ABSTRACT
Structurally, all of the molecules possess a 20-membered macrolactone ring. Modifying the description by Hale et al.,9,10 all bryostatins possess a 20-membered macrolactone in which there are three remotely substituted pyran rings that are linked by a methylene bridge and an (E)-disubstituted alkene; all have geminal dimethyls at C8 and C18, and a four-carbon sidechain (carbons 4 to 1) from the A ring to the lactone oxygen, with another four carbon chain (carbons 24 to 27) on the other side of the lactone oxygen to the C ring. Most have an exocyclic methyl enoate in their B and C rings, though bryostatin 3, in particular, has a butenolide rather than the C-ring methyl enoate, and bryostatins 16 and 17 have glycals in place of the regular C19 and C20 hydroxyl moieties. In the early reviews by Hale9 and Mutter,7 18 structures (bryostatins 1-18) are listed; and the remaining two structures were thought to be desoxy-bryostatin 4 and desoxy-bryostatin 5 isolated from Lissodendoryx isodictyalis.11 Work reported from Peoples’ Republic of China in 1998 (Chinese)12 and 2004 (English),13 gave the structure of bryostatin 19 (Figure 8.1) puriœed from a South China Sea collection of Bugula neritina, which was then followed, also in 2004, by the report of bryostatin 20 (Figure 8.1), isolated from an Atlantic-sourced Bugula neritina by Lopanik et al.14 Comparison with the structures of the other 18 bryostatins shows that these are closely related to bryostatin 3 in terms of their basic ring components. There may well be other naturally occurring versions, as at the end of the bryostatin 20 report, the authors mention at least one more isolable from the larvae that has yet to be fully identiœed.14
