Unusual features involved an oxygenated methine (H 5.81, s, and C 88.2) that showed HMBC correlations with the carbonyl carbon at C 177.0 assigned to a -lactone, and a spiro carbon resonating at C 61.4. Both are characteristic for a spiro-biflavanoid similar to larixinol. Linkages between the four units were further elucidated by HMBC and NOESY (Figure ). Units I and II were recognized as being connected by double (2O7/48) IFLs based on the I-H-4/II-H-2 NOESY correlation, as well as shift of II-C-8 (C 106.3). The presence of a 48 linkage between units II and III was deduced from the cross-peaks between II-H-2 and both III-H-2 and III-H-6 in NOESY spectrum. The spiro-biflavanoid arrangement of units III and IV was corroborated by the HMBC correlations from III-H-2 to III-C-3, III-C-4, III-C-10, III-C-2, III-C-6, and IV-C-8; from IV-H-2 to IV-C-9; and from IV-H-6 to IV-C-5 and IV-C-7. Thus, the planar structure of 2 had to be the first tetrameric spiro-PAC, consisting of one A-type and one spiro-type dimer. Analysis of its ECD spectrum showed a high-amplitude positive Cotton effect in Scheme 1. Proposed biosynthetic pathway for the formation of the spiro element in PAC tetramer 2.