Rodolfo Tello-Aburto

Palladium-catalyzed reactions of cyclohexadienones: regioselective cyclizations triggered by alkyne acetoxylation.

Regioselective cyclizations of alkyne-tethered cyclohexadienones can be accomplished under palladium catalysis. The cyclization involves an initial Pd-mediated acetoxylation of the alkyne, followed by migratory insertion and protonolysis of the resulting palladium enolate. The predictable regioselectivity of these atom-economical and stereoselective reactions is influenced by developing steric interactions during migratory insertion of a vinyl palladium intermediate.

Evolution of a protecting-group-free total synthesis: studies en route to the neuroactive marine macrolide (-)-palmyrolide A.

A full account of our synthetic work toward the first total synthesis of the neuroactive marine macrolide (-)-palmyrolide A is described. Our first-generation approach aimed to unlock the unknown C(5)-C(7) stereochemical relationship via the synthesis of four diastereomers of palmyrolide A aldehyde, a known degradation product. When these efforts provided inconclusive results, recourse to synthesizing all possible stereocombinations of the 15-membered macrolide was undertaken. These studies were critical in confirming the absolute stereochemistry, yielding the first total synthesis of (+)-ent-palmyrolide A. Subsequent to this work, the first protecting-group-free total synthesis of natural (-)-palmyrolide A is also reported.

A formal synthesis of the auriside aglycon.

A highly convergent formal synthesis of the auriside aglycon was achieved. An indene-based thiazolidinethione chiral auxiliary was used for the construction of both the C1-C9 and C10-C17 fragments via acetate aldol reactions. A Meinwald reaction was utilized to install the stereocenter at C2, and a conjugated addition to an ynone was used to construct the C9-C11 enone.

Detailed analysis of (-)-palmyrolide a and some synthetic derivatives as voltage-gated sodium channel antagonists.

A small library of synthetic (−)-palmyrolide A diastereomers, analogues, and acyclic precursors have been examined with respect to their interaction with voltage-gated sodium channels (VGSCs). Toward this goal, the ability of (−)-palmyrolide A and analogues to antagonize veratridine-stimulated Na+ influx in primary cultures of mouse cerebrocortical neurons was assessed. We found that synthetic (−)-palmyrolide A and its enantiomer functioned as VGSC antagonists to block veratridine-induced sodium influx. A detailed NMR and computational analysis of four diastereomers revealed that none had the same combination of shape and electrostatic potential as exhibited by natural (−)-palmyrolide A. These data indicate that the relative configuration about the tert-butyl and methyl substituents appears to be a prerequisite for biological function. Additional testing revealed that the enamide double bond was not necessary for blocking veratridine-induced sodium influx, whereas the acyclic analogues and other macrolide diastereomers tested were inactive as inhibitors of VGSCs, suggesting that the intact macrolide was required.

A total synthesis of (−)-hortonone C

A total synthesis of the cytotoxic terpenoid hortonone C was accomplished and its absolute stereochemistry confirmed. Intermediate (+)-4 was synthesized using either an asymmetric conjugate addition strategy, or by elaboration of the Hajos-Parrish ketone. Reduction of (+)-4 under dissolving-metal conditions and trapping the enolate intermediate served to control the cis-stereochemistry at the ring fusion and provide a silyl enol ether necessary for ring expansion. Comparison of optical rotation data confirmed that the absolute configuration of natural hortonone C is (6S,7S,10S).