Structure of 6-(2-phenethyl)purine, a synthetic cytokinin

Abstract

C13H12N4, M r = 224, monoclinic, P21/c, a= 17.903 (2), b = 5.038 (4), c = 13.193 (3) A, fl= 93.89 (2) ° , D m = 1.25, D e = 1.255 Mg m -3, Z = 4, R = 0.088 on 1079 intensities. The molecule is extended with a trans conformation around the central C-C bond linking the purine and phenyl residues. The aromatic-ring planes are twisted roughly 90 ° with respect to the linking C-C bonds and the rings are twisted 14 ° to each other. Introduction. Cytokinin activity is exhibited by a large variety of N6-substituted adenine derivatives, natural and synthetic (Leonard, 1974). It has been demon- strated that compounds with the linking NH at C(6) replaced by CH 2, S, or O between the purine ring and, for example, the isopentenyl or benzyl side chain also possess cytokinin activity (Henderson, Frihart, Leon- ard, Schmitz & Skoog, 1975). The methylene analog of N6-(2-isopentenyl)adenine is about 20% as active as the natural cytokinin in the tobacco bio-assay, while N6-benzyladenine and 6-(2-phenethyl)purine (I) have nearly equal activity. Thus, an intact purine with an appropriate substituent at the 6 position is necessary and sufficient for cytokinin activity. It was of interest to compare the conformation of the phenethyl side chain directly attached to C(6) of the purine ring in (I) with the conformations that have been determined for the isopentenylamino C(6) substituent in the natural