Cytokinins with different connecting links between purine and isopentenyl or benzyl groups

Abstract

Using the tobacco bioassay a comparison was made between the cytokinin activities of the following series of compounds with different connecting links (6-NH, S, O, CH 2) between the purine ring and isopentenyl or benzyl groups: 6-(3-methyl-2-butenylamino)purine ( 1a), 6-(3-methyl-2- butenylthio)purine ( 1b), 6-(3-methyl-2-butenyloxy)purine ( 1c), and 6-(4-methyl-3-pentenyl)purine ( 1d); 6-benzylaminopurine ( 2a), 6-benzylthiopurine ( 2b), 6-benzyloxypurine ( 2c), and 6-(2-phenethyl)purine ( 2d); also 6- trans-styrylpurine ( 3), the synthetic precursor of 2d. All possess cytokinin activity, thus providing evidence that the intact base, consisting of nucleus and sidechain at the purine 6-position, is necessary and sufficient for such activity as measured in the tobacco bioassay. The biological activity in the 6-(3-methyl- 2-butenyl-X)purine series decreases as a function of the linkage group in the order X = NH > CH 2 > S ⪢ O and in the 6-benzyl- X-purine series in the order X = NH > CH 2 = O ⪢ S. The 6- trans-styrylpurine ( 3) is about equally active as 6-(2-phenethyl)purine ( 2d).