An efficient procedure for synthesis of fructose derivatives

Synthesis of 1-Deoxymannojirimycin from d-Fructose using the Mitsunobu Reaction

Three different Mitsunobu reactions have been investigated for the synthesis of 1-deoxymannojirimycin (1-DMJ) from d-fructose. The highest yielding and most practical synthesis can be undertaken on a 10 g scale with minimal chromatography. In the key step, N,O-di-Boc-hydroxylamine reacts with methyl 1,3-isopropylidene-α-d-fructofuranose under Mitsunobu conditions to give 14. Acidic hydrolysis affords nitrone 15, which reduces quantitatively via catalytic hydrogenolysis to afford 1-DMJ (4) in 55% overall yield from d-fructose (cf. 37% for azide route and 29% for nosyl route).

Synthesis of natural/13C-enriched d-tagatose from natural/13C-enriched d-fructose

A concise, easily scalable synthesis of a rare ketohexose, d-tagatose, was developed, that is compatible with the preparation of d-[UL-13C6]tagatose. Epimerization of the widely available and inexpensive ketohexose d-fructose at the C-4 position via an oxidation/reduction (Dess-Martin periodinane/NaBH4) was a key step in the synthesis. Overall, fully protected natural d-tagatose (3.21 g) was prepared from d-fructose (9 g) on a 50 mmol scale in 23% overall yield, after five steps and two chromatographic purifications. d-[UL-13C6]Tagatose (92 mg) was prepared from d-[UL-13C6]fructose (465 mg, 2.5 mmol) in 16% overall yield after six steps and four chromatographic purifications.

Design of immobilized biocatalyst and optimal conditions for tyrosol β-galactoside production

Tyrosol β-galactoside (TG) is a phenylethanoid glycoside with proven neuroprotective properties. This work deals with its biocatalytic production from tyrosol and lactose using Aspergillus oryzae β-galactosidase in immobilized form. Six commercial carriers were examined to find the optimal biocatalyst. Besides standard biocatalyst performance characteristics, adsorption of the hydrophobic substrate on immobilization carrier matrices was also investigated. The adsorption of tyrosol was significant, but it did not have adverse effects on TG production. On the contrary, TG yield was improved for some biocatalysts. A biocatalyst prepared by covalent binding of β-galactosidase on an epoxy-activated carrier was used for detailed investigation of the effect of reaction conditions on glycoside production. Temperature had a surprisingly weak effect on the overall process rate. A lactose concentration of 0.83 M was found to be optimal to enhance TG formation. The impact of tyrosol concentration was rather complex. This substrate caused inhibition of all reactions. Its concentration had a strong effect on the hydrolysis of lactose and all products. Higher tyrosol concentrations, 30-40 g/L, were favorable as pseudo-equilibrium concentrations of TG and galactooligosaccharide were reached. Repeated batch results revealed excellent operational stability of the biocatalyst.

Hydrogen-Bond-Mediated Aglycone Delivery: Synthesis of β-d-Fructofuranosides

The construction of β-d-fructofuranosidic linkages is one of the major challenges in carbohydrate chemistry. In this work, we developed an efficient method for the synthesis of β-d-fructofuranosides by using a 6-picoloyl-protected fructofuranosyl thioglycoside as the glycosyl donor. Subsequently, we applied the approach to a wide variety of donors and acceptors. Furthermore, the successful synthesis of levantetrose confirmed its applicability in the multistep synthesis of oligosaccharides.

Fluorescent Hexose Conjugates Establish Stringent Stereochemical Requirement by GLUT5 for Recognition and Transport of Monosaccharides

The specificity characteristics of transporters can be exploited for the development of novel diagnostic therapeutic probes. The facilitated hexose transporter family (GLUTs) has a distinct set of preferences for monosaccharide substrates, and while some are expressed ubiquitously (e.g., GLUT1), others are quite tissue specific (e.g., GLUT5, which is overexpressed in some breast cancer tissues). While these differences have enabled the development of new molecular probes based upon hexose- and tissue-selective uptake, substrate design for compounds targeting these GLUT transporters has been encumbered by a limited understanding of the molecular interactions at play in hexose binding and transport. Four new fluorescently labeled hexose derivatives have been prepared, and their transport characteristics were examined in two breast cancer cell lines expressing mainly GLUTs 1, 2, and 5. Our results demonstrate, for the first time, a stringent stereochemical requirement for recognition and transport by GLUT5. 6-NBDF, in which all substituents are in the d-fructose configuration, is taken up rapidly into both cell lines via GLUT5. On the other hand, inversion of a single stereocenter at C-3 (6-NBDP), C-4 (6-NBDT), or C-5 (6-NDBS) results in selective transport via GLUT1. An in silico docking study employing the recently published GLUT5 crystal structure confirms this stereochemical dependence. This work provides insight into hexose-GLUT interactions at the molecular level and will facilitate structure-based design of novel substrates targeting individual members of the GLUT family and forms the basis of new cancer imaging or therapeutic agents.

Solvent Polarity-Controlled Selective Synthesis of Methyl Pyranoside and Furanoside

A selective synthesis of methyl d-glucopyranoside or furanoside has been developed using 2,4,6-trichloro-1,3,5-triazine (TCT)-activated DMSO and d-glucose in methanol. At higher concentrations of DMSO, only pyranoside was formed and at lower concentrations of DMSO, only furanoside was formed. This method was also successfully applied to other sugars. In terms of reaction rates, selectivities, and yields, this method is better than most of the currently used methods.