1,2,3-Triazoles as leaving groups: SNAr reactions of 2,6-bistriazolylpurines with O- and C-nucleophiles

Synthesis of Fluorescent C-C Bonded Triazole-Purine Conjugates

A design toward C-C bonded 2,6-bis(1H-1,2,3-triazol-4-yl)-9H-purine and 2-piperidinyl-6-(1H-1,2,3-triazol-4-yl)-9H-purine derivatives was established using the combination of Mitsunobu, Sonogashira, copper (I) catalyzed azide-alkyne cycloaddition, and SNAr reactions. 11 examples of 2,6-bistriazolylpurine and 14 examples of 2-piperidinyl-6-triazolylpurine intermediates were obtained, in 38-86% and 41-89% yields, respectively. Obtained triazole-purine conjugates expressed good fluorescent properties which were studied in the solution and in the thin layer film for the first time. Quantum yields reached up to 49% in DMSO for bistriazolylpurines and up to 81% in DCM and up to 95% in DMSO for monotriazolylpurines. Performed biological studies in mouse embryo fibroblast, human keratinocyte, and transgenic adenocarcinoma of the mouse prostate cell lines showed that most of obtained triazole-purine conjugates are not cytotoxic. The 50% cytotoxic concentration of the tested derivatives was in the range from 59.6 to 1528.7 µM.

Synthesis of 6-Selanyl-2-triazolylpurine Derivatives Using 2,6-Bistriazolylpurines as Starting Materials

Two pathways toward 6-selanyl-2-triazolylpurine derivatives were designed. The first method involved the synthesis of 2-chloro-6-selanylpurine derivatives, further SNAr reaction with NaN3, and following CuAAC using different alkynes. The second method was based on the synthesis of 2,6-bistriazolylpurine derivatives as starting materials followed by SNAr reaction with commercial or in situ generated selenols as nucleophiles. A series of 2-chloro-6-selanylpurine derivatives were obtained in yields up to 84%. It was found that in the latter compounds, 6-selanyl moiety was the better leaving group compared to 2-chlorosubstituent in SNAr reactions. On the other hand, the SNAr reaction between 2,6-bistriazolylpurines and selenols or diselenides was successful, and 13 examples of 6-selanyl-2-triazolylpurine derivatives were obtained in yields up to 87%. This direct approach for the Se-C bond formation proved the ability of the 1,2,3-triazolyl ring at the C6 position of purine to act as a good leaving group.

Nucleophile-nucleofuge duality of azide and arylthiolate groups in the synthesis of quinazoline and tetrazoloquinazoline derivatives

5-Arylthio-tetrazolo[1,5-c]quinazolines (tautomers of 2-arylthio-4-azido-quinazolines) undergo facile nucleophilic aromatic substitution reactions with amines, alcohols and alkylthiols. This, combined with the recently reported arylsulfanyl group dance, provides straightforward access to 4-azido-2-N-, O-, S-substituted quinazolines and/or their tetrazolo tautomers from commercially available 2,4-dichloroquinazoline. The azidoazomethine-tetrazole tautomeric equilibrium and the electron-withdrawing character of the fused tetrazolo system plays a central role in the developed transformations. 5-Amino-substituted tetrazolo[1,5-c]quinazolines undergo media-controlled tautomeric equilibrium, which permits them to demonstrate the reactivity traditionally associated with the azido substituent. Furthermore, a method for 5-O-substitited tetrazolo[1,5-a]quinazolines from 2,4-diazidoquinazoline was developed during the structural elucidation of the substitution products. The developed methodology will facilitate medicinal chemistry investigations into quinazoline derivatives and the discovered fluorescent properties of some of the products (e.g., 4-(4-phenyl-1H-1,2,3-triazol-1-yl)-2-(4-methylpiperazin-1-yl)quinazoline: λ_em. = 461 nm, Φ_DCM = 0.89) could serve as a starting point for their further applications in analytical and materials science.