Application of 2,6-diazidopurine derivatives in the synthesis of thiopurine nucleosides

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.

SnAr Reactions of 2,4-Diazidopyrido[3,2-d]pyrimidine and Azide-Tetrazole Equilibrium Studies of the Obtained 5-Substituted Tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines

A straightforward method for the synthesis of 5-substituted tetrazolo[1,5-a]pyrido[2,3-e]pyrimidines from 2,4-diazidopyrido[3,2-d]pyrimidine in SnAr reactions with N-, O-, and S- nucleophiles has been developed. The various N- and S-substituted products were obtained with yields from 47% to 98%, but the substitution with O-nucleophiles gave lower yields (20-32%). Furthermore, the fused tetrazolo[1,5-a]pyrimidine derivatives can be regarded as 2-azidopyrimidines and functionalized in copper(I)-catalyzed azide-alkyne dipolar cycloaddition (CuAAC) and Staudinger reactions due to the presence of a sufficient concentration of the reactive azide tautomer in solution. In total, seven products were fully characterized by their single crystal X-ray studies, while five of them were representatives of the tetrazolo[1,5-a]pyrido[2,3-e]pyrimidine heterocyclic system. Equilibrium constants and thermodynamic values were determined using variable temperature ¹H NMR and are in agreement of favoring the tetrazole tautomeric form (ΔG₂₉₈ = -3.33 to -7.52 (kJ/mol), ΔH = -19.92 to -48.02 (kJ/mol) and ΔS = -43.74 to -143.27 (J/mol·K)). The key starting material 2,4-diazidopyrido[3,2-d]pyrimidine presents a high degree of tautomerization in different solvents.

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.

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.

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.

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

A new method for C-N bond transformations into C-P bonds was developed using 1,2,3-triazoles as leaving groups in SNAr-Arbuzov reactions. A series of C6-phosphonated 2-triazolylpurine derivatives was synthesized for the first time, with the isolated yields reaching up to 82% in the C-P-bond-forming event. The SNAr-Arbuzov reaction of 2,6-bistriazolylpurines follows the general regioselectivity pattern of the C6-position being more reactive towards substitution, which was unambiguously proved by X-ray analysis of diethyl (9-heptyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-yl)phosphonate.

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.

2,6-Bis[4-(4-butylphenyl)-1H-1,2,3-triazol-1-yl]-9-dodecyl-9H-purine

Target 2,6-bis[4-(4-butylphenyl)-1H-1,2,3-triazol-1-yl]-9-dodecyl-9H-purine has been prepared via a Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction between 2,6-diazido-9-dodecyl-9H-purine and 4-n-butyl(phenylacetylene) in a 29% yield. The obtained compound was fully characterized by NMR, IR and HRMS.

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.

2,4-Bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines: synthesis and tuning of optical properties by polar substituents

Novel D–π–A–π–D type chromophores – 2,4-bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines were prepared and their photophysical, electrochemical properties in conjunction with quantum chemical calculations were investigated.

2,6-Di-chloro-9-(2',3',5'-tri-O-acetyl-β-d-ribo-furanos-yl)-9H-purine

The title synthetic analog of purine nucleosides, C₁₆H₁₆Cl₂N₄O₇, has its acetyl­ated β-furan­ose ring in a 3′β-envelope conformation, with the corresponding C atom deviating by 0.602 (5) Å from the rest of the ring. The planar part of the furan­ose ring forms a dihedral angle of 65.0 (1)° with the mean plane of the purine bicycle. In the crystal, mol­ecules form a three-dimensional network through multiple C—H⋯O and C—H⋯N hydrogen bonds and C—H⋯π interactions.