Determination of the Absolute Configuration of a Monoglyceride Antibolting Compound and Isolation of Related Compounds from Radish Leaves (<i>Raphanus sativus</i>)

A monoglyceride (<b>1</b>) has been reported to possess an antibolting effect in radish (<i>Raphanus sativus</i>), but its absolute configuration at the C-2 position was not determined earlier. In this work, the absolute configuration of <b>1</b> was determined to be (2<i>S</i>), and it was also accompanied by one new (<b>2</b>) and two known monoglycerides (<b>3</b> and <b>4</b>). The chemical structure of <b>2</b> was determined as β-(7′<i>Z</i>,10′<i>Z</i>,13′<i>Z</i>)-hexadecatrienoic acid monoglyceride (β-16:3 monoglyceride). Qualitative and quantitative analytical methods for compounds <b>1</b>–<b>4</b> were developed, using two deuterium-labeled compounds (<b>8</b> and <b>9</b>) as internal standards. The results revealed a broader range of distribution of <b>1</b>–<b>4</b> in several annual winter crops. It was also found that these isolated compounds have an inhibitory effect on the root elongation of <i>Arabidopsis thaliana</i> seedlings at concentrations of 25 and 50 μM in the medium. However, the inhibitory effect of <b>1</b> was not dependent on coronatin-insensitive 1 (COI1) protein, which may suggest the involvement of an unidentified signaling system other than jasmonic acid signaling.