Biosynthetic origin of the 1-oxygen of umbelliferone in the root tissue of sweet potato.

Oxidation of p-coumarate at the ortho-position is a key step to form umbelliferone. A tracer analysis using (18)O2 was performed in order to take information about the formation of umbelliferone in the root tissue of sweet potato. Mass fragmentation experiments revealed incorporation of an 18O atom into the 1-position of umbelliferone. This result indicates that the lactone of umbelliferone is formed via ortho-hydroxylation of the p-coumarate unit using O2.