Synthesis of Azido and Triazolyl Purine Ribonucleosides

Here, we describe detailed synthetic protocols for preparation of 6-amino/thio-2-triazolylpurine ribonucleosides. First, 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-diazido-9H-purine, to be used as a key starting material, is synthesized in an S_N Ar reaction with NaN₃ starting from commercially available 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-dichloro-9H-purine. Next, 2,6-bis-triazolylpurine ribonucleoside is obtained in a CuAAC reaction between diazidopurine derivative and phenyl acetylene, and used in S_N Ar reactions with N- and S-nucleophiles. In these reactions, the triazolyl ring at the purine C6 position acts as a good leaving group. Cleavage of acetyl protecting groups from the ribosyl moiety is achieved in presence of piperidine. In the S_N Ar reaction with amino acid derivatives, the acetyl groups remain intact. Moreover, 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-2,6-diazido-9H-purine is selectively reduced at the C6 position using a CuSO₄ ·5H₂ O/sodium ascorbate system. This provides a straightforward approach for synthesis of 9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)-6-amino-2-azido-9H-purine. © 2021 Wiley Periodicals LLC Basic Protocol 1: Synthesis of 6-amino-2-triazolylpurine ribonucleosides Basic Protocol 2: Synthesis of 6-thio-2-triazolylpurine ribonucleosides Basic Protocol 3: Synthesis of 6-amino-2-azidopurine ribonucleoside.

Sulfonyl Group Dance: A Tool for the Synthesis of 6-Azido-2-sulfonylpurine Derivatives

9-Substituted 2-chloro-6-sulfonylpurines provide 6-azido-2-sulfonylpurine derivatives with 61-83% yields when treated with sodium azide. Under optimized reaction conditions, the title compounds are obtained in a one-pot process, which involves a sequential treatment of 2,6-dichloropurines with a selected sodium sulfinate and sodium azide. Such a sulfonyl group dance (functional group swap) results from a cascade of S_NAr reactions, which are facilitated by azidoazomethine-tetrazole (azide-tetrazole) tautomeric equilibrium. The formation of Meisenheimer-type intermediates as tetrazolopurine tautomers was supported by various spectroscopic methods, including ¹⁵N NMR.

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

The synthesis of novel fluorescent N(9)-alkylated 2-amino-6-triazolylpurine and 7-deazapurine derivatives is described. A new C(2)-regioselectivity in the nucleophilic aromatic substitution reactions of 9-alkylated-2,6-diazidopurines and 7-deazapurines with secondary amines has been disclosed. The obtained intermediates, 9-alkylated-2-amino-6-azido-(7-deaza)purines, were transformed into the title compounds by CuAAC reaction. The designed compounds belong to the push-pull systems and possess promising fluorescence properties with quantum yields in the range from 28% to 60% in acetonitrile solution. Due to electron-withdrawing properties of purine and 7-deazapurine heterocycles, which were additionally extended by triazole moieties, the compounds with electron-donating groups showed intramolecular charge transfer character (ICT/TICT) of the excited states which was proved by solvatochromic dynamics and supported by DFT calculations. In the 7-deazapurine series this led to increased fluorescence quantum yield (74%) in THF solution. The compounds exhibit low cytotoxicity and as such are useful for the cell labelling studies in the future.

Photochemical behavior of 2-azidopurine tri-O-acetylribonucleoside in aqueous solution: unprecedented transformation into 1-(5'-O-acetyl-β-D-ribofuranosyl)-5-[(2-oxo-1,3,5-oxadiazocan-4-ylidene)amino]-1H-imidazole-4-carbaldehyde

The photochemical behavior of 2-azidopurine 2',3',5'-tri-O-acetylribonucleoside has been investigated in aqueous solution under aerobic and anaerobic conditions. The two major processes under anaerobic irradiation of 2-azidopurine 2',3',5'-tri-O-acetylribonucleoside involve unprecedented transformation into 1-(5'-O-acetyl-β-D-ribofuranosyl)-5-[(2-oxo-1,3,5-oxadiazocan-4-ylidene)amino]-1H-imidazole-4-carbaldehyde and photoreduction to respective 2-aminopurine derivative, whereas under aerobic conditions these two processes occur to a much lesser extent and photooxidation to respective 2-nitropurine derivative dominates. The structures of photoproducts formed were confirmed by NMR and high-resolution electrospray ionization mass spectral data.