Rhodium-Catalyzed Highly Enantioselective Hydroboration of Acyclic Tetrasubstituted Alkenes Directed by an Amide.

Although progress has been made in enantioselective hydroboration of di- and trisubstituted alkenes over the past decades, enantioselective hydroboration of tetrasubstituted alkenes with high diastereo- and enantioselectivities continues as an unmet challenge since the 1950s due to its extremely low reactivity and the difficulties to simultaneously control the regio- and stereoselectivity of a tetrasubstituted alkene. Here, we report highly regio-, diastereo-, and enantioselective catalytic hydroboration of diverse acyclic tetrasubstituted alkenes. The delicate interplay of an electron-rich rhodium complex and coordination-assistance forms a highly adaptive catalyst that effectively overcomes the low reactivity and controls the stereoselectivity. The generality of the catalyst system is exemplified by its efficacy across various tetrasubstituted alkenes with diverse steric and electronic properties.

Iridium-Catalyzed Branch-Selective and Enantioselective Hydroalkenylation of α-Olefins through C-H Cleavage of Enamides.

Catalytic branch-selective hydrofunctionalization of feedstock α-olefins to form enantioenriched chiral compounds is a particularly attractive yet challenging transformation in asymmetric catalysis. Herein we report an iridium-catalyzed asymmetric hydroalkenylation of α-olefins through directed C-H cleavage of enamides. This atom-economical addition process is highly branch-selective and enantioselective, delivering trisubstituted alkenes with an allylic stereocenter. DFT calculations reveal the origin of regio- and enantioselectivity.

Stereodefined Skipped Dienes through Iridium-Catalyzed Formal Addition of Tertiary Allylic C-H Bonds to Alkynes.

Preparation of skipped dienes with a quaternary carbon center at the C-3 position remains a synthetic challenge. We report here an iridium-catalyzed formal addition of tertiary sp3 C-H bond to alkyne for the facile preparation of skipped dienes. The tertiary allylic C-H bond is cleaved regioselectively, at the site of which a new C-C bond is formed. Enantioselective construction of acyclic quaternary carbon stereocenters is also demonstrated.

Phylogeny, recombination, and invasiveness of group B Streptococcus revealed by genomic comparisons of its global strains.

Capsular polysaccharide (CPS) genes and pilus islands encode important virulence factors for group B Streptococcus (GBS) genomes. This study aims to detect phylogenetic inconsistency in CPS genes and pilus islands in GBSs and to explore its relationship with invasiveness. A total of 1016 GBS genomes were downloaded from the NCBI public database. The multi-locus sequence typing (MLST) and Bayesian analysis of Population Structure (BAPS) analyses were both conducted for phylogeny construction. Serotyping and pilus typing were determined in silico using the genomic sequences. The CPS and pilus typing results were generally consistent with MLST and BAPS clustering. GBS isolates of serotype II and of the PI-1 + PI-2b and PI-2a types were more prone to phylogenetic inconsistency than the others. Isolates of serotype Ib and of PI-1 + PI-2a were more likely to appear as colonizing strains, whereas PI-2b was more likely to appear in invasive strains. For serotype V, phylogenetic inconsistency occurred more commonly in colonizing isolates, while for serotype III, the opposite occurred. The present study profiles for the first time the phylogenetic inconsistency of CPS genes and pilus islands in global GBS isolates, which is helpful for infection control and the development of new vaccines for the prevention of GBS occurrence.

Prevention of Benign Endometrial Polyp Recurrence Using a Levonorgestrel-releasing Intrauterine System in Premenopausal Patients: A Retrospective Cohort Study.

STUDY OBJECTIVE: To evaluate the levonorgestrel-releasing intrauterine system (LNG-IUS) to prevent the recurrence of endometrial polyps (EPs) after hysteroscopic polypectomies in premenopausal female patients. DESIGN: A retrospective cohort study. SETTING: A tertiary-care women's hospital. PATIENTS: A total of 451 premenopausal female patients underwent hysteroscopic polypectomies between January 1, 2016, and December 31, 2017. INTERVENTIONS: Treatment with LNG-IUS after hysteroscopic polypectomies. MEASUREMENTS AND MAIN RESULTS: After the hysteroscopic polypectomies and placement of LNG-IUS, transvaginal ultrasounds were performed every 6 months to measure the recurrence of EPs. Overall, 5 (3.47%) of 144 patients in the LNG-IUS cohort and 49 (15.96%) of 307 patients in the control cohort experienced EP recurrence within the follow-up period of up to 3 years. The recurrence exhibited a strongly negative correlation when LNG-IUS was inserted (relative risk, 0.218; 95% confidence interval, 0.089-0.535; p <.05), but this did not significantly correlate with age, polyp size, number of polyps, previous history of polypectomy, and abnormal uterine bleeding. For the LNG-IUS and control cohorts, the recurrence in the first postoperative year was 1.39% and 6.19%, respectively, and 5.41% and 19.23% in the second postoperative year, respectively. CONCLUSION: LNG-IUS reduces the recurrence of postoperative EPs in premenopausal patients.

Complete genome sequence of Salmonella enterica serovar Sendai shows H antigen convergence with S. Miami and recent divergence from S. Paratyphi A.

BACKGROUND: Salmonella enterica consists of over 2500 serovars and displays dichotomy in disease manifestations and host range. Except for the enrichment of pseudogenes in genomes for human-restricted serovars, no hallmark has been identified to distinguish those with host-generalist serovars. The serovar Sendai is rare and human-restricted. Notably, it exhibits an O, H antigen formula as the host-generalist serovar Miami. RESULTS: We sequenced the complete genomes of the two serovars Sendai and Miami. Analysis at both nucleotide identity and gene content level demonstrates the same high degree of similarity between Sendai and Paratyphi A, but their distinct CRISPR spacers suggests a recent divergence history. A frameshift mutation occurred in rfbE for the entire lineage of Paratyphi A but not in Sendai, which may explain their distinct O antigens. The nucleotide sequence of Miami's fliC is nearly identical to Sendai's. The incongruent phylogeny of this gene with that of the adjacent genes suggests a recombination event responsible for Sendai and Miami possessing the same H antigen. Sendai's even greater number of pseudogenes than that of Paratyphi A and Typhi indicates its undergoing continued genomic degradation. The phylogenetically distinct human-restricted serovars/strains share pseudogenes with the same inactivation mutations, therefore suggesting that recombination may have occurred and have been facilitated by their overlap in niches. CONCLUSIONS: Analysis of Sendai's genome and comparison with others reflect the finer evolutionary signatures of Salmonella in the process of niches changing from facultative to obligate parasite.