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1.
Org Biomol Chem ; 18(16): 3012-3016, 2020 04 29.
Artigo em Inglês | MEDLINE | ID: mdl-32267909

RESUMO

The practical synthesis of carbohydrate-based NHC-Rh complexes bearing C1 or C3 sterically differentiated positions, accessed by glycosylation or SNAr strategies, is reported. These catalysts exhibit pseudo-enantiomeric behaviour in the hydrosilylation of acetophenone. We show that steric bulk at C1 gives preference for (S)-phenyl-1-ethanol, while bulk at C3 leads to the (R)-enantiomer. These results represent the first example of pseudo-enantiomeric carbohydrate-based NHC ligands leading to enantiotopic discrimination.

2.
J Phys Chem B ; 121(17): 4448-4455, 2017 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-28394602

RESUMO

Transient electronic and vibrational absorption spectroscopies have been used to investigate whether UV-induced electron-driven proton transfer (EDPT) mechanisms are active in a chemically modified adenine-thymine (A·T) DNA base pair. To enhance the fraction of biologically relevant Watson-Crick (WC) hydrogen-bonding motifs and eliminate undesired Hoogsteen structures, a chemically modified derivative of A was synthesized, 8-(tert-butyl)-9-ethyladenine (8tBA). Equimolar solutions of 8tBA and silyl-protected T nucleosides in chloroform yield a mixture of WC pairs, reverse WC pairs, and residual monomers. Unlike previous transient absorption studies of WC guanine-cytosine (G·C) pairs, no clear spectroscopic or kinetic evidence was identified for the participation of EDPT in the excited-state relaxation dynamics of 8tBA·T pairs, although ultrafast (sub-100 fs) EDPT cannot be discounted. Monomer-like dynamics are proposed to dominate in 8tBA·T.


Assuntos
Adenina/química , DNA/química , Prótons , Timina/química , Raios Ultravioleta , Pareamento de Bases , Elétrons , Teoria Quântica
3.
Org Biomol Chem ; 14(17): 4008-17, 2016 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-27064817

RESUMO

Carbohydrate derivatives are readily available chiral molecules, yet they are infrequently employed as enantioinduction components in stereoselective catalysis. In this review, synthetic approaches to carbohydrate-based ligands and catalysts are outlined, along with example applications in enantioselective catalysis. A wide range of carbohydrate-based functionality is covered, and key trends and future opportunities are identified.


Assuntos
Carboidratos/química , Catálise , Ligantes , Estrutura Molecular , Estereoisomerismo
4.
Angew Chem Int Ed Engl ; 54(49): 14719-22, 2015 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-26459502

RESUMO

Ultrafast deactivation pathways bestow photostability on nucleobases and hence preserve the structural integrity of DNA following absorption of ultraviolet (UV) radiation. One controversial recovery mechanism proposed to account for this photostability involves electron-driven proton transfer (EDPT) in Watson-Crick base pairs. The first direct observation is reported of the EDPT process after UV excitation of individual guanine-cytosine (G⋅C) Watson-Crick base pairs by ultrafast time-resolved UV/visible and mid-infrared spectroscopy. The formation of an intermediate biradical species (G[-H]⋅C[+H]) with a lifetime of 2.9 ps was tracked. The majority of these biradicals return to the original G⋅C Watson-Crick pairs, but up to 10% of the initially excited molecules instead form a stable photoproduct G*⋅C* that has undergone double hydrogen-atom transfer. The observation of these sequential EDPT mechanisms across intermolecular hydrogen bonds confirms an important and long debated pathway for the deactivation of photoexcited base pairs, with possible implications for the UV photochemistry of DNA.


Assuntos
Absorção Fisico-Química/efeitos da radiação , Pareamento de Bases/efeitos da radiação , DNA/química , Hidrogênio/química , Raios Ultravioleta , Soluções
5.
Org Lett ; 17(19): 4846-9, 2015 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-26379123

RESUMO

A general and practical route to carbohydrate-aryl ethers by nucleophilic aromatic substitution (SNAr) is reported. Upon treatment with KHMDS, C-O bond formation occurs between carbohydrate alcohols and a diverse range of fluorinated (hetero)aromatics to provide the targets in good to excellent yields. Commercially available arylating agents, high atom economy, and high regioselectivity are notable features of the protocol. The aryl ether products have potential for wide-ranging applications as exemplified by the synthesis of a novel chiral P,N-ligand.

6.
Chem Commun (Camb) ; 51(43): 8939-41, 2015 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-25925803

RESUMO

The use of (salen)Co catalysts as a new class of bench-stable stereoselective glycosylation promoters of trichloroacetimidate glycosyl donors at room temperature is described. The conditions are practical and do not require the use of molecular sieves with products being isolated in good to high yields.


Assuntos
Cobalto/química , Etilenodiaminas/química , Glicosídeos/síntese química , Acetamidas/química , Catálise , Cloroacetatos/química , Glicosídeos/química , Glicosilação , Estereoisomerismo , Temperatura
7.
Org Biomol Chem ; 12(45): 9180-3, 2014 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-25296562

RESUMO

Versatile syntheses of C2-linked and C2-symmetric carbohydrate-based imidazol(in)ium salts from functionalised amino-carbohydrate derivatives are reported. The novel NHCs were ligated to [Rh(COD)Cl]2 and evaluated in Rh-catalysed asymmetric hydrosilylation of ketones with good yields and promising enantioselectivities.

8.
Psychol Aging ; 17(2): 194-208, 2002 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12061406

RESUMO

The influence of a genetic risk factor, apolipoprotein E (apoE) epsilon4 variant, was assessed in older adults aged 70 to 94 on 3 occasions over 7 years. The results of latent growth curve analyses are reported for individuals genotyped for apoE at the 2nd measurement occasion (n = 601) and for a subsample of individuals without probable or definite dementia during the 1st or 2nd occasion (n = 434). ApoE-epsilon4 status was a significant predictor of level and change in memory performance and change in speed performance in the full sample, and of initial level and change in memory performance in the nondemented subsample. These results support previous findings that apoE-epsilon4 is associated with accelerated memory deterioration in individuals without clinical dementia.


Assuntos
Envelhecimento/psicologia , Apolipoproteínas E/genética , Demência/genética , Demência/fisiopatologia , Transtornos da Memória/genética , Transtornos da Memória/fisiopatologia , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/genética , Transtornos Cognitivos/genética , Transtornos Cognitivos/fisiopatologia , Feminino , Genótipo , Humanos , Masculino , Fatores de Risco
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