13c9 phenylalanine

Methanol (MeOH) and acetonitrile (ACN) were obtained from Riedel de Haen, Honeywell (LC-MS grade, >99.9% purity, Seelze, Germany). Formic acid (MS grade), NaOH (>98% pure), HCl (MS grade), and ethyl acetate (>99.7% pure) were purchased from Sigma (Sigma Aldrich, Vienna, Austria). Water was purified by ion exchange and ultrafiltration with an ELGA system (PURELAB Ultra, Veolia Water, Vienna, Austria). ¹³C₉-phenylalanine (99% isotopic purity, uniformly labelled) was purchased from Euriso-top (St Aubin, France). The following authentic reference standards were used for metabolite identification: phenylalanine (native, >99% pure, Roth), orientin (>99% pure, Extrasynthese), tricin (>95% pure, PhytoLab), ferulic acid (>99% pure, Fluka), vanillin (99% pure, Sigma-Aldrich), pinoresinol (95% pure, Sigma), chlorogenic acid (>95%, Sigma), and coumaric acid (>98%, Sigma). Coumaroylputrescine was kindly provided by G. Adam, BOKU.

The uniformly ¹³C-labeled tracer substance ¹³C₉-phenylalanine (99% isotopic purity) and ¹³CO₂ (99% purity) were purchased from Euriso-top (St-Aubin, Cedex, France). ELGA water was obtained from an ELGA Purelab Ultra-AN-MK2 system (Veolia Water; Vienna, Austria). Liquid chromatography (LC)-gradient methanol (MeOH; LiChrosolv) was purchased from Merck (Darmstadt, Germany). Formic acid (FA, MS grade) was obtained from Sigma-Aldrich (Steinheim, Germany and Vienna, Austria).