7-Phenylethynylimidazo[4,5-b]pyridine and its riboside have been newly developed as fluorescent carbon-substituted cytokinin analogues. Palladium-catalyzed coupling of 7-iodo-3-(tri-O-acetyl-beta-D-ribofuranosyl)imidazo[4,5-b]pyridine with phenylacetylene followed by ammonolysis afforded the 7-phenylethynyl riboside via its tri-O-acetate. Acid hydrolysis of the riboside provided its free base, which showed a marked enhancement in fluorescence intensity in an aqueous alkaline solution. The free base and its riboside were more active than the corresponding 6-phenylethynylpurine and its riboside, respectively, in Amaranthus betacyanin and tobacco callus bioassays. Surprisingly, the imidazo[4,5-b]pyridine base exhibited strong cytokinin activity comparable to that of N(6)-benzyladenine in the tobacco callus bioassay. This compound would be useful for studying localization and transport of cytokinins in cells or tissues of plants.
Utilization of Sugars in Organic Syntheses. Part 30. Thio-Sugars. Part 1. Radical-Promoted Thione-Thiol Rearrangement of Cyclic Thionocarbonates: Synthesis of 5-Thioglucose.-The title rearrangement is investigated in detail under different reaction conditions. If trialkylsilanes are used as reagents instead of the rearranged compounds only reduction products are obtained. Starting with compound (XIII), whose structure is determined by X-ray analysis, the synthesis of the thioglucose derivative (XVI) is performed. -(TSUDA, Y.; SATO, Y.; KANEMITSU, K.; HOSOI, S.; SHIBAYAMA, K.; NAKAO, K.; ISHIKAWA, Y.; Chem.
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