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

Abstract

N6-Isopentenyladenine (L1) was subjected to variously acidic media in 0.1 M, 1 M and 2 M HCl. In dependence on the acidity of the medium, the formation of three main acid hydrolysis products, involving the N6-isopentenyladeninium (HL1) (1), 7,8,9,10-tetrahydro-7,7-dimethyl-3H-pyrimido[2,1-i]purin-6-ium (HL2) (2) or 5-amino-4-(4,4-dimethyl-3,4,5,6-tetrahydropyrimidin-2-yl)-imidazolium (H₂L3) (3–5) cations, were determined and characterized by multinuclear solution-state NMR spectroscopy and in the solid state by single crystal X-ray analysis. The coordination abilities of these transformation products have been also investigated. The compounds of the compositions [Zn(HL1)Cl₃]·H₂O (1), [Zn₃(HL2)₂Cl₈] (2), (H₂L3)[CuCl₄] (4) and (H₂L3)[ZnCl₄] (5) have been prepared in dependence on the acidity of the medium used by the reactions of L1 with ZnCl₂·1.5H₂O or CuCl₂·2H₂O. Based on the NMR spectroscopic and X-ray crystallographic results, the mechanism of transformation of L1 in the acidic medium, involving the protonation, cyclization and ring fission, has been suggested.