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.

The special nucleobase recognition pattern of 5-aza-7-deazaguanine nucleosides makes them valuable for construction of homo purine DNA, silver-mediated base pairs, and expansion of the four letter genetic coding system. To widen the utility of 5-aza-7-deazaguanine nucleosides, side chains were introduced at position-7 of the nucleobase. As key compounds, 7-iodo nucleosides were synthesized. Nucleobase anion glycosylation of the iodo derivative of isobutyrylated 5-aza-7-deazaguanine with the bromo sugar of 2,3,5-tri-O-benzoyl-1-O-acetyl-d-ribofuranose gave the pure β-D anomeric N-9 glycosylation product (67%), whereas one-pot Vorbrüggen conditions gave only 42% of the iodinated nucleoside. The noniodinated nucleoside was formed in 84%. For the synthesis of 2′-deoxyribonucleosides, anion glycosylation performed with Hoffer’s 2′-deoxyhalogenose yielded an anomeric mixture (α-D = 33% and β-D = 39%) of 2′-deoxyribonucleosides. Various side chain derivatives were prepared from nonprotected nucleosides by Pd-assisted Sonogashira or Suzuki–Miyaura cross-coupling. Among the functionalized ribonucleosides and anomeric 2′-deoxyribonucleosides, some of them showed strong fluorescence. Benzofuran and pyrene derivatives display high quantum yields in non-aqueous solvents and solvatochromism. Single-crystal X-ray analysis of 7-iodo-5-aza-7-deaza-2′-deoxyguanosine displayed intermolecular iodo–oxygen interactions in the crystal and channels filled with solvent molecules.

(L.) fruits (CGFs) are commonly used for culinary purposes and has several therapeutic applications in the Southeast Asia. The aim of this work was to evaluate phytochemical profile, aldose reductase inhibitory (ARI), and antioxidant activities of CGF extract. The CGFs were extracted with different solvents including petroleum ether, dichloromethane, acetone, methanol, and water. The highest yield of total extractable compounds (34.82%) and phenolic content (11.7 ± 0.43 mg of GAE/g dried extract) was found in methanol extract, whereas water extract showed the maximum content of total flavonoids (82.8 ± 7.8 mg QE/g dried extract). Gas chromatography-mass spectroscopy (GC-MS) analysis of methanol and water extract revealed the presence of flavonoids, phenolic compounds, alkaloids, and glycosides in the CGFs. Results of the in vitro ARI activity against partially purified bovine lens aldose reductase showed that methanol extract of CGFs exhibited 96.6% ARI activity at IC value 6.12 µg/mL followed by water extract 89.1% with the IC value 6.50 µg/mL. In addition, methanol and water extracts of CGF showed strong antioxidant activities including ABTS scavenging, DPPH* scavenging, and hydroxyl radical scavenging. Our results suggest that high percentage of both flavonoids and phenolic contents in the CGFs are correlated with the ARI and antioxidant activities. The fruits of are thus potential bifunctional agents with ARI and antioxidant activities that can be used for the prevention and management of DM and associated diseases.

Purine–purine base pairs represent an alternative recognition system to the purine-pyrimidine pairing reported by Watson and Crick. Modified purines are the source for non-canonical interactions. To mimic dG–dC interactions, 2′-deoxyisoguanosine (1a) and 8-aza-7-deaza-2′-deoxyisoguanosine (2a) are used to construct base pairs with 2′-deoxyguanosine or 5-aza-7-deaza-2′-deoxyguanosine (dZ). This work reports the chemical functionalization of 1a and its shape mimic 2a in purine–purine base pairs. Clickable rigid ethynyl and more flexible octadiynyl side chain derivatives of 1a and 2a were synthesized. They were protected and converted into phosphoramidites. Building blocks were employed in the synthesis of base-modified 12-mer oligonucleotides with clickable side chains. Pyrene azide was clicked to the linkers. After hybridization, oligonucleotides with purine–purine base pairs were constructed with linkers and pyrene adducts at position-8 of isoguanine and at position-7 of 8-aza-7-deazaisoguanine. Recognition and stability of purine–purine base pairs were explored using T m values, thermodynamic data, and CD-spectroscopic changes. Side chains at position-7 of 8-aza-7-deazaisoguanine–guanine base pairs or with 5-aza-7-deazaguanine are well accommodated in DNA, whereas functionalization at 8-position of isoguanine makes the DNA unstable. Pyrene click adducts verified the observation. In conclusion, position-7 is the place of choice for purine–purine base pair functionalization.