Fluorinated sulphonic esters of sugars: their synthesis and reactions with pyridine

Diastereoselective Synthesis of the Borylated d-Galactose Monosaccharide 3-Boronic-3-Deoxy-d-Galactose and Biological Evaluation in Glycosidase Inhibition and in Cancer for Boron Neutron Capture Therapy (BNCT)

Drug leads with a high Fsp³ index are more likely to possess desirable properties for progression in the drug development pipeline. This paper describes the development of an efficient two-step protocol to completely diastereoselectively access a diethanolamine (DEA) boronate ester derivative of monosaccharide d-galactose from the starting material 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose. This intermediate, in turn, is used to access 3-boronic-3deoxy-d-galactose for boron neutron capture therapy (BNCT) applications. The hydroboration/borane trapping protocol was robustly optimized with BH₃.THF in 1,4-dioxane, followed by in-situ conversion of the inorganic borane intermediate to the organic boron product by the addition of DEA. This second step occurs instantaneously, with the immediate formation of a white precipitate. This protocol allows expedited and greener access to a new class of BNCT agents with an Fsp³ index = 1 and a desirable toxicity profile. Furthermore, presented is the first detailed NMR analysis of the borylated free monosaccharide target compound during the processes of mutarotation and borarotation.

C-3 epimers of sugar amino acids as foldameric building blocks: improved synthesis, useful derivatives, coupling strategies

To obtain key sugar derivatives for making homooligomeric foldamers or α/β-chimera peptides, economic and multigram scale synthetic methods were to be developed. Though described in the literature, the cost-effective making of both 3-amino-3-deoxy-ribofuranuronic acid (H-t X-OH) and its C-3 epimeric stereoisomer, the 3-amino-3-deoxy-xylofuranuronic acid (H-c X-OH) from D-glucose is described here. The present synthetic route elaborated is (1) appropriate for large-scale synthesis; (2) reagent costs reduced (e.g. by a factor of 400); (3) yields optimized are ~80% or higher for all six consecutive steps concluding -t X- or -c X- and (4) reaction times shortened. Thus, a new synthetic route step-by-step optimized for yield, cost, time and purification is given both for D-xylo and D-ribo-amino-furanuronic acids using sustainable chemistry (e.g. less chromatography with organic solvents; using continuous-flow reactor). Our study encompasses necessary building blocks (e.g. -X-OMe, -X-OⁱPr, -X-NHMe, Fmoc-X-OH) and key coupling reactions making -Aaa-t X-Aaa- or -Aaa-t X-t X-Aaa- type "inserts". Completed for both stereoisomers of X, including the newly synthesized Fmoc-c X-OH, producing longer oligomers for drug design and discovery is more of a reality than a wish.

Total Synthesis of (+)-Amphidinolide A. Assembly of the Fragments

The structure elucidation of (+)-amphidinolide A, a cytotoxic macrolide, has been accomplished by employing a combination of total synthesis and NMR spectroscopic analysis. Amphidinolide A possesses two skipped 1,4-diene subunits which are accessible by ruthenium-catalyzed alkene-alkyne couplings. Previous total syntheses had revealed that the reported structure was incorrect; therefore, to incorporate maximum flexibility into the synthesis, with the ultimate goal of determining the correct structure, a highly convergent approach was chosen. Furthermore, liberal use was made of catalytic asymmetric transformations to set individual stereocenters. Three different strategies were envisioned for the end game, and due to the highly convergent nature of the synthesis, all three routes disconnect to the same three key intermediates, 5, 6, and 7. Diastereomers of 6 and 7 were easily prepared by modification of the synthetic routes to allow access to multiple diastereomers of 1 for structural determination.

Towards Highly Activating Leaving Groups: Studies on the Preparation of Some Halogenated Alkyl Sulfonates

The trichloromethylsulfonyl-, dichloromethylsulfonyl-, chlorosulfonyl-, and fluorosulfonyl esters of a neopentyl-type alcohol have been prepared via sulfonylation or sulfinylation followed by oxidation. The preparative usefulness and potential of the transformations are discussed.

Synthesis of sulfur-linked analogues of nigerose, laminarabiose, laminaratriose, gentiobiose, gentiotriose, and laminaran trisaccharide Y

Sulfur-linked analogues of 3-O-alpha-D-glucopyranosyl-D-glucose (nigerose), 3-O-beta-D-glucopyranosyl-D-glucose (laminarabiose), 6-O-beta-D-glucopyranosyl-D-glucose (gentiobiose), O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->3)-D-glucos e (laminaratriose), O-beta-D-glucopyranosyl)-(1-->6)-O-beta-D-glucopyranosyl-(1-->6)-D-gluco se (gentiotriose) and 3,6-di-O-beta-D-glucopyranosyl-D-glucose (laminaran trisaccharide Y), namely, respectively, 3-thionigerose (6), 3-thiolaminarabiose (11), 6-thiogentiobiose (21), 3I,3II-dithiolaminaratriose (16), 6I,6II-dithiogentiotriose (29) and 3I,6I-dithiolaminaran trisaccharide Y (37) have been conveniently prepared by SN2 reactions of the corresponding anomer of D-glucopyranose 1-thiolate with suitably activated monosaccharide derivatives in N,N-dimethylformamide (for 6 and 21) or in tetrahydrofuran in the presence of a crown ether (for 11). A sequence involving the reaction of non-anomeric thiolates with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide was alternatively used for the preparation of 11 and 21 but proved less satisfactory. The preparation of thiotrisaccharides 16, 29, and 37 involved a mixed approach.

Stereocontrolled synthesis of sulfur-linked analogues of the branched tetrasaccharide repeating-unit of the immunostimulant polysaccharide schizophyllan and of its beta-(1-->3)-branched, beta-(1-->6)-linked isomer

The branched, sulfur-linked tetrasaccharide S-(beta-D-glucopyranosyl)-(1-->3)-S-[(6-S-beta-D-glucopyranosyl)-3,6-dit hio- beta-D-glucopyranosyl]-(1-->3)-S-3-thio-D-glucopyranose (9) has been conveniently prepared by SN2 displacement of the triflate group in 1,2:5,6-di-O-isopropylidene-3-O-trifluoromethylsulfonyl-alpha-D-++ +allofuranose with the sodium salt of 2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)- 1,3,6- trithio-beta-D-glucopyranose (5). Conversely, reaction of the sodium salt of 5 with 1,2,3,4-tetra-O-acetyl-6-deoxy-6-iodo-beta-D-glucopyranose afforded the positional isomer S-(beta-D-glucopyranosyl)-(1-->6)-S-[(3-S-beta-D-glucopyranosyl)-3,6-dit hio- beta-D-glucopyranosyl]-(1-->6)-S-6-thio-D-glucopyranose (12).

Alpha-(1-->2)-, and alpha-(1-->3)-, and alpha-(1-->6)-linked thioglycosidic disaccharides: syntheses and anti-HIV testing of thiokojibiose octaacetate, thionigerose, and thioisomaltose

The syntheses of several alpha-linked thioglycosidic disaccharides are described, including thiokojibiose octaacetate (1), thionigerose (2), and thioisomaltose (3). The title compounds were synthesized by coupling 2,3,4,6-tetra-O-acetyl-1.5-acetyl-1-thio-alpha-D-glucopyranose (4) with either 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethylsulfonyl-beta-D-manno pyr anose (7), 1,2:5,6-di-O-isopropylidene-3-O-trifluoromethylsulfonyl-alpha-D-++ +allofuranose (15), or methyl 2,3,4-tri-O-acetyl-6-deoxy-6-iodo-alpha-D-glucopyranoside (17), respectively. Thiokojibiose octaacetate in turn was converted to 3,4,6-tri-O-acetyl-2-S-(2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl)-2 -thio-alpha-D-glucopyranosyl bromide (9), which was used to obtain several related disaccharides and one trisaccharide. All of the compounds, including thiomaltose and thiotrehalose, which were resynthesized by known methods, were tested for their anti-HIV activity in either CEM or MT-2 cells. Anti-HIV activity was noted only with thiokojibiose octaacetate and its 1-thio analogue (14), which had IC50 values of 51 and 48 micrograms/mL in CEM cells, respectively.

Positional isomers of thioxylobiose, their synthesis and inducing ability for D-xylan-degrading enzymes in the yeast Cryptococcus albidus

Isomeric S-linked 2-thioxylobiose 10, 3-thioxylobiose 17, and 4-thioxylobiose 19 were conveniently prepared by SN2 displacement of suitable triflylglycoses with the sodium salt of 2,3,4-tri-O-acetyl-1-thio-beta-D-glucopyranose, either in N,N-dimethylformamide, or in oxolan in the presence of a sodium complexing agent. Allyl 3,5-O-isopropylidene-2-O-trifluoromethanesulfonyl-beta-D-lyxofu ranoside was a convenient electrophilic precursor for 10, which was smoothly obtained after a short sequence of deprotection involving conversion to the 1-propenyl glycoside. 1,2:5,6-Di-O-isopropylidene-3-O-trifluoromethylsulfonyl-alpha-D-++ +allofuranose and 1,2,3-tri-O-benzoyl-4-O-trifluoromethylsulfonyl-beta-L-arabinop yranose were the respective precursors for 17 and 19. 4-Thioxylobiose has a highly stimulatory effect on the synthesis of enzymes of the xylanolytic system in the yeast Cryptococcus albidus when applied to the cells in the presence of the natural disaccharide inducer (1----4)-beta-D-xylobiose.