Step-wise flow synthesis of l-ascorbic acid from L-sorbose

Influence of drugs on liver-ascorbic acid in fish

Copper(I) is able to catalyze Huisgen 1,3-dipolar cycloaddition in a "click" fashion. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction presents excellent chemoselectivity and occurs over a wide-range of reaction conditions. It shows tolerance to variation in both pH and solvent polarity, thereby facilitating the ligation of peptides and proteins to produce peptidomimetics and synthetic proteins. In addition, the only product formed is a 1,4-disubstituted-1,2,3-triazole moiety, in many aspects resembling the natural peptide bond, including hydrogen-bonding capability, planarity, distance between the 1 and 4 substituents, and conformational restriction of the peptide backbone; thus the triazole-backbone-modified peptide, in which a triazole replaces the amide bond, may be anticipated to present a secondary structure similar to that of its natural counterpart. This Focus Review describes the scope and applications of copper(I)-catalyzed alkyne–azide cycloaddition in synthetic peptide/protein chemistry.

1. The synthesis of l-ascorbic acid from either d-glucuronolactone or l-gulonolactone by liver microsomes of rats is decreased under conditions of hypervitaminosis A; under hypervitaminosis D the synthesis from d-glucuronolactone is increased and that from l-gulonolactone is not affected. 2. The microsomal conversion of l-gulonolactone into l-ascorbic acid is impaired in liver tissues of rats made deficient with respect to either vitamin A or vitamin D when compared with the controls maintained on stock diet.

The platinum-catalyzed oxidation of alcohols with molecular oxygen in aqueous medium was discovered one and a half centuries ago [ 1,2]. The method has been improved with the general development of heterogeneous catalysis. At the beginning of this century it was found [ 31 that not only platinum, but dispersed palladium was also a good catalyst for the reaction. Platinum on various supports was tested and compared by Heyns [ 41 when he extended the method to the synthesis of L-ascorbic acid. The next milestone was the promotion of platinum metals with heavy metals such as Bi or Pb to overcome the deactivation problems and change the direction (selectivity) of the reaction [ 5-71. The present review will be focused on the application of biand multi-metallic catalysts in the aqueous phase oxidation of alcohols with molecular oxygen. The reactions discussed are the transformation of primary alcohols to aldehydes or carboxylic acids, and secondary alcohols to ketones. Special attention will be given to the various reasons for the loss of catalytic activity and the role of promoters in the suppression of deactivation. A detailed discussion of the earlier results of alcohol oxidation on platinum metal catalysts, especially in the field of carbohydrate chemistry, can be found in previous reviews [ 818 1. The mild reaction conditions and high selectivity in the oxidation of polyols made the method very attractive for carbohydrate chemistry. As an example, the catalytic route for the oxidation of D-glucose to D-gluconic acid based on the application of promoted Pd catalysts in aqueous alkaline medium can compete economically with the generally applied biochemical oxidation [ 19,201. Various chelating agents, detergent builders or food additives may be prepared by this way from relatively cheap starting materials of natural origin.

L-Ascorbic acid synthesis in a soluble enzyme system from rat-liver microsomes

Pd nanorods (PdNRs) have recently come to attention due to their wide array of applications. The green synthesis of PdNR with a relatively high yield and high aspect ratio is challenging. A continuous millifluidic flow reactor (CMFR) has been explored to precisely control mass and heat transfer as well as mixing in the PdNR synthesis processes. CMFRs demonstrate a few drawbacks, such as the presence of parabolic velocity profile in the laminar flow of the reaction solution, causing uneven axial residence time distribution. The CMFRs are likely to show irreversible fouling, which may cause the product quality to deteriorate or result in the channel being clogged. These shortcomings can be avoided or minimized using a segmented millifluidic flow reactor (SMFR) that consists of the solution forming a train of individual segments in another inert medium. This study explores the use of a sustainable reducing agent (l-ascorbic acid) in the presence of potassium bromide (KBr) as the capping agent and poly(vinyl pyrrolidone) (PVP) as the stabilizing agent for PdNR synthesis in an SMFR employing compartmentalized flow of a reaction solution, in which liquid segments consisting of a reaction solution will be immersed in the steam generated by boiling of the solvent water. The effect of reaction parameters such as reagent concentration has been studied on the size and morphology of synthesized Pd nanostructures. A kinetic study has been conducted to calculate the rate of reduction that can be used as a quantitative measure for manipulation of the type and relative concentration of initially formed seeds. It has been shown that the initial reduction rate during the first 45 min of residence time of the millifluidic reactor is about 66% faster compared to the rest of the reaction. A filtration procedure has been utilized to separate Pd nanostructures other than nanorods synthesized in the SMFR.

714. A distinction between two enzyme induction effects: De Matteis, F. (1964). Increased synthesis of l-ascorbic acid caused by drugs which induce porphyria. Biochim. biophys. Acta82, 641

Phenylhydrazine administered to rats at a dose of 4 mg/100g body weight per day for 3 days, diminished the total ascorbic acid level in liver, kidney and spleen tissues. The total ascorbic acid level in blood was, however, elevated after phenylhydrazine treatment. The other effects of phenylhydrazine treatment were a reduction in the activities of Dglucuronoreductase, L-gulonooxidase, dehydroascorbatase and uronolactonase in liver. The dehydroascorbatase activity in kidney was also diminished after phenylhydrazine treatment. The changes in the activities of liver enzymes were found to be accompanied by a diminution in the level of reduced ascorbic acid and an elevation in the dehydroascorbic acid level. It was concluded that the biosynthesis of L-ascorbic acid from both Dglucuronolactone and L-gulonolactone as substrates, was reduced in phenylhydrazine-treated rats. The degradation of L-ascorbic acid by both liver and kidney was diminished by the phenylhydrazine treatment. It was further concluded that phenylhydrazine-treated rats tried to conserve the level of substrate for the synthesis of L-ascorbic acid, by reducing the hydrolytic cleavage of D-glucuronolactone. The elevated blood ascorbic acid level under the same condition was ascribed to the diminished catabolism of L-ascorbic acid.

SummaryDecrease of L-ascorbic acid synthesis by the liver microsomes of C57/BL mice bearing Ehrlich ascites carcinoma for 13 days could be accounted for by decreased food intake of the animals. On the other hand, the decreased ascorbic acid synthesis by liver microsomes from C3H/Crgl mice infected with Gardner lymphosarcoma was due neither to inanition nor to gross infiltration of the liver with tumor cells but to a decrease in the L-gulono dehydrogenase activity. There was no change in the synthesis of ascorbic acid by liver microsomes from C57/ BL mice made immune to Ehrlich ascites carcinoma cells, although the amount of mi-crosomal protein per gram liver was significantly increased. Neither was there a significant inhibition in the synthesis by the liver microsomes of C3H/Crgl bearing T-15 hepa-toma or of A/HC mice bearing L No. 2 lymphoma.