Enantioselective 1,3-Dipolar Cycloadditions of α-Methylene Lactams to Construct Spirocycles.

Spirocyclic scaffolds are important motifs due to their potential to bestow favorable effects on pharmaceutical compounds. However, there is a need for efficient methods for their enantioselective construction. We report a method for the asymmetric 1,3-dipolar cycloaddition of diazoacetates or nitrile oxides with α-methylene lactams to prepare chiral spirocyclic heterocycles. The methodology is high yielding (up to 91% yield) and enantioselective (up to 89% ee) for a wide range of N-substituents and 6- and 7-membered ring lactam substrates.

Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to α,ß-Unsaturated Lactams: Enantioselective Construction of All-Carbon Quaternary Stereocenters in Saturated Nitrogen-Containing Heterocycles.

Stereogenic nitrogen-containing heterocycles are ubiquitous in natural products and pharmaceutical compounds, but methods for their enantioselective construction have remained elusive. We report a general method for the asymmetric conjugate addition of arylboronic acids to ß-alkyl/aryl α,ß-unsaturated lactams that affords chiral ß,ß-disubstituted lactams. The transformation is operationally simple and air- and moisture-tolerant and uses a commercially available (S)-t-Bu-PyOx ligand. The method is high-yielding (up to 95% yield) and enantioselective (up to 97% ee) for a wide range of arylboronic acids and α,ß-unsaturated lactams, including those with different ring sizes.

Discovery of a new sialic acid binding region that regulates Siglec-7.

Siglec-7 is a human CD33-like siglec, and is localised predominantly on human natural killer (NK) cells and monocytes. Siglec-7 is considered to function as an immunoreceptor in a sialic acid-dependent manner. However, the underlying mechanisms linking sialic acid-binding and function remain unknown. Here, to gain new insights into the ligand-binding properties of Siglec-7, we carried out in silico analysis and site-directed mutagenesis, and found a new sialic acid-binding region (site 2 containing R67) in addition to the well-known primary ligand-binding region (site 1 containing R124). This was supported by equilibrium dialysis, STD-NMR experiments, and inhibition analysis of GD3-binding toward Siglec-7 using synthetic sialoglycoconjugates and a comprehensive set of ganglioside-based glycoconjugates. Our results suggest that the two ligand-binding sites are potentially controlled by each other due to the flexible conformation of the C-C' loop of Siglec-7.

Discovery of a novel olefin derivative as a highly potent and selective acetyl-CoA carboxylase 2 inhibitor with in vivo efficacy.

Novel acetyl-CoA carboxylase 2 (ACC2) selective inhibitors were identified by the conversion of the alkyne unit of A-908292 to the olefin linker. Modification of the center and left part of the lead compound 1b improved the ACC2 inhibitory activity and CYP450 inhibition profile, and afforded a highly selective ACC2 inhibitor 2e which showed in vivo efficacy in C57BL/6 mice.

Identification of a novel benzimidazole derivative as a highly potent NPY Y5 receptor antagonist with an anti-obesity profile.

Optimization of HTS hit 1 for NPY Y5 receptor binding affinity, CYP450 inhibition, solubility and metabolic stability led to the identification of some orally available oxygen-linker derivatives for in vivo study. Among them, derivative 4i inhibited food intake induced by the NPY Y5 selective agonist, and chronic oral administration of 4i in DIO mice caused a dose-dependent reduction of body weight gain.

Identification of a novel and orally available benzimidazole derivative as an NPY Y5 receptor antagonist with in vivo efficacy.

Optimization of lead compound 2 is described, mainly focusing on modification at the C-2 position of the benzimidazole core. Replacement of the phenyl linker of 2 with saturated rings resulted in identification of compound 8b which combines high Y5 receptor binding affinity with a good ADME profile leading to in vivo efficacy.

Design, synthesis and identification of novel benzimidazole derivatives as highly potent NPY Y5 receptor antagonists with attractive in vitro ADME profiles.

Optimization of our HTS hit 1, mainly focused on modification at the C-2 position of the benzimidazole core, is described. Elimination of the flexible and metabolically labile -S-CH(2)- part and utilization of less lipophilic pyridone substructure led to identification of novel NPY Y5 receptor antagonists 6, which have low to sub-nanomolar Y5 receptor binding affinity with improved CYP450 inhibition profiles, good solubilities and high metabolic stabilities.

Developmental stage-dependent expression of an alpha2,8-trisialic acid unit on glycoproteins in mouse brain.

The monoclonal antibody mAb.A2B5 is a marker for the detection of oligodendrocyte progenitor cells that differentiate into type-2 astrocytes and oligodendrocytes. It is also a useful antibody for separating these cells from other lineage populations. The epitope of this antibody is considered to be the gangliosides GT3 and GQ1c. In this study, we sought to define more precisely the structure of the epitope. Accordingly, we chemically synthesized defined oligosialic acid structures linked to phosphatidylethanolamine and bovine serum albumin and used these to determine the antigenic specificity. mAb.A2B5 recognized the Neu5Acalpha2-->8Neu5Acalpha2-->8Neu5Acalpha--> structure on both glycolipids and glycoproteins. We then examined whether the mAb.A2B5 epitope exists on glycoproteins in developing mouse brains. Western blot analyses revealed the expression of four glycoproteins reactive with the mAb.A2B5, and their expression was dependent on the stage of neural development. All the immunoreactivity in these glycoproteins with mAb.A2B5 disappeared after sialidase treatment and were resistant to chloroform/methanol extraction. These epitopes were also detected in brain homogenates from both GD3 synthetase-null and GD3/GD2 synthetase double null mice. These findings show that the alpha2,8-trisialic acid (triSia) unit recognized by mAb.A2B5 resides not only on gangliosides but also on glycoproteins in developing mouse brain. We postulate that the triSia structure on glycoproteins may be involved in oligodendrocyte differentiation, similar to the case with the alpha2,8-triSia structure on gangliosides. Real time polymerase chain reaction analysis of the developmental expression of all known ST8Sia genes, which are responsible for the biosynthesis of alpha2,8-linked Sia residues, showed that ST8Sia III gene expression correlated with expression of the triSia epitope. We suggest that ST8Sia III is the principal sialyltransferase responsible for synthesis of the alpha2,8-triSia units on glycoproteins.

Stereoselective Synthesis of alpha(2,9) Di- to Tetrasialic Acids, Using a 5,4-N,O-Carbonyl Protected Thiosialoside.

An efficient stereoselective synthesis of alpha(2,9) tetra- to disialic acids 1-3, using the 5,4-N,O-carbonyl protected thiosialoside 4, is described. The cyclic protecting group was effective for alpha-sialylation without the need for acetonitrile as the solvent. The donor 4 enabled the formation of a tetramer in excellent yield and selectivity. Deprotection of the cyclic protecting groups of the protected di- to tetrasialica acids proceeded smoothly to give the fully deprotected alpha(2,9) tetra- to disialic acids 1-3.

An efficient convergent synthesis of GP1c ganglioside epitope.

In this report, we describe an efficient convergent synthesis of the GP1c glycolipid epitope, which is one of the most complex c-series gangliosides. The alpha(2,3) and alpha(2,8) sialylations were accomplished by use of 5N,4O-carbonyl and 7,8-O-isopropyliden as well as 5N,4O-carbonyl- and 7,8-di-O-chloroacetyl-protected sialyl donors in good yields with excellent alpha-selectivity, respectively. The two sialyl donors enable synthesis of the di- and trisialylgalactosides by simple glycosylation and deprotection. We synthesized the protected GP1c glycolipid epitope, which is a compact, rigid, branched structure, via direct coupling of tetarasaccharide and pentasaccharide units.

Efficient synthesis of an alpha(2,9) trisialic acid by one-pot glycosylation and polymer-assisted deprotection.

An efficient synthesis of alpha(2,9) trisialic acid has been achieved via one-pot glycosylation and polymer-assisted deprotection. The synthesis involves chemo- and regioselective alpha-sialylation of ethylthiosialoside with the S-benzoxazolyl (S-Box) sialyl donor. Use of a prelinker to link an activated ester and a vinyl ether via a carbon chain enables polymer-assisted deprotection of the protected trisialic acids.

Stereoselective synthesis of oligo-alpha-(2,8)-sialic acids.

An efficient and elegant synthesis of alpha(2,8)-oligosialosides is described. The 5-N,4-O-carbonyl-protected sialyl donor undergoes alpha-sialylation in CH2Cl2 to give alpha(2,8)- and alpha(2,9)-disialosides in excellent yields. The 5-N,4-O-carbonyl protecting group was effective in improving the reactivity of the C8 hydroxyl groups toward glycosylation. Using the sialyl building block, the synthesis of tetra-alpha(2,8)-sialic acid was accomplished by using a simple glycosidation and deprotection protocol.