Yield Of Glycosides Research Articles

A kinetic study of almond-β-glucosidase catalysed synthesis of hexyl-glycosides in low aqueous media: Influence of glycosyl donor and water activity

A variety of alkyl and aryl glycosides were investigated as substrates for almond β-glucosidase catalysed synthesis of hexyl-β- d-glycosides in low aqueous hexanol media. The rate-limiting step in the organic media was determined to be the glycosylation of the enzyme. The kinetic constants V max, K m (glycosyl donor) and V max/ K m were all influenced by the water activity and they all increased in value with increasing water activity. The increase in V max/ K m was mainly determined by the increase in V max and a plot of log( V max/ K m) versus water activity resulted in a straight line with similar slopes for all glycosides but with different absolute values and thus the most reactive substrate p-nitrophenyl glucoside was the best one in the entire water activity range studied (0.53–0.96). The preference for the two competing acceptors, hexanol and water, was not affected by the aglycon part of the glucoside. Surprisingly, the ratio between trans glycosylation and hydrolysis increased with increasing water activity. A decrease in water activity caused an increase in equilibrium yield of hexyl glycoside, as expected, but was not beneficial for the kinetically controlled yield.

Acyl Transfer as a Problematic Side Reaction in Polymer-Supported Oligosaccharide Synthesis

Under a wide variety of glycosylation conditions acyl transfer to the polymer support competed with glycoside formation, including the pivaloyl protecting group. As well as acyl transfer, many glycosylations also led to the formation of polymer-bound β-1,2-linked oligomers of the donor. Using ethyl 2,6-di-O-pivaloyl-3,4-O-isopropylidene-β-d-galactothiopyranoside as donor under promotion of N-iodosuccinimide/silver trifluoromethanesulfonate in the presence of 2-methyl-2-butene, an 82% yield of glycoside was obtained along with pivaloylated polymer. Subsequent work showed that increasing the steric bulk about the alcoholic acceptor in conjunction with this 2-O-pivaloyl-protected glycosyl donor completely suppresses this side reaction, giving a nearly quantitative yield of glycoside. This contraintuitive approach of decreasing the reactivity of both the donor and the acceptor to minimize a side reaction is rationalized by assuming that the barrier to acyl transfer is more sensitive to the protecting groups than that of glycosylation. These developments led to a polymer-supported synthesis of the branch point trisaccharide of the group B type 1A Streptococcus capsular polysaccharide.

A steroid glycoside from the seeds ofYucca macrocarpa

glycosides, of which the more polar one greatly predominated, and also trace amounts of still more polar glycosides. The isolation of the main steroid glycoside (SG) was achieved by defardng the carefully ground seeds with hexane, followed by exlraction with 80% isopropyl alcohol. Evaporation of the alcoholic extract gave a 20% total yield of unpurified glycosides. Crystallization of this mixture from ethanol enabled the main glycoside to be obtained in the practically pure state with a yield of I0%, and two recrystaUizations of this permitted the complete elimination of a contaminating weakly polar glycoside. By TLC, in a complete acid hydrolysate of the SG we identified glucose, galactose, and an aglycon close in chromatographic mobility to authentic specimens of smilagenin and tigogenin. The further determination of the structure of the SG was made with the use of IH and t3C NMR spectroscopy.

Comparison of methods for the extraction of flavonoids from birch leaves (Betula pendula Roth.) carried out using high-performance liquid chromatography

The efficiency of commonly used methods and solvents for the extraction of flavonoids from dried birch leaves was compared, and the responses of individual compounds were determined. The three method compared were (1) a short extraction with a clipping homogenizer in an unheard solvent, (2) reflexing, and (3) Soxhlet extraction. The solvents tested (pure and 80% aqueous solvent) were acetone, ethanol, and methanol. In general, the aqueous solvents were superior to the nonaqueous solvents. Methanolwas the most efficient nonaqueous solvent, and in refluxing and Soxhlet extraction, the yield of flavonoid glycosides was comparable to that in aqueous methanol. Soxhlet extraction and refluxing were found to be efficient methods with several solvents

Silver Zeolite as Promoter in Glycoside Synthesis. The Synthesis of 2-Deoxy-β-D-Glycopyranosides

Abstract The use of silver zeolite as a promoter for the preparation of β-linked 2-deoxygtycosides and disaccharides of biological relevance has been explored. Starting from benzoylated glycosyl bromides, the total yield of glycosides varies from 54 to 84% and the α:β ratio from 0.25 to 1.18.

Teor de glicoalcalóides em Solanum americanum infestado por Aphis fabae solanella

Solanum americanum Miller, uma fonte conhecida de glicosídios de solassodina, foi encontrada infestada por Aphis fabae solanela Theob. Uma vez que esses glicosídios são matérias-primas potenciais para a síntese de outras substâncias esteroídicas, tornou-se de interesse verificar o efeito de infestação sobre o teor destes glicoalcalóides. Plantas fortemente, moderadamente e não infestadas pelo pulgão foram colhidas no campo, determinando-se o teor de glicoalcalóides esteroídicos nos caules, folhas e frutos. Verificou-se que esse teor de glicoalcalóides esteroídicos é dependente do órgão da planta e da fitossanidade do material vegetal. O teor médio de glicoalcalóides em plantas não infestadas é sempre maior que em plantas infestadas, tanto na planta como um todo como em cada órgão examinado. Esses resultados não asseguram que o teor de glicoalcalóides seja responsável pela resistência à infestação, porém que há uma boa correlação entre teor de glicoalcolóides e fitossanidade do material vegetal.

Quantitation of Principal Bufadienolides in Different Cytotypes of Urginea indica

Roots of URGINEA INDICA K UNTH, (Liliaceae) Indian squill, contain high amounts of proscillardin A and scillaren A. The range of variation in proscillaridin A and scillaren A contents in bulbs is 0.004-0.26% in diploids, 0.04-0.07% in triploids and 0.02-0.45% in tetraploids. The relative proportion of proscillaridin A and scillaren A also varies in different cytotypes. A tetraploid cytotype, representing a high yielding strain which can be exploited commercially for better yield of cardiac glycosides, has been obtained from Pune.

The use of 1- O-sulfonyl- d-mannopyranose derivatives in β- d-mannopyranoside synthesis

Several 1- O-sulfonyl derivatives of d-mannopyranose having a nonparticipating benzyl ether group at C-2 and ester functions at C-6 and C-4 were synthesized from the corresponding d-mannopyranosyl chloride derivatives with silver sulfonates in acetonitrile. The reaction of 1- O-sulfonyl- d-mannopyranose compounds with methanol in various solvents at room temperature gave high yields of glycosides with low degrees of stercoselectivity. On the other hand, 1- O-suffonyl- d-mannopyranose derivatives having an acyl participating-group at O-2 and benzyl ethers at C-3, C-4, and C-6 gave high yields and high stereoselectivity of α- d-mannopyranosides with primary and secondary alcohols in several solvents. Model studies were carried out to determine the best combination of 2- O-acyl group, solvent, time, temperature, and 1- O-sufonyl group to give high yields with high stereoselectivity. The method has been used to prepare in good yields more complex glycosides, including perbenzylated methy 2- O-(α- d-mannopyranosyl)-α- d-mannopyranoside.

Improved yields of daunomycinone glycosides in developmental mutants ofStreptomyces coeruleorubidus

When improving Streptomyces coeruleorubidus JA 10092, a producer of antibiotics of the daunomycinone complex, the most active variants were found among isolates of morphological types bld-1 (with a suppressed production of the aerial mycelium on organic media containing glucose) and whi (with an asporogenic aerial mycelium on glucose media and with the bald phenotype on media containing starch). Submerged cultures of the whi mutants produced increased quantities of daunomycinone glycosides in the antibiotic complex, the amount of free anthracyclinones being simultaneously decreased. The whi strains differed from the wild type also in higher demands for aeration, concentration of glucose and in an increased production capacity in starch media. The overall antibiotic activity increased more than 40 times after a six-step selection (application of UV light, gamma-radiation, nitrous acid and natural spreads) combined with an altered fermentation technology.

Thio-sugars. Part 2. Glycosides from acid-catalysed reactions of 1-O-acetyl-2,3-di-O-acyl-4-thiotetrofuranoses

Alcohols and thiols in presence of toluene-p-sulphonic acid readily displace the 1-O-acetyl group from the title compounds, now available by Pummerer rearrangement of the appropriate sulphoxides, thus providing a very convenient synthesis of these thio-sugar glycosides. Glycosyl bromides can also be prepared. The advantages of the phenylboronate function described in Part 1 are further illustrated. O-Glycosides are formed with a high degree of stereoselectivity, S-glycosides are not. Toluene-ω-thiols with electron-repelling substituents react normally, but the corresponding alcohols are acetylated rather than glycosylated. A disaccharide (glycosyl glycoside) has been prepared. Other esters give lower yields of glycosides than the phenylboronates. The reactions with hydrazides of the substituted 3-heteraglutaraldehydes from periodate oxidation of some of these glycosides and related nucleosides were compared with earlier examples.

Aminosaccharides : Part V. Koenigs-knorr reaction of the acetobromo derivatives of 2-deoxy-2-(2,4-dinitroanilino)- d-glucopyranose and its monomethyl ethers

Syntheses of 4,6-di- O-acetyl-2-deoxy-2-(2,4-dinitroanilino)-3- O-methyl-α- d-glucopyranosyl bromide ( 3) and the isomeric 3,6-di- O-acetyl-4- O-methyl ( 4) and 3,4-di- O-acetyl-6- O-methyl ( 2) derivatives are described. 2-Deoxy-2-(2,4-dinitroanilino)-6- O-methyl- d-glucose ( 7) was synthesised via ethyl 3,4-di- O-benzoyl-2-deoxy-2-(2,4-dinitroanilino)-6- O-trityl-α- d-glucopyranoside ( 14) and its de- O-tritylated derivative ( 15). When 15 and its β-anomer 26 were methylated, little migration of benzoyl groups from C-4 to C-6 occurred. Compounds 3, 4, and 2 reacted with ethanol, in nitromethane solution with silver carbonate present, to form mainli β- d-glycopyranosides. In chloroform solution with pyridine as catalyst, 3 and 4 reacted rapidly with ethanol to give α- d-glycopyranosides as the major products, but 2 reacted slowly to give low yields of both glycosides. A possible mechanism for the pyridine-catalysed ethanolysis of 3, 4, and the unmethylated halide 1, involving participation of AcO-6, is discussed.

FURTHER PROOF OF POSTHARVEST „SYNTHESIS” OF GLYCOSIDES IN SOME MEDICINAL PLANTS

The phenomenon of increasing the glycoside content during a wilting period at normal temperature and evaporation rate has been proved for Sophora japonica flowers and Virus communis leaves in addition to Digitalis lanata leaves. These increases in the glycoside yield are inversely proportional to the content of free reducing sugars. Results obtained with Bergenia leaves were not so evident. These results showed that glucosides were „synthesized” during a 24 hours period of postharvest wilting at room temperature in connection with an accompaning moisture loss of 50 %.

Effect of Potassium, Nitrogen, and Phosphorus on the Growth and Glycoside Accumulation in Digitalis lanata I. Leaf Yield and Total Glycosides

Plants of Digitalis lanata were grown in experimental soil cultures with a high level of potassium, nitrogen, and phosphorus. It was observed that plants grown on the high level phosphorus produced a significantly less growth. No significant effects in total glycoside accumulation were observed in plants grown in high level potassium and nitrogen. On the other hand, leaf material from plants grown with a high level phosphorus showed a significant decrease in total glycoside yield.