Catalytic enantioselective Pudovik reaction of aldehydes and aldimines with tethered bis(8-quinolinato) (TBOx) aluminum complex

Catalytic asymmetric Claisen rearrangement of enolphosphonates: construction of vicinal tertiary and all-carbon quaternary centers

A Cu-catalyzed enantioselective Claisen rearrangement of easily-accessible enolphosphonates using commercially available (R, R )-PhBOX as the chiral ligand was developed. A wide range of rearrangement products with contiguous tertiary and all carbon quaternary centers were obtained in excellent yields and stereoselectivities. The α -ketophosphonate products could be easily transformed into other functional groups in high efficiency.

Aromatic phosphonates inhibit the lysophospholipase D activity of autotaxin

Autotaxin (ATX) is an attractive target for the anticancer therapeutics that inhibits angiogenesis, invasion and migration. ATX is an extracellular lysophospholipase D that hydrolyzes lysophosphatidylcholine to form the bioactive lipid lysophosphatidic acid. The aromatic phosphonate S32826 was the first described nanomolar inhibitor of ATX. However, the tridecylamide substituent on aromatic ring contributed to its poor solubility and bioavailability, severely limiting its utility in vivo. cLogP calculations revealed that the lipophilicity of S32826 could be lowered by shortening its hydrophobic chain and by introducing substituents alpha to the phosphonate. Herein, we describe the synthesis of a small set of α-substituted phosphonate analogs of S32826, and we show that shortening the chain and adding α-halo or α-hydroxy substituents increased solubility; however, ATX inhibition was reduced by most substitutions. An optimal compound was identified for examination of biological effects of ATX inhibition in vivo.

Organocatalytic High Enantioselective Synthesis of β-Formyl-α-hydroxyphosphonates

The cross aldol reaction between enolizable aldehydes and α-ketophosphonates was achieved for the first time by using 9-amino-9-deoxy-epi-quinine as the catalyst. β-Formyl-α-hydroxyphosphonates were obtained in high to excellent enantioselectivities. The reaction works especially well with acetaldehyde, which is a tough substrate for organocatalyzed cross aldol reactions. The products were demonstrated to have anticancer activities.

Chiral magnesium BINOL phosphate-catalyzed phosphination of imines: access to enantioenriched α-amino phosphine oxides

A new method to synthesize chiral α-amino phosphine oxides is reported. The reaction combines N-substituted imines and diphenylphosphine oxide and is catalyzed by a chiral magnesium phosphate salt. A wide variety of aliphatic and aromatic aldimines substituted by electron-neutral benzhydryl or dibenzocycloheptene groups were excellent substrates for the addition reaction. The dibenzocycloheptene protected imines afforded improved enantioselectivity in the resulting products. Substituted diphenylphosphine oxide nucleophiles also showed good reactivity.

Synthesis and conformation of substituted chiral binaphthyl-azobenzene cyclic dyads with chiroptical switching capabilities

Optically active binaphthyl-azobenezene cyclic dyads were synthesized to develop a photochromic switching molecule. Azobenezene moieties were cis-trans isomerized by photoirradiation. As a reflection of the structural change, the specific optical rotation and circular dichroism underwent significant shifts. Under certain conditions, the positive-negative and zero-positive (or zero-negative) signals were reversed. Optical rotation may potentially be applied in noise-cancelling nondestructive photoswiches. The conformations were studied by experimental and theoretical methods. The results revealed that the helical chirality, (P) or (M), of the cis-azobenzene moiety was induced by intramolecular axial chirality. The twist direction depended on the axial chirality as well as the azobenzene linkage position to the binaphthyls, but was independent of the identity of substituted groups. 2,2’-Linked-(R)-binaphthyl was found to induce cis-(P)-azobenzene, whereas symmetrically 7,7’-linked-(R)-binaphthyl was found to induce cis-(M)-azobenzene.

Asymmetric hydrophosphylation of chiral N-phosphonyl imines provides an efficient approach to chiral α-amino phosphonates

Chiral N-phosphonylimines were found to react with lithium phosphites to provide various substituted chiral α-amino phosphonates in excellent yields (94-97%) and diastereoselectivities (93:7-99:1). The types of bases utilized for generating the nucleophile are crucial for the effectiveness of asymmetric induction. In addition, N,N-isopropyl group on chiral N-phosphonylimine auxilliary was proven to be superior to other protecting groups in controlling diastereoselectivity. The absolute configuration was unambiguously determined by converting a chiral α-amino phosphonate into its authentic N-Cbz derivative.

Organocatalytic enantioselective synthesis of both diastereomers of alpha-hydroxyphosphinates

Racemic alpha-acylphosphinates and formylphosphinate hydrate were used directly as the substrates in a proline derivative-catalyzed cross aldol reaction with ketones. Because of the preexisting phosphorus stereogenic center, a mixture of two diastereomers of the corresponding alpha-hydroxyphosphinates was obtained in this reaction. Good to high enantioselectivities (up to 99% ee) were obtained simultaneously for the two diastereomers in good yields. Good diastereoselectivities were also obtained when the reaction generates an additional carbon stereogenic center.