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Four series of azidopurines have been synthesized and tested for cytokinin activity in the tobacco callus bioassay: 2-and 8-azido-N6-benzyladenines, -N -(A2-isopentenyl)adenines, and -zeatins, and N -(2-and 4-azidobenzyl)adenines. The compounds having 2-azido substitution on the adenine ring are as active as the corresponding parent compounds, while those with 8-azido substitution are about 10 or more times as active. The 8-azidozeatin, which is the most active cytokinin observed, exhibited higher than minimal detectable activity at 1.2 x 10-5 micromolar, the lowest concentration tested. The shape of the growth curve indicates that even a concentration as low as 5 x 10-6 micromolar would probably be effective. By comparison, the lowest active concentration ever reported for zeatin has been 5 x 10-5 micromolar, representing a sensitivity rarely attained.All of the azido compbunds have been submitted to photolysis in aqueous ethanol, and the photoproducts have been detected and identified by low and high resolution mass spectrometry. They are rationalized as products of abstraction and insertion reactions of the intermediate nitrenes. The potential of the major released products as cytokinins was also assessed by bioassay. 2-Azido-N6-(A2-isopentenyl)adenine competed with 114CIki-netin for the cytokinin-binding protein isolated from wheat germ. When the azido compound was photolysed in the presence of this protein, its attachment effectively blocked the binding of 114Clkinetin.Extensive studies of structure-activity relationships for cytokinins have led to a well-defined concept of the chemical nature of '

Two new azidopurine derivatives, 2-azido-N6-(A2-isopentenyl)adenine and 2-azido-N6-benzyladenine, have been synthesized as potential photoaffinity labels for probing cytokinin-binding sites. The preparation and the biological activity of these compounds are described. pentenyl)adenine (Ic) and 2-azido-N6-benzyladenine (Ilc) as photoaffinity-labeled cytokinins and have tested their activity in the tobacco bioassay.The diverse effects of cytokinins on plant physiological processes, including cell growth and differentiation and the flow of assimilates and nutrients through the plant, presumably stem from a primary "mode of action" which has not yet been determined (6, 10). Recent approaches to definition of cytokininbinding sites have included isolation and partial purification of a cytokinin-binding protein by affinity chromatography (13), utilization of radioactive substrates of very high specific activity for probing plant cell substructures (12), and synthesis of "stretched-out" analogs of cytokinins as potential fluorescent probes (11).Photoaffinity-labeling reagents designed for probing cytokinin-binding sites would not only be nondestructive but would also be capable of reacting with any nearby components of the binding site. In addition, the reactivity of the photolabile functional group can be controlled to maximize labeling selectivity (4).In examining complex systems by photoaffinity-labeling techniques, a high relative binding affinity is desirable so that the distribution of bound substrate favors specific sites over nonspecific sites. Whereas 2-or 8-substitution on the purine ring of zeatin or N6-(A2-isopentenyl)adenine generally lowers the cytokinin activity, substitutionat either of these positions by chlorine does not reduce the activity appreciably (2, 3). The 2-chloro compounds are particularly favorable in this regard. The similarity between the chloro group and the azido group in terms of inductive and hydrophobic characteristics, together with previous applications of photolabile azide compounds (1, 5, 7), suggested the 2-azido derivatives as the initial candidates for investigation. We MATERIALS AND METHODS General. All melting points are uncorrected. PMR3 spectra were recorded on Varian Associates A-60A and HA-100 spectrometers using tetramethylsilane (TMS) as an internal standard. Ultraviolet absorption spectra were measured on a Beckman Acta model MVI spectrophotometer. Mass spectra were obtained on a Varian-MAT CH-5 mass spectrometer coupled with a 620i computer and STATOS recorder. Infrared spectra were determined on a Perkin-Elmer model 337 spectrophotometer. Microanalyses were performed by Mr. Josef Nemeth and his associates.6-Benzylamino-2-chloropurine (Ha). To 1 g (5.3 mmol) of 2,6-dichloropurine (Aldrich) in 35 ml of 1-butanol were added 2 g (18.7 mmol) of benzylamine. The solution was heated at reflux for 3 hr and cooled. Solvent was removed in vacuo, 45 ml water were added to the residue, and the sample was refrigerated for several hours. The 2-Hydrazino-6-(3-methyl...

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Die gewünschten Adeninderivate (III) werden, wie im Formelschema aufgeführt, synthetisiert, wobei die Darstellung von (IIIg) ähnlich, aber über einen etwas längeren Weg wie die von (IIIi) verläuft.