5-Ethynyl-1-β-D-ribofuranosyl-1H-[1,2,3]triazole-4-carboxylic acid amide (ETCAR) and its analogues: synthesis and cytotoxic properties.

Efficient Pd(0)-catalysed synthesis of 5-alkynyl-1-β-D-ribofuranosyl-1H-[1,2,3]triazole-4-carboxylic acid amide depends on the presence of different protecting groups of the ribose moiety. Peracetylated 5-iodo substrate (15) couples with terminal alkynes or trimethyl-[(tributylstannyl)ethynyl]silane in 50-71% and 72% yield (ETCAR), respectively, although its hydrodehalogenation to 19 is noticeable. On the other hand, hydrodehalogenation of acetonide (16) predominates over coupling with terminal alkyne and slightly decreases a yield of cross-coupling reaction with trimethyl[(tributylstannyl)ethynyl]silane. Alternative conditions of reaction with terminal alkynes, to exclude so far identified hydride sources to produce hydridopalladium species, have been established for acetonide 16 and allowed to achieve 72% of coupling. Fluoromethyl derivative (42) was prepared from its 5-hydroxymethyl precursor by fluorination with DAST. Additionally, X-ray structural analysis of 42 was performed. All 1,2,3-triazolonucleosides and two synthesized cycloSal-pronucleotides were evaluated for cytotoxic activity against K562, HeLa and HUVEC cells.