A carbohydrate based chiron approach to the lactone intermediate employed in the synthesis of BC-ring fragment of (+)-spirastrellolide A

Synthesis and Biological Evaluation of the Southern Hemisphere of Spirastrellolide A and Analogues

The synthesis and biological evaluation of truncated spirastrellolide A analogues comprised of the southern hemisphere against protein phosphatase 2A are described. A convergent synthesis was designed featuring two gold-catalyzed cyclization reactions, specifically, a dehydrative cyclization of monoallylic diols for the synthesis of the tetrahydropyran (A-ring) and a regioselective spiroketalization for the efficient generation of the [6,6]-spiroketal (B, C-ring system). The synthesis of the southern hemisphere of spirastrellolide A was achieved involving the longest linear sequence of 19 steps. A total of eight spirastrellolide A analogues were synthesized, and preliminary PP2A enzyme assay inhibition studies were performed for the first time on analogues of the southern hemisphere. Several analogues showed inhibition, which is a positive indication and perhaps suggests that the unsaturated spiroketal fragment might be crucial to induce PP2A inhibition.

Synthesis of the C9-C25 Subunit of Spirastrellolide B

The synthesis of the C9-C25 subunit of the marine natural product spirastrellolide B is reported. The key synthetic features included the union of the two key fragments 5 and 6 via a Suzuki-Miyaura coupling reaction and a late-stage, one-pot sequential deprotection/cascade Achmatowicz rearrangement-spiroketalization to install the key spirocyclic intermediate present in the C9-C25 fragment of spirastrellolide B. The synthesis of the C9-C16 fragment 6 was accomplished via a phosphate tether mediated ring-closing metathesis (RCM), a subsequent hydroboration-oxidation protocol, followed by other stereoselective transformations in a facile manner. The spirocyclic intermediate was further functionalized utilizing a Lindlar/NaBH4 reduction protocol to furnish the C9-C25 subunit 3.

Spirastrellolide E: Synthesis of an advanced C(1)-C(24) southern hemisphere

The synthesis of a C(1)-C(24) advanced southern hemisphere fragment towards the total synthesis of spirastrellolide E has been achieved. Highlights of the route include a highly convergent Type I Anion Relay Chemistry (ARC) tactic for fragment assembly, in conjunction with a directed, regioselective gold-catalyzed alkyne functionalization to generate the central unsaturated [6,6]-spiroketal.