Glycerol-ω-hydroxyacid-ferulic acid oligomers in cork suberin structure

Abstract

Abstract Cork suberin was partially depolymerised by methanolysis catalysed by Ca(OH)2. The solubilised depolymerisate was analysed by ESI-MS/MS. The compounds identified included monomers and “dimeric” and “trimeric” oligomers. Among the latter, an oligomer of glycerol esterified to a ω-hydroxyacid esterified to ferulic acid was identified. The “dimeric” structures of glycerol esterified to a ω-hydroxyacid and of a ω-hydroxyacid esterified to ferulic acid were also found in the partially depolymerised fraction. The identification of these molecules was confirmed by synthesis of model compounds and comparison of their ESI-MS/MS spectra. The glycerol-ω-hydroxyacid-ferulic acid trimeric oligomer could be an important constituent block in the suberin structure. Its function is probably to link the two main polymers present in suberised cell walls, namely, polyaliphatic polyesters and lignin-related polyaromatics. The glycerol-ω-hydroxyacid moiety is part of the polyaliphatic polyester and the ferulic acid moiety is esterified to the polyaromatics. These oligomers provide a new insight to understanding of the macromolecular structure of suberin, since they could allow cross-linking of the two structurally different biopolymers.