Both enantiomers [(1'R)-6 and (1'S)-6] of N6-(1, 3-dimethyl-2-butenyl)adenine and their 9-β-D-ribofuranosides [(1"R)-16 and (1"S)-16] have been synthesized for the first time from both enantiomers of alanine (15) in nine steps. These aglycones and nucleosides, together with N6-(3-methyl-2-butenyl)adenine (5) and its 9-β-D-ribofuranoside (18) as well as 9-β-D-ribofuranosyl-cis-zeatin (20) and 9-(2-deoxy-β-D-ribofuranosyl)-cis-zeatin (19), were tested for cytokinin activity in the tobacco callus bioassay. The order of their activity was 5>(1'R)-6>(1"R)-16≈18>(1'S)-6>(1"S)-16>20>19. The bioassay results are compared with those obtained previously for the derivatives modified analogously in the N6-substituent in the cis- and trans-zeatin series.