A new, stereocontrolled approach to iminosugar C-glycosides from L-sorbose

1-O-Benzyl-2,3-O-iso-propyl-idene-6-O-tosyl-α-l-sorbo-furan-ose

IN THE TITLE COMPOUND (SYSTEMATIC NAME

{(3aS,5S,6R,6aS)-3a-[(benz-yloxy)meth-yl]-6-hy-droxy-2,2-di-methyl-tetra-hydro-furo[2,3-d][1,3]dioxol-5-yl}methyl 4-methyl-benzene-sulfonate), C23H28O8S, the absolute structure and relative stereochemistry of the four chiral centres have been established by X-ray crystallography, with the absolute configuration inferred from the use of l-sorbose as the starting material. The central furan-ose ring adopts a slightly twisted envelope conformation (with the C atom bearing the methyl-benzene-sulfonate substituent as the flap) from which three substituents depart pseudo-axially (-CH2-O-benzyl, -OH and one acetonide O atom) and two substituents pseudo-equatorially (-CH2-O-tosyl and second acetonide O atom). The dioxalane ring is in a flattened envelope conformation with the fused CH C atom as the flap. In the crystal, mol-ecules pack in columns along [010] linked by O-H⋯O hydrogen bonds involving the furan-ose hy-droxy group and furan-ose ether O atom.

Synthesis of N-substituted iminosugars from 2'-carbonyl-C-glycofuranosides

Under basic conditions 2'-carbonyl 5-N-substituted-C-glycofuranosides undergo a tandem beta-elimination and intramolecular hetero-Michael addition to form N-substituted iminosugar derivatives in good to excellent yields.

General access to iminosugar C-glycoside building blocks by means of cross-metathesis: a gateway to glycoconjugate mimetics

[reaction: see text] Cross-metathesis reactions of alpha-1-C-allyl-1-deoxynojirimycin derivatives 7a,b and various functionalized alkenes mediated by Grubbs's catalyst 3 are reported. The reactions showed reasonable to very good yields and excellent E/Z selectivity. This methodology allows the efficient and convergent synthesis of iminosugar C-glycosides with a great degree of structural diversity in the aglycone, opening the way to a variety of new glycoconjugate mimetics of biological interest.

Synthesis of 5'-amino-5'-phosphonate analogues of pyrimidine nucleoside monophosphates

The 5'-amino-5'-phosphono derivatives of cytidine, cytosine arabinoside (ara-C), and uridine have been prepared via the corresponding nucleoside aldehydes. Phosphite addition to imines derived from the nucleoside aldehydes and p-methoxybenzylamine was efficient, and use of this amine allowed cleavage of the products to the parent amino phosphonic acids. The phosphite additions proved to be diastereoselective, with the cytidine and uridine derivatives favoring the 5'S stereochemistry and the ara-C derivative favoring the 5'R isomer. The stereochemistry of one cytidine derivative was established by single-crystal diffraction analysis, and detailed comparisons of the (13)C NMR data allowed assignments of the other amino phosphonates.

A general strategy for the practical synthesis of nojirimycin C-glycosides and analogues. Extension to the first reported example of an iminosugar 1-phosphonate

An efficient and versatile strategy for the synthesis of nojirimycin C-glycosides and related compounds with full stereocontrol is reported. The key steps of the process are the addition of organometallic reagents onto an L-sorbose-derived imine (13) followed by an internal reductive amination. The addition step, which controls the alpha- vs beta-configuration at the pseudoanomeric center in the final product, is highly diastereoselective (re-face addition), and the stereoselectivity can be effectively inverted by adding an external monodentate Lewis acid (si-face addition). The complete synthesis could be achieved in 10 steps only from commercially available 2,3;4,6-di-O-isopropylidene-alpha-L-sorbofuranose and provided alpha- or beta-1-C-substituted 1-deoxynojirimycin derivatives in 27-52% overall yield. The strategy was successfully extended to the first example of an iminosugar 1-phosphonate. The methodology provides access to a wide range of biologically relevant glycoconjugate mimetics in which the glycosidic function is replaced by an imino-C-glycosidic linkage.