The 1H-1H COSY
correlations established the linkages of C-9/C-12, C-5/C-16, C-15/
C-20/C-21, and C-18/C-20, as shown in Figure 1, which suggested
that 1 possessed a similar carbon skeleton to that of (19S,20R)-
dihydroperaksine.32 However, the key difference between the two
compounds was that compound 1 possessed one more ring