Enantioselective Synthesis of Chiral Phosphonates via Rh/f-spiroPhos Catalyzed Asymmetric Hydrogenation of β,β-Disubstituted Unsaturated Phosphonates

The first asymmetric hydrogenation of β,β-diaryl unsaturated phosphonates has been realized for synthesis of β,β-diaryl chiral phosphonates with excellent enantioselectivities (up to 99.9% ee) catalyzed by the Rh-(R,R)-f-spiroPhos complex. Furthermore, this catalyst also exhibits comparably excellent performance for β-aryl-β-alkyl unsaturated phosphonates providing the corresponding chiral phosphonates with up to 99.9% ee values. This methodology provides a straightforward access to asymmetric synthesis of chiral phosphonates.

Mechanistic binding insights for 1-deoxy-D-Xylulose-5-Phosphate synthase, the enzyme catalyzing the first reaction of isoprenoid biosynthesis in the malaria-causing protists, Plasmodium falciparum and Plasmodium vivax

We have successfully truncated and recombinantly-expressed 1-deoxy-D-xylulose-5-phosphate synthase (DXS) from both Plasmodium vivax and Plasmodium falciparum. We elucidated the order of substrate binding for both of these ThDP-dependent enzymes using steady-state kinetic analyses, dead-end inhibition, and intrinsic tryptophan fluorescence titrations. Both enzymes adhere to a random sequential mechanism with respect to binding of both substrates: pyruvate and D-glyceraldehyde-3-phosphate. These findings are in contrast to other ThDP-dependent enzymes, which exhibit classical ordered and/or ping-pong kinetic mechanisms. A better understanding of the kinetic mechanism for these two Plasmodial enzymes could aid in the development of novel DXS-specific inhibitors that might prove useful in treatment of malaria.

Pd-catalyzed carbonylative access to aroyl phosphonates from (hetero)aryl bromides

This first carbonylative coupling employing a phosphorus-based nucleophile provides easy and safe access to acyl phosphonates under mild conditions.

Copper-catalyzed asymmetric synthesis and comparative aldose reductase inhibition activity of (+)/(-)-1,2-benzothiazine-1,1-dioxide acetic acid derivatives

A copper catalyst system for the asymmetric 1,4-hydrosilylation of the α,β-unsaturated carboxylate class was developed by which synthesis of (+)- and (-)-enantiomers of 1,2-benzothiazine-1,1-dioxide acetates has been achieved with a good yield and an excellent level of enantioselectivity. A comparative structure-activity relationship study yielded the following order of aldose reductase inhibition activity: (-)-enantiomers > racemic > (+)-enantiomers. Further, a molecular docking study suggested that the (-)-enantiomer had significant binding affinity and thus increased inhibition activity.

Filling gaps in asymmetric hydrogenation methods for acyclic stereocontrol: application to chirons for polyketide-derived natural products

The large volume of research studying hydrogenation catalysis might suggest that stereoselective hydrogenation of alkenes is a solved problem, but we believe the most important parts of asymmetric hydrogenation methodology remain unmastered. The most popular chiral catalysts, Rh- and Ir-diphosphine complexes, do not hydrogenate the largest categories of prochiral alkenes, hindered tri- and tetra-substituted ones, at useful rates unless the substrate has a "classical" coordinating functional group (CFG), for example, amides or homoallylic alcohols, to anchor the substrate to the metal. Therefore, while many methods are available for the asymmetric hydrogenation of alkenes with appropriate CFGs, synthetic chemistry would benefit from chiral hydrogenations of substrates with functional groups that typically do not coordinate in Rh- and Ir-diphosphine complexes. In this Account, we demonstrate the application of chiral analogues of Crabtree's catalyst to asymmetric hydrogenations of coordinating unfunctionalized, trisubstituted alkenes. Crabtree's catalyst, a complex of iridium with 1,5-cyclooctadiene, tris-cyclohexylphosphine, and pyridine, differs from Rh- and Ir-diphosphine complexes, which we broadly refer to as "chiral analogues of Wilkinson's catalyst." Crabtree's catalyst analogues hydrogenate substrates that do not contain functionalities generally recognized as CFGs, and we propose reasons for this chemistry based on the catalytic mechanisms. Thus, chiral analogues of Crabtree's catalyst facilitate many hydrogenations that would not be possible using Rh- or Ir-diphosphine complexes. Directed hydrogenations have been used in acyclic stereocontrol for decades, but the realization that these catalysts can be used for acyclic stereocontrol without the types of directing groups that are necessary for other hydrogenations significantly broadens the scope of hydrogenations for this purpose. Recently, we have prepared chirons for polyketide-derived natural products using an N,carbene-Ir complex (1). This approach has led to catalytic syntheses of several important chirons to facilitate preparations of these ubiquitous natural products.