The Structure and Synthesis of Cytokinin Metabolites. 1. The 7- and 9-β-D-Glucofuranosides and Pyranosides of Zeatin and 6-Benzylaminopurine

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Abstract
The structures of the major stable plant metabolites of the cytokinins zeatin and 6-benzylaminopurine have been confirmed by synthesis to be 7- and 9-β-D-glucopyranosides. The small quantities of metabolites initially isolated (< 100 μg) precluded assignment of the glucose ring size or configuration of the anomeric linkage so that synthesis of both the furanose and pyranose forms of 7-β-D- and 9-β-D-glucosylzeatin and 6-benzylaminopurine was undertaken which allowed direct u.v., m.s. and t.l.c. comparison with the metabolites. Numerous synthetic routes to the unusual 7-glucosides of the two cytokinins were explored, the most successful utilizing a one-pot pyrimidine ring closure of an imidazole derivative to afford directly in high yield the required 7-glucosides of zeatin and 6-benzylaminopurine.