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.

Phospholipid Cyclosporine Prodrugs Targeted at Inflammatory Bowel Disease (IBD) Treatment: Design, Synthesis, and in Vitro Validation.

Novel phospholipid (PL)-cyclosporine conjugates were prepared and studied as potential prodrugs for inflammatory bowel disease (IBD). Our approach relies on phospholipase A2 (PLA2 ), which is overexpressed in the inflamed intestinal tissues, as the prodrug activator to potentially release cyclosporine at the site of inflammation. PL-cyclosporine prodrug conjugates with methylene linkers of various lengths between the sn-2 position of the PL and cyclosporine were synthesized and evaluated for in vitro activation. Surprisingly, despite previous work indicating that conjugates with six methylene linkers between the lipid and drug would suffer rapid enzymatic hydrolysis, with cyclosporine this was not observed. However, compounds with longer linkers (n=10, 12 methylene units) display complete release of the drug by PLA2 -catalyzed hydrolysis, thus demonstrating the importance and profound impact of structural fine-tuning. This study represents a proof-of-concept for our hypothesis and a first step towards a truly targeted IBD treatment with cyclosporine that could be administered throughout the GI tract.

Synthesis of the spirastrellolide A, B/C spiroketal: enabling solutions for problematic Au(I)-catalyzed spiroketalizations.

A synthesis of the spirastrellolide A, B/C-ring monounsaturated spiroketal is reported. The key step relies on a Au-catalyzed spiroketalization of a propargyl triol employing an acetonide as a regioselectivity regulator. Through observation and analysis, a set of conditions has been developed that facilitates the use of a mixture of diastereomeric substrates, obviating the need to control the stereochemistry of the propargyl stereocenter and enabling a convenient retrosynthetic disconnection. The key reaction proceeds in 80% yield in 1 min at ambient temperature with the Me3PAuCl/AgOTf catalyst system. These conditions should be widely applicable for new synthetic endeavors as they appear to overcome all issues with the Au-catalyzed spiroketalization.