Stereochemistry and hydrogen bonding of cytokinins: Crystal and molecular structure of 6-(4-hydroxy-3-methyl-cis-2-butenyl) aminopurine (cis-zeatin)

The title compound is C₁₀H₁₃N₅O, monoclinic,P2₁/a,a=13.829 (7),b=7.834 (7),c=20.138 (9) Å, and =100.75 (6)°. The structure was solved by direct methods and refined by least-squares techniques to anR factor of 0.079 for 1581 observed reflections. There are two crystallographically independent molecules (I andI). The N⁶-substituent is distal to the imidazole ring of the adenine moiety. It is interesting to note that the conformation of the N⁶-substituent relative to the adenine ring base in these two crystallographically independent molecules shows considerable resemblance with the preferred one usually adopted in other cytokinins. The angles between the mean planes of the adenine base and the N⁶-substituent are 65.6 and 63.3° for theI andI molecules, respectively. The molecules are linked by pairs of N(9)-H·N(3) hydrogen bonds. The dimer-like structures are stabilized by a three-dimensional network of O-H·O, O-H·N, N-H·O, and C-H·N hydrogen bonds.