Carbohydrates periodate

Carbohydrates—periodic acid— Schiff (use ref. 12 controls) Nucleic acids—azure bluea... 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

Periodic acid cleavage of vicinal diols is often used for analytical purposes as an aid m structure determination By identifying the carbonyl compounds produced the con stitution of the starting diol may be deduced This technique finds its widest application with carbohydrates and will be discussed more fully in Chapter 25... 

Cleavage reactions of carbohydrates also occur on treatment with aqueous base for prolonged periods as a consequence of base catalyzed retro aldol reactions As pointed out m Section 18 9 aldol addition is a reversible process and (3 hydroxy carbonyl com pounds can be cleaved to an enolate and either an aldehyde or a ketone... 

Periodic acid oxidation (Section 15 12) finds extensive use as an analytical method m carbohydrate chemistry Structural information is obtained by measuring the number of equivalents of periodic acid that react with a given compound and by identifying the reaction products A vicinal diol consumes one equivalent of penodate and is cleaved to two carbonyl compounds... 

When three contiguous carbons bear hydroxyl groups two moles of periodate is consumed per mole of carbohydrate and the central carbon is oxidized to a molecule of formic acid... 

Vicinal diol and a hydroxy carbonyl functions in carbohydrates are cleaved by periodic acid Used analytically as a tool for structure determination... 

Even higher organisms can be used for the production of labeled compounds. Plants, tobacco, or Canna indica for example, when grown in an exclusive atmosphere of radioactive carbon dioxide, [ 002], utilize the labeled precursor as the sole source of carbon for photosynthesis. After a suitable period of growth, almost every carbon atom in the plant is radioactive. Thus, plants can serve as an available source of C-labeled carbohydrates (9). 

Reproducibility of separation for a Dextran T-500 sample was tested on a semipreparative Sephacryl system S-500/S-1000 (65 + 95x1.6 cm) over a period of 6 months. The elution profiles of Dextran T-500 could be superimposed with deviations in the elution axis of 3 ml ( 1 fraction), and deviations in carbohydrate content within 5% referring to the maximum value at V,e, = 213 ml (Fig. 16.8). 

FIGURE 16.8 Dextran T-SOO ( ) separated on Sephacryl S-SOO/S-IOOO (60 + 9S x 1.6 cm) sampled in 3-ml fractions normalized (area = 1.0) eluogram profiles (ev) constructed from an off-line determined mass of carbohydrates within each of the fractions flow rate 0.42 ml/min Vexd = 126 ml, V,o, = 273 ml eluent 0.005 M NaOH reproducibility of results over a period of 6 months 5% of ev maximum and 3 ml ( 1 fraction). 

At one stage in our project we were surprised to learn that some workers had found difficulties in preparing the tetroxide from the dioxide, until we experienced the same trouble. This problem has now been resolved (3). Ruthenium dioxide is available commercially in both anhydrous and hydrated forms, the former being obtained by direct oxidation of ruthenium metal and the latter by a precipitation process. Only the hydrated form is oxidizable under the mild conditions (2,3) that we use and this form must be specified when purchasing the dioxide. It is noteworthy that the dioxide recovered from carbohydrate oxidations is always easily re-oxidized to the tetroxide. The stoichiometry has been determined of both the oxidation of the dioxide by periodate and reduction of the tetroxide which results on oxidation of an alcohol. 

Starting from the appropriately substituted carbohydrates (e.g., II), 1,5-dialdehydcs are obtained by periodate oxidation. Subsequent double Henry reaction33 with nitromethane furnishes a variety of nitro-substituted carbohydrate derivatives. In most cases pure stereoisomers are obtained by crystallization of the reaction mixture3. 

Periodic samples were taken at the starting point after introducing the inocula, on the fust, second and thud day of each experimental ran. The optical cell density, COD, carbohydrate concentration and dissolved oxygen were monitored for various air flow rates. The COD was measured by the closed reflux colorimetric method at 600 nm with a spectrophotometer using potassium dichromate as a reducing reagent.7 All organic chemicals... 

When a-glucosidase activity is inhibited, carbohydrate digestion is prolonged and takes place further along the intestinal tract. This in turn delays and spreads the period of glucose absorption, which reduces the extent of the postprandial rise in blood glucose concentrations. The effectiveness of a-glucosidase inhibitors is dq en-dent on the consumption of a meal rich in complex carbohydrate. 

Between academic terms in the period 1929-1933, he traveled regularly to the London School of Hygiene and Tropical Medicine to participate, on a part-time basis, in research at Professor Raistrick s laboratory on the complex carbohydrates of molds and bacteria. Stacey s Ph.D. thesis, Investigation into the Ascent of The Series and High Polymers in the Carbohydrate Group, based on work carried out in both Birmingham and London, was presented in May 1932. 

Periodate Oxidation, Acid Hydrolysis, and Structure-Activity Relationships of Human Pituitary, Follicle-Stimulating Hormone, and Human Chorionic Gonadotrophin, J. F. Kennedy, M. F. Chaplin, and M. Stacey, Carbohydr. Res. 36 (1974) 369-377. 

---