Additional file 10 .
Biosynthesis of terpenic moiety of secoiridoids. The biosynthetic steps for the production of the terpenic moiety of oleuropein in Olea europaea according to Obied et al. is reported, with some modifications. Based on our data, we propose that in the olive fruits geraniol for the secoiridoid synthesis derives from the MEP pathway. Iridoidal is produced through a series of hydroxylation and oxidation reactions on geraniol followed by a cyclisation reaction. Further oxidation yields iridotrial and deoxyloganic acid aglycone. Deoxyloganic acid is converted to 7-epi-loganic acid through the hydroxylation of the cyclopentane ring, then the hydroxyl group is oxidised to form 7-ketologanic acid. An esterification reaction is required for the conversion of 7-ketologanic acid to 7-ketologanin, and subsequently, oleoside 11-methyl ester is produced through the oxidation of the ketonic group. In a reaction catalysed by glucosyl transferase, oleoside 11-methyl ester is converted to 7-β-1-D-glucopyranosyl 11-methyl oleoside, which is the precursor of ligstroside and oleuropein.
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Alagna et al. BMC Plant Biology 2012 12:162 doi:10.1186/1471-2229-12-162