A Convenient Synthesis of the (+) Enantiomer of Levoglucosenone and its 5-Hydroxymethyl Analog

Synthesis of sugar enones and their use as powerful synthetic precursors of thiodisaccharides

Monosaccharide derivatives having a double bond conjugated to a carbonyl (sugar enones or enuloses) are relevant synthetic tools. They are also suitable starting materials, or versatile intermediates, for the synthesis of a wide variety of natural or synthetic compounds with a broad spectrum of biological and pharmacological activities. The preparation of enones is mainly focused on the search for more efficient and diastereoselective synthetic methodologies. The usefulness of enuloses relies on the diverse reaction possibilities offered by alkene and carbonyl double bonds, which are prone to undergo varied reactions such as halogenation, nitration, epoxidation, reduction, addition, etc. The addition of thiol groups that led to sulfur glycomimetics, such as thiooligosaccharides, is particularly relevant. Therefore, the synthesis of enuloses and the Michael addition of sulfur nucleophiles to give thiosugars or thiodisaccharides are discussed here. Chemical modifications of the conjugate addition products to afford biologically active compounds are also reported.

Catalytic fast pyrolysis of cellulose to prepare levoglucosenone using sulfated zirconia

Sulfated zirconia was employed as catalyst for fast pyrolysis of cellulose to prepare levoglucosenone (LGO), a very important anhydrosugar for organic synthesis. The yield and the selectivity of LGO were studied in a fixed-bed reactor at different temperatures and cellulose/catalyst mass ratios. The experiments of catalyst recycling were also carried out. The results displayed that from 290 to 400 °C, the liquid and solid accounted for more than 95 wt % of products, and the higher temperature led to more liquid and less solid products. The introduction of SO₄²⁻/ZrO₂ could promote cellulose conversion and LGO production. The temperature had a similar effect on the yield and selectivity of LGO at different cellulose/catalyst mass ratios. The maximum yield was obtained at 335 °C. Although the structure of the parent ZrO₂ was retained after recycles, which was confirmed by X-ray diffraction and N₂ adsorption-desorption measurements, the activity of SO₄²⁻/ZrO₂ could only be partially recovered by simply calcination. The catalytic activity decrease could be mainly attributed to SO₄²⁻ leaching, and the activity could be restored by further impregnation of H₂SO₄.

A click chemistry approach to glycomimetics: Michael addition of 2,3,4,6-tetra-O-acetyl-1-thio-β-d-glucopyranose to 4-deoxy-1,2-O-isopropylidene-l-glycero-pent-4-enopyranos-3-ulose – a convenient route to novel 4-deoxy-(1→5)-5-C-thiodisaccharides

The base catalyzed conjugate Michael addition of the 1-thiosugar, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranose, 1, to a new highly reactive enone 4-deoxy-1,2-O-isopropylidene-L-glycero-pent-4-enopyranos-3-ulose, 2, proceeds steroselectively with formation of adduct 3 in 94% yield. Convenient stereoselective reduction of the C-3 keto function of 3 with L-Selectride followed by in situ acetylation produces thiodisaccharide 4 in good 82% yield. Cleavage of the 1,2-O-isopropylidene protecting group with p-toluenesulfonic acid in methanol, followed by de-O-acetylation, produced an inseparable anomeric mixture of methyl 4-deoxy-5-C-(beta-D-glucopyranosyl)-thio-alpha/beta-L-ribo-pyranoside 5 in 72% overall yield. This approach constitutes a new general two-step click chemistry route to the previously unknown class of 4-deoxy-(1-->5)-5-C-thiodisaccharides as stable and biologically important glycomimetics.

Thio-sugars VII. Effect of 3-deoxy-4-S-(beta-D-gluco- and beta-D-galactopyranosyl)-4-thiodisaccharides and their sulfoxides and sulfones on the viability and growth of selected murine and human tumor cell lines

The first conversion of (1-->4)-thiodisaccharides into corresponding sulfoxides and sulfones by conventional oxidation with m-chloroperoxybenzoic acid (MCPBA) is reported. The effects of alpha-(1-->4)-3'-deoxythiodisaccharides (8-9) and their sulfoxide (14-15) and sulfone (16-17) derivatives on murine leukemia and human colon and pancreatic carcinoma cell viability were studied. Concentrations of thio-sugars that decreased tumor cell line viability by 50% (IC(50)), measured via the MTT assay, ranged from 6.4 to 38.3 microg/mL. The effect of alpha-(1-->4)-3'-deoxythiodisaccharide derivatives were most profound on human pancreatic epithelial carcinoma (PANC-1) cells with compounds 8 and 9 having IC(50) values of 6.4 microg/mL and 8.2 microg/mL, respectively. Sulfone derivatives 16 and 17 also had pronounced effects on PANC-1 cell viability (IC(50)=10.2 microg/mL and 9.6 microg/mL, respectively). These results indicate that deoxythio-disaccharide analogs generated by functionalization of the universal chiral precursor levoglucosenone may have cytotoxic properties and therapeutic potential as anticancer agents.

Continuous indirect electrochemical regeneration of galactose oxidase

The development of an indirect anaerobic electrochemical regeneration of galactose oxidase (GOase) allows the prevention of the undesired production of the enzyme inhibitor hydrogen peroxide, which is generated under aerobic regeneration conditions during synthetic applications of GOase. The pH optimum for the electrochemical regeneration of GOase with polyethyleneglycol-modified ferrocene mediators in carbonate buffer is 10.8. Total turnover numbers achieved by either electrochemical or aerobic regeneration of GOase are almost the same. The electrochemical regeneration is half as fast as the aerobic regeneration. It is not necessary to work under anaerobic conditions, because at pH 10.8 the aerobic regeneration of GOase is prevented. The enzyme can be stabilized most effectively by immobilization on an aminopropylated polysiloxane (DELOXAN) via the glutaric dialdehyde procedure with good activity yields up to 37%. Buffers containing amino groups proved to be fatal for long-term GOase stability.