SynopsisBy means of carbon-13 nmr (at 25 MHz) the transleis conformer ratio in glycyl-L-proline has been measured in aqueous (DzO) solution over the temperature range 33-96 "C. It is found that AHo = -4.2 kJ/mole and ASo = -9.7 J/mole/K.Measurements of the 2'1 values for the proline ring carbons yielded values consistent with a fast puckering process involving both the 0-and y-carbons.Measurements of the rate of cis-trans conformational interconversion in glycyl-L-proline, using complete line-shape analysis for the glycyl a-carbon resonance, gave values for the trans -cis isomerization as follows: AHf = 83.5 f 0.2 kJ/mole; A S # = 0.0 f 10 J/mole/K. A more approximate determination from coalescence temperature observations gave a value of AG# of 82.0 f 0.4 kJ/mole for this process in acetyl-L-proline in aqueous solution. The presence of 12M NaSCN lowered this barrier by ca. 2.6 kJ/mole.Such measurements are relevant to present theoretical models of the denaturation-renaturation processes in proteins, in which proline residues may play a key role.

An efficient kinetic resolution of sulfoximines with enals was realized using chiral N-heterocyclic carbene (NHC) catalysts. The stereoselective amidation proceeds without additional acyl transfer agent. Both enantiomers of the sulfoximines can be obtained with excellent ee values (up to 99% ee and -97% ee, respectively). Performing the catalysis on a gram scale allowed using the recovered sulfoximine (+)-1j in an asymmetric synthesis of FXa inhibitor F.

A ruthenium-catalyzed arylation reaction of oxa-and azabicyclic alkenes with (hetero)arenes by C−H bond activation has been discovered. The reaction does not require additives and utilizes dioxygen in realizing the catalytic cycle leading to monosubstituted 7-oxa and 7-azabenzonorbornane derivatives.

Ball milling techniques have been applied in the development of a mechanosynthesis of [Cp*Co(CO)I2], which proved highly efficient as catalyst in mechanochemical C−H bond amidations of indoles in a mixer ball mill. A wide range of amidated products is obtained in excellent yields. Compared to the solution‐based methods, the procedure opens a more feasible and environmentally‐friendly access to both the cobalt(III) catalyst and 2‐amidated indoles.magnified image

Under an atmosphere of dioxygen, copper-catalyzed de-alkylation/amination sequences provide sulfonimidamides from unprotected sulfoximines in moderate to good yields. Mechanistic studies suggest the involvement of radicals in both the C-S bond cleavage and the formation of the new N-S bond.