The Role of 9- and/or 10-oxygenated Derivatives of Geraniol, Geranial, Nerol, and Neral in the Biosynthesis of Loganin and Ajmalicine

Abstract

A number of deuterium labelled 9- and/or 10-oxygenated derivatives of geraniol, geranial, nerol, and neral were used as substrates in feeding experiments with a cell suspension culture of Catharanthus roseus. The 9- and 10-oxo derivatives of geraniol, geranial, nerol, and neral as well as 9,10-dihydroxygeraniol, 9-oxo-10-hydroxygeraniol, and 9,9,10,10-tetraethoxygeranial were found to be good precursors of the indole alkaloid ajmalicine. The compounds 9-hydroxygeraniol, 9-hydroxynerol, 9,10-dihydroxynerol, 9-oxo-10-hydroxynerol, 9-hydroxy-10-oxonerol, 9-hydroxy-10-oxogeraniol, 9,9,10,10-tetraethoxynerol, and 9,9,10,10-tetraethoxygeraniol were relatively poor precursors. Competitive feeding experiments, employing mixtures of unlabelled citral and labelled 9-oxogeranial, 10-oxonerol, 10-oxoneral, or 9,10-dihydroxygeraniol were also carried out. The incorporation of 9,10-dihydroxygeraniol into ajmalicine was not significantly affected by the presence of citral, while the incorporations of the other labelled substrates were greatly reduced.

Key Word Index

Catharanthus roseus - Cell culture - 9,10-dihydroxygeraniol - 9-oxo-10-hydroxygeraniol - 9,9,10,10-tetraethoxygeranial - Precursor incorporation - Alkaloid biosynthesis