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A series of new AHX derivatives were synthesized by Pd-catalyzed C-H arylation. Their rice-growth-promoting activity was evaluated in vivo. Among the synthesized compounds, C8 phenyl-substituted AHX showed remarkable growth-promoting activity on rice. The present study shows the power and significant opportunity of C-H functionalization chemistry to rapidly transform biologically active natural products into more active compounds.

The metabolism of imidazole-4-carboxamide (ICA) in plants has been unknown. Two metabolites (1 and 2) were isolated from ICA-treated rice, and their structures were determined by spectroscopic analysis including the single-crystal X-ray diffraction technique and synthesis. The ribotide of ICA (3), whose existence was predicted, was also synthesized and detected from the treated rice by LC-MS/MS. These results indicated that rice might interconvert ICA, 1, and 3 to regulate the biological activity.

Plant growth stimulators, 2-azahypoxanthine (AHX) and 2-aza-8-oxohypoxanthine (AOH), were isolated from the fairy-ring-forming fungus, Lepista sordida, and AHX-treated rice, respectively. Further metabolites of AHX were detected in AHX-treated rice by HPLC, and the metabolites 1–4 were isolated from the rice. The structures of 1–4 were determined by spectroscopic analysis and synthesis. Compounds 1–4 exhibited no significant activity against rice, indicating that rice regulates the activity of AHX and AOH by converting them into their glucosides.

Five fatty acid amides, termitomycamides A to E (1 to 5), were isolated from the giant edible mushroom Termitomyces titanicus. The structures of 1-5 were determined by the interpretation of spectral data and/or synthesis. Compounds 2 and 5 showed protective activity against endoplasmic reticulum stress-dependent cell death.