instill resistance to proteolytic dentin degradation. Continuing these interdisciplinary efforts at the interface of natural products chemistry and dentistry, exploration of structurally unique compounds from bioactive PAC oligomer fractions led to three structurally distinctive new PACs (13) (Figure ). Pinutwindoublin (1) is the first A-type-only trimer linked with (2O5,46) and (2O7,48) bonds. This unprecedented linkage combination is the plausible reason for the observed atropisomeric line-broadening in its NMR spectra, which otherwise is atypical of A-type PACs. Pinuspirotetrin (2) represents the first PAC with a heterodimeric framework consisting of a spiro-type dimer connected with an A-type dimer. Also characterized in underivatized form, and exhibiting dentin bioactivity, pinumassohexin (3) was elucidated as a hexameric PAC with mixed A+B-type interflavanyl linkages (IFLs), assembled from the known tetramer, peanut procyanidin E, and the dimer, epicatechin-(2O7,48)-ent-catechin (5), via a 46 bond. Structure elucidation of 13 utilized 1D/2D NMR, ECD, 13 C NMR -gauche effects, as well as phloroglucinolysis, a recently established toolbox for absolute stereochemical assignments in PACs. The molecular formula C45H34O18 of 1 was determined using the C NMR carbon counts and the ()-HRESIMS ion at m/z 863.1823 M  H  . Two pairs of characteristic AX-resonances at H 3.87 and 4.26 (both d, J = 4.0 Hz), as well as H 4.22 and 4.87 (both d, J = 4.3 Hz), revealed the presence of two doubly linked interflavanyl bonds and, in connection with the molecular formula, indicated the 2A-type trimer nature of 1. The NMR data (Table ) showed the characteristic H AMX patterns of the three 1,3,4-trisubstituted aromatic B-, E-, and H-rings. Additionally, a small J coupling (1 Hz) between III-H-2 and III-H-3 suggested the terminal unit III to be 2,3-cis configured (ent)-epicatechin. The IFLs were elucidated via HMBC and NOESY data (Figure ): the presence of 2O7/48 linkages between units II and III was assigned by the HMBC cross-peaks from both II-H-4 (H 4.87) and III-H-2 (H 4.96) to III-C-9 (C 152.4). The NOESY correlations from II-H-8 to II-H-2 and II-H-6, and from I-H-2 to II-H-4 and III-H-2 indicated that 2O5/46 bonds connected units I and II. This established the planar structure of 1.