TOBACCO POLYPHENOLS: II. ON THE BIOSYNTHESIS OF CHLOROGENIC ACID

Leaf disks of Nicotiana tabacum var. Delcrest were supplied with α-C14-labelled 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 conversion to p-coumaroyl-quinic acid. Chlorogenic acid synthesis from 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 incorporated essentially intact into both p-coumaroyl-quinic and chlorogenic acids. These findings are discussed in relation to the pathway of chlorogenic acid biosynthesis postulated for potato tuber tissue.