Prodrug Approaches of Nucleotides and Oligonucleotides

Abstract

The main threshold for the therapeutic applications of nucleotides and oligonucleotides is their ionic structure which implies poor cellular uptake and unfavorable pharmacokinetic parameters. To circumvent these problems, the anionic phosphate moieties may be temporarily masked with enzymolabile protecting groups to form neutral pronucleotides or pro-oligonucleotides. In cells, enzymes cleave the protecting groups and release the parent drug. Several prodrug strategies have been developed, but the kinetics and mechanisms of the deprotection of potential prodrug candidates are still often poorly known. The purpose of the present review is to summarize the current knowledge on the chemical aspects of alternative prodrug strategies at nucleotide and oligonucleotide level.

Hydrolytic Reactions of Thymidine 5′‐O‐Phenyl‐N‐Alkylphosphoramidates, Models of Nucleoside 5′‐Monophosphate Prodrugs

“…[1] Phosphoramidate pronucleotides constitute one class of such prodrug candidates. [2,3] In particular, aryl esters of nucleoside 5'-phosphoramidates derived from a-amino acid esters, such as 1, have received attention. [4][5][6][7][8] This kind of prodrug has shown higher antiviral potency on cell lines than the parent nucleoside analogues.…”

“…Hydroxide-ioncatalyzed P À OPh bond cleavage of the starting material 3 occurred as a side reaction. Comparative measurements with thymidine 5'-{N-[(1S)-2-oxo-2-methoxy-1-methylethyl]phosphoramidate} (4) revealed that, under acidic conditions, this diester-like compound is hydrolyzed by P À N bond cleavage three orders of magnitude more rapidly than (3) has been studied over a wide pH range (from H 0 = 0 to pH 8) at 908C by analyzing the composition of aliquots withdrawn from the reaction mixture at appropriate time intervals by reversed-phase (RP) HPLC. Comparative measurements have been carried out with thymidine 5'-{N-[(1S)-2-oxo-2-methoxy-1-methylethyl]phosphoramidate} (4) and thymidine 5'-(O-phenyl-Nisopropylphosphoramidate) (5).…”

A Review on Anti-HCV Agents Targeting Active Site and Allosteric Sites of Non-Structural Protein 5b [Ns5b]

“…The ionic nature of the phosphate group present in nucleotides prevents them from penetrating into the cell membrane; hence they are delivered as uncharged nucleosides. Once delivered these nucleosides are phosphorylated to 5'-triphosphate form [active form) by cellular kinases, where the formation of the monophosphate form is the rate limiting step [21,22]. Many of these compounds have progressed to clinical trials and they act in synergy with interferon and Ribavirin combination.…”

4-Oxoheptanedioic acid: an orthogonal linker for solid-phase synthesis of base-sensitive oligonucleotides

“…Synthesis of acid-and base-labile conjugates of oligonucleotides, oligosaccharides or small molecular alcohols on a solid support may require utilization of an orthogonal linker which (1) anchors the molecule via a hydroxyl group, (2) withstands various chemical manipulations, but (3) may still be cleaved under mild conditions. Antisense oligonucleotides bearing biodegradable phosphate protections offer an illustrative example.…”

“…Antisense oligonucleotides bearing biodegradable phosphate protections offer an illustrative example. 1 The biodegradability is usually based on enzymatically hydrolyzable ester linkages which do not withstand conventional ammonolytic deprotection and, hence, an orthogonally cleavable linker and orthogonally removable nucleobase protections have to be used. 2 Unfortunately, there are few such linkers which are readily available.…”