Crystal structure and conformation of beta-substituted (Z)- and (E)-6-styrylpurines as conformer models.
Crystal structures of conformationally restricted (Z)- and (E)-6-styrylpurines with the beta-substituents involving hydrogen, chlorine, and bromine atoms as well as a methylthio group were studied as conformer models of N(6)-adenines in relation to active conformation of cytokinins. X-ray crystallographic analyses confirmed that all of the trans-isomers exist in an anti conformation, whereas the cis-isomers except the (E)-methylthio derivative adopt a syn conformation. The derivative with a bulky beta-substituent was found to be in an anti conformation in contrast to the other cis-isomers. The preferred anti conformation and potent cytokinin activity of the trans-isomers supports the anti-transoid form as the most plausible active conformation of N(6)-adenines. In addition, it is likely that the syn-cisoid form of N(6)-adenines is also involved in receptor binding, by considering both the preferred syn conformation of the cis-isomers and their moderate activity, although it does not play a major role compared to the anti-transoid form.
Nishikawa
S
S
Department of Bioscience, Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan. nisikawa@bio.mie-u.ac.jp
Mizuno
H
H
Ohgami
N
N
Tada
T
T
Kumazawa
Z
Z
Inagaki
M
M
Kashimura
N
N
D018360:Crystallography, X-Ray / Q000379:methods; D003583:Cytokinins / Q000737:chemistry* / Q000494:pharmacology; D008958:Models, Molecular; D008968:Molecular Conformation; D010947:Plants, Toxic; D011687:Purines / Q000737:chemistry* / Q000494:pharmacology; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000187:drug effects
D003583:Cytokinins; D011687:Purines