Synthesis of Dimethyldisilabicycloalkanes: Cage-Size Effects on the Relative Stabilities between In,Out and Twist-Out,Out Forms.

In large bicycloalkanes, several in/out forms exist, wherein substituents on the bridgehead atoms are oriented either outside or inside the cage. The relative stability between the in,out and twist-out,out forms, which can interconvert through homeomorphic conversion, was found to depend upon the cage size. The in,out form demonstrated thermodynamic stability in the smaller C10 derivative, whereas the twist-out,out form prevailed in the larger derivatives of C14 and C18 plausibly as a result of dispersion forces among the chains.

Simultaneous synthesis and characterization of in/out-isomers of disilabicyclo[14.14.14]alkanes.

Facile and simultaneous synthesis of diphenyl-disilabicyclo[14.14.14]alkane in/out-isomers was achieved by using organosilicon chemistry. Although the formation of several in/out-isomers would be conceivable, only two diastereomers, i.e. the (traditional-)out,out-isomer and the twist-out,out-isomer, could be isolated because of homeomorphic isomerization. Crystal structures of the diastereomers were confirmed.

Intermolecular autocatalytic activation of serine protease zymogen factor C through an active transition state responding to lipopolysaccharide.

Horseshoe crab hemolymph coagulation is believed to be triggered by the autocatalytic activation of serine protease zymogen factor C to the active form, α-factor C, belonging to the trypsin family, through an active transition state of factor C responding to bacterial lipopolysaccharide (LPS), designated factor C*. However, the existence of factor C* is only speculative, and its proteolytic activity has not been validated. In addition, it remains unclear whether the proteolytic cleavage of the Phe737-Ile738 bond (Phe737 site) of factor C required for the conversion to α-factor C occurs intramolecularly or intermolecularly between the factor C molecules. Here we show that the Phe737 site of a catalytic Ser-deficient mutant of factor C is LPS-dependently hydrolyzed by a Phe737 site-uncleavable mutant, clearly indicating the existence of the active transition state of factor C without cleavage of the Phe737 site. Moreover, we found the following facts using several mutants of factor C: the autocatalytic cleavage of factor C occurs intermolecularly between factor C* molecules on the LPS surface; factor C* does not exhibit intrinsic chymotryptic activity against the Phe737 site, but it may recognize a three-dimensional structure around the cleavage site; and LPS is required not only to complete the substrate-binding site and oxyanion hole of factor C* by interacting with the N-terminal region but also to allow the Phe737 site to be cleaved by inducing a conformational change around the Phe737 site or by acting as a scaffold to induce specific protein-protein interactions between factor C* molecules.

Iridium-catalyzed triple C(sp3)-H borylations: construction of triborylated sp3-carbon centers.

An unprecedented catalytic C(sp(3))-H triborylation at a single carbon was developed with the assistance of a nitrogen directing group.