YKC1 (TOK1, DUK1, YORK) encodes the outwardly rectifying K+ channel of the yeast plasma membrane. Non‐targeted mutations of YKC1 were isolated by their ability to completely block proliferation when expressed in yeast. All such mutations examined occurred near the cytoplasmic ends of the transmembrane segments following either of the duplicated P loops, which we termed the ‘post‐P loop’ (PP) regions. These PP mutations specifically caused marked defects in the ‘C1’ states, a set of interrelated closed states that Ykc1 enters and exits at rates of tens to hundreds of milliseconds. These results indicate that the Ykc1 PP region plays a role in determining closed state conformations and that non‐targeted mutagenesis and microbial selection can be a valuable tool for probing structure–function relationships of ion channels.
Triphenylsiloxide
is one of the most successful ancillary ligands
for Mo(VI)-alkyne metathesis catalysts. It was proposed that flexible
siloxide ligands allow Mo–O–Si bond angles to modulate
the electrophilicity of MoC and thereby promote the catalysis.
Introduction of a siloxide podand ligand allowed elucidation of the
effect of ligand flexibility and Mo–O–Si angles on the
electrophilicity of MoC. It also allowed for the isolation
of a rare metallatetrahedrane of Mo(VI) which was found to be dynamic
in solution.
The
intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2
+ 2] cycloaddition-based mechanism is a well-established paradigm
in alkyne metathesis with alternative species viewed as off-cycle
decomposition products that interfere with efficient product formation.
Recent work has shown that the exclusive intermediate isolated from
a siloxide podand-supported molybdenum-based catalyst was not the
expected metallacyclobutadiene but instead a dynamic metallatetrahedrane.
Despite their paucity in the chemical literature, theoretical work
has shown these species to be thermodynamically more stable as well
as having modest barriers for cycloaddition. Consequentially, we report
the synthesis of a library of group VI alkylidynes as well as the
roles metal identity, ligand flexibility, secondary coordination sphere,
and substrate identity all have on isolable intermediates. Furthermore,
we report the disparities in catalyst competency as a function of
ligand sterics and metal choice. Dispersion-corrected DFT calculations
are used to shed light on the mechanism and role of ligand and metal
on the intermediacy of metallacyclobutadiene and metallatetrahedrane
as well as their implications to alkyne metathesis.
A new type of rhodium-catalyzed [5+2] cycloaddition was developed for the synthesis of seven-membered rings with diverse functionalities. The ring formation was accompanied by a 1,2-acyloxy migration event. The 5- and 2-carbon components of the cycloaddition are 3-acyloxy-1,4-enynes (ACEs) and alkynes respectively. Cationic rhodium (I) catalysts worked most efficiently for the intramolecular cycloaddition, while only neutral rhodium (I) complexes could facilitate the intermolecular reaction. In both cases, electron-poor phosphite or phosphine ligands often improved the efficiency of the cycloadditions. The scope of ACEs and alkynes was investigated in both intra- and intermolecular reactions. The resulting seven-membered ring products have three double bonds that could be selectively functionalized.
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