Anna Bernardi

Inhibition of DC-SIGN-mediated HIV infection by a linear trimannoside mimic in a tetravalent presentation

HIV infection is pandemic in humans and is responsible for millions of deaths every year. The discovery of new cellular targets that can be used to prevent the infection process represents a new opportunity for developing more effective antiviral drugs. In this context, dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN), a lectin expressed at the surface of immature dendritic cells and involved in the initial stages of HIV infection, is a promising therapeutic target. Herein we show the ability of a new tetravalent dendron containing four copies of a linear trimannoside mimic to inhibit the trans HIV infection process of CD4+ T lymphocytes at low micromolar range. This compound presents a high solubility in physiological media, a neglectable cytotoxicity, and a long-lasting effect and is based on carbohydrate-mimic units. Notably, the HIV antiviral activity is independent of viral tropism (X4 or R5). The formulation of this compound as a gel could allow its use as topical microbicide.

Stereoselective synthesis of statin analogues.

Abstract Statin analogues can be synthesized stereoselectively (diastereomeric ratios up to 4:1) starting from malic acid. The key step involves an unprecedented cis-selective allylation of an α-alkoxy N-acyliminium ion.

Enantioselective mukaiyama-michael reactions of 2-carbomethoxy cyclopentenone catalyzed by chiral bis(Oxazoline)-Cu(II) complexes

Abstract The conjugate addition of propionate silylketene acelal 1 to 2-carbomethoxy cyclopentenone is promoted by bis(oxazoline)-Cu(II) complexes with high diastereoselectivity and good enantiomeric excesses. The absolute configuration of the product can be controlled by varying the copper counterion. A catalytic version of the reaction was developed, which gave ketoacid 5a in 72% d.e. and 63% e.e.

Pseudosaccharide Functionalized Dendrimers as Potent Inhibitors of DC-SIGN Dependent Ebola Pseudotyped Viral Infection

The development of compounds with strong affinity for the receptor DC-SIGN is a topic of remarkable interest due to the role that this lectin plays in several pathogen infection processes and in the modulation of the immune response. DC-SIGN recognizes mannosylated and fucosylated oligosaccharides in a multivalent manner. Therefore, multivalent carbohydrate systems are required to interact in an efficient manner with this receptor and compete with the natural ligands. We have previously demonstrated that linear pseudodi- and pseudotrisaccharides are adequate ligands for DC-SIGN. In this work, we show that multivalent presentations of these glycomimetics based on polyester dendrons and dendrimers lead to very potent inhibitors (in the nanomolar range) of cell infection by Ebola pseudotyped viral particles by blocking DC-SIGN receptor. Furthermore, SPR model experiments confirm that the described multivalent glycomimetic compounds compete in a very efficient manner with polymannosylated ligands for binding to DC-SIGN.

Lewis acid mediated aldol condensations using thioester silyl ketene acetals

Abstract BF3-OEt2 mediated thioester silylketene acetal additions to aldehydes are stereoconvergent and give high anti-syn ratios and good chemical yields. An acyclic transition state model was hypothesized in order to account for the observed selectivity. Theoretical methods (MNDO) were used to evaluate the ground-state conformations of thioester silylketene acetals and to model the acyclic transition states. Lewis acid mediated additions of thioester silylketene acetals to 2-phenylpropion-aldehyde (BF3-OEt2), O-benzyl lactic aldehyde (SnCl4), 2,3-0,O-dibenzyl glyceraldehyde (SnCl4), and 3-benzyloxy-2-methylpropionaldehyde (TiCl4) were found to be highly diastereoface selective so that three contiguous stereocenters could be established. With α-, β- , or α,β-alkoxy aldehydes, relative stereoselection (chelation) effectively controls internal stereolection. The ground state conformations of the chiral aldehydes were studied using molecular mechanics (MM2).

1,2-mannobioside mimic: Synthesis, DC-SIGN interaction by NMR and docking, and antiviral activity

The design and preparation of carbohydrate ligands for DC‐SIGN is a topic of high interest because of the role played by this C‐type lectin in immunity and infection processes. The low chemical stability of carbohydrates against enzymatic hydrolysis by glycosylases has stimulated the search for new alternatives more stable in vivo. Herein, we present a good alternative for a DC‐SIGN ligand based on a mannobioside mimic with a higher enzymatic stability than the corresponding disaccharide. NMR and docking studies have been performed to study the interaction of this mimic with DC‐SIGN in solution demonstrating that this pseudomannobioside is a good ligand for this lectin. In vitro studies using an infection model with Ebola pseudotyped virus demonstrates that this compound presents an antiviral activity even better than the corresponding disaccharide and could be an interesting ligand to prepare multivalent systems with higher affinities for DC‐SIGN with potential biomedical applications.

A multivalent inhibitor of the DC-SIGN dependent uptake of HIV-1 and Dengue virus

DC-SIGN is a C-type lectin receptor on antigen presenting cells (dendritic cells) which has an important role in some viral infection, notably by HIV and Dengue virus (DV). Multivalent presentation of carbohydrates on dendrimeric scaffolds has been shown to inhibit DC-SIGN binding to HIV envelope glycoprotein gp120, thus blocking viral entry. This approach has interesting potential applications for infection prophylaxis. In an effort to develop high affinity inhibitors of DC-SIGN mediated viral entry, we have synthesized a group of glycodendrimers of different valency that bear different carbohydrates or glycomimetic DC-SIGN ligands and have studied their DC-SIGN binding activity and antiviral properties both in an HIV and a Dengue infection model. Surface Plasmon Resonance (SPR) competition studies have demonstrated that the materials obtained bind efficiently to DC-SIGN with IC50s in the μm range, which depend on the nature of the ligand and on the valency of the scaffold. In particular, a hexavalent presentation of the DC-SIGN selective antagonist 4 displayed high potency, as well as improved accessibility and chemical stability relative to previously reported dendrimers. At low μm concentration the material was shown to block both DC-SIGN mediated uptake of DV by Raji cells and HIV trans-infection of T cells.

Interfering with the Sugar Code: Design and Synthesis of Oligosaccharide Mimics

Oligosaccharide determinants of cellular glycoconjugates interact with protein receptors triggering a variety of cellular responses within a wide range of physiological and pathological processes and with exquisitely tuned selectivity. This has led to the formulation of the hypothesis that a sugar code exists and that sugar-binding proteins (lectins) act to decipher it and translate it into biological responses. Interference with these recognition events by functional mimics of carbohydrates could thus be used to modulate or alter signal transmission, or to prevent the onset of diseases. Attempts to design and prepare glycomimetic inhibitors of well-known target lectins (cholera toxin, DC-SIGN) are reviewed in this concept paper.

Synthesis of Novel DC-SIGN Ligands with an α-Fucosylamide Anchor

The dendritic cell‐specific intercellular adhesion molecule (ICAM) 3‐grabbing nonintegrin (DC‐SIGN) is a C‐type lectin that appears to perform several different functions. Besides mediating adhesion between dendritic cells and T lymphocytes, DC‐SIGN recognizes several pathogens some of which, including HIV, appear to exploit it to invade host organisms. The intriguing diversity of the roles attributed to DC‐SIGN and their therapeutic implications have stimulated the search for new ligands that could be used as biological probes and possibly as lead compounds for drug development. The natural ligands of DC‐SIGN consist of mannose oligosaccharides or fucose‐containing Lewis‐type determinants. Using the known 3D structure of the Lewis‐x trisaccharide, we have identified some monovalent α‐fucosylamides that bind to DC‐SIGN with inhibitory constants 0.4–0.5 mM, as determined by SPR, and have characterized their interaction with the protein by STD NMR spectroscopy. This work establishes for the first time α‐fucosylamides as functional mimics of chemically and enzymatically unstable α‐fucosides and describes interesting candidates for the preparation of multivalent systems able to block the receptor DC‐SIGN with high affinity and with potential biomedical applications.

Asymmetric synthesis of functionalized α -amino-β-hydroxy acids via chiral norephedrine-derived oxazolidines

Abstract Both anti and syn enantiomerically pure functionalized α -amino-β-hydroxy acids and derivatives were synthesized starting from norephedrine-derived oxazolidine (1). The key-steps of the synthesis were the nucleophilic epoxidation of (1) and the nucleophilic opening of epoxy acid (3) with ammonia, both reactions proved regio- and diastereospecific. High yield preparation of the target anti aldehyde (9) was accomplished using standard procedures. The complementary syn aldehyde (23) was obtained via alkaline isomerization of the cis oxazolidinone (13) to the trans one. The aldehyde function of (9) and (23) provides a useful handle for manipulation to more complex structures, allowing potential access to a range of optically pure α -amino-β-hydroxy acids. The formal total synthesis of the monocyclic β-lactam antibiotic “carumonam” was accomplished using the present methodology.