N-Metallocenoylsphingosines as targeted ceramidase inhibitors: Syntheses and antitumoral effects.

Three N-metallocenoylsphingosines with variance in the central metal (Fe, Co, Ru), the charge (neutral or cationic), and the arene ligands (Cp2, Cp*Ph) were synthesized from serine and metallocene carboxylic acids as substrate-analogous inhibitors of human acid ceramidase (AC). Their inhibitory potential was examined using the recombinant full length ASAH1 enzyme, expressed and secreted from High Five insect cells, and the fluorescent substrate Rbm14-12. All complexes inhibited AC, most strongly so ruthenium(II) complex 13a. Some antitumoral effects of the complexes, such as the interference with the microtubular and F-actin cytoskeleton of cancer cells, were correlated to their AC-inhibition, whereas others, e.g. their cytotoxicity and their induction of caspase-3/-7 activity in cancer cells, were not. All complexes accumulated preferentially in the lysosomes of cancer cells like their target AC, arrested the cells in G1 phase of the cell cycle, and displayed cytotoxicity with mostly single-digit micromolar IC50 values while inducing cancer cell apoptosis.

Synthesis and anticancer profile of novel sphingoid base-like compounds with a quaternary stereocentre.

The synthesis of novel sphingoid base-like compounds with a quaternary stereocentre was achieved in a sequence featuring [3,3]-sigmatropic rearrangements and olefin cross-metathesis transformation as the key reaction steps, which were accompanied by the rational selection of suitable functional group transformations. The stereochemistry of the desired tetra-substituted carbon bearing nitrogen functionality was determined via NOESY experiments of the advanced oxazolidine-2-thiones. Cell viability experiments revealed significant antiproliferative/cytotoxic activity of the target compounds 7, ent-7 and 29 against the Jurkat cell line, with the IC50 values of 6.6 µM, 5.6 µM and 6.1 µM, respectively.

Synthesis and biological evaluation of 2-epi-jaspine B analogs as selective sphingosine kinase 1 inhibitors.

2-Epi-jaspine B is an isomer of the natural product jaspine B and shows certain selectivity for SphK1 and potent antitumor activity. Based on the crystal structure of SphK1, we transformed the structure of 2-epi-jaspine B and modified the hydrophobic side chain to obtain a series of 2-epi-jaspine B analogs. The MTT assay was used to examine the antitumor activities of these analogs. We identified a novel 2-epi-jaspine B analog YHR17, which has potent antiproliferative activities for tested cell lines with IC50 values that ranged from 0.68 to 5.68 µM and inhibited the proliferation of the A375 cell line by affecting the cell cycle and apoptosis. Furthermore, YHR17 inhibited SphK1 with more than 125-fold selectivity over SphK2.

Synthetic analogues of marine cytotoxic jaspine B and its stereoisomers.

Synthetic analogues of the cytotoxic jaspine B and its stereochemical congeners have become an attractive target in the synthetic organic community owing to the search for novel therapeutic candidates with more potent anticancer activity, as cancer is the second leading cause of death worldwide. This review article provides insights into the different approaches and strategies available in the literature for the construction of jaspine B-related compounds.

Stereoselective synthesis and antiproliferative activity of the isomeric sphinganine analogues.

A flexible synthetic approach to biologically active sphingoid base-like compounds with a 3-amino-1,2-diol framework was achieved through a [3,3]-sigmatropic rearrangement and late stage olefin cross-metathesis as the key transformations. The stereochemistry of the newly created stereogenic centre was assigned via a single crystal X-ray analysis of the (4S,5R)-5-(hydroxymethyl)-4-vinyloxazolidine-2-thione. In order to rationalise the observed stereoselectivity of the aza-Claisen rearrangement, DFT calculations were carried out. The targeted isomeric sphingoid bases were screened in vitro for anticancer activity on a panel of seven human malignant cell lines. Cell viability experiments revealed that C17-homologues are more active than their C12 congeners.

In search of constrained FTY720 and phytosphingosine analogs as dual acting anticancer agents targeting metabolic and epigenetic pathways.

A series of compounds containing pyrrolidine and pyrrolizidine cores with appended hydrophobic substituents were prepared as constrained analogs of FTY720 and phytosphingosine. The effect of these compounds on the viability of cancer cells, on downregulation of the nutrient transport systems, and on their ability to cause vacuolation was studied. An attempt to inhibit HDACs with some phosphate esters of our analogs was thwarted by our failure to reproduce the reported inhibitory action of FTY720-phosphate.

Alkyne-Tagged Analogue of Jaspine†B: New Tool for Identifying Jaspine†B Mode of Action.

The first biologically relevant clickable probe related to the antitumor marine lipid jaspine B is reported. The concise synthetic route to both enantiomers relied on the supercritical fluid chromatography (SFC) enantiomeric resolution of racemic materials. The eutomeric dextrogyre derivative represents the first jaspine B analogue with enhanced cytotoxicity with IC50 down to 30 nm. These enantiomeric probes revealed a chiralitydependent cytoplasmic imaging of U2OS cancer cells by in situ click labeling.

Introduction of a Polar Functional Group to the Lipid Tail of 4-epi-Jaspine B Affects Sphingosine Kinase Isoform Selectivity.

Sphingosine kinases (SphKs) are key enzymes that regulate sphingosine 1-phosphate production levels, and are involved in a range of cellular processes. Focusing on a hydrophilic residue in the hydrophobic binding pocket of SphKs, we designed and synthesized 4-epi-jaspine B derivatives containing a polar functional group in the lipid tail. A biological evaluation revealed that the introduction of ether groups to the lipid tail of 4-epi-jaspine B modulated its isoform selectivity toward SphKs.

Fluorinated triazole-containing sphingosine analogues. Syntheses and in vitro evaluation as SPHK inhibitors.

Sphingosine analogues with a rigid triazole moiety in the aliphatic chain and systematic modifications in the polar head and different degrees of fluorination at the terminus of the alkylic chain were synthesized from a common alkynyl aziridine key synthon. This key synthon was obtained by enantioselective organocatalyzed aziridination and it was subsequently ring opened in a regioselective manner in acidic medium. Up to 16 sphingosine analogues were prepared in a straightforward manner. The in vitro activity of the obtained products as SPHK1 and SPHK2 inhibitors was evaluated, displaying comparable activity to that of DMS.

Synthesis of the cytotoxic phytosphingosines and their isomeric analogues.

A straightforward synthesis of l-lyxo- and l-xylo-phytosphingosine along with their isomeric analogues has been accomplished. The salient features of this approach are the utilization of [3,3]-sigmatropic rearrangements to install a C-N bond and application of a late stage Wittig or OCM reaction to incorporate the hydrophobic chain unit. The final compounds were evaluated regarding their ability to alter both leukaemia and solid tumor cancer cells viability.

Synthesis and characterization of some atypical sphingoid bases.

Sphingolipids are ubiquitous and abundant components of all eukaryotic and some prokaryotic organisms. Sphingolipids show a large structural variety not only between the different species, but also within an individual cell. This variety is not limited to alterations in the polar headgroups of e.g. glycosphingolipids, but also affects the lipophilic anchors comprised of different fatty acids on the one hand and different sphingoid bases on the other hand. The structural variations within different sphingoid bases e.g. in pathogens can be used to identify novel biomarkers and drug targets and the specific change in the profile of common and uncommon sphingolipids are associated with pathological conditions like diabetes or cancer. Therefore, the emerging field of sphingolipidomics is dedicated to collect data on the sphingolipidome of a cell and hence to assign changes therein to certain states of a cell or to pathological conditions. This powerful tool however is still limited by the availability of structural information about the individual lipid species as well as by the availability of appropriate internal standards for quantification. Herein we describe the synthesis of a variety of 1-deoxy-sphingoid bases. 1-DeoxySphingolipids have recently acquired significant attention due to its pathological role in the rare inherited neuropathy, HSAN1 but also as predictive biomarkers in diabetes type II. Some of the compounds synthesized and characterized herein, have been used and will be used to elucidate the correct structure of these disease-related lipids and their metabolites.

A rapid synthesis of sphingosine from phytosphingosine.

A simple and efficient protocol for the synthesis of a sphingosine starting from cost-effective phytosphingosine has been described. Two alternative synthetic pathway have been disclosed based on the use of two different kinds of protective groups for the protection of the amino group in the phytosphingosine. The protected phytosphingosine was subsequently transformed into sphingosine in 5 steps i.e. protection of the amine group, protection of 1,3-diol, leaving group insertion, elimination, and one-pot deprotection.

Discovery of novel jaspine B analogues as autophagy inducer.

A series of 2-alkylaminomethyl jaspine B analogues were synthesized and evaluated for their cytotoxic effects on human lung adenocarcinoma, breast cancer, and prostate cancer cell lines and a mouse melanoma cell line. Most of the compounds exhibited moderate to good activity against the cancer cell lines. Compound 7f showed the best overall cytotoxicity on PC-3 cells (IC50 = 0.85 µM). Further mechanistic studies revealed that compound 7f induced marked changes in PC-3 cell morphology, disrupted the mitochondrial membrane potential, and increased expression of the autophagy proteins beclin-1, LC3, and P62.

Stereoselective preparation of quaternary 2-vinyl sphingosines and ceramides and their effect on basal sphingolipid metabolism.

The dicyclohexylborane-mediated addition of allene 1 to (E)-2-tridecenal affords a quaternary protected 2-amino-2-vinyl-1,3-diol in good yield as a single diastereomer. This compound is readily transformed into the four stereoisomers of the quaternary (E)-2-vinyl analogs of sphingosine. The metabolic fate and the effect of these compounds on the basal sphingolipid metabolism in human A549 lung adenocarcinoma cells has been studied, together with the ceramide analog of the most relevant vinylsphingosine derivative.

Multicomponent cis- and trans-Aziridinatons in the Syntheses of All Four Stereoisomers of Sphinganine.

All four stereoisomers of sphinganine can be synthesized by a multicomponent aziridination of an aldehyde, an amine and an α-diazo carbonyl compound mediated by a BOROX catalyst with high asymmetric induction (≥96% ee). The threo isomers are available from ring-opening of cis-aziridines by an oxygen nucleophile with inversion at the C-3 position and the erythro-isomers are likewise available from trans-aziridines.

Synthetic Studies on a Pachastrissamine Sulfur Analogue: Synthesis of a 4-epi-Sulfur Analogue.

A versatile synthetic procedure for a sulfur analogue of pachastrissamine (jaspine B), which involves the tandem thiolation-cyclization of a 1,4-ditosylate to construct a tetrahydrothiophene ring, was developed. Nucleophilic amino substitution of a tetrahydrothiophene-4-sulfonate with unexpected retention of the configuration afforded the sulfur analogue of 4-epi-pachastrissamine.

Practical Synthesis of Pachastrissamine (Jaspine B), 2-epi-Pachastrissamine, and the 2-epi-Pyrrolidine Analogue.

The practical syntheses of pachastrissamine (jaspine B), 2-epi-pachastrissamine, and the 2-epimer of the pyrrolidine analogue were accomplished via the stereoselective reduction of an allylketone derived from commercially available diethyl D-tartrate and the cross-metathesis of an allyltetrahydrofuran or allypyrrolidine with 1-tridecene as key steps.

Total synthesis and antiproliferative/cytotoxic profiling of 2-epi-jaspine B.

A straightforward access to 2-epi-jaspine B (4.HCl) has been developed. Key to the approach was the use of Overman rearrangement for the instalment of a stereocentre bearing a nitrogen atom. Subsequent rational execution of the stereoselective transformations furnished the functionalized scaffold 38, whose coupling with a lipophilic segment under Wittig conditions, followed by deprotection and a THF core construction, completed the convergent synthesis of 2-epimer of 1. The final anhydrophytosphingosine 4.HCl was screened for its antiproliferative/cytotoxic activity employing multiple human cancer cell lines. In vitro evaluation revealed that 2-epi-jaspine B exhibited significant antitumour growth inhibitory activity against all used cells.

Marine cytotoxic jaspine B and its stereoisomers: biological activity and syntheses.

Conformationally constrained sphingolipids such as anhydrophytosphingosines represented by jaspine B (also known as pachastrissamine) and its stereoisomers have become an attractive and timely target for total synthesis due to their significant biological activity as well as the unique structures. This review article describes the biological activity and chemistry of the natural jaspine B and its seven stereoisomers.

Bifunctional Sphingosine for Cell-Based Analysis of Protein-Sphingolipid Interactions.

Sphingolipids are essential structural components of cellular membranes and are crucial regulators of cellular processes. While current high-throughput approaches allow for the systematic mapping of interactions of soluble proteins with their lipid-binding partners, photo-cross-linking is the only technique that enables for the proteome-wide mapping of integral membrane proteins with their direct lipid environment. Here, we report the synthesis of a photoactivatable and clickable analog of sphingosine (pacSph). When administered to sphingosine-1-phosphate lyase deficient cells, pacSph allows its metabolic fate and the subcellular flux of de novo synthesized sphingolipids to be followed in a time-resolved manner. The chemoproteomic profiling yielded over 180 novel sphingolipid-binding proteins, of which we validated a number, demonstrating the unique value of this technique as a discovery tool. This work provides an important resource for the understanding of the global cellular interplay between sphingolipids and their interacting proteins.