Solid-Phase Synthesis of Glyco-Oligonucleotide Conjugates

Solid-phase supports for oligonucleotide synthesis

This unit attempts to provide a reasonably complete inventory of over 280 solid supports available to oligonucleotide chemists for preparation of natural and 3'-modified oligonucleotides. Emphasis is placed on non-nucleosidic solid supports. The relationship between the structural features of linkers and their behavior in oligonucleotide synthesis and deprotection is discussed wherever the relevant observations are available.

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.

Synthesis, biophysical characterization, and anti-HIV activity of glyco-conjugated G-quadruplex-forming oligonucleotides

Novel hybrid oligonucleotides carrying the G-quadruplex-forming d(5'TGGGAG3') sequence, conjugated with mono- or disaccharides at the 3' or 5'-end through phosphodiester bonds, have been synthesized as potential anti-HIV agents, via a fully automated, online phosphoramidite-based solid-phase strategy. CD-monitored thermal denaturation studies on the resulting quadruplexes indicated the insertion of a single monosaccharide at the 3'-end as the optimal modification, conferring improved stability to the quadruplex complex. In addition, the 3'-conjugation with glucose or mannose converted the anti-HIV inactive unmodified oligomer into active compounds. On the contrary, the 5'-tethering with these monosaccharides, as well as the conjugation, either at the 5' or 3'-end, with sucrose, were in all cases detrimental to quadruplex stability and did not improve the biological activity. On the basis of the assumption that the kinetically and thermodynamically favored formation of the quadruplex complex is a prerequisite for efficient antiviral activity, a novel bis-conjugated oligonucleotide was designed. This combined a mannose residue at the 3'-phosphate end with bulky aromatic tert-butyldiphenylsilyl (TBDPS) group at the 5'-end, previously shown to markedly favor the formation of quadruplex complexes. The 5',3'-bis-conjugated 6-mer, for which a detailed biophysical characterization has been carried out, resulted in 3-fold greater antiviral activity against HIV-1 than the sole 3'-glyco-conjugated oligonucleotide.

Synthesis and applications of oligonucleotide-carbohydrate conjugates

Nowadays, oligonucleotide-carbohydrate conjugates are used in antisense biotechnology and in the study of glycosylated DNA functioning in vitro. The application of mono- and disaccharide phosphoramidites, solid-phase supports with immobilized carbohydrates, glycosylated nucleoside phosphoramidites, and postsynthetic conjugation of reactive sugar derivatives with oligonucleotides for preparation of oligonucleotide-carbohydrate conjugates have been systematically studied. The advantages and disadvantages of these approaches are considered. Possible strategies for synthesis of glycoclusters with different topologies conjugated to DNA are discussed. Applications of oligonucleotide-carbohydrate conjugates are highlighted. Studies of interactions of glycosylated oligonucleotides with proteins and effective cell-specific delivery of oligonucleotide-carbohydrate conjugates are discussed.

Glycotargeting to improve cellular delivery efficiency of nucleic acids

Nucleic acids bearing glycans of various structures have been under vigorous investigation in the past decade. The carbohydrate moieties of such complexes can serve as recognition sites for carbohydrate-binding proteins-lectins-and initiate receptor-mediated endocytosis. Therefore, carbohydrates can enhance cell targeting and internalization of nucleic acids that are associated with them and thus improve the bioavailability of nucleic acids as therapeutic agents. This review summarizes nucleic acid glycosylation in nature and approaches for the preparation of both non-covalently associated and covalently-linked carbohydrate-nucleic acid complexes.