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

Design, Synthesis, and Cellular Uptake of Oligonucleotides Bearing Glutathione-Labile Protecting Groups

Glutathione-labile protecting groups for phosphodiester moieties in oligonucleotides were designed, synthesized, and incorporated into oligonucleotides. The protecting groups on the phosphodiester moieties were cleaved in a buffer containing 10 mM glutathione, which was used as a model of intracellular fluid. Cellular uptake of oligonucleotides bearing glutathione-labile protecting groups was strongly affected by the location and number of the protecting groups.

Development of Protecting Groups for Prodrug-Type Oligonucleotide Medicines

In recent years, nucleic acid-based drug therapeutics have gained considerable attention for their potential in the treatment of various diseases. However, their therapeutic value is greatly hindered by the challenge of delivering them into cells. One possible strategy to improve cellular uptake is the use of "prodrug-type oligonucleotide medicine" in which negatively charged phosphodiester moieties are masked by bio-labile protecting groups. In this review, we describe our recent studies related to bio-labile protecting groups for phosphodiester moieties in the development of prodrug-type oligonucleotide medicines.

Convergent synthesis and properties of photoactivable NADPH mimics targeting nitric oxide synthases

A new series of photoactivable NADPH mimics bearing one or two O-carboxymethyl groups on the adenosine moiety have been readily synthesized using click chemistry. These compounds display interesting one- or two-photon absorption properties. Their fluorescence emission wavelength and quantum yields (Φ) are dependent on the solvent polarity, with a red-shift in a more polar environment (λ_max,em = 460-467 nm, Φ > 0.53 in DMSO, and λ_max,em = 475-491 nm, Φ < 0.17 in Tris). These compounds show good binding affinity towards the constitutive nNOS and eNOS, confirming for the first time that the carboxymethyl group can be used as a surrogate of phosphate. Two-photon fluorescence imaging of nanotriggers in living cells showed that the presence of one carboxymethyl group (especially on the 3' position of the ribose) strongly favors the addressing of nanotriggers to eNOS in the cell context.

Synthesis and Deprotection of Biodegradably and Thermally Protected Dinucleoside-2',5'-Monophosphate Prodrug Model of 2-5A

Protected dinucleoside-2',5'-monophosphate has been prepared to develop a prodrug strategy for 2-5A. The removal of enzymatically and thermally labile 4-(acetylthio)-2-(ethoxycarbonyl)-3-oxo-2-methylbutyl phosphate protecting group and enzymatically labile 3'-O-pivaloyloxymethyl group was followed at pH 7.5 and 37 °C by HPLC from the fully protected dimeric adenosine-2',5'-monophosphate 1 used as a model compound for 2-5A. The desired unprotected 2',3'-O-isopropylideneadenosine-2',5'-monophosphate (9) was observed to accumulate as a major product. Neither the competitive isomerization of 2',5'- to a 3',5'-linkage nor the P-O5' bond cleavage was detected. The phosphate protecting group was removed faster than the 3'-O-protection and, hence, the attack of the neighbouring 3'-OH on phosphotriester moiety did not take place.

Synthesis and Characterization of Cell-Permeable Oligonucleotides Bearing Reduction-Activated Protecting Groups on the Internucleotide Linkages

Cell-permeable oligodeoxyribonucleotides (ODNs) bearing reduction-activated protecting groups were synthesized as oligonucleotide pro-drugs. Although these oligonucleotides were amenable to solid-phase DNA synthesis and purification, the protecting group on their phosphodiester moiety could be readily cleaved by nitroreductase and NADH. Moreover, these compounds exhibited good nuclease resistance against 3'-exonuclease and endonuclease and good stability in human serum. Fluorescein-labeled ODNs modified with reduction-activated protecting groups showed better cellular uptake compared with that of naked ODNs.

Glutathione-triggered activation of the model of pro-oligonucleotide with benzyl protecting groups at the internucleotide linkage

We have examined substituted benzyl protecting groups for the phosphodiester in oligodeoxyribonucleotides. Stability of the protecting groups in buffer and rates of deprotection by glutathione (GSH) were strongly influenced by benzyl ring substituents.

Development of a photolabile protecting group for phosphodiesters in oligonucleotides

A photolabile protecting group, consisting of an o-nitrobenzyl group and a 3-(2'-hydroxy-3',6'-dimethylphenyl)-2,2-dimethylpropyl moiety, was developed for phosphodiesters in oligodeoxyribonucleotides. Deprotection was triggered by photoirradiation and subsequent spontaneous cyclization to release the naked oligonucleotide.

Solid-phase synthesis of 5'-triphosphate 2'-5'-oligoadenylates analogs with 3'-O-biolabile groups and their evaluation as RNase L activators and antiviral drugs

5'-Triphosphate 2'-5'-oligoadenylate (2-5A) is the central player in the 2-5A system that is an innate immunity pathway in response to the presence of infectious agents. Intracellular endoribonuclease RNase L activated by 2-5A cleaves viral and cellular RNA resulting in apoptosis. The major limitations of 2-5A for therapeutic applications is the short biological half-life and poor cellular uptake. Modification of 2-5A with biolabile and lipophilic groups that facilitate its uptake, increase its in vivo stability and release the parent 2-5A drug in an intact form offer an alternative approach to therapeutic use of 2-5A. Here we have synthesized the trimeric and tetrameric 2-5A species bearing hydrophobic and enzymolabile pivaloyloxymethyl groups at 3'-positions and a triphosphate at the 5'-end. Both analogs were able to activate RNase L and the production of the trimer 2-5A (the most active) was scaled up to the milligram scale for antiviral evaluation in cells infected by influenza virus or respiratory syncytial virus. The trimer analog demonstrated some significant antiviral activity.

Synthesis and enzymatic deprotection of fully protected 2'-5' oligoadenylates (2-5A): towards a prodrug strategy for short 2-5A

Fully protected pA2'p5'A2'p5'A trimers 1a and 1b have been prepared as prodrug candidates for a short 2'-5' oligoadenylate, 2-5A, and its 3'-O-Me analog, respectively. The kinetics of hog liver carboxyesterase (HLE)-triggered deprotection in HEPES buffer (pH 7.5) at 37° has been studied. The deprotection of 1a turned out to be very slow, and 2-5A never appeared in a fully deprotected form. By contrast, a considerable proportion of 1b was converted to the desired 2-5A trimer, although partial removal of the 3'-O-[(acetyloxy)methyl] group prior to exposure of the adjacent phosphodiester linkage resulted in 2',5'→3',5' phosphate migration and release of adenosine as side reactions.

Synthesis and preliminary evaluation of pro-RNA 2'-O-masked with biolabile pivaloyloxymethyl groups in an RNA interference assay

The cellular delivery of bioactive nucleic acid-based drugs such as small interfering RNA (siRNA) represents a major technical hurdle for their pharmaceutical application. Prodrug-like approaches provide an attractive concept to address the delivery problem. With the aim to prepare RNA-based prodrugs bearing biolabile protections which facilitate cellular uptake and are prone to be removed enzymatically inside cells in order to release functional RNA, we synthesized pro-RNA totally or partially masked in 2'-OH position with pivaloyloxymethyl (PivOM) groups. A suitable strategy has been developed to synthesize and to purify base-sensitive mixed 2'-OH/2'-O-PivOM oligoribonucleotides, and to include them in siRNA. In this strategy, the fluoride labile [(triisopropylsilyl)oxy]-benzyloxycarbonyl group (tboc) as nucleobase protection (for A and C), the TBS group as 2'-OH protection and the Q-linker to solid-support were compatible with the PivOM groups masking some 2'-OH. We have taken advantage of the specific stability of the PivOM group to apply selected acidic, basic, and fluoride ions treatment for the deprotection and release of pro-RNA. This kind of pro-siRNA was studied in a human cell culture-based RNAi assay and preliminary promising data are discussed.