11. ON THE BIOSYNTHESIS OF CHLOROGENIC ACID

Leaf disks of Nicotiana tabacum var. Delcrest were supplied with a-Cl4labelled cinnamic, p-coumaric, and caffeic acids, p-coumaroyl-quinic acid, and the 1-glucose esters of cinnamic and p-coumaric acids. Considerable incorporation of radioactivity into chlorogenic acid occurred in 40 hours from all substrates except caffeic acid. In particular, p-coumaric acid was found to be a good precursor of chlorogenic acid in contrast to the findings of other workers with potato tuber tissue. More p-coumaric acid than cinnamic acid is converted to chlorogenic acid, although the reverse holds for coilversion to p-coumaroyl-quinic acid. Chlorogenic acid synthesis froin caffeic acid involves breakdown and resynthesis of the acid supplied, leading to the incorporation of radioactivity into other positions in the caffeic acid molecule and into the quinic acid moiety. Cinnamic and p-coumaric acids, on the other hand, are iilcorporated essentially intact into both pcoumaroyl-quinic and chlorogenic acids. These findings are discussed in relation to the pathway of chlorogenic acid biosynthesis postulated for potato tuber tissue.