7‐Deazapurine (pyrrolo[2,3‐d]pyrimidine) nucleosides are important analogues of biogenic purine nucleosides with diverse biological activities. Replacement of the N7 atom with a carbon atom makes the five‐membered ring more electron rich and brings a possibility of attaching additional substituents at the C7 position. This often leads to derivatives with increased base‐pairing in DNA or RNA or better binding to enzymes. Several types of 7‐deazapurine nucleosides with potent cytostatic or cytotoxic effects have been identified. The most promising are 7‐hetaryl‐7‐deazaadenosines, which are activated in cancer cells by phosphorylation and get incorporated both to RNA (causing inhibition of proteosynthesis) and to DNA (causing DNA damage). Mechanism of action of other types of cytostatic nucleosides, 6‐hetaryl‐7‐deazapurine and thieno‐fused deazapurine ribonucleosides, is not yet known. Many 7‐deazaadenosine derivatives are potent inhibitors of adenosine kinases. Many types of sugar‐modified derivatives of 7‐deazapurine nucleosides are also strong antivirals. Most important are 2′‐C‐methylribo‐ or 2′‐C‐methyl‐2′‐fluororibonucleosides with anti‐HCV activities (several compounds underwent clinical trials). Some underexplored areas of potential interest are also outlined.

2′‐Deoxyadenosine triphosphate (dATP) derivatives bearing diverse substituents (Cl, NH₂, CH₃, vinyl, ethynyl, and phenyl) at position 2 were prepared and tested as substrates for DNA polymerases. The 2‐phenyl‐dATP was not a substrate for DNA polymerases, but the dATPs bearing smaller substituents were good substrates in primer‐extension experiments, producing DNA substituted in the minor groove. The vinyl‐modified DNA was applied in thiol–ene addition and the ethynyl‐modified DNA was applied in a CuAAC click reaction to form DNA labelled with fluorescent dyes in the minor groove

Synthesis and systematic study of T7 RNA polymerase incorporation of base-modified ribonucleotides for the enzymatic synthesis of modified RNA.

Cyclic dinucleotides (CDNs) are second messengers that activate stimulator of interferon genes (STING). The cGAS-STING pathway plays a promising role in cancer immunotherapy. Here, we describe the synthesis of CDNs containing 7-substituted 7-deazapurine moiety. We used mouse cyclic GMP-AMP synthase and bacterial dinucleotide synthases for the enzymatic synthesis of CDNs. Alternatively, 7-(het)aryl 7-deazapurine CDNs were prepared by Suzuki-Miyaura cross-couplings. New CDNs were tested in biochemical and cell-based assays for their affinity to human STING. Eight CDNs showed better activity than 2'3'-cGAMP, the natural ligand of STING. The effect on cytokine and chemokine induction was also evaluated. The best activities were observed for CDNs bearing large aromatic substituents that point above the CDN molecule. We solved four X-ray structures of complexes of new CDNs with human STING. We observed π-π stacking interactions between the aromatic substituents and Tyr240 that are involved in the stabilization of CDN-STING complexes.