STRUCTURE ELUCIDATION AND ISOTOPIC LABELING EXPERIMENTS PROVIDE INSIGHTS INTO THE BIOSYNTHESIS OF THREE PHYTOCHEMICALS ALKAMIDES, AVENACIN, AND HYDROXYLATED FATTY ACIDS %D8%B1%D8%B3%D8%A7%D9%84%D8%A9 %D8%AF%D9%83%D8%AA%D9%88%D8%B1%D8%A7%D9%87