There
is an increasing demand for facile delivery of silyl groups
onto organic bioactive molecules. One of the common methods of silylation
via a transition-metal-catalyzed coupling reaction employs hydrosilane,
disilane, and silylborane as major silicon sources. However, the labile
nature of the reagents or harsh reaction conditions sometimes render
them inadequate for the purpose. Thus, a more versatile alternative
source of silyl groups has been desired. We hereby report a design,
synthesis, and implementation of storable sodium silylsilanolates
that can be used for the silylation of aryl halides and pseudohalides
in the presence of a palladium catalyst. The developed method allows
a late-stage functionalization of polyfunctionalized compounds with
a variety of silyl groups. Mechanistic studies indicate that (1) a
nucleophilic silanolate attacks a palladium center to afford a silylsilanolate-coordinated
arylpalladium intermediate and (2) a polymeric cluster of silanolate
species assists in the intramolecular migration of silyl groups, which
would promote an efficient transmetalation.
The multifaceted implementation of silanols in organic synthesis is reviewed from the standpoint of developments in transition metal-catalyzed reactions. The major properties of silanols are summarized according to the research fields that have utilized these intriguing species: silanols as nucleophiles to serve as bulky surrogates for water; silanols as temporary ligands to control regioselectivity of metal-catalyzed reactions; silanols as coupling partners for transferring functional groups. These topics are summarized to provide opportunities for future developments in the chemistry of silanols.
Silylcoppers function as convenient and effective sources of silicon functional groups. Commonly used precursors for those species have been limited to certain symmetric disilanes and silylboranes. This fact renders the...
The first twofold silylmetalation across a C≡C triple bond was achieved. In the presence of a catalytic amount of copper cyanide, diarylacetylenes were converted into 1,2-dimetalated 1,2-disilyl-1,2-diarylethanes on treatment with silylpotassium species generated in situ from disilane and t-BuOK. The dimetalated species were subsequently protonated to yield a series of 1,2-disilyl-1,2-diarylethanes.
In order to clarify the role of natural killer (NK) cells in delayed xenograft rejection (DXR) of discordant xenotransplantation, we used in vitro xenogeneic combination of human NK cells and pig kidney target cells (PK15), and investigated the mechanism of xenogeneic cytotoxicity caused by human NK cells. In the presence of decomplemented human serum or human IgG, freshly isolated human peripheral blood lymphocytes (PBLs) caused both membrane (51Cr release) and DNA (3H release) damage on PK15. In contrast, only membrane damage was detected in the presence of normal human serum. To clarify the participation of perforin/granzymescell mediated cytotoxicity (P/G-CMC), when EGTA or concanamycin B (CMB) was added to the cytotoxicity assays, both cytotoxicities were completely inhibited by these drugs in a dose-dependent manner. In terms of the involvement of Fas/FasL-based cytotoxicity (F-CMC), while the cytotoxicity assays were performed in the presence of antagonistic anti-human FasL mAb, this antibody was not able to block the cytotoxicity. From these results, it is concluded that xenogeneic cytotoxicity is due to NK cell dependent ADCC (antibody-dependent cell-mediated cytotoxicity), and their effector mechanism can cause apoptosis on target cells via P/G-CMC.
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