Stereodivergent Synthesis of Biologically Active Spironucleoside Scaffolds via Catalytic Cyclopropanation of 4-exo-Methylene Furanosides.

Cyclopropane fusion of the only rotatable carbon-carbon bond in furanosyl nucleosides (i.e., exocyclic 4'-5') is a powerful design strategy to arrive at conformationally constrained analogues. Herein, we report a direct stereodivergent route toward the synthesis of the four possible configurations of 4-spirocyclopropane furanoses, which have been transformed into the corresponding 4'-spirocyclic adenosine analogues. The latter showed differential inhibition of the protein methyltransferase PRMT5-MEP50 complex, with one analogue inhibiting more effectively than adenosine itself, demonstrating the utility of rationally probing 4'-5' side chain orientations.

Preparation of 4'-Spirocyclobutyl Nucleoside Analogues as Novel and Versatile Adenosine Scaffolds.

Despite the large variety of modified nucleosides that have been reported, the preparation of constrained 4'-spirocyclic adenosine analogues has received very little attention. We discovered that the [2+2]-cycloaddition of dichloroketene on readily available 4'-exo-methylene furanose sugars efficiently results in the diastereoselective formation of novel 4'-spirocyclobutanones. The reaction mechanism was investigated via density functional theory (DFT) and found to proceed either via a non-synchronous or stepwise reaction sequence, controlled by the stereochemistry at the 3'-position of the sugar substrate. The obtained dichlorocyclobutanones were converted into nucleoside analogues, providing access to a novel class of chiral 4'-spirocyclobutyl adenosine mimetics in eight steps from commercially available sugars. Assessment of the biological activity of designed 4'-spirocyclic adenosine analogues identified potent inhibitors for protein methyltransferase target PRMT5.

Regio- and Stereoselective Synthesis of C-4' Spirocyclobutyl Ribofuranose Scaffolds and Their Use as Biologically Active Nucleoside Analogues.

Novel C-4',C-5' cyclobutane-fused spirocyclic ribonucleoside analogues were prepared. Thermal [2 + 2] cycloaddition between dichloroketene and readily derived 4'-exo-methylene furanoses afforded a first entry to the required constrained ribofuranoses, relying on a carbonyl transposition sequence. Alternatively, an unusual stereoselective ionic [2 + 2] cycloaddition using methyl propiolate promoted by methylaluminoxane gave a complementary, more direct approach to such ribofuranoses. Further conversion to the constrained adenosine analogues revealed promising structure-dependent inhibition of the protein methyltransferase PRMT5:MEP50 complex in the (sub)micromolar range.

Synthesis of NAM-thiazoline derivatives as novel O-GlcNAcase inhibitors.

Human O-GlcNAcase (GH 84) and human ß-N-acetyl-D-hexosaminidase (GH 20) from Homo sapiens are two therapeutic enzyme targets that share the same catalytic mechanism but play different physiological roles in vivo. Selective inhibition toward one of these enzymes is therefore of importance to regulate the corresponding bioprocess. Here ten new NAM-thiazoline derivatives were synthesized and subsequently characterized by NMR and HRMS. A preliminary bioassay showed that most of the synthesized compounds exhibited obvious selective inhibition against human O-GlcNAcase over human ß-N-acetyl-D-hexosaminidase. Among the compounds tested, compound 7d (IC50 = 6.4 µM, hOGA; IC50>1 mM, hHex) and 7f (IC50 = 11.9 µM, hOGA; IC50>1 mM, hHex) proved to be a highly selective and potent inhibitor. Structure-activity relationship analysis indicated a correlation between the inhibitory activity and the size of the groups linked to the thiazoline ring.

Synthesis of NAG-thiazoline-derived inhibitors for ß-N-acetyl-d-hexosaminidases.

ß-N-Acetyl-d-hexosaminidases are responsible for the metabolism of glycoconjugates in diverse physiological processes that are important targets for medicine and pesticide development. Fourteen new NAG-thiazoline derivatives were synthesized by cyclization and click reaction using d-glucosamine hydrochloride as the starting material. All the compounds created were characterized by NMR and HRMS spectra. A preliminary bioassay, using four enzymes from two ß-N-acetyl-d-hexosaminidase families, showed that most of the compounds synthesized exhibit selective inhibition of GH84 ß-N-acetyl-d-hexosaminidase. Among the compounds tested, compounds 5a (IC50=12.6 µM, hOGA) and 5e (IC50=12.5 µM, OfOGA) proved to be a highly selective and potent inhibitor.