Abstract
The biosynthetic origins of the isoprene units of 4-nerolidylcatechol (1), the major constituent of Potomorphe umbellata, have been studied through feeding experiments with [14C]- and [13C]-glucose, and with precursors of the mevalonic acid and triose/pyruvate pathways, namely, [2-14C]-mevalonolactone and [U-14C]-glyceraldehyde-3-phosphate, respectively. The pattern of incorporation of label from [1-13C]-glucose into 1 was determined by quantitative 13C NMR spectroscopy. The labelling pattern revealed that the additive was specifically incorporated, and that the isoprene units of the sesquiterpenoid moiety of 4-nerolidylcatechol were derived from both the mevalonic acid and the triose/pyruvate pathways. The results indicate that both plastidic and cytoplasmic pathways are able to provide isopentenyl diphosphate units for the biosynthesis of 1.
Highlights
The terpenoids represent one of the largest classes of secondary metabolites comprising, together with the steroids, more than 30,000 compounds to date.[1]
There is some reason to believe that the triose/pyruvate pathway is compartmentalised in the plastids of plant cells and is involved in the formation of mono, di, and tetraterpenoids, whilst the mevalonic acid (MVA) pathway is located in the cytoplasm and is responsible for the synthesis of sesquiterpenes and sterols.[9]
The conversion of [1-13C]-glucose into isopentenyl diphosphate (IPP) via the MVA pathway would lead to the incorporation of label at positions 2, 4 and 5 of each isoprene unit
Summary
The terpenoids represent one of the largest classes of secondary metabolites comprising, together with the steroids, more than 30,000 compounds to date.[1]. The aim of the present study was, to determine the route of formation of the C moiety of 1 in leaves of P. umbellate through feeding experiments involving appropriately labelled precursors. Determination of the 13C-enrichment pattern in 1 following the incorporation of label from [1-13C]-glucose revealed that the sesquiterpene portion was derived from both the MVA and the triose/pyruvate pathways.
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