RESUMO
Tetrabutylammonium tribromide (TBATB) has been found to be a unique bromodeboronation reagent for organotrifluoroborates. When compared to previously reported bromodeboronation methods, the mild and metal-free reaction conditions tolerate a wider range of functional groups. High regio- and chemoselectivity are observed in the presence of both unsaturated carbon-carbon bonds and aldehyde functional groups. An efficient synthetic route to (Z)-dibromoalkenes from terminal alkynes has been developed using the TBATB-mediated bromodeboronation as a key step.
RESUMO
An alternate reaction mechanism for the boron tribromide mediated deprotection of aryl propargyl ethers based on the isolation of a key boron-containing byproduct is proposed. On the basis of the new mechanistic insight, we discovered that HBBr(2) x SMe(2) can also be used for cleaving aryl propargyl ethers.
Assuntos
Alcenos/síntese química , Alcinos/química , Compostos de Boro/química , Brometos/química , Éteres/química , Hidrocarbonetos Bromados/síntese química , Compostos de Boro/síntese química , Compostos de Vinila/síntese químicaRESUMO
Short homo-oligomers of a new building block, cis-beta(2,3)-furanoid sugar aminoxy acid, are designed, characterized, and found to exhibit rigid ribbon-like secondary structures composed of 5/7 bifurcated intramolecular hydrogen bonds.
Assuntos
Carboidratos/química , Química Orgânica/métodos , Peptídeos/química , Amidas/química , Aminoácidos/química , Dimerização , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Conformação Molecular , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Residue based control of specific helical folding is explored in hybrid peptide oligomers consisting of alternating L-Ala and cis-beta-furanoid sugar amino acid (FSAA) residues as building blocks; two series of these hybrid oligomers are designed, synthesized and extensively characterized by using NMR, CD, FT-IR and MD simulation studies; results show the co-existence of left-handed 11- and 14/15-helical conformations in these short oligomers of Boc-(alpha/beta) and Boc-(beta/alpha) series.
Assuntos
Alanina/química , Carboidratos/química , Simulação por Computador , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , Peptídeos , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
A highly chemoselective conjugate reduction of electron-deficient Michael acceptors, including alpha,beta-unsaturated ketones, carboxylic esters, nitriles and nitro compounds with PMHS in the presence of catalytic B(C6F5)3 is described.
RESUMO
The oligomers of constrained cis-exo-beta-norbornene amino acid were synthesised and characterised by extensive NMR, CD, IR and MD studies. The results showed the formation of both right and left handed consecutive 6-membered hydrogen-bonded strands for [2S,3R] and [2R,3S] enantiomers, respectively.
Assuntos
Aminoácidos/química , Biomimética , Norbornanos/química , Oligopeptídeos/química , Ligação de Hidrogênio , Oligopeptídeos/síntese química , Estrutura Secundária de Proteína , Análise Espectral , EstereoisomerismoRESUMO
The design, synthesis and characterization of a new class of peptide nanotubes, self-assembled from cyclic homo- and hetero-beta-peptides based on cis-furanoid sugar amino acid and beta-hGly residues are described; these results represent the expansion of the conformational pool of cis beta-sugar amino acids in the design of peptide nanotubes.
Assuntos
Nanotubos de Peptídeos/química , Nanotubos de Peptídeos/ultraestrutura , Conformação ProteicaRESUMO
Tendencies of forming stable helices of heterooligomers composed of alternating rigid cis-beta-sugar amino acid and flexible beta-hGly motifs have been investigated, using a combination of molecular mechanics, CD, FT-IR, and NMR techniques. The results show that the solution structures of these oligomers exist as robust right-handed 14-helices. Here, we examine the role of conformationally rigid cis-beta-sugar amino acid in preorganizing the conformation of beta-hGly to form the 14-helix. Our findings also show that a right-handed 14-helix can be formed with as few as four properly sequenced heterogeneous residues. These results represent the expansion of the conformational pool of sugar amino acid in the design of well-folded 14-helices, which can be used to develop beta-peptides endowed with biological activity.
Assuntos
Carboidratos/química , Glicina/química , Dicroísmo Circular , Modelos Moleculares , Conformação Molecular , Estrutura Secundária de ProteínaRESUMO
Oligomers of a new class of sugar amino acids (SAA) using a xylofuranoic acid has been shown to generate a robust 14-helix. The design involved the use of xylofuranose with a cis arrangement between the amine and carboxyl groups to promote the adoption of a 14-helix instead of a mixed 12/10-helix observed in a sugar oligomer using a ribofuranoic acid and beta-Ala. The observation of a stable right-handed 14-helix in a cis-SAA is unprecedented.
