Expedient access to the okadaic acid architecture: a novel synthesis of the C1-C27 domain.

A newly designed synthetic entry to the C1-C27 domain of okadaic acid has been developed. This incorporates substantial improvements in the preparations of the key okadaic acid building blocks representing the C3-C8, C9-C14, and C16-C27 portions. The synthesis of the C3-C8 lactone used (R)-glycidol as the origin of the C4 stereogenic center and featured a late-stage optional incorporation of the C7 hydroxyl group. The complementary C9-C14 fragment was synthesized in a concise route from (R)-3-tert-butyldimethylsilyloxy-2-methylpropanal and propargyl bromide. Assembly of the C3-C14 spiroketal-containing intermediate from the constitutent fragments revealed a dramatic effect of C7 functionalization upon spiroketalization efficiency. In contrast, both (9E)- and (9Z)-enones converged readily to the C8 spiroketal upon treatment with acid. Modifications to the central C16-C27 fragment of okadaic acid included the early replacement of benzylic protecting groups by more suitable functionalities to facilitate both the generation of the C15-C27 intermediate and the deprotection of the final products. These modular building blocks were deployed for the synthesis of the C1-C27 scaffold of 7-deoxyokadaic acid. This work demonstrates improvements in the formation of versatile okadaic acid intermediates, as well as a reordering of fragment couplings. This alternative order of coupling was designed to promote the late stage incorporation of nonnatural lipophilic extensions from the C27 terminus.

Potent reversible inhibitors of the protein tyrosine phosphatase CD45.

The cytosolic portion of CD45, a major transmembrane glycoprotein found on nucleated hematopoietic cells, contains protein tyrosine phosphatase activity and is critical for T-cell receptor-mediated T-cell activation. CD45 inhibitors could have utility in the treatment of autoimmune disorders and organ graft rejection. A number of 9,10-phenanthrenediones were identified that reversibly inhibited CD45-mediated p-nitrophenyl phosphate (pNPP) hydrolysis. Chemistry efforts around the 9,10-phenanthrenedione core led to the most potent inhibitors known to date. In a functional assay, the compounds were also potent inhibitors of T-cell receptor-mediated proliferation, with activities in the low micromolar range paralleling their enzyme inhibition. It was also discovered that the nature of modification to the phenanthrenedione pharmacophore could affect selectivity for CD45 over PTP1B (protein tyrosine phosphatase 1B) or vice versa.

Importance of the C28-C38 hydrophobic domain of okadaic acid for potent inhibition of protein serine-threonine phosphatases 1 and 2A.

Okadaic acid is a potent inhibitor of select serine/threonine protein phosphatases. The importance of the C28-C38 hydrophobic domain of okadaic acid for inhibition of PP1 and PP2A was investigated. The hydrophobic domain is required but not sufficient for potent inhibition, and it also contributes to differential inhibition between PP1 and PP2A.