Stereocontrol via Propeller Chirality in FLP-Catalyzed Asymmetric Hydrogenation.

Utilization of chiral frustrated Lewis pairs as catalysts in enantioselective hydrogenation of unsaturated molecules represents a promising approach in asymmetric synthesis. In our effort to improve our current understanding of the factors governing the stereoselectivity in these catalytic processes, herein we examined the mechanism of direct hydrogenation of aromatic enamines catalyzed by a binaphthyl-based chiral amino-borane. Our computational analysis reveals that only one particular conformer of the key borohydride reaction intermediate can be regarded as a reactive form of this species. This borohydride conformer has a well-defined chiral propeller shape, which induces facial selectivity in the hydride transfer to pro-chiral iminium intermediates. The propeller chirality of the reactive borohydride conformer is generated by the axially chiral binaphthyl scaffold of the amino-borane catalyst through stabilizing π-π stacking interactions. This new computational insight can be readily used to interpret the high degree of stereoinduction observed for these reactions. We expect that the concept of chirality relay could be further exploited in catalyst design endeavors.

Replacing C6F5 groups with Cl and H atoms in frustrated Lewis pairs: H2 additions and catalytic hydrogenations.

2-(Dialkylamino)phenylboranes containing the BXZ group, where X, Z = C6F5, Cl, and H, were prepared in a few synthetic steps and demonstrated the cleavage of H2 under mild conditions. Depending on the nature of the dialkylamino group, X, and Z, the stability of the produced zwitterionic H2 adducts varies from isolated solids indefinitely stable in an inert atmosphere to those quickly equilibrating with the initial aminoborane and H2. Using a combined experimental/computational approach on a series of isostructural aminoboranes (dialkylamino = 2,2,6,6-tetramethylpiperid-1-yl), it was demonstrated that the electronegativity and the steric effect of the substituents generally follow the trend C6F5 ∼ Cl ≫ H. This observation is useful for designing new FLPs for practical applications. As an example, we demonstrated the hydrogenation of alkynes to cis-alkenes under mild conditions that was catalyzed by a chloro-analogue of the C6F5-substituted aminoborane developed previously. The presence of a BHCl group in the aminochloroboranes or in their H2 adducts features facile redistribution of the H and Cl atoms and the formation of polychloro and polyhydrido species.

[Indications and limits of local tri-methacycline therapy in pyogenic infections of the eye (author's transl)]. / Indikationen und Grenzen der lokalen Tri-Methacyclin-Behandlung von pyogenen Infektionen des Auges

In addition to the preoperative treatment of acute dacryocystitis local administration of tri-methacycline proved to be of benefit in cases of endophthalmitis consequent to injury. Its subconjunctival administration is the therapy of choice for serpentic ulcers of the cornea.

Lymphocyte-dependent antibodies in uveitis.

Lymphocyte-dependent antibodies were revealed in the serum of patients suffering from uveitis of various aetiologies. The serum was incubated with normal uveal tissue and the binding of non-immune human lymphocytes was investigated. In three cases of sympathetic ophthalmitis the lymphocytes accumulated around the melanine granules, while in another 17 patients with uveitis cases the lymphocytes accumulated around the capillaries. Uveal tissue incubated with control sera failed to bound lymphocytes. The lymphocytic infiltration in certain cases of chronic uveitis suggested the role of lymphocyte-mediating antibodies in the aetiology of these cases.