4 research outputs found
Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne–Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Brønsted Acid
Catalytic enantioselective syntheses
enable a practical approach
to enantioenriched molecules. While most of these syntheses have been
accomplished by reaction at the prochiral sp<sup>2</sup>-hybridized
carbon atom, little attention has been paid to enantioselective nucleophilic
substitution at the sp<sup>3</sup>-hybridized carbon atom. In particular,
substitution at the chiral sp<sup>3</sup>-hybridized carbon atom of
racemic electrophiles has been rarely exploited. To establish an unprecedented
enantioselective substitution reaction of racemic electrophiles, enantioconvergent
Nicholas reaction of an alkyne–dicobalt complex derived from
racemic propargylic alcohol was developed using a chiral phosphoric
acid catalyst. In the present enantioconvergent process, both enantiomers
of the racemic alcohol were transformed efficiently to a variety of
thioethers with high enantioselectivity. The key to achieving success
is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric
cationic intermediates generated via dehydroxylation of the starting
racemic alcohol under the influence of the chiral phosphoric acid
catalyst. The present fascinating DYKAT involves the efficient racemization
of these enantiomeric intermediates and effective resolution of these
enantiomers through utilization of the chiral conjugate base of the
phosphoric acid
Quantification of the Steric Influence of Alkylphosphine–Sulfonate Ligands on Polymerization, Leading to High-Molecular-Weight Copolymers of Ethylene and Polar Monomers
A series
of palladium/​​alkylphosphine–​sulfonate
catalysts were synthesized and examined in the homopolymerization
of ethylene and the copolymerization of ethylene and polar monomers.
Catalysts with alkylÂphosphine–​sulfonate ligands
containing sterically demanding alkyl substituents afforded (co)Âpolymers
whose molecular weight was increased by up to 2 orders of magnitude
relative to polymers obtained from previously reported catalyst systems.
The polymer molecular weight was found to be closely correlated to
the Sterimol B5 parameter of the alkyl substituents in the alkylÂphosphine–​sulfonate
ligands. Thus, the use of bulky alkylÂphosphine–​sulfonate
ligands represents an effective and versatile method to prepare high-molecular-weight
copolymers of ethylene and various polar monomers, which are difficult
to obtain by previously reported methods
Table_1_Novel insights into genetic characteristics of blaGES-encoding plasmids from hospital sewage.DOCX
IntroductionThe prevalence of Guiana extended-spectrum (GES)-type carbapenemase producers is increasing worldwide, and hospital water environments are considered as potential reservoirs. However, the genetic features underlying this resistance are not yet fully understood. This study aimed to characterize blaGES-encoding plasmids from a single-hospital sewage sample in Japan.MethodsCarbapenemase producers were screened using carbapenemase-selective agar and polymerase chain reaction. Whole-genome sequencing analyzes were performed on the carbapenemase-producing isolates.ResultsEleven gram-negative bacteria (four Enterobacter spp., three Klebsiella spp., three Aeromonas spp., and one Serratia spp.) with blaGES-24 (n = 6), blaGES-6 (n = 4), and blaGES-5 (n = 1) were isolated from the sewage sample. Five blaGES-24 and a blaGES-5 were localized in IncP-6 plasmids, whereas three blaGES-6 plasmids were localized in IncC plasmids with IncF-like regions. The remaining blaGES-6 and blaGES-24 were, respectively, localized on IncFIB-containing plasmids with IncF-like regions and a plasmid with an IncW-like replication protein. The IncP-6 and IncW-like plasmids had a close genetic relationship with plasmids from Japan, whereas the IncC/IncF-like and IncFIB/IncF-like plasmids were closely related to those from the United States and Europe. All blaGES genes were located on the class 1 integron cassette of the Tn3 transposon-related region, and the IncC/IncF-like plasmid carried two copies of the integron cassette. Eight of the eleven blaGES-encoding plasmids contained toxin-antitoxin system genes.DiscussionThe findings on the plasmids and the novel genetic content from a single wastewater sample extend our understanding regarding the diversity of resistance and the associated spread of blaGES, suggesting their high adaptability to hospital effluents. These findings highlight the need for the continuous monitoring of environmental GES-type carbapenemase producers to control their dissemination.</p
Image_1_Novel insights into genetic characteristics of blaGES-encoding plasmids from hospital sewage.pdf
IntroductionThe prevalence of Guiana extended-spectrum (GES)-type carbapenemase producers is increasing worldwide, and hospital water environments are considered as potential reservoirs. However, the genetic features underlying this resistance are not yet fully understood. This study aimed to characterize blaGES-encoding plasmids from a single-hospital sewage sample in Japan.MethodsCarbapenemase producers were screened using carbapenemase-selective agar and polymerase chain reaction. Whole-genome sequencing analyzes were performed on the carbapenemase-producing isolates.ResultsEleven gram-negative bacteria (four Enterobacter spp., three Klebsiella spp., three Aeromonas spp., and one Serratia spp.) with blaGES-24 (n = 6), blaGES-6 (n = 4), and blaGES-5 (n = 1) were isolated from the sewage sample. Five blaGES-24 and a blaGES-5 were localized in IncP-6 plasmids, whereas three blaGES-6 plasmids were localized in IncC plasmids with IncF-like regions. The remaining blaGES-6 and blaGES-24 were, respectively, localized on IncFIB-containing plasmids with IncF-like regions and a plasmid with an IncW-like replication protein. The IncP-6 and IncW-like plasmids had a close genetic relationship with plasmids from Japan, whereas the IncC/IncF-like and IncFIB/IncF-like plasmids were closely related to those from the United States and Europe. All blaGES genes were located on the class 1 integron cassette of the Tn3 transposon-related region, and the IncC/IncF-like plasmid carried two copies of the integron cassette. Eight of the eleven blaGES-encoding plasmids contained toxin-antitoxin system genes.DiscussionThe findings on the plasmids and the novel genetic content from a single wastewater sample extend our understanding regarding the diversity of resistance and the associated spread of blaGES, suggesting their high adaptability to hospital effluents. These findings highlight the need for the continuous monitoring of environmental GES-type carbapenemase producers to control their dissemination.</p