AbstractDie 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.

A selective synthesis of 1,6-dimethylpurine (16) and the preparations of the 1-(azidobenzyl)adenines (11)–(13), 8-azido-1-benzyladenine (10), and 1-methyladenine derivatives (2)–(9) with various 8-substituents (azido, chloro, bromo, amino, alkyl, and hydroxymethyl) are described. The syntheses were based upon the 1-atkylation of the corresponding 9-substituted purines followed by deprotection at N-9. The ability of those compounds to replace the hormone 1-methyladenine (1) in releasing meiosis inhibition in starfish oocytes was tested, and the earlier hypothesis about structure-activity relationships has been confirmed. The low level of activity of the 8-azido derivatives of 1-methyl- and 1-benzyl-adenines, probably due to blocking of the N-7, N-9 region and reduction of the pKa, value, precludes their use as photoaffinity labelling reagents for the receptors of 1-methyladenine. The active compounds 1-(4-azidobenzyl)adenine (13) and 1-(3-azidobenzyl)adenine (12) are possibly better candidates for this purpose.

FOUR SERIES OF AZIDOPURINES HAVE BEEN SYNTHESIZED AND TESTED FOR CYTOKININ ACTIVITY IN THE TOBACCO CALLUS BIOASSAY: 2- and 8-azido-N(6)-benzyladenines, -N(6)-(Delta(2)-isopentenyl)adenines, and -zeatins, and N(6)-(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 compounds 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-N(6)-(Delta(2)-isopentenyl)adenine competed with [(14)C]kinetin 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 [(14)C]kinetin.

Two new azidopurine derivatives, 2-azido-N(6)-(Delta(2)-isopentenyl)adenine and 2-azido-N(6)-benzyladenine, have been synthesized as potential photoaffinity labels for probing cytokinin-binding sites. The preparation and the biological activity of these compounds are described.