ABSTRACT
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.
Subject(s)
Cytokinins/chemistry , Purines/chemistry , Crystallography, X-Ray/methods , Cytokinins/pharmacology , Models, Molecular , Molecular Conformation , Plants, Toxic , Purines/pharmacology , Stereoisomerism , Structure-Activity Relationship , Nicotiana/drug effectsABSTRACT
6-Alkynylated purines were conveniently transformed to the corresponding 6-alkyl- and 6-alkenylpurines by three methods: (i) hydrogenation with 10% palladium-carbon or palladium acetate-sodium borohydride, (ii) addition of hydrogen halides or water and (iii) formal addition of diethylamine to the triple bond. Some of the products exhibited strong cytokinin activity.
Subject(s)
Alkynes , Purines , Chemical Phenomena , Chemistry , Cytokinins , Oxidation-ReductionABSTRACT
Coupling reaction of 6-iodo- or 6-chloropurine with alkynes in the presence of (PPh3) 2PdCl2-CuI catalyst in triethylamine to give 6-alkynylated purines was achieved by the use of dipolar aprotic solvent as co-solvent. Under the reaction conditions, ribonucleoside as well as its tri-O-acetate of 6-chloropurine also gave the corresponding alkynylated products in high yields. Though similar reaction for 8-bromo-derivatives of adenine and guanine gave poor yields, the 8-alkynylated free bases could be obtained by acid hydrolysis of the alkynylated ribonucleosides. 6-Alkynylated purines exhibited moderate to weak cytokinin activity in Amaranthus test.
