Effect of Borate Cocatalysts toward Activity and Comonomer Incorporation in Ethylene Copolymerization by Half-Titanocene Catalysts in Methylcyclohexane.

Ethylene copolymerizations with 2-methyl-1-pentene, 1-dodecene (DD), vinylcyclohexane (VCH), [Me2Si(C5Me4)(N t Bu)]TiCl2 (1), Cp*TiMe2(O-2,6- i Pr2-4-RC6H2) [R = H (2), SiEt3 (3)]-borate, and [A(H)]+[BAr4]- [Ar = C6F5; A(H)+ = N+(H)Me(n-C18H37)2, N+(H)(CH2CF3)(n-C18H37)2, HO+(n-C14H29)2·O(n-C14H29)2, HO+(n-C16H33)2·O(n-C16H33)2; Ar = C10F7, A(H)+ = HO+(n-C14H29)2·O(n-C14H29)2 (B5), N+(H)(CH2CF3)(n-C18H37)2] catalyst systems conducted in methylcyclohexane (MCH) exhibited better comonomer incorporation than those conducted in toluene (in the presence of methylaluminoxane (MAO) or borate cocatalysts). The activity was affected by the borate cocatalyst and 1,3-B5 catalyst systems in MCH and showed the highest activity in the ethylene copolymerizations with VCH and DD.

Syntheses of prodrug-type 2'-O-methyldithiomethyl oligonucleotides modified at natural four nucleoside residues and their conversions into natural 2'-hydroxy oligonucleotides under reducing condition.

We previously reported that reducing-environment-responsive prodrug-type small interfering RNA (siRNA) bearing 2'-O-methyldithiomethyl (2'-O-MDTM) uridine exhibits efficient knockdown activity and nuclease resistance. In this report, we describe the preparation of 2'-O-MDTM oligonucleotides modified not only at uridine but also at adenosine, guanosine and cytidine residues by post-synthetic modification. Precursor oligonucleotides bearing 2'-O-(2,4,6-trimethoxybenzylthiomethyl) (2'-O-TMBTM) adenosine, guanosine, and cytidine were reacted with dimethyl(methylthio)sulfonium tetrafluoroborate to form 2'-O-MDTM oligonucleotides in the same manner as the oligonucleotide bearing 2'-O-TMBTM uridine. Furthermore, the oligonucleotides bearing 2'-O-MDTM adenosine, guanosine, and cytidine were efficiently converted into corresponding natural 2'-hydroxy oligonucleotides under the cytosol-mimetic reducing condition.

Gene silencing by 2'-O-methyldithiomethyl-modified siRNA, a prodrug-type siRNA responsive to reducing environment.

RNAs bearing various 2'-modifications have been synthesized in an effort to improve nuclease resistance. However, the gene silencing activity of small interfering RNAs (siRNAs) has been decreased or sometimes completely suppressed by the chemical modifications. We previously developed a post-synthetic approach for the synthesis of 2'-O-methyldithiomethyl-modified RNA, which can be converted into unmodified RNA under reducing conditions, and named it Reducing-Environment-Dependent Uncatalyzed Chemical Transforming RNA (REDUCT RNA). Here, the gene silencing activity of REDUCT siRNA bearing 2'-O-methyldithiomethyl groups was evaluated. REDUCT siRNA showed more effective gene silencing than unmodified siRNA regardless of the modification site. This result suggests that REDUCT siRNA is converted into unmodified siRNA inside cells as a prodrug-type siRNA.