Targeting dihydroceramide desaturase 1 (Des1): Syntheses of ceramide analogues with a rigid scaffold, inhibitory assays, and AlphaFold2-assisted structural insights reveal cyclopropenone PR280 as a potent inhibitor.

Dihydroceramide desaturase 1 (Des1) catalyzes the formation of a CC double bond in dihydroceramide to furnish ceramide. Inhibition of Des1 is related to cell cycle arrest and programmed cell death. The lack of the Des1 crystalline structure, as well as that of a close homologue, hampers the detailed understanding of its inhibition mechanism and difficults the design of new inhibitors, thus making Des1 a strategic target. Based on previous structure-activity studies, different ceramides containing rigid scaffolds were designed. The synthesis and evaluation of these compounds as Des1 inhibitors allowed the identification of PR280 as a better Des 1 inhibitor in vitro (IC50 = 700 nM) than GT11 and XM462, the current reference inhibitors. This cyclopropenone ceramide was obtained in a 6-step synthesis with a 24 % overall yield. The highly confident 3D structure of Des1, recently predicted by AlphaFold2, served as the basis for conducting docking studies of known Des1 inhibitors and the ceramide derivatives synthesized by us in this study. For this purpose, a complete holoprotein structure was previously constructed. This study has allowed a better knowledge of key ligand-enzyme interactions for Des1 inhibitory activity. Furthermore, it sheds some light on the inhibition mechanism of GT11.

Probing Site-Selective Conjugation Chemistries for the Construction of Homogeneous Synthetic Glycodendriproteins.

Methods that site-selectively attach multivalent carbohydrate moieties to proteins can be used to generate homogeneous glycodendriproteins as synthetic functional mimics of glycoproteins. Here, we study aspects of the scope and limitations of some common bioconjugation techniques that can give access to well-defined glycodendriproteins. A diverse reactive platform was designed via use of thiol-Michael-type additions, thiol-ene reactions, and Cu(I)-mediated azide-alkyne cycloadditions from recombinant proteins containing the non-canonical amino acids dehydroalanine, homoallylglycine, homopropargylglycine, and azidohomoalanine.

Revealing 2-dimethylhydrazino-2-alkyl alkynyl sphingosine derivatives as sphingosine kinase 2 inhibitors: Some hints on the structural basis for selective inhibition.

Sphingosine kinase (SphK), which catalyzes the transfer of phosphate from ATP to sphingosine (Sph) generating sphingosine-1-phosphate (S1P) has emerged as therapeutic target since the discovery of connections of S1P with cancer progress. So far, most effort has focused on the development of inhibitors of SphK1, and selective inhibitors of SphK2 have been much less explored. Here, we describe the syntheses of new sphingosine derivatives bearing a tetrasubstituted carbon atom at C-2, dimethylhydrazino or azo moieties in the polar head, and alkane, alkene or alkyne moieties as linkers between the polar ahead and the fatty tail. In vitro inhibitory assays based on a time resolved fluorescence energy transfer (TR-FRET) have revealed the hydrazino and alkynyl moieties as the best combination for the design of selective SphK2 inhibitors (19a and 19b). Docking studies showed that compounds 19a-b have the optimal binding to SphK2 through the exploitation of polar but also hydrophobic interactions of their head group with the head of the enzyme binding pocket, while also producing full contact of the fatty tail with the hydrophobic pocket of the enzyme. By contrast, this elongation causes loss of contact surface with the shorter hydrophobic toe of the SphK1 isoform, thus accounting for the SphK2-biased selectivity of these compounds. Cell viability assays of the most promising candidates 19a-b have shown that 19a is not cytotoxic to human endothelial cells at 30 µM.

Enantioselective Synthesis of 3-Heterosubstituted-2-amino-1-ols by Sequential Metal-Free Diene Aziridination/Kinetic Resolution.

A general protocol for the enantioselective synthesis of 3-heterosubstituted-2-amino-1-ols was developed based on metal- free intramolecular regio- and stereoselective diene aziridination and regioselective opening. Kinetic resolution of the resulting (1'-NR1 R2 and 1'-SR)-4-oxazolidinones was performed using ABCs organocatalysts, expanding the application of this methodology.

Enantioselective Synthesis of Aminodiols by Sequential Rhodium-Catalysed Oxyamination/Kinetic Resolution: Expanding the Substrate Scope of Amidine-Based Catalysis.

Regio- and stereoselective oxyamination of dienes through a tandem rhodium-catalysed aziridination-nucleophilic opening affords racemic oxazolidinone derivatives, which undergo a kinetic resolution acylation process with amidine-based catalysts (ABCs) to achieve s values of up to 117. This protocol was applied to the enantioselective synthesis of sphingosine.

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.

Chemical Access to d-Sarmentose Units Enables the Total Synthesis of Cardenolide Monoglycoside N-1 from Nerium oleander.

Herein we present a chemical approach for the ready preparation of d-sarmentosyl donors enabling the first total synthesis and structure validation of cardenolide N-1, a challenging 2,6-dideoxy-3-O-methyl-ß-d-xylo-hexopyranoside extracted from Nerium oleander twigs that displays anti-inflammatory properties and cell growth inhibitory activity against tumor cells. The strategy highlights the synthetic value of the sequential methodology developed in our group for the synthesis of 2-deoxyglycosides. Key steps include Wittig-Horner olefination of a d-xylofuranose precursor, [I+]-induced 6-endo cyclization, and 1,2-trans stereoselective glycosylation.

Palladium-catalyzed allylic amination: a powerful tool for the enantioselective synthesis of acyclic nucleoside phosphonates.

Acyclic nucleoside phosphonates have been prepared in a straightforward manner and in high yields by an enantioselective palladium-catalyzed allylic substitution involving nucleic bases as nucleophiles followed by cross-metathesis reaction with diethyl allylphosphonate.

Enantioselective Formal Synthesis of Nectrisine Using a Palladium-Catalyzed Asymmetric Allylic Amination and Cross-Metathesis as Key Steps.

A formal enantioselective synthesis of nectrisine, a potent α-glucosidase inhibitor, was carried out starting from butadiene monoepoxide through a synthetic sequence involving enantioselective allylic substitution, cross-metathesis, dihydroxylation, and cyclization.

Chemo-, regio-, and stereoselective silver-catalyzed aziridination of dienes: scope, mechanistic studies, and ring-opening reactions.

Silver complexes bearing trispyrazolylborate ligands (Tp(x)) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI═NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C═C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of ß-amino alcohols have also been developed.

Tuning the stereoelectronic properties of 1-sulfanylhex-1-enitols for the sequential stereoselective synthesis of 2-deoxy-2-iodo-ß-D-allopyranosides.

The preparation of challenging 2-deoxy-2-iodo-ß-D-allo precursors of 2-deoxy-ß-D-ribo-hexopyranosyl units and other analogues is reported using a robust olefination-cyclization-glycosylation sequence. Here, we particularly focus on tuning the stereoelectronic properties of the alkenyl sulfides intermediates in order to improve the diastereoselectivity of the cyclization step and, hence, the efficiency of the overall transformation. Phosphine oxides with the general formula Ph2P(O)CH2SR (R = t-Bu, Cy, p-MeOPh, 2,6-di-ClPh, and 2,6-di-MePh) were easily synthesized and subsequently used in the olefination reaction with 2,3,5-tri-O-benzyl-D-ribose and -D-arabinose. The corresponding sugar-derived alkenyl sulfides were submitted to a 6-endo [I(+)]-induced cyclization, and the resulting 2-deoxy-2-iodohexopyranosyl-1-thioglycosides were used as glycosyl donors for the stereoselective synthesis of 2-deoxy-2-iodohexopyranosyl glycosides. Among the different S-groups studied, t-Bu derivative was the best performer for the synthesis of cholesteryl 2-deoxy-2-iodomannopyranosides, whereas for the synthesis of 2-deoxy-2-iodoallopyranosides none of the derivatives here studied proved superior to the phenyl analogue previously described. Glycosylation of cholesterol with different d-allo and d-manno derivatives produced 2-deoxy-2-iodoglycosides with stereoselectivities in the same order in each case, reinforcing the involvement of an oxocarbenium ion as the common intermediate of this crucial glycosylation step.

Advances in the enantioselective synthesis of carbocyclic nucleosides.

Carbocyclic nucleosides are nucleoside analogues in which the furanosidic moiety has been replaced by a carbocycle. Several members of this family have been isolated from natural sources and include a 5-membered ring carbocycle. The aim of this review is to examine critically the different methodologies for the enantioselective construction of 3- to 6-membered rings, with a particular focus on 5-membered rings and their modifications. The procedures for bonding the heterocyclic moiety and the carbohydrate are treated separately. The methods for synthesising the carbocyclic moiety mainly focus on the construction of the cycle, although precise details about the functionalisation are provided in some cases. The selected methods aim to provide an overview of the synthesis of carbocycles related to the synthesis of carbocyclic nucleosides. The methods of synthesis of 5-membered rings are classified into two types: methods in which the cyclopentane ring is formed by ring closing reactions (C=C and C-C formation) and methods that start from preformed 5-membered rings, based mainly on cycloaddition reactions. With respect to the methods of synthesis of 3-, 4- and 6-membered ring carbocyclic nucleosides, a selection of the more relevant enantioselective procedures is presented in a systematic manner.

Sequential directed epoxydation-acidolysis from glycals with MCPBA. A flexible approach to protected glycosyl donors.

4,6-Di-O-protected glucal and allal derivatives react with MCPBA to afford manno- and allo-1-O-m-chlorobenzoate derivatives, respectively, as a result of a syn epoxidation directed by the allylic hydroxyl group, and consecutive ring-opening by m-ClBzOH. When glucal and allal derivatives are fully protected, initial epoxidation proceeds mainly anti to the allylic group to give, after ring-opening, the corresponding pyranosyl chlorobenzoates. Stereoselectivity in the reaction of fully protected galactal derivatives was complete, although only a moderate increase in the syn epoxidation product was observed in 4,6- and 3,4-di-O-protected derivatives. 1-O-m-Chlorobenzoate 18 was selectively protected and activated as donor in the synthesis of disaccharide 21.

Short and general procedure for synthesizing cis-1,2-fused 1,3-oxathiolan-, 1,3-oxaselenolan-, and 1,3-oxazolidin-2-imine carbohydrate derivatives.

Novel cis-1,2-fused 1,3-oxathiolan-, 1,3-oxaselenolan-, and 1,3-oxazolidin-2-imine carbohydrate derivatives have been prepared by treatment of the corresponding 1,2-anhydrosugars with potassium thiocyanate, potassium selenocyanate, and sodium cyanamide, respectively. The procedure is compatible with several protecting groups such as acyl, benzyl, and silyl and also with sugars of different configurations.

Asymmetric sulfur ylide based enantioselective synthesis of D-erythro-sphingosine.

An asymmetric sulfur ylide reaction was employed to prepare an epoxide intermediate in a convergent manner. This epoxide was efficiently transformed into D-erythro-sphingosine.

Stannyl ceramides as efficient acceptors for synthesising beta-galactosyl ceramides.

beta-Galactosyl ceramides have been obtained in excellent yields and stereoselectivities by reacting disarmed glycosyl donors with stannyl ethers. The broad compatibility of stannyl ethers with various leaving group-promoter pairs is demonstrated.

Highly reactive 2-deoxy-2-iodo-d-allo and d-gulo pyranosyl sulfoxide donors ensure ß-stereoselective glycosylations with steroidal aglycones.

The preparation of well-defined d-xylo and d-ribo glycosides represents a synthetic challenge due to the limited configurational availability of starting materials and the laborious synthesis of homogeneous 2-deoxy-ß-glycosidic linkages, in particular that of the sugar-steroid motif, which represents the "stereoselective determining step" of the overall synthesis. Herein we describe the use of 2-deoxy-2-iodo-glycopyranosyl sulfoxides accessible from widely available d-xylose and d-ribose monosaccharides as privileged glycosyl donors that permit activation at very low temperature. This ensures a precise kinetic control for a complete 1,2-trans stereoselective glycosylation of particularly challenging steroidal aglycones.

Synthesis of carbohydrate-based vinyl selenides via Wittig-type reactions.

Carbohydrate-based vinyl selenides of the arabino, ribo and 2-deoxy-ribo configuration have been prepared by Wittig-type reactions of various protected furanoses. Moderate yields were always obtained due to the nature and reactivity of both carbohydrate lactols and selenium-based olefinating reagents under the conditions tested. A detailed study of the olefination reaction and the behaviour of vinyl selenides towards the electrophilic-induced cyclization will be discussed.

Recent advances in the glycosylation of sphingosines and ceramides.

Glycosphingolipids (GSLs) are ubiquitous components of eukaryotic cell membranes. They are highly bioactive and are involved in many aspects of cell signalling like cell-cell interaction, cell-substratum interaction and cell-pathogen interaction. GSLs also are involved in the modulation of signal transduction, resulting in regulation of cell proliferation and differentiation. The biological importance and complexity of these compounds afford many opportunities to prepare synthetic analogues for studies of their metabolism in intra- and intercellular processes. This review focuses on recent contributions in the synthesis of GSLs, highlighting improvements in glycosylation reactions leading to alpha and beta glycosyl sphingosines and ceramides and related compounds. Literature from 2000 to the present is covered. The glycosylation reactions leading to the synthesis of GSLs are classified in function of the configuration of the created glycosidic bond (alpha or beta) and of the acceptor used, either azido-sphingosine or ceramide.

General method for synthesizing pyranoid glycals. A new route to allal and gulal derivatives.

[reaction: see text] Pyranoid glycals of all configurations can be obtained from pentoses through an olefination-cyclization-elimination sequence. The elimination can be carried out with excellent yields under radical conditions or by using common reductive reagents such as Zn/Cu, TiCl(4)/LiAlH(4), or lithium naphthalenide. The proposed method is appropriate for the synthesis of glycals with allo or gulo configurations because the cyclization step is more efficient for these substrates.