Fluorescent 5‑Pyrimidine and 8‑Purine Nucleosides Modified with an N‑Unsubstituted 1,2,3-Triazol-4-yl Moiety

The Cu­(I)- or Ag­(I)-catalyzed cycloaddition between 8-ethynyladenine or guanine nucleosides and TMSN3 gave 8-(1-H-1,2,3-triazol-4-yl) nucleosides in good yields. On the other hand, reactions of 5-ethynyluracil or cytosine nucleosides with TMSN3 led to the chemoselective formation of triazoles via Cu­(I)-catalyzed cycloaddition or vinyl azides via Ag­(I)-catalyzed hydroazidation. These nucleosides with a minimalistic triazolyl modification showed excellent fluorescent properties with 8-(1-H-1,2,3-triazol-4-yl)-2′-deoxyadenosine (8-TrzdA), exhibiting a quantum yield of 44%. The 8-TrzdA 5′-triphosphate was incorporated into duplex DNA containing a one-nucleotide gap by DNA polymerase β.