Department of Food Chemistry and Phytochemistry, Karlsruhe Institute of Technology (KIT) , Adenauerring 20a, 76131 Karlsruhe, Germany.
Department of Safety and Quality of Fruit and Vegetables, Max Rubner-Institut, Federal Research Institute of Nutrition and Food , Haid-und-Neu-Straße 9, 76131 Karlsruhe, Germany.
J Agric Food Chem. 2016 Sep 28;64(38):7244-50. doi: 10.1021/acs.jafc.6b02720. Epub 2016 Sep 13.
Besides ferulate dimers, higher oligomers of ferulic acid such as trimers and tetramers were previously demonstrated to occur in plant cell walls. This paper reports the identification of two new triferulic acids. 8-O-4/8-5(cyclic)-triferulic acid was synthesized from ethyl ferulate under oxidative conditions using copper(II)-tetramethylethylenediamine [CuCl(OH)-TMEDA] as a catalyst, whereas 8-8(cyclic)/5-5-triferulic acid was isolated (preparative size exclusion chromatography, reversed-phase HPLC) from saponified insoluble maize fiber. Structures of both trimers were unambiguously elucidated by high-resolution LC-ToF-MS/MS and one- ((1)H) and two-dimensional (HSQC, HMBC, COSY, NOESY) NMR spectroscopy. The newly described trimers were identified by LC-MS/MS in alkaline hydrolysates of insoluble fibers from maize, wheat, and sugar beet, indicating that ferulic acid cross-links between cell wall polymers are more diverse than previously recognized. Saponification experiments also suggest that the newly identified 8-O-4/8-5(cyclic)-triferulic acid is the naturally occurring precursor of the previously identified 8-O-4/8-5(noncyclic)-triferulic acid in plant cell walls.
除了阿魏酸二聚体外，先前已证明植物细胞壁中还存在阿魏酸的更高聚合体，如三聚体和四聚体。本文报道了两种新的三聚阿魏酸的鉴定。在氧化条件下，使用铜(II)-四甲基乙二胺[CuCl(OH)-TMEDA]作为催化剂，从乙基阿魏酸合成 8-O-4/8-5(环状)-三聚阿魏酸，而 8-8(环状)/5-5-三聚阿魏酸则从皂化不溶性玉米纤维中（制备尺寸排阻色谱、反相 HPLC）分离出来。通过高分辨率 LC-ToF-MS/MS 和一维（(1)H 和二维（HSQC、HMBC、COSY、NOESY）NMR 光谱，明确阐明了这两种三聚体的结构。通过 LC-MS/MS 在玉米、小麦和甜菜不溶性纤维的碱性水解产物中鉴定出新描述的三聚体，这表明细胞壁聚合物之间的阿魏酸交联比以前认识的更为多样化。皂化实验还表明，新鉴定的 8-O-4/8-5(环状)-三聚阿魏酸是植物细胞壁中先前鉴定的 8-O-4/8-5(非环状)-三聚阿魏酸的天然前体。
