding. Selenoproteins act as antioxidant warriors for thyroid regulation, male-fertility enhancement, and anti-inflammatory actions. They also participate indirectly in the mechanism of wound healing as oxidative stress reducers. Glutathione peroxidase (GPX) is the major selenoprotein present in the human body, which assists in the control of excessive production of free radical at the site of inflammation. Other than GPX, other selenoproteins include selenoprotein-S that regulates the inflammatory cytokines and selenoprotein-P that serves as an inducer of homeostasis. Previously, reports were mainly focused on the cellular and molecular mechanism of wound healing with reference to various animal models and cell lines. In this review, the role of selenium and its possible routes in translational decoding of selenocysteine, synthesis of selenoproteins, systemic action of selenoproteins and their indirect assimilation in the process of wound healing are explained in detail. Some of the selenium containing compounds which can acts as cancer preventive and therapeutics are also discussed. These compounds directly or indirectly exhibit antioxidant properties which can sustain the intracellular redox status and these activities protect the healthy cells from reactive oxygen species induced oxidative damage. Although the review covers the importance of selenium/selenoproteins in wound healing process, still some unresolved mystery persists which may be resolved in near future.

Graphic abstract

Synthesis and Glycan-Protein Interaction Studies of Se-Sialosides by 77Se NMR

To expand the potential of Se-carbohydrates for multifunctional mimicry of sugars, herein we addressed the synthesis of the highly challenging and biologically significant Se-glycosides of sialic acid (Se-sialosides). An α-sialyl selenolate anion generated in situ smoothly reacted with electrophiles to give α-Se-sialosides as single stereoisomers. A Se-sialoside was sequentially incorporated with selenium, producing a triseleno-sialoside. This molecule was used as a ⁷⁷Se NMR-active handle for studying glycan-protein interaction, revealing different binding profiles of sialic acid binding proteins.

Synthesis, cytotoxicity and anti-inflammatory activity of rhamnose-containing ursolic and betulinic acid saponins

Betulinic acid and ursolic acid are ubiquitous, naturally-occurring triterpenoids exhibiting various pharmacological activities including cytotoxic and anti-inflammatory activities. However, these triterpenoids display unfavorable pharmacokinetic properties as well as low aqueous solubility. It has been shown that the presence of α-l-rhamnose moieties positively modulates the anticancer activity of secondary metabolites. Herein we report the synthesis and in vitro evaluation of cytotoxic and anti-inflammatory activities of a series of rhamnose-containing ursolic and betulinic acid saponins. Relying on Schmidt's normal and inverse procedures, monorhamnosides, (1→4)-linked dirhamnosides as well as branched trirhamnosides and tetrarhamnosides were synthesized in high yields with full control of stereoselectivity. A betulinic acid saponin bearing a 3-O-α-l-rhamnopyranosyl-(1→4)-α-l-rhamnopyranosyl residue was found to be a potent cytotoxic agent against human colorectal adenocarcinoma cells without damaging the healthy cells (selectivity ratio > 20) whereas rhamnose-containing ursolic acid saponins potently inhibited NO overproduction induced by LPS-stimulated macrophages. Our results reveal that rhamnose-containing ursolic and betulinic acid saponins represent promising therapeutic agents.

Rhamnose-containing saponins featuring betulinic and ursolic acid as aglycones were synthesized using both Schmidt's normal and inverse procedures. Some of these synthetic saponins exhibited selective cytotoxic and/or anti-inflammatory activities.

Organic selenium compounds as potential chemotherapeutic agents for improved cancer treatment

Selenium(Se)-containing compounds have attracted a growing interest as anticancer agents over recent decades, with mounting reports demonstrating their high efficacy and selectivity against cancer cells. Typically, Se compounds exert their cytotoxic effects by acting as pro-oxidants that alter cellular redox homeostasis. However, the precise intracellular targets, signalling pathways affected and mechanisms of cell death engaged following treatment vary with the chemical properties of the selenocompound and its metabolites, as well as the cancer model that is used. Naturally occurring organic Se compounds, besides encompassing a significant antitumor activity with an apparent ability to prevent metastasis, also seem to have fewer side effects and less systemic effects as reported for many inorganic Se compounds. On this basis, many novel organoselenium compounds have also been synthesized and examined as potential chemotherapeutic agents. This review aims to summarize the most well studied natural and synthetic organoselenium compounds and provide the most recent developments in our understanding of the molecular mechanisms that underlie their potential anticancer effects.

New selenosteroids as antiproliferative agents

Starting from natural steroids (diosgenin, hecogenin, smilagenin, estrone), we have prepared a wide panel of selenoderivatives, including benzoselenazolones, selenosemicarbazones, isoselenocyanates, selenoureas, selenocyanates and diselenides, with the aim of developing new families of potential chemotherapeutic agents. The modification of the organoselenium moieties, and their position on the steroid provided valuable information concerning the antiproliferative activities. Among all the families accessed herein, the best profile was achieved for selenoureas on the A ring of estrone, which exhibited GI₅₀ values in the range 2.0-4.1 μM for all the tested tumor cell lines, with increased potency compared with commonly used chemotherapeutic agents, like 5-fluorouracil and cisplatin. Cell cycle analysis revealed that selenoureas induced accumulation of cells in the G₁ phase of the cell cycle in the breast cancer cell lines HBL-100 and T-47D; therefore, a different mechanism than cisplatin, that induces cell cycle accumulation in the S phase as a result of DNA damage, must be involved. In the rest of the tumor cells, a slight increase of the S compartment was observed. Moreover, selenosteoids turned out to be excellent glutathione peroxidase (GPx) mimics for the catalytic removal of deleterious H₂O₂ (t_1/2 8.0-22.5 min) and alkyl peroxides (t_1/2 23.0-38.9 min) when used in substoichiometric amounts (1% molar ratio), thus providing a valuable tool for reducing the intrinsic oxidative stress in tumor progression.