Facile preparation of the oxetane-nucleosides

Stereocontrolled synthesis of α-d-allulofuranosides using α-selective d-fructofuranosidation reaction

Stereocontrolled synthesis of rare sugar derivatives, namely α-d-allulofuranosides, was achieved using d-fructose, one of the most abundant carbohydrates in nature. The following are the key steps of the α-d-allulofuranosides' synthesis. (1) An α-selective glycosidation reaction of 1,3,4,6-tetra-O-benzoylated d-fructofuranosyl donor to obtain α-d-fructofuranosides with 98 %-75 % isolated yields. (2) A regioselective 1,4,6-tri-O-pivaloylation reaction of the tetraol of α-d-fructofuranosides with the C3-hydroxy group remaining intact. (3) The oxidation of the C3-hydroxy group followed by the stereoselective reduction of the C3-carbonyl group. Primary and secondary alcohols and sugars can be used as glycosyl acceptors and aglycones for the following pivaloylation and stereoinversion reactions to obtain α-d-allulofuranosides.

Novel conformationally constrained 2'-C-methylribonucleosides: synthesis and incorporation into oligonucleotides

Synthesis of two novel conformationally constrained bicyclic ribonucleoside phosphoramidites bearing a 2'-C-methyl substituent has been accomplished. These phosphoramidites were used to incorporate the corresponding 2'-C-methyl nucleotides into oligonucleotides and to study their effects on duplex thermal stability. Whereas the C2'-O4'-linked LNA-type derivative induced severe destabilization of duplexes formed with complementary DNA and RNA, the C3'-O4'-linked derivative induced RNA-selective hybridization with increased affinity relative to that of the unmodified DNA-based probe.

Diastereoselective synthesis of (+/-)-1',4'-dimethyluridine

The de novo synthesis of racemic 1',4'-dimethyluridine was accomplished in 12 steps starting from 2,5-dimethylfuran and vinylene carbonate. Key steps of the sequence include the stereoconvergent preparation of a meso diacid, and a stereoselective glycosylation without neighboring group participation. Such 1',4'-disubstituted ribonucleoside analogues are undisclosed compounds, which may present interesting biological activities.

O2,1'-anhydro-(beta-D-psicofuranosyl)thymine and 1-(1',4'-O-anhydro-beta-D-psicofuranosyl)thymine: the crystal structures versus the 1H NMR and ab initio data

The crystal structures of the title compounds 1 and 2 have been determined. Relation between the stereochemistry of both nucleosides in the crystal state and the (1)H NMR data in solution as well as the ab initio calculations is discussed.