Tri- and Tetrameric Proanthocyanidins with Dentin Bioactivities from Pinus massoniana

Guided by dentin biomechanical bioactivity, this phytochemical study led to the elucidation of an extended set of structurally demanding proanthocyanidins (PACs). Unambiguous structure determination involved detailed spectroscopic and chemical characterization of four A-type dimers (2, 4–6), seven trimers (10–16), and six tetramers (17–22). New outcomes confirm the feasibility of determining the absolute configuration of the catechol monomers in oligomeric PACs by 1D and 2D NMR. Electronic circular dichroism (ECD) as well as phloroglucinolysis followed by MS and chiral phase HPLC analysis generated the necessary chiral reference data.