Investigation of 8-Aza-7-Deaza Purine Nucleoside Derivatives

Crystal structure determination and analyses of Hirshfeld surface, crystal voids, inter-molecular inter-action energies and energy frameworks of 1-benzyl-4-(methyl-sulfan-yl)-3a,7a-di-hydro-1H-pyrazolo-[3,4-d]pyrimidine

The pyrazolo-pyrimidine moiety in the title mol-ecule, C13H12N4S, is planar with the methyl-sulfanyl substituent lying essentially in the same plane. The benzyl group is rotated well out of this plane by 73.64 (6)°, giving the mol-ecule an approximate L shape. In the crystal, C-H⋯π(ring) inter-actions and C-H⋯S hydrogen bonds form tubes extending along the a axis. Furthermore, there are π-π inter-actions between parallel phenyl rings with centroid-to-centroid distances of 3.8418 (12) Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (47.0%), H⋯N/N⋯H (17.6%) and H⋯C/C⋯H (17.0%) inter-actions. The volume of the crystal voids and the percentage of free space were calculated to be 76.45 Å3 and 6.39%, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the cohesion of the crystal structure is dominated by the dispersion energy contributions.

Crystal structure determination, Hirshfeld surface, crystal void, inter-molecular inter-action energy analyses, as well as DFT and energy framework calculations of 2-(4-oxo-4,5-di-hydro-1H-pyra-zolo[3,4-d]pyrimidin-1-yl)acetic acid

In the title mol-ecule, C7H6N4O3, the bicyclic ring system is planar with the carb-oxy-methyl group inclined by 81.05 (5)° to this plane. In the crystal, corrugated layers parallel to (010) are generated by N-H⋯O, O-H⋯N and C-H⋯O hydrogen-bonding inter-actions. The layers are associated through C-H⋯π(ring) inter-actions. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯O/O⋯H (34.8%), H⋯N/N⋯H (19.3%) and H⋯H (18.1%) inter-actions. The volume of the crystal voids and the percentage of free space were calculated to be 176.30 Å3 and 10.94%, showing that there is no large cavity in the crystal packing. Computational methods revealed O-H⋯N, N-H⋯O and C-H⋯O hydrogen-bonding energies of 76.3, 55.2, 32.8 and 19.1 kJ mol-1, respectively. Evaluations of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via dispersion energy contributions. Moreover, the optimized mol-ecular structure, using density functional theory (DFT) at the B3LYP/6-311G(d,p) level, was compared with the experimentally determined one. The HOMO-LUMO energy gap was determined and the mol-ecular electrostatic potential (MEP) surface was calculated at the B3LYP/6-31G level to predict sites for electrophilic and nucleophilic attacks.

Isoguanine (2-Hydroxyadenine) and 2-Aminoadenine Nucleosides with an 8-Aza-7-deazapurine Skeleton: Synthesis, Functionalization with Fluorescent and Clickable Side Chains, and Impact of 7-Substituents on Physical Properties

7-Functionalized 8-aza-7-deaza-2'-deoxyisoguanine and 8-aza-7-deaza-2-aminoadenine 2'-deoxyribonucleosides decorated with fluorescent pyrene or benzofuran sensor tags or clickable side chains with terminal triple bonds were synthesized. 8-Aza-7-deaza-7-iodo-2-amino-2'-deoxyadenosine was used as the central intermediate and was accessible by an improved two-step glycosylation/amination protocol. Functionalization of position-7 was performed either on 8-aza-7-deaza-7-iodo-2-amino-2'-deoxyadenosine followed by selective deamination of the 2-amino group or on 7-iodinated 8-aza-7-deaza-2'-deoxyisoguanosine. Sonogashira and Suzuki-Miyaura cross-coupling reactions were employed for this purpose. Octadiynyl side chains were selected as linkers for click reactions with azido pyrenes. K_Taut values calculated from H₂O/dioxane mixtures revealed that side chains have a significant influence on the tautomeric equilibrium. Photophysical properties (fluorescence, solvatochromism, and quantum yields) of the new 8-aza-7-deazapurine nucleosides with fluorescent side chains were determined. Remarkably, a strong excimer fluorescence in H₂O was observed for pyrene dye conjugates of 8-aza-7-deazaisoguanine and 2-aminoadenine nucleosides with a long linker. In other solvents including methanol, excimer fluorescence was negligible. The 2-aminoadenine and isoguanine nucleosides with the 8-aza-7-deazapurine skeleton expand the class of nucleosides applicable to fluorescence detection with respect to diagnostic and therapeutic purposes.

Novel Pyrazolo[3,4-d]pyrimidin-4-one Derivatives as Potential Antifungal Agents: Design, Synthesis, and Biological Evaluation

Plant pathogenic fungi seriously threaten agricultural production. There is an urgent need to develop novel fungicides with low toxicity and high efficiency. In this study, we designed and synthesized 44 pyrazolo[3,4-d]pyrimidin-4-one derivatives and evaluated them for their fungicidal activities. The bioassay data revealed that most of the target compounds possessed moderate to high in vitro antifungal activities. Especially compound g22 exhibited remarkable antifungal activity against Sclerotinia sclerotiorum with an EC₅₀ value of 1.25 mg/L, close to that of commercial fungicide boscalid (EC₅₀ = 0.96 mg/L) and fluopyram (EC₅₀ = 1.91 mg/L). Moreover, compound g22 possessed prominent protective activity against S. sclerotiorum in vivo for 24 h (95.23%) and 48 h (93.78%), comparable to positive control boscalid (24 h (96.63%); 48 h (93.23%)). Subsequent studies indicated that compound g22 may impede the growth and reproduction of S. sclerotiorum by affecting the morphology of mycelium, destroying cell membrane integrity, and increasing cell membrane permeability. In addition, the application of compound g22 did not injure the growth or reproduction of Italian bees. This study revealed that compound g22 is expected to be developed for efficient and safe agricultural fungicides.

Novel fleximer pyrazole-containing adenosine analogues: chemical, enzymatic and highly efficient biotechnological synthesis

Nucleoside analogues have long served as key chemotherapeutic drugs for the treatment of viral infections and cancers. Problems associated with the development of drug resistance have led to a search for the design of nucleosides capable of bypassing point mutations in the target enzyme's binding site. As a possible answer to this, the Seley-Radtke group developed a flexible nucleoside scaffold (fleximers), where the heterocyclic purine base is split into its two components, i.e. pyrimidine and imidazole. Herein, we present a series of new pyrazole-containing flex-bases and the corresponding fleximer analogues of 8-aza-7-deaza nucleosides. Subsequent studies found that pyrazole-containing flex-bases are substrates of purine nucleoside phosphorylase (PNP). We have compared the chemical synthesis of fleximers and enzymatic approaches with both isolated enzymes and the use of E. coli cells overproducing PNP. The latter provided stereochemically pure pyrazole-containing β-d-ribo- and β-d-2'-deoxyribo-fleximers and are beneficial in terms of environmental issues, are more economical, and streamline the steps required from a chemical approach. The reaction is carried out in water, avoiding hazardous chemicals, and the products are isolated by ion-exchange chromatography using water/ethanol mixtures for elution. Moreover, the target nucleosides were obtained on a multi-milligram scale with >97-99% purity, and the reactions can be easily scaled up.