Front Cover: An AZT Analog with Strongly Pairing Ethynylpyridone Nucleobase and Its Antiviral Activity against HSV1 (Chem. Biodiversity 1/2021)

High Fidelity Enzyme‐Free Primer Extension with an Ethynylpyridone Thymidine Analog

“…The elaboration of C ‐nucleosides is more complicated than that of N ‐nucleosides, both in nature and in organic synthesis. The assembly of 1 w required 14 steps in our case, including the elaboration of the glycosyl donor and the base,[ 35 , 38 ] and a spontaneous formation of such a structure under prebiotic conditions appears unlikely to us. This may help to explain why this structure is not found in nature.…”

“…[40] Besides pyridone C-nucleotide 1 w, the OAt esters of the four building blocks with canonical bases (1 a-t) were employed. [23,26] The synthesis of 1 w (Figure 1A) started from 3'-azido nucleoside 7, [38] which is accessible via a Heck reaction between a glycal and the iodide of the aglycone, [41,42] followed by protecting group manipulations, reduction to the xylofuranoside, and a Mitsunobu reaction installing the azido group. Azide 7 was converted to aminonucleoside 8 via Staudinger reduction and then Azoc-protected to give 9.…”

“…Figure 1.Building block synthesis and primer extension. A) Synthesis of 1 w from 7;[38] a) PPh 3 , THF/H 2 O, 45 °C; b) azidomethyl(4-nitrophenyl) carbonate, DIPEA, DMF, 72 % over two steps; c) POCl 3 , pyridine, H 2 O, CH 3 CN, À 10 °C, 56 %; d) HOAt, EDC, H 2 O, pH 5, 68 %; B) enzyme-free primer extension with template 2 on magnetic beads, extension buffer = 0.2 M HEPBS 0.4 M NaCl, 0.08 M MgCl 2 , pH 8.9; deprotection with 0.3 M tris(2-carboxyethyl)-phosphine (TCEP) in buffer at 0 °C for 60 min.…”

“…[ 36 , 37 ] Further, an ethynylpyridone analog of azidothymidine (AZT) has recently shown detectable antiviral activity. [38] This prompted us to ask whether nucleotide monomers with the ethynylpyridone base would be successfully incorporated in primer extension assays.…”

“…On the other hand, our results show that structure space holds interesting analogs of thymidine in store, and suggests that strongly pairing nucleotides, accessibly by organic synthesis, may be developed into new antivirals. [38] …”