1,2,3-Triazoles as leaving groups in SNAr-Arbuzov reactions: synthesis of C6-phosphonated purine derivatives

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.

Improvements, Variations and Biomedical Applications of the Michaelis-Arbuzov Reaction

Compounds bearing the phosphorus–carbon (P–C) bond have important pharmacological, biochemical, and toxicological properties. Historically, the most notable reaction for the formation of the P–C bond is the Michaelis–Arbuzov reaction, first described in 1898. The classical Michaelis–Arbuzov reaction entails a reaction between an alkyl halide and a trialkyl phosphite to yield a dialkylalkylphosphonate. Nonetheless, deviations from the classical mechanisms and new modifications have appeared that allowed the expansion of the library of reactants and consequently the chemical space of the yielded products. These involve the use of Lewis acid catalysts, green methods, ultrasound, microwave, photochemically-assisted reactions, aryne-based reactions, etc. Here, a detailed presentation of the Michaelis–Arbuzov reaction and its developments and applications in the synthesis of biomedically important agents is provided. Certain examples of such applications include the development of alkylphosphonofluoridates as serine hydrolase inhibitors and activity-based probes, and the P–C containing antiviral and anticancer agents.

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

A new approach was designed for the synthesis of C6-substituted 2-triazolylpurine derivatives. A series of substituted products was obtained in SNAr reactions between 2,6-bistriazolylpurine derivatives and O- and C-nucleophiles under mild conditions. The products were isolated in yields up to 87%. The developed C-O and C-C bond forming reactions clearly show the ability of the 1,2,3-triazolyl ring at the C6 position of purine to act as leaving group.