A Plausible Prebiotic Path to Nucleosides: Ribosides and Related Aldosides Generated from Ribulose, Fructose, and Similar Abiotic Precursors.

The prebiotic origins of ribose, nucleosides, and eventually RNA are enduring questions whose answers are central to the RNA world hypothesis. The abiotic synthesis of sugars was first demonstrated over a century ago, but no known prebiotic reaction produces ribose (an aldose sugar) selectively and in good yield. In contrast, ribulose, and fructose (ketose sugars) and other monosaccharides are formed in high yield by several robust abiotic reactions. It is reported here that ketose sugars - both ketopentoses and ketohexoes - serve as precursors for the formation of ribosides and other aldosides, as demonstrated by glycoside-forming reactions involving barbituric acid, a plausibly prebiotic nucleobase. Moreover, a one-pot reaction of glyceraldehyde and barbituric acid was discovered which under mild conditions, and without special minerals or other catalysts, results in the formation of glycosides. These results reveal that an exclusive or high-yielding generation of free ribose was not required for its incorporation into processes that provided the foundations for life.

Facile Enzymatic Synthesis of Ketoses.

Studies of rare ketoses have been hampered by a lack of efficient preparation methods. A convenient, efficient, and cost-effective platform for the facile synthesis of ketoses is described. This method enables the preparation of difficult-to-access ketopentoses and ketohexoses from common and inexpensive starting materials with high yield and purity and without the need for a tedious isomer separation step.

Natural Deep Eutectic Solvents for Solubility and Selective Fractionation of Bioactive Low Molecular Weight Carbohydrates.

Natural deep eutectic solvents (NADESs) have been shown to be selective and environmentally friendly solvents for the extraction of bioactive compounds. However, studies on the solubility of low-molecular-weight carbohydrates (LMWCs) in NADESs are scarce. In this work, new solubility data of LMWCs in NADESs are provided and a new approach based on the use of these solvents for the efficient fractionation of bioactive carbohydrates was explored for the first time. Several mono- and disaccharides and three NADESs based on choline chloride (ChCl) and different donors (2-ethylene glycol (EtG), glycerol (Gly) and ethanedioic acid dihydrate (Eth)) were considered. While the degradation of carbohydrates, mainly ketoses, was detected with ChCl:Eth due to its acidic nature, ChCl:EtG and ChCl:Gly were found to be useful alternatives for selectively separating bioactive ketoses and their corresponding aldoses (e.g., lactulose/lactose and tagatose/galactose) present in equimolar binary mixtures. In addition, the usefulness of ChCl:EtG for the selective enrichment of lactulose to be used as food ingredient or nutraceutical was proven (from a 25% in the reaction mixture to a 56% in the purified sample). NADESs could be used for the selective fractionation of value-added carbohydrates from interfering sugars for several applications, including food science, engineering or pharmaceuticals.

Cascade synthesis of rare ketoses by whole cells based on L-rhamnulose-1-phosphate aldolase.

Dihydroxyacetone phosphate (DHAP)-dependent aldolases demonstrate important values in the production of rare ketoses due to their unique stereoselectivities. As a specific example, we developed an efficient Escherichia coli whole-cell biocatalytic cascade system in which rare ketoses were produced from abundant glycerol and catalyzed by four enzymes based on L-rhamnulose-1-phosphate aldolase (RhaD). For the semicontinuous bioconversion in which D-glyceraldehyde was continuously added, once D-glyceraldehyde was consumed, the final yields of D-sorbose and D-psicose were 15.30 g/L and 6.35 g/L, respectively. Moreover, the maximum conversion rate and productivity of D-sorbose and D-psicose were 99% and 1.11 g/L/h at 8 h, respectively. When L-glyceraldehyde was used instead of the D-isomer, the final yield of L-fructose was 16.80 g/L. Furthermore, the maximum conversion rate and productivity of L-fructose were 95% and 1.08 g/L/h at 8 h, respectively. This synthetic platform was also compatible with other various aldehydes, which allowed the production of many other high-value chemicals from glycerol.

Labeling monosaccharides with stable isotopes.

Chemical and chemi-enzymic methods are discussed for the preparation of monosaccharide isotopomers that are singly and multiply labeled with (13)C, (2)H, (17/18)O, and (15)N isotopes. The discussion focuses primarily on chemical methods to incorporate stable isotopes into monosaccharides and not on methods to assemble labeled monosaccharides into more complex biomolecules such as oligosaccharides or oligonucleotides. Two primary isotope insertion reactions are considered: cyanohydrin reduction (CR) and molybdate-catalyzed epimerization (MCE). Both methods are described in detail, including discussions of their mechanistic features, and their advantages and limitations. The integration of CR, MCE, and other chemical synthetic processes with enzyme-mediated synthesis is also discussed to illustrate how a wide range of singly and multiply labeled monosaccharides can be prepared for subsequent use in the assembly of more complex isotopically labeled biomolecules.

Indicadores bioquímicos e hormonais de casos naturais de toxemia da prenhez em ovelhas / Biochemical and hormonal indicators of natural cases of pregnancy toxaemia of in sheep

Toxemia da prenhez é considerada um transtor-acordo com a resolução clínica dos animais, alta hospitano metabólico de grande impacto econômico na produção lar (G1) e aqueles que morreram (G2). A manifestação cli-de ovinos, porém as particularidades de repercussão sis-nica da doença foi observada no período do pré-parto em têmicas deste distúrbio ainda são pouco esclarecedoras. O 100 por cento dos animais, destes 66,2 por cento (n=51) receberam alta presente estudo teve por objetivo avaliar o perfil bioquí-clínica e 33,8 por cento (n=26) morreram. Dos casos de toxemia mico e hormonal de 77 ovelhas com diagnóstico clínico de da prenhez estudados havia gestação múltipla em 55,8 por cento. toxemia da penhez e comparar os achados laboratoriais de Dentre os parâmetros estudados, cortisol, uréia, AST e CK estavam mais elevados no G2 em relação ao G1 com diferenças significativas (P0,05). Não ocorreram alterações nas taxas de colesterol e triglicerídios. Houve redução nos índices da insulina, não havendo diferenças entre G1 e G2 (P>0,05). Todas as ovelhas apresentaram cetonúria e acidúria.

Toxemia of pregnancy is a metabolic disorder with considerable economic impact on the production of sheep. However, the particularities of the systemic repercussion of the disorder have not yet been fully clarified. The aim of the present study was to assess the biochemical and hormonal profile of 77 ewes with a clinical diagnosis of toxemia of pregnancy and to compare the laboratory findings based on the clinical outcome: discharge (G1) or death (G2). The clinical manifestation of the disease was observed in the pre-birth period in 100 percent of the ewes, from which 66.2 percent (n=51) were discharged and 33.8 percent (n=26) died. A total of 55,8 percent of the cases were of multiple pregnancies.. Considering the parameters analyzed, cortisol, urea, AST and CK were significantly higher in G2 in comparison to G1 (p<0.05). An increase was found in the concentration of plasma glucose, fructosamine, albumin, creatinine, ß-hydroxybutyrate, non-esterified fatty acids and L-lactate, with no statistically significant differences between groups (p>0.05). No changes were found in cholesterol or triglycerides. A reduction in insulin levels was found, with no statistically significant difference between groups (p>0.05). All ewes exhibited ketonuria and aciduria.