Abstract Conformationally restricted (Z)-and (E)-β-substituted 6-styrylpurines were synthesized by addition reaction to 6-phenylethynylpurine and photoisomerization. The crystalline (Z)-and (E)-β-chloro-substituted compounds exist in the anti-and syn-forms, respectively. While the (Z)-β-chloro-and bromo-substituted compounds were almost as active as (E)-6-styrylpurine and N 6-benzyladenine (BA) in the Amaranthus betacyanin ...
