Structure and biological activity of novel FN analogs as flowering inducers.

(12Z,15Z)-9-Hydroxy-10-oxooctadeca-12,15-dienoic acid (1) and norepinephrine (2) undergo cycloaddition to afford FN1 (3) and FN2 (4), both of which induce flowering in Lemna paucicostata. Although the derivatives of 1 were suggested to also yield FN-like compounds after reacting with 2, their structures have not been elucidated. In this report, we investigated the structure and stereochemistry of seven novel FN analogs. These analogs were shown to be formed in the same regio- and stereocontrolled manner as FNs. Moreover, the activity of FN analogs on flowering induction was investigated, and we determined that all analogs, except for compound 8, were effective flowering inducers for L. paucicostata.