Synthesis and antiviral effects of 2-heteroaryl substituted adenosine and 8-heteroaryl substituted guanosine derivatives

Postsynthetic on column RNA labeling via Stille coupling

Stille Coupling is a versatile C-C bond forming reaction with high functional group tolerance under mild conditions. Our on column synthesis concept for RNA modification is based on the incorporation of iodo substituted nucleotide precursors to RNA during automated standard solid phase synthesis via TBDMS-, TC-, and ACE- protecting group strategies. Subsequently, the RNA, still bound on solid support, is ready for orthogonal postsynthetic functionalization via Stille cross-couplings utilizing the advantages of solid phase synthesis. Several monomer test reactions were employed with 2-iodo adenosine and 5-iodo uridine and organostannanes as coupling partners under different conditions, changing the catalyst/ligand system, temperature, and reaction time as well as conventional heating and microwave irradiation. Finally, Stille cross-couplings under optimized conditions were transferred to fully protected 5-mer and 12-mer RNA oligonucleotides on-column. Deprotection and cleavage from solid support resulted in site-specifically labeled oligonucleotides. Derivatizations via Stille cross-couplings were performed initially with vinyltributylstannane as well as later with 2-furanyl-, 2-thiophene-, and benzothiophene-2-tributylstannanes yielding fluorescently functionalized RNA.

Furan Decorated Nucleoside Analogues as Fluorescent Probes: synthesis, photophysical evaluation and site-specific incorporation

The synthesis and photophysical evaluation of modified nucleoside analogues in which a five-membered heterocycle (furan, thiophene, oxazole and thiazole) is attached to the 5 position of 2'-deoxyuridine are reported. The furan containing derivative is identified as the most promising responsive nucleoside of this family due to its emission quantum efficiency and degree of sensitivity to its microenvironment. The furan moiety was then attached to the 5 position of 2'-deoxycytidine as well as the 8 position of adenosine and guanosine. Photophysical evaluation of these four furan containing nucleoside analogues reveal distinct differences in the absorption, emission and quantum efficiency depending upon the class of nucleoside (pyrimidine or purine). Comparing the photophysical properties of all furan containing nucleosides, identifies the furan thymidine analogue, 5-(fur-2-yl)-2'-deoxyuridine, as the best candidate for use as a responsive fluorescent probe in nucleic acids. 5-(fur-2-yl)-2'-deoxyuridine was then converted to the corresponding phosphoramidite and site specifically incorporated into DNA oligonucleotides with greater than 88% coupling efficiency. Such furan-modified oligonucleotides form stable duplexes upon hybridization to their complementary DNA strands and display favorable fluorescent features.

Cross-coupling reactions of unprotected halopurine bases, nucleosides, nucleotides and nucleoside triphosphates with 4-boronophenylalanine in water. Synthesis of (purin-8-yl)- and (purin-6-yl)phenylalanines

An expeditious and highly efficient single-step methodology for the introduction of a phenylalanine moiety into position 8 and 6 of the purine scaffold was developed based on aqueous-phase Pd-catalysed Suzuki-Miyaura cross-coupling reactions of unprotected 4-boronophenylalanine with 8-bromo- or 6-chloropurines. The scope of the methodology was demonstrated by syntheses of unprotected (adenin-8-yl)phenylalanine base, nucleosides, nucleotides and nucleoside triphosphates as well as (purin-6-yl)phenylalanine base and nucleosides. All these products were obtained in high yields and in optically pure form.