Synthesis of protected 5'-aminouridine for modification of solid-support in synthesis of modified sIRNA

Abstract

My research was focused on the multi-step synthesis of solid support bearing 5'-aminouridine for automated synthesis of siRNAs. The project started with the preparation of 5'-azidouridine using either a Mitsonobu reaction with hydrazoic acid or a reaction of uridine with lithium azide, triphenylphosphine and carbon tetrabromide. Azide was hydrogenated to form 5'-aminouridine and further treated with para-methoxytrityl chloride to protect the amino group. The generated 5'-amino-5'-N-methoxytrityluridine was then treated with a solution of ortho-chlorobenzoyl chloride to protect the 2' hydroxyl group, followed by succinic anhydride in the presence of 4-dimethylaminopyridine (DMAP) to form a mixture of protected 2' and 3' succinates. All new compounds were analyzed and characterized using NMR techniques. The protected amino uridine succinate was then loaded onto solid support - long chain aminoalkyl controlled pore glass (LCAA-CPG) to be used in solid phase synthesis of amide modified siRNA. The succinate moiety was coupled to the free amino groups on the CPG using N,N'-dicyclohexylcarbodiimide (DCC ) N-hydroxybenzotriazole (HOBT ) to generate a stable amide bond between the ribonucleoside and the CPG. The loading of the protected 5'-aminouridine on CPG was quantified by following acid catalyzed detritylation at 478 nm using a UV-VIS spectrometer. The solid phase support will be used for preparation of amide modified siRNAs. We propose that these non-ionic mimics of the phosphate backbone will confer high nuclease resistance to siRNAs. Further, the backbone of the modified siRNAs will have an overall decreased negative charge, which may help crossing the cellular membrane. We anticipate that these properties may improve the biodistribution and pharmacokinetics of modified siRNAs.