Biosynthetic pathway to the cancer chemopreventive secoisolariciresinol diglucoside-hydroxymethyl glutaryl ester-linked lignan oligomers in flax (Linum usitatissimum) seed

Application of stable and radioisotope precursor/tracer experiments resulte d in the identification of various phenylpropanoid, monolignol, and lignan metabolites involved in the biosynthesis of the cancer chemopreventive seco isolariciresinol diglucoside (SDG; U-containing ester-linked "polymer(s)" i n flax (Linum usitatissimum) seed. Individual analysis of size-segregated f lax seed capsules at five early stages of their development provided a meta bolic profile of intermediates leading to "biopolymer" biosynthesis. The us e of H-1 and C-13 NMR and HRMS analyses resulted in the identification of 6 a-HMG (hydroxymethyl glutaryl) SDG (17) and 6a,6a'-di-HMG SDG (IS) as the t wo major components of the ester-linked "biopolymer(s)". Based on metabolic tracer analyses and relative radioisotopic incorporations throughout each of these five stages of seed development, a biochemical pathway is proposed from phenylalanine to SDG (1), with subsequent mono- and di-substitutions of SDG (1) with HMG CoA. These metabolites then serve as precursors for for mation of the SDG-HMG ester-linked oligomers. Results from this study will facilitate future isolation and characterization of the proteins and enzyme s involved in biosynthesis of the SDG-HMG ester-linked oligomers in flax se ed.