Amadeu Llebaria

Synthesis and biological properties of Pachastrissamine (jaspine B) and diastereoisomeric jaspines

The synthesis of isomeric jaspines (anhydro phytosphingosines), arising from intramolecular cyclization of the corresponding phytosphingosines with different configurations at C3 and C4 positions of the sphingoid backbone, is reported. Natural jaspine B is the most cytotoxic isomer on A549 cells and it induces cell death in a dose-dependent manner. The cytotoxicity of jaspine B has been correlated with a significant increase of intracellular dihydroceramides, which seem to play an active role in autophagy.

Synthesis and Biological Activity of a Novel Inhibitor of Dihydroceramide Desaturase

A novel mechanism‐based dihydroceramide desaturase inhibitor (XM462) in which the substrate C5 methylene group is replaced by a sulfur atom is reported. Dihydroceramide desaturase inhibition occurred both in vitro and in cultured cells with IC50 values of 8.2 and 0.78 μM, respectively, at a substrate concentration of 10 μM. In vitro experiments showed that XM462 produced a mixed‐type inhibition (Ki=2 μM, α=0.83). LC‐MS analyses showed that accumulation of endogenous dihydroceramides occurred in cells upon treatment with XM462 in serum‐free medium, whereas ceramides built up in controls. In addition, XM462 was found to be metabolised to its 1‐glucosyl and 1‐phosphocholine derivatives, and to the products of N‐deacylation and reacylation with palmitoyl and stearoyl groups. In Jurkat A3 cells cultured in serum‐free medium, viability, as the percentage of trypan blue unstained cells in total cells, was reduced upon XM462 treatment (5 μM, 24 h), but not in controls. The interest of this compound is discussed.

Blockade of arachidonic acid incorporation into phospholipids induces apoptosis in U937 promonocytic cells

Arachidonic acid (AA) participates in a reacylation/deacylation cycle of membrane phospholipids, the so-called Lands cycle, that serves to keep the concentration of this free fatty acid in cells at a very low level. To manipulate the intracellular AA level in U937 phagocytes, we have used several pharmacological strategies to interfere with the Lands cycle. We used inhibitors of the AA reacylation pathway, namely thimerosal and triacsin C, which block the conversion of AA into arachidonoyl-CoA, and a CoA-independent transacylase inhibitor that blocks the movement of AA within phospholipids. In addition, we used cells overexpressing group VIA phospholipase A2, an enzyme with key roles in controlling basal fatty acid deacylation reactions in phagocytic cells. All of these different strategies resulted in the expected increase of cellular free AA but also in the induction of cell death by apoptosis. Moreover, when used in combination with any of the aforementioned drugs, AA itself was able to induce apoptosis at doses as low as 10 μM. Blocking cyclooxygenase or lipoxygenases had no effect on the induction of apoptosis by AA. Collectively, these results indicate that free AA levels within the cells may provide an important cellular signal for the onset of apoptosis and that perturbations of the mechanisms controlling AA reacylation, and hence free AA availability, may decisively affect cell survival.

An allosteric modulator to control endogenous G protein-coupled receptors with light

Controlling drug activity with light offers the possibility of enhancing pharmacological selectivity with spatial and temporal regulation, thus enabling highly localized therapeutic effects and precise dosing patterns. Here we report on the development and characterization of what is to our knowledge the first photoswitchable allosteric modulator of a G protein-coupled receptor. Alloswitch-1 is selective for the metabotropic glutamate receptor mGlu5 and enables the optical control of endogenous mGlu5 receptors.

Versatile synthesis of bicyclo[4.3.0]nonenes and bicyclo[4.4.0]decenes by a domino Heck-Diels-Alder reaction

Abstract Various 2-bromo-1,6- and 2-bromo-1,7-dienes were cyclized under palladium catalysis producing vicinal exodimethylenecycloalkanes which reacted with dienophiles (either present during the cyclization or added afterwards in a one-pot process) to give bicyclo[4.3.0]nonene and bicyclo[4.4.0]-decene derivatives in good to excellent yields. Among the examples reported are the first cases of intramolecular Heck reactions with a (bromomethylene)cyclopropane starter or/and a methylenecyclopropane terminator which occur without ring opening of the cyclopropyl group.

Chemical tools to investigate sphingolipid metabolism and functions

Sphingolipids comprise an important group of biomolecules, some of which have been shown to play important roles in the regulation of many cell functions. From a structural standpoint, they all share a long 2‐amino‐1,3‐diol chain, which can be either saturated (sphinganine), hydroxylated at C4 (phytosphingosine), or unsaturated at C4 (sphingosine) as in most mammalian cells. N‐acylation of sphingosine leads to ceramide, a key intermediate in sphingolipd metabolism that can be enzymatically modified at the C1‐OH position to other biologically important sphingolipids, such as sphingomyelin or glycosphingolipids. In addition, both ceramide and sphingosine can be phosphorylated at C1‐OH to give ceramide‐1‐phosphate and sphingosine‐1‐phosphate, respectively. To better understand the biological and biophysical roles of sphingolipids, many efforts have been made to design synthetic analogues as chemical tools able to unravel their structure–activity relationships, and to alter their cellular levels. This last approach has been thoroughly studied by the development of specific inhibitors of some key enzymes that play an important role in biosynthesis or metabolism of these intriguing lipids. With the above premises in mind, the aim of this review is to collect, in a systematic way, the recent efforts described in the literature leading to the development of new chemical entities specifically designed to achieve the above goals.

NKT TCR Recognition of CD1d-α-C-Galactosylceramide

NKT cells respond to a variety of CD1d-restricted glycolipid Ags that are structurally related to the prototypic Ag α-galactosylceramide (α-GalCer). A modified analog of α-GalCer with a carbon-based glycosidic linkage (α-C-GalCer) has generated great interest because of its apparent ability to promote prolonged, Th1-biased immune responses. In this study, we report the activation of spleen NKT cells to α-C-GalCer, and related C-glycoside ligands, is weaker than that of α-GalCer. Furthermore, the Vβ8.2 and Vβ7 NKT TCR affinity for CD1d–α-C-GalCer, and some related analogs, is ∼10-fold lower than that for the NKT TCR–CD1d–α-GalCer interaction. Nevertheless, the crystal structure of the Vβ8.2 NKT TCR–CD1d–α-C-GalCer complex is similar to that of the corresponding NKT TCR–CD1d–α-GalCer complex, although subtle differences at the interface provide a basis for understanding the lower affinity of the NKT TCR–CD1d–α-C-GalCer interaction. Our findings support the concept that for CD1d-restricted NKT cells, altered glycolipid ligands can promote markedly different responses while adopting similar TCR-docking topologies.

Polyhydroxylated Bicyclic Isoureas and Guanidines Are Potent Glucocerebrosidase Inhibitors and Nanomolar Enzyme Activity Enhancers in Gaucher Cells

Four diastereomeric series of N-alkylated [6+5] bicyclic isoureas having hydroxyl substituents mimicking glucose hydroxyl groups have been synthesized as potential β-glucocerebrosidase (GCase) inhibitors with the aim of developing pharmacological chaperones for enzyme deficiency in Gaucher disease (GD). The bicyclic compounds differ either by the configuration of the ring fusion carbon atoms or by the nature of the N-alkyl substituents. When assayed for effects on GCase activity, the isoureas displayed selective inhibition of GCase with low micromolar to nanomolar IC(50)s in isolated enzyme experiments. One of the series of isoureas, a family having a specific cis ring fusion, exhibited strong inhibition of recombinant GCase activity with K(i) values in the 2-42 nM range. In addition, the [6+5] bicyclic guanidine derivatives with a substitution pattern analogous to the most active isoureas were also found to be potent inhibitors of GCase with K(i) values between 3 and 10 nM. Interestingly, the active bicyclic isoureas and guanidines also behaved as GCase inhibitors in wild-type human fibroblasts at nanomolar concentrations. The potential of these compounds as pharmaceutical chaperones was determined by analyzing their capacity for increasing GCase activity in GD lymphoblasts derived from N370S and L444P variants, two of the most prevalent Gaucher mutations. Six compounds were selected from the different bicyclic isoureas and guanidines obtained that increased GCase activity by 40-110% in N370S and 10-50% in L444P cells at low micromolar to nanomolar concentrations following a 3 day incubation. These results describe a promising series of potent GCase ligands having the cellular properties required for pharmacological chaperones.

Potent Aminocyclitol Glucocerebrosidase Inhibitors are Subnanomolar Pharmacological Chaperones for Treating Gaucher Disease

Amino-myo-inositol derivatives have been found to be potent inhibitors of glucocerebrosidase (GCase), the β-glucosidase enzyme deficient in Gaucher disease (GD). When tested using lymphoblasts derived from patients with GD homozygous for N370S or L444P mutations, the compounds enhanced GCase activity at very low concentrations. The most potent inhibitor, (1R,2S,3R,4S,5S,6R)-5-(nonylamino)-6-(nonyloxy)cyclohexane-1,2,3,4-tetraol had a K(i) of 1 nM using isolated enzyme and an IC(50) of 4.3 nM when assayed in human fibroblast cell culture. This aminocyclitol produced maximum increases of GCase activities of 90% in N370S lymphoblasts at 1 nM and 40% in L444P at 0.01 nM following a three-day incubation. In addition to inhibitory potency, this compound has the permeability, subcellular distribution, and cell metabolism characteristics that are important for use as a pharmacological chaperone. It is a remarkable finding that picomolar concentrations of aminocyclitols are sufficient to enhance activity in the L444P variant, which produces a severe neuronopathic form of GD without clinical treatment.

New Glucocerebrosidase Inhibitors by Exploration of Chemical Diversity of N-Substituted Aminocyclitols Using Click Chemistry and in Situ Screening

A library of aminocyclitols derived from CuAAC reaction between N-propargylaminocyclitol 4 and a series of azides [1-25] is described and tested against GCase. Azides have been chosen from a large collection of potential candidates that has been filtered according to physical and reactivity constraints. A synthetic methodology has been optimized in order to avoid the use of protecting groups on the aminocyclitol scaffold. Because the reaction can be carried out in an aqueous system, the resulting library members can be screened in situ with minimal manipulation. From the preliminary GCase inhibition data, the most potent library members have been individually resynthesized for further biological screening and complete characterization. Some of the library members have shown biochemical data (IC(50), K(i), and stabilization ratio) similar or superior to those reported for NNDNJ. Docking studies have been used to postulate ligand-enzyme interactions to account for the experimental results.