Distal p-benzylic deuteration via N-heterocyclic carbene catalyzed ring opening of p-cyclopropylbenzaldehydes.

Deuterium incorporation at selective sites of organic compounds has long attracted the interest of the pharmaceutical industry. Here, we present a distal p-benzylic deuteration via N-heterocyclic carbene catalyzed ring-opening of cyclopropylbenzaldehydes with MeOD as the deuterium source. The corresponding 4-alkylbenzoates with high deuterium incorporation at the benzylic position were obtained in good yields. The stable benzylic deuterium remained intact for further chemical transformations.

Enantioselective N-Heterocyclic Carbene Catalyzed α-Oxidative Coupling of Enals with Carboxylic Acids Using an Iodine(III) Reagent.

The enantioselective α-oxidative coupling of enals with carboxylic acids was developed via the umpolung of an NHC-bound enolate with an iodine(III) reagent. The corresponding α-acyloxyl-ß,γ-unsaturated esters were afforded in good yields, with high regio- and enantioselectivities. The key step of the reaction involves the formation of enol iodine(III) intermediate from the enolate with iodosobenzene, which changes the polarity of α-carbon of the enal from nucleophilic to electrophilic, and thus facilitates the subsequent addition of carboxylate.

Bifunctional NHC-Catalyzed Remote Enantioselective Mannich-type Reaction of 5-(Chloromethyl)furfural via Trienolate Intermediates.

N-heterocyclic carbene (NHC)-catalyzed enantioselective Mannich-type reactions of the biomass-derived platform compound 5-(chloromethyl)furfural (CMF) with imines were developed. A series of high-value-added chiral amines were afforded in good to high yields with excellent regio- and enantioselectivities. The bifunctional NHC derived from ʟ-pyroglutamic acid efficiently steered the remote addition of the trienolate intermediate to the imine in a highly stereocontrolled manner. This represents the first enantioselective reaction proceeding via an NHC-bound trienolate intermediate.

ε-Benzylation via Cooperative Photoredox and N-Heterocyclic Carbene Catalysis.

The ε-benzylation of γ-alkenyl-γ-oxidized enals via dual photoredox and N-heterocyclic carbene catalysis has been developed, affording the corresponding ε-benzyl-α,ß-γ,δ-bisunsaturated esters in moderate to good yields with exclusive regioselectivities. The reaction is proposed via the generation of benzyl radical under photocatalysis, followed by its addition to an NHC-bound trienolate intermediate.

Bifunctional N-Heterocyclic Carbenes Derived from l-Pyroglutamic Acid and Their Applications in Enantioselective Organocatalysis.

In nature, enzymes are a powerful medium for the construction of enantiomerically pure chemicals, which always inspires synthetic chemists to explore new catalysts to imitate the enzyme machinery for asymmetric transformations. Vitamin B1, a bifunctional thiazolium N-heterocyclic carbene (NHC) precursor, is the coenzyme for transketolase. In the past two decades, a series of chiral NHCs, including monocyclic, bicyclic, tetracyclic, and even bridged ones, have been synthesized and successfully utilized as efficient organocatalysts for a wide variety of asymmetric organic reactions. The utility of bifunctional catalysts can enhance catalytic activity and improve stereochemical control through their synchronous activation of both reaction partners. However, the NHCs possessing multiple activation sites are far less developed.This Account gives an overview of our research on the design, development, and applications of bifunctional NHCs in organocatalysis. We synthesized a series of l-pyroglutamic acid-derived bifunctional NHCs bearing a free hydroxyl group which can interact with carbonyl or imino groups via hydrogen-bonding. Further studies revealed that these bifunctional catalysts worked well for a variety of reactions. We have developed bifunctional NHC-catalyzed aza-benzoin reactions, [2 + 2], [2 + 3], and [2 + 4] cycloadditions of ketenes, [3 + 2] and [3 + 4] annulations of enals, and aza-MBH and Rauhut-Currier reactions of Michael acceptors. In addition to these reactions via nucleophilic Breslow intermediates, enolates, homoenolates, and zwitterionic azolium intermediates, the bifunctional NHC-catalyzed [3 + 3] annulation via 1,3-biselectrophilic α,ß-unsaturated acyl azolium intermediates was also developed.In these reactions, bifunctional NHCs showed amazing effects compared to normal nonbifunctional NHCs. In some cases, the bifunctional NHCs facilitated reactions which did not work under normal NHC catalysis, possibly due to additional activation via H-bonding. More interestingly, the bifunctional NHCs could not only improve but also switch the enantioselectivity to get products with opposite stereochemistry through H-bond controlled stereochemical directing. Furthermore, the reaction mode could be totally changed from [3 + 2] to [3 + 4] annulation to give kinetically favored products when bifunctional NHCs were employed. In future, the applications of bifunctional NHCs in other challenging reactions, such as asymmetric reactions with carbon-carbon unsaturated bonds, and the reactions involving alkyl or heteroatom radicals will be the major focus in our group.

New type of autocollimator based on the normal tracing method and Risley prisms.

In the present study, we proposed a new type of autocollimator for high-accuracy angular measurement within a large angle range. The new system comprises a traditional autocollimator and Risley prisms, and it employs the normal tracing method to measure the angle. By rotating the Risley prisms, the outgoing beam of the autocollimator can be deflected close to the normal direction of the reflecting mirror and then reflected back to the system by the mirror along the near normal direction to realize normal tracing. Based on the angle measured by the the autocollimator and the rotation angles of Risley prisms, we can calculate the tilt angle of the mirror. Since the beam returns to the system close to the original path, the angle error caused by aberration, optical component processing defects, nonuniform refractive index, and so on, can be ignored. Due to the normal tracing measurement method, theoretically, the angle error is not affected by the working distance. ZEMAX non-sequential simulation shows that the angle error caused by aberration in the new system can be significantly reduced.

An AUTS2-Polycomb complex activates gene expression in the CNS.

Naturally occurring variations of Polycomb repressive complex 1 (PRC1) comprise a core assembly of Polycomb group proteins and additional factors that include, surprisingly, autism susceptibility candidate 2 (AUTS2). Although AUTS2 is often disrupted in patients with neuronal disorders, the mechanism underlying the pathogenesis is unclear. We investigated the role of AUTS2 as part of a previously identified PRC1 complex (PRC1-AUTS2), and in the context of neurodevelopment. In contrast to the canonical role of PRC1 in gene repression, PRC1-AUTS2 activates transcription. Biochemical studies demonstrate that the CK2 component of PRC1-AUTS2 neutralizes PRC1 repressive activity, whereas AUTS2-mediated recruitment of P300 leads to gene activation. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) demonstrated that AUTS2 regulates neuronal gene expression through promoter association. Conditional targeting of Auts2 in the mouse central nervous system (CNS) leads to various developmental defects. These findings reveal a natural means of subverting PRC1 activity, linking key epigenetic modulators with neuronal functions and diseases.

PCGF homologs, CBX proteins, and RYBP define functionally distinct PRC1 family complexes.

The heterogeneous nature of mammalian PRC1 complexes has hindered our understanding of their biological functions. Here, we present a comprehensive proteomic and genomic analysis that uncovered six major groups of PRC1 complexes, each containing a distinct PCGF subunit, a RING1A/B ubiquitin ligase, and a unique set of associated polypeptides. These PRC1 complexes differ in their genomic localization, and only a small subset colocalize with H3K27me3. Further biochemical dissection revealed that the six PCGF-RING1A/B combinations form multiple complexes through association with RYBP or its homolog YAF2, which prevents the incorporation of other canonical PRC1 subunits, such as CBX, PHC, and SCM. Although both RYBP/YAF2- and CBX/PHC/SCM-containing complexes compact chromatin, only RYBP stimulates the activity of RING1B toward H2AK119ub1, suggesting a central role in PRC1 function. Knockdown of RYBP in embryonic stem cells compromised their ability to form embryoid bodies, likely because of defects in cell proliferation and maintenance of H2AK119ub1 levels.

Mammalian PRC1 Complexes: Compositional Complexity and Diverse Molecular Mechanisms.

Polycomb group (PcG) proteins function as vital epigenetic regulators in various biological processes, including pluripotency, development, and carcinogenesis. PcG proteins form multicomponent complexes, and two major types of protein complexes have been identified in mammals to date, Polycomb Repressive Complexes 1 and 2 (PRC1 and PRC2). The PRC1 complexes are composed in a hierarchical manner in which the catalytic core, RING1A/B, exclusively interacts with one of six Polycomb group RING finger (PCGF) proteins. This association with specific PCGF proteins allows for PRC1 to be subdivided into six distinct groups, each with their own unique modes of action arising from the distinct set of associated proteins. Historically, PRC1 was considered to be a transcription repressor that deposited monoubiquitylation of histone H2A at lysine 119 (H2AK119ub1) and compacted local chromatin. More recently, there is increasing evidence that demonstrates the transcription activation role of PRC1. Moreover, studies on the higher-order chromatin structure have revealed a new function for PRC1 in mediating long-range interactions. This provides a different perspective regarding both the transcription activation and repression characteristics of PRC1. This review summarizes new advancements regarding the composition of mammalian PRC1 and accompanying explanations of how diverse PRC1-associated proteins participate in distinct transcription regulation mechanisms.

N-Heterocyclic Carbene Catalyzed Synthesis of Dihydroxybenzophenones from ß-Methylenals and Aurones.

N-heterocyclic carbene catalyzed synthesis of 2,2'-dihydroxybenzophenones from ß-methylenals and aurones was developed. The cleavage of the C-O bond by a retro-Michael addition is the key step from the spirocyclic intermediate to final product.

Impact of depth filtration on disulfide bond reduction during downstream processing of monoclonal antibodies from CHO cell cultures.

Monoclonal antibody interchain disulfide bond reduction was observed in a Chinese Hamster Ovary manufacturing process that used single-use technologies. A similar reduction has been reported for processes that involved high mechanical shear recovery unit operations, such as continuous flow centrifugation and when the clarified harvest was stored under low dissolved oxygen (DO) conditions (Trexler-Schmidt et al., 2010. Biotechnology and Bioengineering, 106(3), 452-461). The work described here identifies disposable depth filtration used during cell culture harvest operations as a shear-inducing unit operation causing cell lysis. As a result, reduction of antibody interchain disulfide bonds was observed through the same mechanisms described for continuous flow centrifugation. Small-scale depth-filtration models were developed, and the differential pressure (Δ P) of the primary depth filter was identified as the key factor contributing to cell lysis. Strong correlations of Δ P and cell lysis were generated by measuring the levels of lactate dehydrogenase and thiol in the filtered harvest material. A simple risk mitigation strategy was implemented during manufacturing by providing an air overlay to the headspace of a single-use storage bag to maintain sufficient DO in the clarified harvest. In addition, enzymatic characterization studies determined that thioredoxin reductase and glucose-6-phosphate dehydrogenase are critical enzymes involved in antibody reduction in a nicotinamide adenine dinucleotide phosphate (NADP + )/NADPH-dependent manner.

Visible-Light-Promoted Oxo-difluoroalkylation of Alkenes with DMSO as the Oxidant.

Visible-light-promoted oxo-difluoroalkylation (acetylation and acetamidation) of alkenes with dimethyl sulfoxide as both the solvent and the oxidant was developed, affording the corresponding α,α-difluoro-γ-ketoacetates and acetamides in modest yields. Both terminal and internal alkenes worked well for the reaction. This reaction features simple starting materials, a green oxidant, mild reaction conditions, and highly functional products.

Visible light mediated oxidative lactonization of 2-methyl-1,1'-biaryls for the synthesis of benzocoumarins.

A visible light mediated oxidative lactonization of 2-methyl-1,1'-biaryls was developed, giving benzocoumarins in good yields. The reaction features multiple C-H functionalization processes with oxygen as the final oxidant. The corresponding 2-aldehdyes, alcohols and carboxylic acids of the 1,1'-biaryls also worked well for the reaction.

L3MBTL2 protein acts in concert with PcG protein-mediated monoubiquitination of H2A to establish a repressive chromatin structure.

We have identified human MBT domain-containing protein L3MBTL2 as an integral component of a protein complex that we termed Polycomb repressive complex 1 (PRC1)-like 4 (PRC1L4), given the copresence of PcG proteins RING1, RING2, and PCGF6/MBLR. PRC1L4 also contained E2F6 and CBX3/HP1γ, known to function in transcriptional repression. PRC1L4-mediated repression necessitated L3MBTL2 that compacted chromatin in a histone modification-independent manner. Genome-wide location analyses identified several hundred genes simultaneously bound by L3MBTL2 and E2F6, preferentially around transcriptional start sites that exhibited little overlap with those targeted by other E2Fs or by L3MBTL1, another MBT domain-containing protein that interacts with RB1. L3MBTL2-specific RNAi resulted in increased expression of target genes that exhibited a significant reduction in H2A lysine 119 monoubiquitination. Our findings highlight a PcG/MBT collaboration that attains repressive chromatin without entailing histone lysine methylation marks.

(Dynamic) Kinetic Resolution of Enamines/Imines: Enantioselective N-Heterocyclic Carbene Catalyzed [3+3] Annulation of Bromoenals and Enamines/Imines.

The enantioselective N-heterocyclic carbene catalyzed [3+3] annulation of α-bromoenals by dynamic kinetic resolution (DKR) of enamines and normal resolution of α,α-disubstituted imines were developed. The corresponding substituted dihydropyridones were isolated in good yields with excellent diastereo- and enantioselectivities, and a high selective factor (up to 83) was realized for the resolution of α,α-disubstituted imines.

Visible-Light-Driven N-Heterocyclic Carbene Catalyzed γ- and ϵ-Alkylation with Alkyl Radicals.

The merging of photoredox catalysis and N-heterocyclic carbene (NHC) catalysis for γ- and ϵ-alkylation of enals with alkyl radicals was developed. The alkylation reaction of γ-oxidized enals with alkyl halides worked well for the synthesis γ-multisubstituted-α,ß-unsaturated esters, including those with challenging vicinal all-carbon quaternary centers. The synthesis of ϵ-multisubstituted-α,ß-γ,δ-diunsaturated esters by an unprecedented NHC-catalyzed ϵ-functionalization was also established.

N-Heterocyclic Carbene-Catalyzed Annulation of α-Chloroaldehydes with γ-/δ-Amino-α,ß-Unsaturated Ketones: Enantioselective Synthesis of Pyrrolidones and Piperidones.

The N-heterocyclic carbene-catalyzed [2+3] and [2+4] annulations of α-chloroaldehydes with γ-/δ-amino-α,ß-unsaturated ketones were developed, giving the corresponding pyrrolidones and piperidones in good yields with exclusive trans-selectivities and excellent enantioselectivities.

Enantioselective N-Heterocyclic Carbene-Catalyzed Synthesis of Spirocyclic Oxindole-benzofuroazepinones.

Herein, we report an enantioselective synthesis of azepinones via the N-heterocyclic carbene (NHC) catalyzed [3+4] annulation reaction of isatin-derived enals and aurone-derived azadienes. The corresponding spirocyclic oxindole-benzofuroazepinones were obtained in good yields, with excellent diastereo- and enantioselectivities. The resulted azepinones were evaluated for their in vitro cytotoxic activities against six human tumor cell lines, with two compounds showing significant inhibitory activity comparable with that of cisplatin.

Bifunctional N-heterocyclic carbene catalyzed [3+4] annulation of enals and aurones.

Bifunctional N-heterocyclic carbenes with a free hydroxy group are demonstrated as efficient catalysts for the [3+4] annulation of enals with aurones to give the corresponding benzofuran-fused ε-lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Control experiments reveal that the [3+4] cycloadducts are kinetically favored and could be transformed to the thermodynamically favored [3+2] cycloadducts with a non-bifunctional NHC catalyst.

N-heterocyclic carbene catalyzed cyclocondensation of α,ß-unsaturated carboxylic acids: enantioselective synthesis of pyrrolidinone and dihydropyridinone derivatives.

The catalytic cyclocondensation of in situ activated α,ß-unsaturated carboxylic acids was developed. N-heterocyclic carbenes efficiently catalyzed the generation of α,ß-unsaturated acyl azolium intermediates from α,ß-unsaturated carboxylic acids via in situ generated mixed anhydrides for the enantioselective [3+2] and [3+3] cyclocondensation with α-amino ketones and alkyl(aryl)imines, respectively. The corresponding pyrrolidinones and dihydropyridinones were isolated in good yields with high to excellent enantioselectivities.