High-Yielding Method for On-Column Derivatization of Protected Oligodeoxy- nucleotides and Its Application to the Convergent Synthesis of 5‘,3‘-Bis-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.

Synthesis of Oligonucleotide Conjugates and Phosphorylated Nucleotide Analogues: An Improvement to a Solid Phase Synthetic Approach

An improvement to our solid phase strategy to generate pharmacologically interesting molecule libraries is proposed here. The synthesis of newo-chlorophenol-functionalised solid supports with very high loading (0.18–0.22 meq/g for control pore glass (CPG) and 0.25–0.50 meq/g for TG) is reported. To test the efficiency of these supports, we prepared nucleotide and oligonucleotide models, and their coupling yields and the purity of the crude detached materials were comparable to previously available results. These supports allow the facile and high-yield preparation of highly pure phosphodiester and phosphoramidate monoester nucleosides, conjugated oligonucleotides, and other yet unexplored classes of phosphodiester and phosphoramidate molecules.

Photocaging strategy for functionalisation of oligonucleotides and its applications for oligonucleotide labelling and cyclisation

We have used a photocaging strategy to develop novel phosphoramidites and expand the repertoire of protecting groups for modification of oligonucleotides by solid-phase synthesis. We synthesised five photolabile phosphoramidites and four new photolabile controlled pore glasses (CPGs). By using these photolabile phosphoramidites and CPGs, modified oligodeoxynucleotides (ODNs) with phosphate, amine, acid, thiol and carbonyl moieties at 5' and/or 3' ends were readily synthesised. To the best of our knowledge, this is the first report of introducing a carbonyl at the 5' end and thiol groups at both ends of ODNs with photolabile modifiers. Terminal labelling was also easily realised in solution or by on-column solid-phase synthesis. By using the photolabile amine modifier and the photolabile acid CPG, cyclisation of an oligodeoxynucleotide was achieved with good yields. This study provides an alternative way to introduce functional groups into oligonucleotides and expand the scope of oligonucleotide bio-orthogonal labelling.

Novel strategies for the site-specific covalent labelling of nucleic acids

To broaden the scope of applications in DNA nano- and biotechnology, material science, diagnostics and molecular recognition the functionalization of DNA is of utmost importance. In the last decade many new methods have been developed to achieve this goal. Apart from the direct chemical synthesis of modified DNA by automated phosphoramidite chemistry incorporation of labelled triphosphates and the post-synthetic labelling approach evolved as valuable methods. New bioorthogonal reactions as Diels-Alder, click and Staudinger ligations pushed forward the post-synthetic approach as new insights into DNA polymerase substrate specificity allowed generation and amplification of labelled DNA strands. These novel developments are summarized herein.

Attachment of reporter and conjugate groups to the 3' termini of oligonucleotides

Conjugation of oligonucleotides at the 3 terminus is less common because this site is used for covalent linkage to solid-phase oligonucleotide synthesis supports. However, 3-oligonucleotide conjugates have several valuable physicochemical properties, including their ability to stabilize nucleic acid hybridization complexes and to retard the activity of exonucleases. This unit discusses methods for preparing oligonucleotides conjugated at the 3 terminus.

An efficient and versatile solid-phase synthesis of 5'- and 3'-conjugated oligonucleotides

[reaction: see text] An easy and efficient solid-phase strategy to obtain 5'- and 3'-oligonucleotide conjugates in highly pure form has been developed. Ad hoc derivatized solid supports, to which the first nucleoside unit can be attached through a phosphate linkage, have been exploited both in a pre- and post-DNA assembly conjugation approach. A number of 5'- or 3'- oligonucleotide conjugates, incorporating a variety of labels covalently linked through a phosphodiester or a phosphoramidate bond, have been synthesized and characterized.

New strategy for the synthesis of 3',5'-bifunctionalized oligonucleotide conjugates through sequential formation of chemoselective oxime bonds

A convenient strategy for the synthesis of bifunctionalized oligonucleotide conjugates bearing two different reporters at the 3' and 5' ends of the oligonucleotide is presented. The method involves the preparation of oligonucleotides bearing an aldehyde and/or aminooxy functionality at each end, followed by reaction to form oxime bonds with appropriately functionalized reporters. The conjugation reactions are carried out under mild aqueous conditions with good reaction yield.

Synthesis of 2'-modified oligodeoxynucleotides via on-column conjugation

Oligodeoxynucleotides modified at the 2'-position of 2'-amino-2'-deoxyuridine or uridine were prepared in high yield and purity using phosphoramidites 2 and 3, respectively. Oligodeoxynucleotide conjugates were prepared on the solid-phase synthesis support following selective unmasking of the nucleophile incorporated in these phosphoramidites. Synthesis of oligodeoxynucleotides modified at the 2'-position of an internal nucleotide provides molecules that are complementary to those previously prepared via a similar approach using C5-substituted pyrimidines. The efficiency of functionalization of the 2'-O-alkylamino-uridine derived from 3 in a protected oligodeoxynucleotide was less susceptible to steric hindrance than the 2'-amino-2'-deoxyuridine in the same polymeric substrate. However, the greater reactivity of the 2'-O-alkylamine containing nucleotide gave rise to undesired acetamide formation resulting from nucleophilic attack on the 5'-terminal acetate in capped failure sequences. This problem was overcome by using 2,2,2-trimethylacetyl anhydride as a capping agent during the automated synthesis cycles. Finally, the efficiency of the photochemical unmasking of the support bound alkylamine on a 1 mumole scale was improved by using two 20 min photolysis cycles, coupled with removing reaction byproducts between cycles.

Synthesis of modified oligodeoxyribonucleotides on a solid-phase support via derivatization of a selectively revealed 2'-amino-2'-deoxyuridine

[formula: see text] High yields of oligodeoxyribonucleotides modified at the C2'-position of site specifically incorporated 2'-amino-2'-deoxyuridine are obtained by photolytically unmasking the nucleophile in an otherwise protected solid-phase support-bound biopolymer.

Convergent solution-phase synthesis of a nucleopeptide using a protected oligonucleotide

A nucleopeptide was prepared in a convergent manner via segmental coupling of the protected biopolymers in solution. The resulting nucleopeptide (4b, 72%) containing the binding site of lambda repressor and a peptide containing the consensus sequence of the DNA binding helix of the helix turn-helix-proteins was obtained using only five equivalents of the peptide relative to the oligonucleotide. This demonstrates that the recently developed method for the solution phase coupling of protected oligonucleotides is amenable to the convergent synthesis of larger nucleopeptides that are potentially capable of adopting secondary structure.