Oxidation reactions are key transformations in organic chemistry because they can increase chemical complexity and incorporate heteroatom substituents into carbon-based molecules. This principle is ...manifested in the conversion of petrochemical feedstocks into commodity chemicals and in the synthesis of fine chemicals, pharmaceuticals, and other complex organic molecules. The utility and function of these molecules correlate directly with the presence and specific placement of oxygen and nitrogen heteroatoms and other functional groups within the molecules. Methods for selective oxidation of C–H bonds have expanded significantly over the past decade, and their role in the synthesis of organic chemicals will continue to increase. Our group’s contributions to this field are linked to our broader interest in the development and mechanistic understanding of aerobic oxidation reactions. Molecular oxygen (O2) is the ideal oxidant. Its low cost and lack of toxic byproducts make it a highly appealing reagent that can address key “green chemistry” priorities in industry. With strong economic and environmental incentives to use O2, the commmodity chemicals industry often uses aerobic oxidation reactions. In contrast, O2 is seldom used to prepare more-complex smaller-volume chemicals, a limitation that reflects, in part, the limited synthetic scope and utility of existing aerobic reactions. Pd-catalyzed reactions represent some of the most versatile methods for selective C–H oxidation, but they often require stoichiometric transition-metal or organic oxidants, such as CuII, AgI, or benzoquinone. This Account describes recent strategies that we have identified to use O2 as the oxidant in these reactions. In Pd-catalyzed C–H oxidation reactions that form carbon-heteroatom bonds, the stoichiometric oxidant is often needed to promote difficult reductive elimination steps in the catalytic mechanism. To address this challenge, we have identified new ancillary ligands for Pd that promote reductive elimination, or replaced Pd with a Cu catalyst that undergoes facile reductive elimination from a CuIII intermediate. Both strategies have enabled O2 to be used as the sole stoichiometric oxidant in the catalytic reactions. C–H oxidation reactions that form the product via β-hydride or C–C reductive elimination steps tend to be more amenable to the use of O2. The use of new ancillary ligands has also overcome some of the limitations in these methods. Mechanistic studies are providing insights into some (but not yet all) of these advances in catalytic reactivity.
Abstract
BACKGROUND
IVF for the treatment of infertility offers unique opportunities to observe human preimplantation development. Progress in time-lapse technology (TLT) and preimplantation genetic ...testing (PGT) has greatly expanded our knowledge of developmental patterns leading to a healthy pregnancy or developmental failure. These technologies have also revealed unsuspected plastic properties of the preimplantation embryo, at macromolecular, cellular and multicellular levels.
OBJECTIVE AND RATIONALE
This review focuses on the emerging concept of plasticity of the human embryo as revealed by recent evidence derived from TLT and PGT, calling for an updated and more precise redefinition of the boundaries between normal and abnormal development.
SEARCH METHODS
PubMed was used to search the MEDLINE database for peer-reviewed English-language original articles and reviews concerning human preimplantation development. Cross-searches were performed by adopting ‘fertilisation‘, ‘pronucleus’, ‘cleavage’, ‘multinucleation’, ‘compaction’, ‘embryo’, ‘preimplantation genetic testing’, ‘aneuploidy’, mosaicism’, ‘micromanipulation’, ‘time-lapse microscopy’ and ‘IVF/assisted reproduction’ as main terms. The most relevant publications, i.e. those concerning major phenomena occurring during normal and abnormal development—with a focus on the human species—were assessed and discussed critically.
OUTCOMES
Advances in TLT and PGT have revealed an astonishing plasticity and self-correction ability of the human preimplantation embryo in vitro. At fertilisation, an abnormal number of pronuclei do not always result in the formation of an aneuploid blastocyst. Animal studies and preliminary human observations indicate that combining of parental genomes may occur at the early cleavage stage, if not at fertilisation. Multinucleation occurs with much higher prevalence than previously thought and may be corrected at later cleavage stages. Irregular cleavage (multichotomous, direct, rapid and reverse cleavages) can generate chromosome segregation abnormalities that often lead to developmental arrest, but that sporadically may be confined to cells excluded from the blastocyst, and may sometimes result in viable pregnancy. Mitotic errors can generate mosaic blastocysts, but alternatively normal embryos may form from selective death or clonal depletion of aneuploid cells.
WIDER IMPLICATIONS
Deviations from developmental dogmas and the increasing evidence of plasticity of the human embryo challenge current embryological notions and suggest the need to write new rules governing cell cycle, cell determination and chromosome segregation during preimplantation development.
STUDY QUESTION
Can the approach to, and terminology for, time-lapse monitoring of preimplantation embryo development be uniformly defined in order to improve the utilization and impact of this novel ...technology?
SUMMARY ANSWER
The adoption of the proposed guidelines for defining annotation practice and universal nomenclature would help unify time-lapse monitoring practice, allow validation of published embryo selection algorithms and facilitate progress in this field.
WHAT IS KNOWN ALREADY
An increasing quantity of publications and communications relating to time-lapse imaging of in vitro embryo development have demonstrated the added clinical value of morphokinetic data for embryo selection. Several articles have identified similar embryo selection or de-selection variables but have termed them differently. An evidence-based consensus document exists for static embryo grading and selection but, to date, no such reference document is available for time-lapse methodology or dynamic embryo grading and selection.
STUDY DESIGN, SIZE AND DURATION
A series of meetings were held between September 2011 and May 2014 involving time-lapse users from seven different European centres. The group reached consensus on commonly identified and novel time-lapse variables.
PARTICIPANTS/MATERIALS, SETTING, METHODS
Definitions, calculated variables and additional annotations for the dynamic monitoring of human preimplantation development were all documented.
MAIN RESULTS AND THE ROLE OF CHANCE
Guidelines are proposed for a standard methodology and terminology for the of use time-lapse monitoring of preimplantation embryo development.
LIMITATIONS, REASONS FOR CAUTION
The time-lapse variables considered by this group may not be exhaustive. This is a relatively new clinical technology and it is likely that new variables will be introduced in time, requiring revised guidelines. A different group of users from those participating in this process may have yielded subtly different terms or definitions for some of the morphokinetic variables discussed. Due to the technical processes involved in time-lapse monitoring, and acquisition of images at varied intervals through limited focal planes, this technology does not currently allow continuous monitoring such that the entire process of preimplantation embryo development may be visualized.
WIDER IMPLICATIONS
This is the first time that a group of experienced time-lapse users has systematically evaluated current evidence and theoretical aspects of morphokinetic monitoring to propose guidelines for a standard methodology and terminology of its use and study, and its clinical application in IVF. The adoption of a more uniform approach to the terminology and definitions of morphokinetic variables within this developing field of clinical embryology would allow practitioners to benefit from improved interpretation of data and the sharing of best practice and experience, which could impact positively and more swiftly on patient treatment outcome.
STUDY FUNDING/COMPETING INTEREST(S)
There was no specific funding for the preparation of these proposed guidelines. Meetings were held opportunistically during scientific conferences and using online communication tools.
H.N.C. is a scientific consultant for ESCO, supplier of Miri TL. I.E.A. is a minor shareholder in Unisense Fertilitech, supplier of the EmbryoScope. Full disclosures of all participants are presented herein. The remaining authors have no conflict of interest.
Remodelling of the human embryo at implantation is indispensable for successful pregnancy. Yet it has remained mysterious because of the experimental hurdles that beset the study of this ...developmental phase. Here, we establish an in vitro system to culture human embryos through implantation stages in the absence of maternal tissues and reveal the key events of early human morphogenesis. These include segregation of the pluripotent embryonic and extra-embryonic lineages, and morphogenetic rearrangements leading to generation of a bilaminar disc, formation of a pro-amniotic cavity within the embryonic lineage, appearance of the prospective yolk sac, and trophoblast differentiation. Using human embryos and human pluripotent stem cells, we show that the reorganization of the embryonic lineage is mediated by cellular polarization leading to cavity formation. Together, our results indicate that the critical remodelling events at this stage of human development are embryo-autonomous, highlighting the remarkable and unanticipated self-organizing properties of human embryos.
Pd-catalyzed C−H oxidation reactions often require the use of oxidants other than O2. Here we demonstrate a ligand-based strategy to replace benzoquinone with O2 as the stoichiometric oxidant in ...Pd-catalyzed allylic C−H acetoxylation. Use of 4,5-diazafluorenone (1) as an ancillary ligand for Pd(OAc)2 enables terminal alkenes to be converted to linear allylic acetoxylation products in good yields and selectivity under 1 atm O2. Mechanistic studies have revealed that 1 facilitates C−O reductive elimination from a π-allyl−PdII intermediate, thereby eliminating the requirement for benzoquinone in this key catalytic step.
Palladium-catalyzed aerobic oxidative cross-couplings of indoles and benzene have been achieved by using 4,5-diazafluorene derivatives as ancillary ligands. Proper choice of the neutral and anionic ...ligands enables control over the reaction regioselectivity.
At implantation, the embryo establishes contacts with the maternal endometrium. This stage is associated with a high incidence of preclinical pregnancy losses. While the maternal factors underlying ...uterine receptivity have been investigated, the signals required by the embryo for successful peri-implantation development remain elusive. To explore these, we studied integrin β1 signaling, as embryos deficient for this receptor degenerate at implantation. We demonstrate that the coordinated action of pro-survival signals and localized actomyosin suppression via integrin β1 permits the development of the embryo beyond implantation. Failure of either process leads to developmental arrest and apoptosis. Pharmacological stimulation through fibroblast growth factor 2 (FGF2) and insulin-like growth factor 1 (IGF1), coupled with ROCK-mediated actomyosin inhibition, rescues the deficiency of integrin β1, promoting progression to post-implantation stages. Mutual exclusion between integrin β1 and actomyosin seems to be conserved in the human embryo, suggesting the possibility that these mechanisms could also underlie the transition of the human epiblast from pre- to post-implantation.
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•Integrin β1 is required for epiblast survival upon implantation•Integrin β1 regulates epiblast morphogenesis by basal actomyosin inhibition•Prosurvival signals and local actomyosin suppression enables epiblast development
Molè et al. show that the coordinated stimulation of pro-survival signals together with ROCK-mediated localized suppression of actomyosin downstream of integrin β1 regulate morphogenesis and survival of the embryonic lineage during the transition from pre- to post-implantation.
Although there is empricial support for the old adage that “we never forget a face” (Journal of Experimental Psychology: General 104 (1975) 54–75), the cognitive processes responsible for our ...long-term face memories are not well understood. By manipulating the upright and inverted orientation of faces during encoding and retrieval, we investigated the influence of holistic processing on our ability to recognize faces stored in long-term memory. In Experiment 1, participants were trained to identify 12 novel upright faces (six male, six female) by name (e.g., “Joe,” “Sue”) to a criterion of 100% accuracy. Following learning, holistic memory for the upright and inverted faces was tested using the parts/wholes face recognition task. Different groups of participants were tested either immediately, one week, or two weeks after learning. A significant holistic effect was found for faces tested in their original upright orientation that was stable over the immediate, one-week, and two-week testing periods. In contrast, recognition of the same faces when shown inverted was poor and showed no evidence of holistic processing. In Experiment 2, faces were learned in their inverted orientations with 100% accuracy and tested in their upright and inverted orientations. At the immediate, one-week, or two-week intervals, recognition of inverted faces was relatively poor and there was no evidence of holistic processing for faces tested either in inverted or upright orientations. Collectively, these results indicate holistic processing provides an efficient means for the encoding and retrieval of faces in long-term memory that are relatively stable with the passage of time.
Abstract
Following implantation, the human embryo undergoes major morphogenetic transformations that establish the future body plan. While the molecular events underpinning this process are ...established in mice, they remain unknown in humans. Here we characterise key events of human embryo morphogenesis, in the period between implantation and gastrulation, using single-cell analyses and functional studies. First, the embryonic epiblast cells transition through different pluripotent states and act as a source of FGF signals that ensure proliferation of both embryonic and extra-embryonic tissues. In a subset of embryos, we identify a group of asymmetrically positioned extra-embryonic hypoblast cells expressing inhibitors of BMP, NODAL and WNT signalling pathways. We suggest that this group of cells can act as the anterior singalling centre to pattern the epiblast. These results provide insights into pluripotency state transitions, the role of FGF signalling and the specification of anterior-posterior axis during human embryo development.
Platinum and silver work together: Activation of (xylyl‐phanephos)PtCl2 by silver generates an electrophilic catalyst that can enantioselectively, diastereoselectively, and regioselectively promote ...the stereospecific oxidative cyclization of polyene‐ols (see scheme; Tr=trityl). Mechanistic experiments indicate that the stereochemistry‐determining step is not the initial cyclization step, but rather a subsequent step in the reaction.
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