Transformations of the natural cytokinin zeatin in aqueous acidic media

Abstract

The behaviour of the naturally occurring cytokinin zeatin 1 in aqueous acidic conditions has been studied, after it was observed that this compound was relatively more stable than another related cytokinin, 6-(3-methylbut-2-eny1amino)purine 2. Zeatin 1 reacted readily in 1 rnol dm-3 aqueous HCI at 100 "C. Three products were characterized, a diol resulting from the hydration of the double bond of the aliphatic chain, and two cyclized products, a hydroxypyrrolidine and a dihydropyrrole. A scheme is proposed to explain the formation of these products. However, zeatin was found to be stable in 0.1 rnol dm-3 aqueous HCI at 100 "C and in 1 rnol dm-3 aqueous HCI at 50 "C, conditions which allow the hydrolysis of zeatin riboside.The plant hormones zeatin 1 and 6-(3-methylbut-2-enyIamino)purine 2, of the cytokinin family, are present in plantsnot only as the free bases, but also as the 9-P-~-ribofuranosides, as the corresponding 5'-nucleotides and as various N-glucosides. In the case of 1 and of its riboside, 0-glycosyl conjugates are also found.' It has been shown that 2 is particularly unstable in HCI solution2*3 and the products resulting from the reactivity of the chain have been fully characterized (Scheme 1). Acidic treatment of zeatin 1 with HCl(1 rnol dm-3) Scheme 1 at 100 0C,4.5 gave rise to two products, one of them being a hydration product of the chain double bond, the second being unknown. The question of the stability of the allylic chain of cytokinins in acidic media has to be considered, since acidic treatments are commonly performed during their isolation and purification from plant tissues, in particular the hydrolysis of the N-glucosyl conjugates when a quantitative determination of the hormone pool is required.We describe here the study of the transformation of zeatin 1 in aqueous HCI which allowed us to characterize additional products not seen in the previous ~tudies,~,' and to define acidic conditions under which zeatin is stable and which can therefore be used to hydrolyse zeatin N-glycosides, especially zeatin riboside.

High Performance Liquid Chromatography/Electrochemistry/High Resolution Electrospray Ionization‐Mass Spectrometry (HPLC/EC/HR ESI‐MS) Characterization of Selected Cytokinins Oxidation Products

“…Products cB, cG and cH represent the biggest challenge to identification. Former study, observing modifications of side-chain hydroxylated iP molecule under acidic conditions in vitro, confirmed the possibility of forming a cyclized intermediate, which underwent further reactions to finally form a stable cyclized compound, but without a confirmation of whether cis-or trans-zeatin was used as a precursor substance [30]. Cyclization of cZ was since then hypothesized [31] and its possible occurrence made responsible for some observed physiological reactions [32].…”

Transformations of the natural cytokinin N6-isopentenyladenine in aqueous acidic media: structural aspects

“…If we compare the interatomic parameters of H 2 L3 in 3 and 5, we find significant differences which are caused by different hydrogen bonding system. The biggest difference, like in the case of 4, was found for the C7-N12-C11 angle [121.54 (12) • and 123.6(3) • in 3 and 5]. The heterocyclic rings, i.e.…”

“…2 Later, it was found that the compounds of similar performed. 12 The transformation of zeatin in 1 M HCl at 100 • C was studied; a mixture of three products was acquired and characterized by elemental analysis, IR, UV and 1 H NMR spectroscopy, EI MS spectrometry and HPLC analysis. These compounds were identified as a diol resulting from the hydration of the double bond of the aliphatic chain, and as two cyclized products, a hydroxypyrrolidine and dihydropyrrole.…”