A series of novel N-(2-(phenylamino)-4-fluorophenyl)-pyrazole-4-carboxamides 1–15 and aromatic carboxamides with a diphenylamine scaffold 16–29 were designed, synthesized, and evaluated for their antifungal activities. In vitro experiments showed that compound 6 (EC50 = 0.03 mg/L) was superior to bixafen (EC50 = 0.04 mg/L) against Rhizoctoinia solani and compound 6 (IC50 = 1.41 mg/L) was close to bixafen (IC50 = 1.22 mg/L) against succinate dehydrogenase from R. solani. Additionally, in vivo pot experiments showed that compound 6 (EC50 = 1.93 mg/L) was better than bixafen (EC50 = 3.72 mg/L) and close to thifluzamide (EC50 = 1.83 mg/L) against R. solani. In vivo field trials showed that compound 6 at 200 g ai ha–1 had 64.10% control efficacy against rice sheath blight after 21 days with two sprayings, close to thifluzamide (71.40%). Furthermore, molecular docking showed that compound 6 anchors in the binding site of SDH.

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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.