Rare A-Type, New Spiro-Type, and Highly Oligomeric Proanthocyanidins from Pinus massoniana

Isolation of underivatized PACs led to three new, structurally unique PACs (1-3) from pine bark. Pinutwindoublin (1) is the first known trimer with double A-type interflavanyl linkages (2α→O→5,4α→6 and 2α→O→7,4α). Pinuspirotetrin (2) represents the first PAC tetramer with a heterodimeric framework consisting of one spiro-type and one A-type dimer. Pinumassohexin (3) was elucidated as a mixed A + B type hexamer that consists of the tetramer, peanut procyanidin E, and an A-type dimer (5).