Nishikawa S, Mizuno H, Ohgami N, Tada T, Kumazawa Z, Inagaki M, Kashimura N
Department of Bioscience, Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan.
J Agric Food Chem. 2000 Nov;48(11):5302-6. doi: 10.1021/jf000318a.
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.
研究了具有涉及氢、氯、溴原子以及甲硫基的β-取代基的构象受限的（Z）-和（E）-6-苯乙烯基嘌呤的晶体结构，将其作为N（6）-腺嘌呤与细胞分裂素活性构象相关的构象异构体模型。X射线晶体学分析证实，所有反式异构体均以反式构象存在，而除（E）-甲硫基衍生物外的顺式异构体均采用顺式构象。与其他顺式异构体相比，发现具有庞大β-取代基的衍生物处于反式构象。反式异构体的优选反式构象和强大的细胞分裂素活性支持反式-反式构象作为N（6）-腺嘌呤最合理的活性构象。此外，考虑到顺式异构体的优选顺式构象及其适度的活性，N（6）-腺嘌呤的顺式-顺式构象也可能参与受体结合，尽管与反式-反式构象相比它不发挥主要作用。
