Synthesis and enzymatic deprotection of biodegradably protected dinucleoside-2′,5′-monophosphates: 3-(Acetyloxy)-2,2- bis(ethoxycarbonyl)propyl phosphoesters of 3′-O-(acyloxymethyl)adenylyl- 2′,5′-adenosines

Article abstract of DOI:10.1002/cbdv.201000288

As a first step towards a viable prodrug strategy for short oligoribonucleotides, such as 2-5A and its congeners, adenylyl-2′, 5′-adenosines bearing a 3-(acetyloxy)-2,2-bis(ethoxycarbonyl)propyl group at the phosphate moiety, and an (acetyloxy)methyl- or a (pivaloyloxy)methyl- protected 3′-OH group of the 2′-linked nucleoside have been prepared. The enzyme-triggered removal of these protecting groups by hog liver carboxyesterase at pH 7.5 and 37° has been studied. The (acetyloxy)methyl group turned out to be too labile for the 3′-O-protection, being removed faster than the phosphate-protecting group, which results in 2′,5′- to 3′,5′-isomerization of the internucleosidic phosphoester linkage. In addition, the starting material was unexpectedly converted to the 5′-O-acetylated derivative. (Pivaloyloxy)methyl group appears more appropriate for the purpose. The fully deprotected 2′,5′-ApA was accumulated as a main product, although, even in this case, the isomerization of the starting material takes place.