Efficient synthesis of β-C-glucosides via radical cyclization with a silicon tether based on the conformational restriction strategy

Recent development in the synthesis of C-glycosides involving glycosyl radicals

C-Glycosylation involving glycosyl radical intermediates is a particularly effective approach to access C-glycosides, which are core units of a great number of natural products, bioactive compounds and marketed drugs.

[Development of highly nuclease-resistant chemically-modified oligonucleotides]

Chemical modification of therapeutic oligodeoxyribonucleotides (ODNs) is necessary to avoid not only degradation by endo- and exo-nucleases but also recognition by sensors such as an innate immune system. We have been developing modified nucleosides having an aminoalky linker at the pyrimidine nucleobase or sugar moiety. ODNs containing 5-N-(6-aminohexyl)carbamoyl-2'-deoxyuridine (7) were thermally stabilized about 3°C per modification and were about 160 times more stable to hydrolysis by snake venom phosphodiesterase (a 3'-exonuclease) than unmodified ODNs, but not by endonucleases. On the other hand, ODNs containing 4'-C-(aminoethyl)thymidine (14b), which was synthesized by a newly developed radical cyclization-ring-enlargement reaction by us, were 87 times more stable to hydrolysis by DNase I (an endonuclease) and 133 times more stable in 50% human serum than unmodified ODNs. The highly stereoselective synthesis of 4'-thioribonuclesides ((S)Ns) was also developed using a Pummerer reaction. Human thrombin RNA aptamer (CII-1-37) containing 4'-thiouridine and 4'-thiocytidine was obtained by SELEX with a K(d) value of 4.7 nM, while a previously known RNA aptamer (RNA-24) has a K(d) value of 85 nM. Studies of the modification pattern-RNAi activity relationships by using (S)Ns have been carried out against luciferase genes. We found that siRNAs, which have 4 residues of (S)Ns on both ends of the sense strand and 4 residues on the 3'-end of the antisense strand, were the most effective. 4'-ThioRNA is about 1100 times more stable in 50% human plasma than unmodified RNA. However, oligoribonucleotides ((SM)ONs) containing 2'-O-methyl-4'-thioribonucleosides were 9800 times more stable in 50% human plasma than unmodified RNA. Since (SM)ON duplexes were thermally more stable than unmodified ON duplexes, therefore they would be quite suitable to use for oligonucleotide therapeutics.

Radical Reactions with 2-Bromobenzylidene Group, a Protecting/Radical-Translocating Group for the 1,6-Radical Hydrogen Transfer Reaction

[Structure: see text] The 2-bromobenzylidene group, designed as a novel protecting/radical-translocating (PRT) group, proved to be effective for an unusual 1,6-hydrogen transfer reaction. Using this PRT group, 4-branched ribose derivatives were stereoselectively prepared.