Which Is the Actual Catalyst: Chiral Phosphoric Acid or Chiral Calcium Phosphate?

Enantioselective heterogeneous Brønsted acid catalysis

This highlight describes the state-of-the-art applications of appropriately designed heterogeneous chiral Brønsted acid catalysts and their applications in organic synthesis.

Enantioselective Prins cyclization: BINOL-derived phosphoric acid and CuCl synergistic catalysis

The synergistic catalysis between a chiral phosphoric acid and CuCl allows the development of the first enantioselective Prins cyclization.

Enantio- and chemoselective Brønsted-acid/Mg(nBu)2 catalysed reduction of α-keto esters with catecholborane

The first enantio- and chemoselective Brønsted-acid catalysed reduction of α-keto esters with catecholborane has been developed.

Development and mechanism of an enantioselective bromocycloetherification reaction via Lewis base/chiral Brønsted acid cooperative catalysis

The development of a binary catalyst system for bromocycloetherification, consisting of an achiral Lewis base and a chiral Brønsted acid, is described in detail. The results of preliminary kinetic studies are also presented.

Calcium Orthophosphate-Based Bioceramics

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells.

Direct catalytic asymmetric Mannich-type reaction of α-sulfanyl lactones

Catalytic asymmetric Mannich-type reactions of α-sulfanyl lactones to aldimines were promoted by a chiral Ag complex/DBU binary catalyst. The reaction proceeded in a syn-selective manner in high enantioselectivity. Alkylative activation of the sulfide of the Mannich adduct allowed for the formation of trisubstituted aziridines.

Chiral calcium iodide for asymmetric Mannich-type reactions of malonates with imines providing β-aminocarbonyl compounds

Out of the pybox: We have developed a novel chiral calcium iodide catalyst from CaI2 and a pybox that is stable under moisture and oxygen. This catalyst was applied to catalytic asymmetric Mannich-type reactions of malonates with both N-Boc-protected aromatic and aliphatic imines, and resulted in moderate to high yields with high enantioselectivities. To the best of our knowledge, this is the first example of highly enantioselective metal-catalyzed asymmetric Mannich-type reactions of malonates with N-Boc-protected aliphatic imines. The Mannich adduct was successfully converted into the α-hydroxy β-amino acid derivative. We have also shown the unique structure of the chiral Ca complexes with malonates.

Catalytic enantioselective O-nitrosocarbonyl aldol reaction of β-dicarbonyl compounds

The first example of a Cu-catalyzed asymmetric O-nitrosocarbonyl aldol reaction is described. This novel protocol allows convenient access to highly enantioenriched α-hydroxy-β-ketoesters including the antibacterial natural product kjellmanianone (up to 99% ee). MnO(2) was introduced as a mild efficient oxidant for the in situ generation of nitrosocarbonyl species from hydroxamic acid derivatives.

Catalytic enantioselective tert-aminocyclization by asymmetric binary acid catalysis (ABC): stereospecific 1,5-hydrogen transfer

Selective H transfer by ABC: A new asymmetric binary acid catalyst was developed to promote 1,5-H transfer specifically and stereoselectively in tert-aminocyclization reactions with excellent activity, high enantioselectivity, and broad substrate scope. The H atom (in red) was proven to transfer through a stereospecific suprafacial pathway (see scheme).

Highly enantioselective electrophilic α-bromination of enecarbamates: chiral phosphoric acid and calcium phosphate salt catalysts

Metal-free chiral phosphoric acids and chiral calcium phosphates both catalyze highly enantio- and diastereoselective electrophilic α-bromination of enecarbamates to provide an atom-economical synthesis of enantioenriched vicinal haloamines. Either enantiomer can be formed in good yield with excellent diastereo- and enantioselectivity simply by switching the catalyst from a phosphoric acid to its calcium salt.