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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.

The analogue of zeatin bearing a vinylic fluorine atom and its geometrical isomer were synthesized. The fluorine atom exerts a favorable influence on cytokinin activity in the fluoro analogue of cis-zeatin, but not in the fluoro analogue of zeatin itself. Another series of zeatin derivatives in which the methyl group was replaced by alkyl (ethyl, propyl, and isopropyl), phenyl, and benzyl groups were also obtained. The ethyl analogue was found to be more active than zeatin, while the others were inactive or slightly active. Keywords: Cytokinins; fluoro compounds; synthesis; biological activity

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The mesylate (III), prepared from the carbinol (I), reacts with ZnI2 and the ortho esters (IV) to give the acetals (V) of 4‐mesyloxy‐2‐butynal.