Synthesis of 8-Substituted 2'-Deoxyisoguanosines via Unprotected 8-Brominated 2-Amino-2'-deoxyadenosine

Optimized Method for the Synthesis of Alkyne-Modified 2'-Deoxynucleoside Triphosphates

A general approach is presented for synthesizing alkyne-modified nucleoside triphosphates via the Sonogashira cross-coupling reaction of unprotected halogenated 2'-deoxynucleoside, followed by monophosphorylation and the reaction of the corresponding phosphoromorpholidate with tributylammonium pyrophosphate. A highly efficient approach for the milligram-scale synthesis of base-modified nucleoside triphosphates with an amino acid-like side chain was developed. The present chemical method outweighs the other reported methods of a base-modified nucleoside triphosphates synthesis in terms of it being a protection-free strategy, the shortening of reaction steps, and increased yields (about 70%). The resulting 8-alkynylated dATP was tested as a substrate for DNA polymerases in a primer extension reaction.

DNA with Purine-Purine Base Pairs: Size and Position of Isoguanine and 8-Aza-7-deazaisoguanine Clickable Residues Control the Molecular Recognition of Guanine and 5-Aza-7-deazaguanine

Purine-purine base pairs represent an alternative recognition system to the purine-pyrimidine pairing reported by Watson and Crick. Modified purines are the source for non-canonical interactions. To mimic dG-dC interactions, 2'-deoxyisoguanosine (1a) and 8-aza-7-deaza-2'-deoxyisoguanosine (2a) are used to construct base pairs with 2'-deoxyguanosine or 5-aza-7-deaza-2'-deoxyguanosine (dZ). This work reports the chemical functionalization of 1a and its shape mimic 2a in purine-purine base pairs. Clickable rigid ethynyl and more flexible octadiynyl side chain derivatives of 1a and 2a were synthesized. They were protected and converted into phosphoramidites. Building blocks were employed in the synthesis of base-modified 12-mer oligonucleotides with clickable side chains. Pyrene azide was clicked to the linkers. After hybridization, oligonucleotides with purine-purine base pairs were constructed with linkers and pyrene adducts at position-8 of isoguanine and at position-7 of 8-aza-7-deazaisoguanine. Recognition and stability of purine-purine base pairs were explored using T_m values, thermodynamic data, and CD-spectroscopic changes. Side chains at position-7 of 8-aza-7-deazaisoguanine-guanine base pairs or with 5-aza-7-deazaguanine are well accommodated in DNA, whereas functionalization at 8-position of isoguanine makes the DNA unstable. Pyrene click adducts verified the observation. In conclusion, position-7 is the place of choice for purine-purine base pair functionalization.

Bright fluorescent purine analogues as promising probes

Modified bright fluorescent nucleosides that respond to the microenvironment have great potential as probes. A series of novel 8-(phenylethynyl)phenylated 2-amino-2'-deoxyadenosine and 2'-deoxyisoguanosine derivatives have been synthesized by Sonogashira-type coupling reaction and Suzuki reaction. The maximum emission of the new compounds is in the visible region, with strong solvatochromicity and pH-dependent fluorescent properties. Furthermore, some of them exhibit bright fluorescence emissions in various solvents (ε × Φ = 4000-39,000 cm-1 M-1). These consequences indicate that purine analogues could respond to the microenvironment and serve as promising fluorescent probes.Supplemental data for this article is available online at https://doi.org/10.1080/15257770.2021.2004418 .