Synthesis and application of a new 2',3'-isopropylidene guanosine substituted cap analog.

The synthesis and biological evaluation of a new cap analog, which is modified at the C2' and C3' positions of N(7)-methylguanosine is reported. The new cap analog, P(1)-2',3'-isopropylidene, 7-methylguanosine-5'P(3)-guanosine-5'triphosphate was assayed with respect to its effects on efficiency of incorporation into RNAs during in vitro transcription, and intracellular stability and translational activity of its 5'-capped mRNAs, upon transfection into HeLa cells. The intracellular stability of 5'-capped and uncapped full length test mRNAs was measured by using a real-time RT-PCR assay. The RNA with the 5'-modified cap was found to be approximately 1.7 times more stable than the RNA with the 5'-standard cap and approximately 2.5 times more stable than the uncapped control RNA. The translational efficiency was monitored by measuring the luciferase activity of a variety of in vitro synthesized and capped RNAs coding for a luciferase fusion protein after transfection into HeLa cells. The RNA capped with the 2',3'-isopropylidene substituted analog, (m(7,2',3'-isopropylidene)G[5']ppp[5']G), was translated the most efficiently, with approximately 2.9-fold more activity than the standard cap (m(7)G[5']ppp[5']G). The observed increase in the level of protein synthesis is likely resulted as a consequence of exclusively forward capped transcripts and increased cellular stability of the 5'-modified capped mRNA (Poly A).