Conspectus Developing new methods that enable the synthesis of new and complex molecules with complete control of their 3-D shape is central to the advancement of synthetic chemistry with ...applications spanning from medicine to materials. Our approach consists of the iterative combination of small building blocks through the use of boron chemistry to essentially “grow” molecules. This approach, which we term assembly-line synthesis (ALS), resembles the way that nature assembles natural products (e.g., the polyketide synthase machinery) and has the advantage that many structural variations can be easily introduced and the products can be evaluated in structural or biological contexts. Chiral boronic esters have been recognized as valuable building blocks due to their unique chemical properties. They are both chemically and configurationally stable, and they can be prepared with very high levels of enantioselectivity. Additionally they undergo a broad array of transformations that lead to the stereocontrolled formation of C–C and C–X (X = heteroatom) bonds. This versatility makes boronic acids ideal building blocks for iterative molecular assembly. A powerful reaction platform for chemical diversification using chiral boronic esters is their homologation using lithium carbenoids via 1,2-metalate rearrangement. In the 1980s, Matteson described the use of boronic esters bearing a chiral diol in a two-step homologation process with dichloromethyl lithium and Grignard reagents (substrate-controlled approach). We have focused on reagent control and have found that Hoppe’s chiral lithiated carbamates can be used as carbenoid equivalents in conjunction with achiral boronic esters. This reagent-controlled process offers many advantages due to the easy access of both the chiral lithiated carbamates and stable boronic esters. The carbamates can be derived from primary or secondary alcohols, and a broad range of functionalized boronic esters and boranes can be employed. Multiple homologations can be carried out in a one-pot sequence thereby streamlining the process to a single operation. This methodology has enabled the synthesis of many molecules containing multiple contiguous stereogenic centers with exquisite 3-D control. In this Account, we trace our own studies to establish the lithiation–borylation methodology and describe selected synthetic applications.
Distal enhancers characterized by the H3K4me1 mark play critical roles in developmental and transcriptional programs. However, potential roles of specific distal regulatory elements in regulating RNA ...polymerase II (Pol II) promoter-proximal pause release remain poorly investigated. Here, we report that a unique cohort of jumonji C-domain-containing protein 6 (JMJD6) and bromodomain-containing protein 4 (Brd4) cobound distal enhancers, termed anti-pause enhancers (A-PEs), regulate promoter-proximal pause release of a large subset of transcription units via long-range interactions. Brd4-dependent JMJD6 recruitment on A-PEs mediates erasure of H4R3me2(s), which is directly read by 7SK snRNA, and decapping/demethylation of 7SK snRNA, ensuring the dismissal of the 7SK snRNA/HEXIM inhibitory complex. The interactions of both JMJD6 and Brd4 with the P-TEFb complex permit its activation and pause release of regulated coding genes. The functions of JMJD6/ Brd4-associated dual histone and RNA demethylase activity on anti-pause enhancers have intriguing implications for these proteins in development, homeostasis, and disease.
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•Anti-pause enhancers (A-PEs) regulate Pol II promoter-proximal pause release•A-PEs-associated JMJD6 exhibits dual H4R3me2(S) and 7SK demethylase activities•7SK snRNA is a “reader” of H4R3me2(S)•A-PEs loop with their cognate gene promoters to regulate Pol II pause release
JMJD6 and Brd4 protein complexes are recruited to certain enhancers to release repressive machinery imposed on the P-TEFb complex, therefore releasing promoter pause of RNA polymerase II. This cohort of enhancers was termed as anti-pause enhancers.
This Minireview highlights advances in the Suzuki–Miyaura cross‐coupling of secondary boron reagents for the creation of CC bonds with control of stereochemistry. It also includes ...non‐transition‐metal coupling of secondary and tertiary boronic esters to electron‐rich aromatics.
Just couple it: In the past decade, highly efficient protocols have been developed to allow the stereospecific arylation of chiral organoborons. This Minireview documents the rapid development of this area, thus providing a clear overview of the various processes available together with mechanisms, as well as their scope and limitations.
Photoredox‐catalyzed methylcyclobutanations of alkylboronic esters are described. The reactions proceed through single‐electron transfer induced deboronative radical addition to an electron‐deficient ...alkene followed by single‐electron reduction and polar 4‐exo‐tet cyclization with a pendant alkyl halide. Key to the success of the methodology was the use of easily oxidizable arylboronate complexes. Structurally diverse cyclobutanes are shown to be conveniently prepared from readily available alkylboronic esters and a range of haloalkyl alkenes. The mild reactions display excellent functional group tolerance, and the radical addition‐polar cyclization cascade also enables the synthesis of 3‐, 5‐, 6‐, and 7‐membered rings.
Arylboronate complexes formed from alkylboronic esters and phenyllithium were found to undergo facile single‐electron oxidation to form alkyl radicals. The novel use of these complexes as radical precursors enabled the development of a photoredox‐catalyzed cyclobutane synthesis proceeding through a radical‐polar crossover mechanism.
The use of pyridinium‐activated primary amines as photoactive functional groups for deaminative generation of alkyl radicals under catalyst‐free conditions is described. By taking advantage of the ...visible light absorptivity of electron donor–acceptor complexes between Katritzky pyridinium salts and either Hantzsch ester or Et3N, photoinduced single‐electron transfer could be initiated in the absence of a photocatalyst. This general reactivity platform has been applied to deaminative alkylation (Giese), allylation, vinylation, alkynylation, thioetherification, and hydrodeamination reactions. The mild conditions are amenable to a diverse range of primary and secondary alkyl pyridiniums and demonstrate broad functional group tolerance.
Electron donor–acceptor complexes between pyridinium‐activated primary amines and Hantzsch ester or triethylamine undergo catalyst‐free photoinduced single‐electron transfer with visible light. Fragmentation leads to alkyl radicals that could be intercepted with a variety of acceptors. This deaminative radical generation was applied to catalyst‐free Giese, allylation, vinylation, alkynylation, thioetherification, and hydrodeamination reactions.
Human Activity Analysis: A Review AGGARWAL, J. K; RYOO, M. S
ACM computing surveys,
04/2011, Letnik:
43, Številka:
3
Journal Article
Recenzirano
Human activity recognition is an important area of computer vision research. Its applications include surveillance systems, patient monitoring systems, and a variety of systems that involve ...interactions between persons and electronic devices such as human-computer interfaces. Most of these applications require an automated recognition of high-level activities, composed of multiple simple (or atomic) actions of persons. This article provides a detailed overview of various state-of-the-art research papers on human activity recognition. We discuss both the methodologies developed for simple human actions and those for high-level activities. An approach-based taxonomy is chosen that compares the advantages and limitations of each approach.
Recognition methodologies for an analysis of the simple actions of a single person are first presented in the article. Space-time volume approaches and sequential approaches that represent and recognize activities directly from input images are discussed. Next, hierarchical recognition methodologies for high-level activities are presented and compared. Statistical approaches, syntactic approaches, and description-based approaches for hierarchical recognition are discussed in the article. In addition, we further discuss the papers on the recognition of human-object interactions and group activities. Public datasets designed for the evaluation of the recognition methodologies are illustrated in our article as well, comparing the methodologies' performances. This review will provide the impetus for future research in more productive areas.
1,3‐Disubstituted bicyclo1.1.1pentanes (BCPs) are valuable bioisosteres of para‐substituted aromatic rings. The most direct route to these structures is via multicomponent ring‐opening reactions of ...1.1.1propellane. However, challenges associated with these transformations mean that difunctionalized BCPs are more commonly prepared by multistep reaction sequences with BCP‐halide intermediates. Herein, we report three‐ and four‐component 1,3‐difunctionalizations of 1.1.1propellane with organometallic reagents, organoboronic esters, and a variety of electrophiles. This process is achieved by trapping intermediate BCP‐metal species with boronic esters to form boronate complexes, which are versatile intermediates whose electrophile‐induced 1,2‐metallate rearrangement chemistry enables a broad range of C−C bond‐forming reactions.
A modular synthesis of 1,3‐difunctionalized bicyclo1.1.1pentanes (BCPs) has been achieved through multicomponent couplings between organometallic reagents, 1.1.1propellane, and organoboronic esters. By utilizing the versatile 1,2‐metallate rearrangement chemistry of boronate complexes generated in situ, a range of C−C bond‐forming reactions could be performed without the need for transition‐metal catalysis.
Homologation of readily available α‐boryl pyrrolidines with metal carbenoids is especially challenging even when good leaving groups (Cl−) are employed. By performing a solvent switch from Et2O to ...CHCl3, efficient 1,2‐metalate rearrangement of the intermediate boronate occurs with both halide and ester leaving groups. The methodology was used in the total synthesis of the Stemona alkaloid (−)‐stemaphylline in just 11 steps (longest linear sequence), with high stereocontrol (>20:1 d.r.) and 11 % overall yield. The synthesis also features a late‐stage lithiation–borylation reaction with a tertiary amine containing carbenoid.
Full stereocontrol: α‐Boryl pyrrolidines can be employed in lithiation–borylation reactions but require a solvent switch from Et2O to CHCl3 for efficient 1,2‐metalate rearrangement. The methodology was used in the total synthesis of the Stemona alkaloid (−)‐stemaphylline.
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