RESUMO
We examined the interactions of nucleotides with the CMP-sialic acid transporter in order to better understand which features play a role in binding and to investigate the relationship between binding and subsequent transport. With respect to the sugar, the transporter requires a complete ribose ring for tight binding, and the 2'-ara hydrogen makes an important contact. The enzyme exhibits little specificity with respect to the 2'- and 3'-hydroxyls, as it tolerated substitutions ranging from fluorine to an azido group. In the base, the C4 amine and C2 carbonyl groups make important contacts, while the N3 nitrogen does not. However, adding a methyl group to N3 dramatically reduced binding, indicating that mass at this position sterically hinders binding. Adding a group at C5 had either no effect or slightly enhanced binding. To determine if the transporter recognizes these CMP analogues as substrates, we assayed them for their ability to trans stimulate CMP-sialic acid import. These data suggest that the enzyme transports a wide variety of NMPs, and the rate of transport is inversely proportional to the K(I) of the analogue. The importance of our findings for understanding the specificities of the different nucleotide-sugar tranlocators and the design of novel glycosylation inhibitors are discussed.
Assuntos
Proteínas de Transporte/metabolismo , Ácido N-Acetilneuramínico do Monofosfato de Citidina/metabolismo , Complexo de Golgi/metabolismo , Proteínas de Membrana/metabolismo , Nucleotídeos/metabolismo , Animais , Transporte Biológico , Proteínas de Transporte/antagonistas & inibidores , Monofosfato de Citidina/análise , Citosol/química , Glicosilação/efeitos dos fármacos , Fígado , Proteínas de Membrana/antagonistas & inibidores , Modelos Químicos , Nucleotídeos/farmacologia , Nucleotídeos Cíclicos/análise , Ratos , Uridina Monofosfato/análiseRESUMO
[figure: see text] The cyclic sulfamidate 5 was synthesized in 60% overall yield from L-serine benzyl ester. Compound 5 reacted cleanly with the sodium thiolate salt of a variety of unprotected 1-thio sugars in aqueous buffer to afford the corresponding S-linked amino acid glycoconjugates in good yields after hydrolysis of the N-sulfates.
Assuntos
Aminoácidos/síntese química , Carboidratos/química , Glicoconjugados/síntese química , Soluções , Sulfonamidas/síntese químicaRESUMO
To probe the conformational requirements of O-linked glycoproteins for binding to various enzymes and receptors, two conformationally constrained glycosylated amino acids, 2 and 3, were designed. The analogues were found to represent two potential low energy conformations of the parent conjugate, 1, by molecular modeling. A convergent synthesis of both 2 and 3 from D-galactose and L-methionine is presented.
Assuntos
Aminoácidos/síntese química , Aminoácidos/química , Antígenos Glicosídicos Associados a Tumores/química , Sequência de Carboidratos , Glicoproteínas/química , Glicosilação , Modelos Moleculares , Dados de Sequência Molecular , Conformação ProteicaRESUMO
[reaction: see text]This report describes intramolecular thermal [2 + 2] cycloadditions between ketenes and allenes. The formation of ketenes and the subsequent cycloadditions occurred under a variety of conditions, affording 7-methylidinebicyclo[3.2.0]heptanones and 7-methylidinebicyclo[3.1.1]heptanones in 45-78% yields. The regioselectivity of the cycloaddition varied with the substitution of the allene, and the yield of cyclized products varied with reaction conditions.
Assuntos
Alcenos/síntese química , Compostos Bicíclicos com Pontes/síntese química , Ciclização , Indicadores e Reagentes , Espectroscopia de Ressonância Magnética , Espectrofotometria Infravermelho , Espectrofotometria Ultravioleta , EstereoisomerismoRESUMO
[reaction: see text]The ring system of phomactin D was synthesized in racemic form in an efficient manner from 2,3-dimethylcyclohexanone. Notable transformations include (1) an alkylation of the enolate of a vinylogous thiolester to install a quaternary stereocenter, (2) a conjugate addition of cyanide to an alpha,beta-unsaturated aldehyde, (3) the formation of a Weinreb amide directly from a cyanohydrin, and (4) an intramolecular Pd-mediated Suzuki coupling of a B-alkyl-9-BBN derivative and a vinyl iodide to form the macrocyclic ring.
Assuntos
Compostos de Epóxi/síntese química , Fator de Ativação de Plaquetas/antagonistas & inibidores , Ciclização , Indicadores e Reagentes , EstereoisomerismoRESUMO
alpha-2,3-Sialyltransferase catalyzes the transfer of sialic acid from CMP-sialic acid (1) to a lactose acceptor. An analogue of 1 was synthesized in which the anomeric oxygen atom was replaced with a sulfur atom (1S). The key step in the synthesis of 1S was a tetrazole-promoted coupling of a cytidine-5'-phosphoramidite with a glycosyl thiol of a protected sialic acid. Compounds 1 and 1S were characterized for their activity in a sialyl transfer assay. The rate of solvolysis in aqueous buffer of analogue 1S was 50-fold slower than that of 1. Analogue 1S was found to be substrate for alpha-2,3-sialyltransferase. The K(m) of 1S was just 3-fold higher than that of 1, while the k(cat) of 1S was 2 orders of magnitude lower compared to 1.
Assuntos
Monofosfato de Citidina/análogos & derivados , Monofosfato de Citidina/síntese química , Ácidos Siálicos/síntese química , Sequência de Carboidratos , Cromatografia Líquida de Alta Pressão , Monofosfato de Citidina/química , Cinética , Espectroscopia de Ressonância Magnética , Dados de Sequência Molecular , Ácidos Siálicos/química , Sialiltransferases/química , Solventes , Enxofre/química , Termodinâmica , beta-Galactosídeo alfa-2,3-SialiltransferaseRESUMO
A symmetry-based strategy for the synthesis of the zaragozic acids is reported. Two enantioselective dihydroxylations were used to establish the absolute configuration of a C(2) symmetric intermediate. Noteworthy transformations include a group-selective lactonization, which accomplished an end-differentiation of a pseudo-C(2) symmetric intermediate. Late stage protecting group adjustments and oxidations accomplished a formal synthesis of zaragozic acid A.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/síntese química , Inibidores Enzimáticos/síntese química , Farnesil-Difosfato Farnesiltransferase/antagonistas & inibidores , Ácidos Tricarboxílicos/síntese química , Cristalografia por Raios X , Fungos/química , Espectroscopia de Ressonância MagnéticaRESUMO
[reaction: see text] The synthesis of a six-carbon truncated sialic acid is described. A key step in the synthesis was an indium-mediated allyl addition to a serine-derived aldehyde. Careful choice of protecting groups was found to be necessary in order to prevent unwanted side reactions throughout the sequence. The truncated sialic acid was obtained in a form suitable for activation as a glycosyl donor.