Enantioselective Synthesis of Thailanstatin A Methyl Ester and Evaluation of in Vitro Splicing Inhibition.

Thailanstatin A has been isolated recently from the fermentation broth of B. thailandensis MSMB43. We describe here an enantioselective convergent synthesis of thailanstatin A methyl ester and evaluation of its splicing activity. Synthesis of both highly functionalized tetrahydropyran rings were carried out from commercially available tri- O-acetyl-d-glucal as the key starting material. Our convergent synthesis involved the synthesis of both tetrahydropyran fragments in a highly stereoselective manner. The fragments were then coupled using cross-metathesis as the key step. The synthesis of the diene subunit included a highly stereoselective Claisen rearrangement, a Cu(I)-mediated conjugate addition of MeLi to set the C-14 methyl stereochemistry, a reductive amination reaction to install the C16-amine functionality, and a Wittig olefination reaction to incorporate the diene unit. The epoxy alcohol subunit was synthesized by a highly selective anomeric allylation, a Peterson olefination, and a vanadium catalyzed epoxidation that installed the epoxide stereoselectively. Cross-metathesis of the olefins provided the methyl ester derivative of thailanstatin A. We have carried out in vitro splicing studies of the methyl ester derivative, which proved to be a potent inhibitor of the spliceosome.