Harri Lönnberg

Solid-Phase Synthesis of Oligonucleotide Conjugates Useful for Delivery and Targeting of Potential Nucleic Acid Therapeutics

Olignucleotide-based drugs show promise as a novel form of chemotherapy. Among the hurdles that have to be overcome on the way of applicable nucleic acid therapeutics, inefficient cellular uptake and subsequent release from endosomes to cytoplasm appear to be the most severe ones. Covalent conjugation of oligonucleotides to molecules that expectedly facilitate the internalization, targets the conjugate to a specific cell-type or improves the parmacokinetics offers a possible way to combat against these shortcomings. Since workable chemistry is a prerequisite for biological studies, development of efficient and reproducible methods for preparation of various types of oligonucleotide conjugates has become a subject of considerable importance. The present review summarizes the advances made in the solid-supported synthesis of oligonucleotide conjugates aimed at facilitating the delivery and targeting of nucleic acid drugs.

1-Alkylthioalkylation of nucleoside hydroxyl functions and its synthetic applications : a new versatile method in nucleoside chemistry

Abstract Treatment of appropriately protected nucleosides with a mixture of acetic acid, acetic anhydride and dialkylsulfoxide was shown to give O-(1-alkylthioalkylated) nucleosides that were oxidized to the corresponding sulfoxides and sulfones, or converted via O-halogenomethyl derivatives to various O-substituted nucleosides.

The effect of secondary structure on cleavage of the phosphodiester bonds of RNA.

This review discusses the effects the secondary structure of an RNA molecule has on the inherent reactivity of its phosphodiester bonds, and on the catalytic activity of metal ion-based cleaving agents. The basic principles of the intramolecular transesterification of RNA phosphodiester bonds, particularly cleavage, are first briefly described. Studies of the structural effects on the cleavage, in the absence and in the presence of metal ion catalysts, are then reviewed, and the sources of the reactivity differences observed in different structures are discussed.

A novel solid support for derivatization and subsequent N-alkylation of secondary amines: Preparation of N-alkylated 5- and 6-alkoxy-1,2,3,4-tetrahydroisoquinolines via mitsunobu reaction

Abstract A hydroxymethylated polystyrene resin has been converted to its vinylsulfonylethyl ether (1) by DBU catalyzed addition of the hydroxy groups to divinyl sulfone. The support obtained was used to convert 5- and 6-(tetrahydropyran-2-yloxy)-1,2,3,4-tetrahydroisoquinolines to a set of N -alkylated tetrahydroisoquinolines bearing various 5- and 6-alkoxy substituents (5a-m). The synthesis involved attachment of the starting material to the support by Michael addition, acid-catalyzed removal of the tetrahydropyranyl protection, Mitsunobu etherification, quaternarization with alkyl amines, and release in solution with diisopropylethylamine.

Novel solid supports for the preparation of 3′-derivatized oligonucleotides: Introduction of 3′-alkylphosphate tether groups bearing amino, carboxy, carboxamido, and mercapto functionalities

Abstract Syntheses of 5 non-nucleosidic solid supports (1–5) that enable preparation of oligonucleotides bearing a carboxy,-amino,-carboxamido,- or mercaptoalkyl spacer arm at their 3′-terminus are described. They all contain an ester bond of moderate susceptibility toward nucleophiles. Upon the completion of oligonucleotide chain assembly, this bond may be cleaved by a variety of nucleophiles. These release the oligonucleotide from the support and simultaneously introduce the desired functionality. Differences in the reactivity between the supports prepared are discussed.

Prodrug approaches of nucleotides and oligonucleotides.

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.

The mechanism of the metal ion promoted cleavage of RNA phosphodiester bonds involves a general acid catalysis by the metal aquo ion on the departure of the leaving group

A series of uridine 3′-alkyl phosphates and 3′-aryl phosphates were synthesised and their cleavage was studied in the presence of Zn2+ aquo ions. A βlg value was determined for the Zn2+ promoted cleavage of both types of compounds. Comparison of the results obtained to those reported previously for the cleavage of the same substrates in the absence of metal ion catalysts suggests that the alkyl leaving group departs as an alcohol in the presence of metal ion catalysts. Furthermore, metal ion catalysts seem to enhance the departure. The aryl leaving group, in contrast, departs as an oxyanion.

The effect of protecting groups of the nucleobase and the sugar moieties on the acidic hydrolysis of the glycosidic bond of 2-́deoxyadenosine: a kinet

Abstract The rate constants for the hydrolysis of several N 6 -substituted 2 - deoxyadenosines were measured at different concentrations of oxonium ion in order to assess the role of various N 6 and sugar protecting groups in depurination reaction encountered in nucleic acid synthesis. The site of protonation was established by recording the 15N NMR spectra in DMSO- d 6 both in the absence and presence of trifluoroacetic acid. The exceptional lability of the monocations of N 6-acyl-2 - deoxyadenosines has been accounted for by a preferred N 7 protonation.

The acid-catalyzed hydrolysis of β-d-xylofuranosides

Abstract The rate constants for the hydrolysis of six alkyl and four aryl β- d -xylofuranosides in aqueous perchloric acid at various temperatures have been measured. The effects of varying the aglycon structure on the hydrolysis rate are interpreted in terms of two concurrent reactions. Either, the substrate, protonated on the glycosidic oxygen atom, undergoes a rate-limiting heterolysis to form a cyclic oxocarbonium ion, or, an initial rapid protonation of the ring oxygen is followed by a unimolecular cleavage of the five-membered ring, all subsequent reactions being fast. It is suggested that xylofuranosides having strongly electron-attracting aglycon groups react mainly by the former pathway, whereas the latter is more favourable for substrates having electron-repelling aglycon groups. The negative entropies of activation obtained with the latter compounds are attributed to the rate-limiting opening of the five-membered ring. The rate variations of the hydrolyses of alkyl β- d -xylofuranosides in aqueous perchloric acid-methyl sulfoxide mixtures are interpreted as lending further support for the suggested chance in mechanism.

Complexing of 3d transition metal ions with 9-substituted purines. I. Binding sites in aqueous solution

Abstract Stability constants for cobalt(II), nickel(II), copper(II), and zinc(II) ions with 9-methylpurine and its 2-, 6-, and 8-methyl derivatives have been determined in aqueous solution at 298.2 K. All methyl substituents reduce the complexing ability of 9-methylpurine, the destabilizing effect of the 6-methyl group being far greater than that of the 2- or 8-methyl groups. The equilibrium data obtained are accounted for by competitive attachment of metal ions to N1 and N7 of 9-methylpurine. The downfield shifts that zinc(II) ions exert on the 1H NMR signals of the purine protons are discussed in terms of this model.