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Abstract Background Studies have suggested that demographic and lifestyle factors could shape the composition of fecal microbiota in early life. This study evaluated infant stool microbiota signatures in two Asian populations, Singapore (n = 42) and Indonesia (n = 32) with contrasting socioeconomic development, and examined the putative influences of demographic factors on these human fecal associated bacterial signatures. Results Longitudinal analysis showed associations of geographical origin with Clostridium leptum, Atopobium and Bifidobacterium groups. Mode of delivery had the largest effect on stool microbiota signatures influencing the abundance of four bacterial groups. Significantly higher abundance of bacterial members belonging to the Bacteroides-Prevotella, Bifidobacterium and Atopobium groups, but lower abundance of Lactobacilli-Enterococci group members, were observed in vaginal delivered compared to caesarean delivered infants. Demographic factors influencing the structure of infants stool microbiota during the first year of life included breastfeeding, age of weaning, sibship size and exposure to antibiotics. Conclusions Differences in stool microbiota signatures were observed in relation to various demographic factors. These features may confound studies relating to the association of the structure of fecal microbiota and the predisposition to human modern disease.

Protein aggregation plays key roles in age-related degenerative diseases, but how different proteins coalesce to form inclusions that vary in composition, morphology, molecular dynamics and confer physiological consequences is poorly understood. Here we employ a general reporter based on mutant Hsp104 to identify proteins forming aggregates in human cells under common proteotoxic stress. We identify over 300 proteins that form different inclusions containing subsets of aggregating proteins. In particular, TDP43, implicated in Amyotrophic Lateral Sclerosis (ALS), partitions dynamically between two distinct types of aggregates: stress granule and a previously unknown non-dynamic (solid-like) inclusion at the ER exit sites (ERES). TDP43-ERES co-aggregation is induced by diverse proteotoxic stresses and observed in the motor neurons of ALS patients. Such aggregation causes retention of secretory cargos at ERES and therefore delays ER-to-Golgi transport, providing a link between TDP43 aggregation and compromised cellular function in ALS patients., (© 2024. The Author(s).)

Chiral guanidines have been widely used as Brønsted base catalysts and phase transfer catalysts in enantioselective reactions. Due to their amendable structure and powerful catalytic ability, they have attracted much interest. Several new catalysts containing a guanidinium moiety have been reported over the past decade and many promising outcomes have been achieved. This article illustrates the progress of chiral guanidine catalysis in asymmetric synthesis from 2009 to 2018. It is an update of a review of the same title published in 2009., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Guanidines, which exist widely in nature, have been frequently utilised as strong Brønsted bases in organic chemistry. As ligands, guanidines can have different coordination modes with the metal center. However, the exploitation of these guanidine complexes as catalysts has been much less successful. The anionic counterpart of guanidine, which is known as guanidinate, is also able to function as a ligand. The catalytic activities of metal-guanidinate complexes are of great interest to chemists. The potential of catalytic guanidine or guanidinate metal complexes to catalyse unique chemical transformations is immensely promising. This field is currently being pursued with great interest by synthetic organic chemists. In this review, the representative reactions enabled by guanidine and guanidinate metal complexes are highlighted.

A mild photocatalytic hydroperoxyarylation of styrenes has been developed, in which a novel photocatalyst, remazol brilliant blue R (RBBR), is employed at low catalytic loading (1 mol %). The operationally easy procedure uses air as the dioxygen source. Simple mono-substituted styrenes react with aryl hydrazines in moderate-to-good yields. RBBR is proposed to act as a photosensitizer for the generation of singlet oxygen., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Ortho-C(sp(2))-H olefination and acetoxylation of broadly useful synthetic building blocks phenylacetyl Weinreb amides, esters, and ketones are developed without installing an additional directing group. The interplay between the distal weak coordination and the ligand-acceleration is crucial for these reactions to proceed under mild conditions. The tolerance of longer distance between the target C-H bonds and the directing functional groups also allows for the functionalizations of more distal C-H bonds in hydrocinnamoyl ketones, Weinreb amides, and biphenyl Weinreb amides. Mechanistically, the coordination of these carbonyl groups and the bisdentate amino acid ligand with Pd(II) centers provides further evidence for our early hypothesis that the carbonyl groups of the potassium carboxylate are responsible for the directed C-H activation of carboxylic acids.

Amides are prevalent in organic synthesis. Developing an efficient synthesis that avoids expensive oxidants and heating is highly desirable. Here the oxidative amidation of aromatic aldehydes is reported using an inexpensive metal-free visible light photocatalyst, phenazine ethosulfate, at low catalytic loading (1-2 mol %). The reaction proceeds at ambient temperature and uses air as the sole oxidant. The operationally easy procedure provides an economical, green, and mild alternative for the formation of amide bonds.

Density functional theory investigations have elucidated the mechanism and origins of meta-regioselectivity of Pd(II)-catalyzed C-H olefinations of toluene derivatives that employ a nitrile-containing template. The reaction proceeds through four major steps: C-H activation, alkene insertion, β-hydride elimination, and reductive elimination. The C-H activation step, which proceeds via a concerted metalation-deprotonation (CMD) pathway, is found to be the rate- and regioselectivity-determining step. For the crucial C-H activation, four possible active catalytic species-monomeric Pd(OAc)2, dimeric Pd2(OAc)4, heterodimeric PdAg(OAc)3, and trimeric Pd3(OAc)6-have been investigated. The computations indicated that the C-H activation with the nitrile-containing template occurs via a Pd-Ag heterodimeric transition state. The nitrile directing group coordinates with Ag while the Pd is placed adjacent to the meta-C-H bond in the transition state, leading to the observed high meta-selectivity. The Pd2(OAc)4 dimeric mechanism also leads to the meta-C-H activation product but with higher activation energies than the Pd-Ag heterodimeric mechanism. The Pd monomeric and trimeric mechanisms require much higher activation free energies and are predicted to give ortho products. Structural and distortion energy analysis of the transition states revealed significant effects of distortions of the template on mechanism and regioselectivity, which provided hints for further developments of new templates.

The Pd(II)-catalyzed intramolecular C-H amination of 2-pyridinesulfonyl-protected phenethylamine derivatives has been achieved using PhI(OAc)2 as a bystanding oxidant, providing access to a variety of substituted indoline derivatives in good yields. The use of the 2-pyridinesulfonyl protecting group allows for facile deprotection following C-H functionalization.

Functionalization of unactivated carbon-hydrogen (C-H) single bonds is an efficient strategy for rapid generation of complex molecules from simpler ones. However, it is difficult to achieve selectivity when multiple inequivalent C-H bonds are present in the target molecule. The usual approach is to use σ-chelating directing groups, which lead to ortho-selectivity through the formation of a conformationally rigid six- or seven-membered cyclic pre-transition state. Despite the broad utility of this approach, proximity-driven reactivity prevents the activation of remote C-H bonds. Here we report a class of easily removable nitrile-containing templates that direct the activation of distal meta-C-H bonds (more than ten bonds away) of a tethered arene. We attribute this new mode of C-H activation to a weak 'end-on' interaction between the linear nitrile group and the metal centre. The 'end-on' coordination geometry relieves the strain of the cyclophane-like pre-transition state of the meta-C-H activation event. In addition, this template overrides the intrinsic electronic and steric biases as well as ortho-directing effects with two broadly useful classes of arene substrates (toluene derivatives and hydrocinnamic acids).

Pd-catalyzed highly para-selective C-H arylation of monosubstituted arenes (including toluene) is developed for the first time using an F(+) reagent as a bystanding oxidant. This finding provides a new retrosynthetic disconnection for para-substituted biaryl synthesis via C-H/C-H cross-coupling.

Bicyclic guanidines are able to catalyze the protonation reactions of 2-phthalimidoacrylates with thiols in excellent yields and enantioselectivities. The protonation reaction of itaconimides with secondary phosphine oxides is also known. Herein, the tandem conjugate addition-enantioselective protonation of N-substituted itaconimides with thiols catalyzed by chiral bicyclic guanidine is investigated. The rotational barrier of the C-N axis of N-2-tert-butyl phenylitaconimide is also studied, both experimentally and computationally.

We report that chiral bicyclic guanidine 1 is found to catalyze the isomerization of alkynes to chiral allenes with high enantioselectivities. This Brønsted base catalyzed 1,3-proton shift reaction, an efficient and atom economical reaction, proceeds through deprotonation and protonation sequences. The axial chirality of the allenes is efficiently transferred to functionalized butenolides and cycloaddition products. We also successfully demonstrate the stereospecific synthesis of butenolide through allenoate cyclization with a catalytic cationic Au(I) complex.

Chiral guanidine catalysts share common characteristics such as high pK(a) values and dual hydrogen-bonding modes of activation, and high catalytic activities and enantioselectivities can often be achieved. The utilization of guanidines as catalysts has been growing at a steady pace. In the past few years, it has attracted tremendous attention through several landmark achievements. This article highlights the development of chiral guanidine catalysis in asymmetric synthesis.