6-Cyclopropylpurines as Novel Potent Analogs of Cytokinins.

6-Alkynyl-, trans-6-alkenyl-, trans-6-cyclopropyl- and 6-alkylpurines structurally related to the cytokinin 6-benzylaminopurine (BAP) have been synthesized and examined with a radish cotyledon assay as plant growth stimulators. The growth stimulation obtained with the 6-alkylpurines trans-cyclopropylpurines was very close to that obtained with BAP, and the trans-styrylpurines were somewhat less effective. The fact that the conformationally locked cyclopropanes exhibit growth-stimulating effects comparable to the flexible 6-alkylpurines and to BAP, supports the hypothesis that the orientation of the NH-CH2 bond in "the active conformation" of BAP is close to anti, which means that the torsion angle C(6)-N(6)-CH2-C is approximately 180 degrees. [ABSTRACT FROM AUTHOR]