Glyceryl-acyl and aryl-acyl dimers in Pseudotsuga menziesii bark suberin

The cork from the outer bark of Douglas-fir (Pseudotsuga menziesii) was exhaustively extracted and submitted to a mild CaO-catalyzed methanolic depolymerization. The solubilized material (2.5 % yield) was derivatized and analysed with GC-MS. Glycerol was the main component (41.2%), followed by aliphatic acid monomers (30.6 %) and glyceryl and feruloyl dimers (14.5 %). Monoacylglyceryl esters of alpha,omega-diacids were dominant (68% of glyceryl dimers), followed by monoacylglyceryl esters of alkanoic acids and of omega-hydroxyacids (respectively 20% and 9%). For all cases 1- and 2-monoacylglyceryl esters were present. Dimers of w-hydroxyacids esterified to ferulic acid through their primary hydroxyl were also found. The feruloyl ester of docosanol could also be identified. The relative abundance of the dimers followed the proportion of acid monomers. The direct evidence found here for P. menziesii, and previously for Q. suber, that glycerol is esterified to all suberinic acids and that omega-hydroxyacids are esterified to ferulic acid supported the discussion of a suberin structure developing on glyceryl-diacyl-glyceryl and glyceryl-hydroxyacyl-feruloyl backbones.