AVALIAÇÃO DA PRODUÇÃO DE METIL-GALACTOPIRANOSÍDEOS NA GLICOSIDAÇÃO DE FISCHER:: INFLUÊNCIA DE CATALISADORES ÁCIDOS HETEROGÊNEOS

A glicosidação de Fischer foi o primeiro método desenvolvido para a síntese de alquil-piranosídeos e é considerado um dos métodos mais econômicos. Porém, o piranosídeo majoritário desta reação, quando se parte da D-galactose, é o metil-α-Galp. Tendo em conta o alto custo do metil-β-Galp, sua importância no mercado de química fina e as vantagens da glicosidação de Fischer, este trabalho teve por objetivo estudar a influência dos catalisadores ácidos heterogêneos na produção de metil-Galps na glicosidação de Fischer, reagindo a galactose com o metanol na presença de diferentes catalisadores ácidos heterogêneos(sílica-ácido-sulfúrico, sílica-ácido-clorossulfónico, alumina sulfúrica e resina catiônica AMBERLITE-IR-120), em diferentes tempos de reação e diferentes temperaturas. O estudo foi realizado em duas etapas. Na etapa I, todos os catalisadores acima citados, foram avaliados nas mesmas condições reacionais. Os principais resultados obtidos nesta etapa, foram otimizados na etapa II, em diferentes condições reacionais, com o uso de ultrassom, quantidades adicionais de água, metanol desidratado e molecular sieives. Os parâmetros que mais contribuiram para os resultados, foram o tempo de reação e temperatura. Os melhores resultados foram obtidos com a sílica-ácido sulfúrico e sílica-ácido clorossulfônico, na temperatura de 64,7ºC. Na temperatura ambiente, o percentual de metil-Galps foi baixíssimo. Ainda na temperatura de 64,7ºC, a maior produção de metil-Galps foi obtida entre 48 h - 72 h, com algumas exceções. Os melhores resultados do estudo, foram obtidos com os catalisadores sílica-ácido sulfúrico em 48 h (56%metil-α-Galp/43%metil-β-Galp) e sílica-ácido clorossulfônico em 5 h (26%metil-α-Galp/33%metil-β-Galp)

Dihydropyridine C-glycoconjugates by organocatalytic Hantzsch cyclocondensation. Stereoselective synthesis of alpha-threofuranose C-nucleoside enantiomers

The Hantzsch reaction of C-glycosyl aldehyde/enamino ester/beta-ketoester systems under L-proline catalysis to give dihydropyridine C-glycoconjugates is reported. Asymmetric cyclocondensations of differentially substituted enamine and beta-dicarbonyl components with formyl alpha-L-C-threofuranoside and with the alpha-D-isomer were also carried out. Each reaction occurred with high yet opposite stereoselectivity (de >95%) so that the pair of alpha-threofuranose C-nucleoside enantiomers was prepared

Agar from Gracilaria gracilis (Gracilariales, Rhodophyta) of the Patagonic coast of Argentina-Content, structure and physical properties

Milled summer thalli of Gracilaria gracilis from Argentina were sequentially extracted with water at room temperature (RTW1-3), 70 C (W701-3) and 90 C (W901-2). Both W701 and W901 consisted of high molecular weight polysaccharides (ca. 540,000 Da), but polydispersity was higher for the major product W701 (yield, 72% of the recovered). Structural analyzes by methylation and 13C NMR spectroscopy revealed that W701 was mainly agarose. Alkaline treatment, together with structural analyzes, indicated a negligible proportion of precursor L-galactose 6-sulfate residues in this product, while they were clearly detected in the 13C NMR spectra of RTW2-3. The presence of floridean starch in W901 had an antagonistic effect on its gel strength, which resulted nearly three times lower than that of fraction W701. Ultrastructural observation by transmission electron microscopy showed that, after extraction with hot water, a partial loss of cell wall stratification and disorganization of the cuticle had occurred. Final cellular debris exhibited swelling in the microfibrillar component. After this first thorough study of the chemical composition and physical properties of the products of G. gracilis from Bahía Bustamante we conclude that a good quality agarose is obtained in high yield after extraction with water at 70 C without the requirement of alkaline pretreatment, which usually produces degradation of the polysaccharide.Fil: Rodríguez, María Cecilia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Matulewicz, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Noseda, M. D.. Universidade Federal do Paraná; BrasilFil: Ducatti, D. R. B.. Universidade Federal do Paraná; BrasilFil: Leonardi, Patricia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Aqueous semisynthesis of C-glycoside glycamines from agarose

Agarose was herein employed as starting material to produce primary, secondary and tertiary C-glycoside glycamines, including mono- and disaccharide structures. The semisynthetic approach utilized was generally based on polysaccharide-controlled hydrolysis followed by reductive amination. All reactions were conducted in aqueous media and without the need of hydroxyl group protection. We were able to identify optimal conditions for the reductive amination of agar hydrolysis products and to overcome the major difficulties related to this kind of reaction, also extending it to reducing anhydrosugars. The excess of ammonium acetate, methyl- or dimethylamine, and the use of a diluted basic (pH 11) reaction media were identified as important aspects to achieve improved yields, as well as to decrease the amount of byproducts commonly related to reductive amination of carbohydrates. This strategy allowed the transposition of the 3,6-anhydro-α-L-galactopyranose unit (naturally present in the agarose structure) to all glycamines synthesized, constituting an amino-substituted C-threofuranoside moiety, which is closely related to (+)-muscarine

Resection for intrahepatic cholangiocellular cancer. New advances

Intrahepatic cholangiocarcinoma (ICC) is the second most prevalent primary liver neoplasm after hepatocellular carcinoma (HCC), corresponding to 10% to 15% of cases. Pathologies that cause chronic biliary inflammation and bile stasis are known predisposing factors for development of ICC. The incidence and cancer-related mortality of ICC is increasing worldwide. Most patients remain asymptomatic until advance stage, commonly presenting with a liver mass incidentally diagnosed. The only potentially curative treatment available for ICC is surgical resection. The prognosis is dismal for unresectable cases. The principle of the surgical approach is a margin negative hepatic resection with preservation of adequate liver remnant. Regional lymphadenectomy is recommended at time of hepatectomy due to the massive impact on outcomes caused by lymph node (LN) metastasis. Multicentric disease, tumor size, margin status and tumor differentiation are also important prognostic factors. Staging laparoscopy is warranted in high-risk patients to avoid unnecessary laparotomy. Exceedingly complex surgical procedures, such as major vascular, extrahepatic bile ducts and visceral resections, ex vivo hepatectomy and autotransplantation, should be implemented in properly selected patients to achieve negative margins. Neoadjuvant therapy may be used in initially unresectable lesions in order to downstage and allow resection. Despite optimal surgical management, recurrence is frustratingly high. Adjuvant chemotherapy with radiation associated with locoregional treatments should be considered in cases with unfavorable prognostic factors. Selected patients may undergo re-resection of tumor recurrence. Despite the historically poor outcomes of liver transplantation for ICC, highly selected patients with unresectable disease, especially those with adequate response to neoadjuvant therapy, may be offered transplant. In this article, we reviewed the current literature in order to highlight the most recent advances and recommendations for the surgical treatment of this aggressive malignancy