Active Cytokinins

Abstract

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 '

A Cytokinin-binding Protein from Wheat Germ

“…The '4C of the pooled void (124,000 cpm) was extracted without loss into n-butyl alcohol and dried in vacuo at 40 C. The residue was dissolved in 35% ethanol and chromatographed along with unlabeled kinetin and adenine standards on a Sephadex LH-20 column in 35% ethanol. In the resulting profile, 88% of the label comigrated with the kinetin standard, and I 1% was spread through- In similar competition experiments, the isolated protein has been used to demonstrate the utility of a photoaffmity-labeling cytokinin in binding studies (21).…”

Azido Auxins: Synthesis and Biological Activity of Fluorescent Photoaffinity Labeling Agents

“…Recently, 4-Cl-IAA, the most active auxin presently known, has been reported to occur in nature (10). (c) The electronic and steric similarities between halogens and the azido group (56) (40,53). Based on bond strengths, known reactivities of aryl azides, and the lack of precedent for biological hydrogenolytic cleavage of the Car-N bond, the possibility that the N3-IAA might be metabolized to IAA itself is negligible (1,5,8,56).…”

The Synthesis of 3H-Labelled 8-Azido-N6-Benzyladenine and Related Compounds for Photoaffinity Labelling of Cytokinin-Binding Proteins

“…Unlabelled 8-azido-BA has been synthesized by three methods:From 8-bromo-adenosine by conversion to 8-azido-adenosine, followed by benzylation and ribose cleavage [43]. From 6,8-dichloropurine by four steps including blocking and deblocking N-9 [42]. By direct bromination of BA and reaction with sodium azido under novel conditions [44].…”

“…Firstly, the 8-azido compounds are markedly more effective as cytokinins. Thus, in the tobacco tissue bioassay while 2-azido-BA has activity similar to that of BA, 8-azido-BA is “over 25 times as active” as BA [42] (the least detectable concentrations are about 3 × 10 −5 and 10 −3 µM respectively). Secondly, the 8-azido compounds do not require extended irradiation for photolysis.…”