Carbon transfer

Triturate 20 g. of dry o-toluidine hydrochloride and 35 5 g. of powdered iodine in a mortar and then grind in 17 -5 g. of precipitated calcium carbonate. Transfer the mixture to a conical flask, and add 100 ml. of distilled water with vigorous shaking of the flask. Allow the mixture to stand for 45 minutes with occasional agitation, then heat gradually to 60-70° for 5 minutes, and cool. Transfer the contents of the flask to a separatory funnel, extract the base with three 80 ml. portions of ether, diy the extract with anhydrous calcium chloride or magnesium sulphate, and remove the excess of solvent. The crude 5-iodo-2-aminotoluene separates in dark crystals. The yield is 32 g. Recrystallise from 50 per cent, alcohol nearly white crystals, m.p. 87°, are obtained. 

Sodium salt of eosin. Grind together in a mortar 12 g. of eosin with 2 g. of anhydrous sodium carbonate. Transfer the mixture to a 250 ml. conical flask, moisten it with 10 ml. of rectified spirit, add 10 ml. of water and warm on a water bath, with stirring, until the evolution of carbon dioxide ceases. Add 50 ml. of ethyl alcohol, heat to boiling, and filter the hot solution through a fluted filter paper (supported in a short-stemmed funnel) into a beaker, and allow to stand overnight. Filter ofiF the browiiish-red crystals of sodium eosin, wash with a little alcohol, and dry. The yield is 10 g. 

Subsequent knowledge of the stmcture, function, and biosynthesis of the foHc acid coenzyme gradually allowed a picture to be formed regarding the step in this pathway that is inhibited by sulfonamides. The biosynthetic scheme for foHc acid is shown in Figure 1. Sulfonamides compete in the step where condensation of PABA with pteridine pyrophosphate takes place to form dihydropteroate (32). The amino acids, purines, and pyrimidines that are able to replace or spare PABA are those with a formation that requkes one-carbon transfer catalyzed by foHc acid coenzymes (5). 

S. W.. Simard. D. M. Durall, and M. D. Jones, Carbon allocation and carbon transfer between Betula papyrtfera and Psuedotsuga nienziesii seedlings using a C pulselabelling method. Plant Soil /9/ 41 (1997). 

Sodium Salt of Eosin.—Grind 6 g. of eosin with 1 g. of anhydrous sodium carbonate, transfer the mixture to a moderate-sized, widenecked, conical flask, moisten with a little alcohol, add 5 c.c. of water, and warm on the water bath until evolution of carbon dioxide ceases. To the aqueous solution of the sodium salt thus obtained now add 20 g. of alcohol, heat to boiling, and filter the hot solution. From the cooled filtrate there separate beautiful brownish-red crystals with metallic lustre, often only after long standing. Collect them at the pump and wash with alcohol. 

TK =transketolase TA = transaldolase AL = aldolase Simplest solution to the problem of pentoses (only reactions of carbon transfer are indicated). 

Figure 15.2 Structural formula of tetrahydrofolate and representation of derivatives involved in single carbon transfer. The tetrahydrofolate is always part of a complex with several glutamate residues. The parent compound, pteroylglutamate (folate) lacks four hydrogen atoms, one each from carbon atoms 5, 6, 7 and 8. Tetrahydrofolate can exist in any one of three oxidation states, as shown they are interconvertible through oxidereduction reactions. Each plays a individual and different role is synthesis of key compounds (See below).

Figure 20.8 Summary of pathways for de novo synthesis of purine and pyrimidine nucleotides. C represents transfer of a single carbon atom (a one-carbon transfer). Details are provided in Appendix 20.1. IMP - inosine monophosphate. For thymi-dylate synthesis, see Figure 20.12a.

Tetrahydrofolic acid (THF) Loose Folic acid Methyl group donor in one-carbon transfer reactions critical in biosynthesis of purines and pyrimidines... 

By one-carbon transfer by enzymes that use tetrahydrofolate (THF) coenzymes. 

C. Deoxythymidylate (dTMP) is formed from 2 -deoxyuridylate (dUMP) in a one-carbon transfer by thymidylate synthetase (Figure 10-5). 

The donor coenzyme for the one-carbon transfer is AT, Ar °-methylene tetrahydrofolate (A A °-methylene THF) simultaneous reduction to a methyl group leaves dihydrofolate (DHF) as byproduct. 

In their approach of applying transition matrices for the description of the carbon transfer in metabolic networks, Wiechert et al. [16] defined the labeling pattern of a molecule via cumulated isotopomer (cumomer) fractions, whereby the isotopomers belonging to the same cumomer fraction share labelings at specific carbon positions. For a Cj compound, three 1-cumomer fractions... 

Because of their ring-chain tautomeric character, tetrahydro-l,3-oxazines can be used as aldehyde sources in acid-catalyzed condensation reactions involving the carbon transfer via the open forms. This approach is especially advantageous in those cases where the aldehydes required for the condensations are unstable or difficult to access <2003EJ03025>. 

An asymmetric carbon-transfer reaction was also performed by using 2-(/>-tolyl)sulfmylmethyltetrahydro-l,3-oxa-zine 143 as the chiral aldehyde equivalent in the Pictet-Spengler ring closure with tryptamine, but only moderate diastereoselectivity ( 40% de) was observed in favor of the (l/ )-tetrahydro-/3-carboline 165, and the enantiopure main product could be isolated only in low yield (Scbeme 26) <2001H(55)1937, 2004T9171>. 

I I 3. The answer is c. (Hardman, pp 1243-1247.) Antimetabolites of folic acid such as methotrexate, which is an important cancer chemotherapeutic agent, exert their effect by inhibiting the catalytic activity of the enzyme dihydrofolate reductase. The enzyme functions to keep folic acid in a reduced state. The first step in the reaction is the reduction of folic acid to 7,8-dihydrofolic acid (FH2), which requires the cofactor nicotinamide adenine dinucleotide phosphate (NADPH). The second step is the conversion of FH2 to 5,6,7,8-tetrahydrofolic acid (FH ). This part of the reduction reaction requires nicotinamide adenine dinucleotide (NADH) or NADPH. The reduced forms of folic acid are involved in one-carbon transfer reactions that are required during the synthesis of purines and pyrimidine thymidylate. The affinity of methotrexate for dihydrofolate reductase is much greater than for the substrates of folic acid and FH2. The action of... 

Tetrahydrofolate cofactors participate in one-carbon transfer reactions. As described earlier in the discussion of vitamin B12, one of these essential reactions produces the dTMP needed for DNA synthesis. In this reaction, the enzyme... 

Prepare a thoroughly ground mixture of 1 g of the cadmium sulphide obtained previously, 5 g of sulphur, and 5 g of potassium carbonate. Transfer the mixture into a porcelain crucible, and fuse it at the lowest possible temperature. 

Preparation of Tin by Reduction with Charcoal. Prepare a mixture of 2.5 g tin(IV) oxide, 1 g of charcoal, and 0.5 g of ammonium carbonate. Transfer the mixture into a crucible and roast it in a muffle furnace. Write the equation of the reaction. Transfer the obtained bead into another crucible and fuse it with borax. After cooling, break the crucible and wash off the borax with hot water. 

FIGURE 18-16 Some enzyme cofactors important in one-carbon transfer reactions. The nitrogen atoms to which one-carbon groups are attached in tetrahydrofolate are shown in blue. 

Tetrahydrobiopterin, another cofactor of amino acid catabolism, is similar to the pterin moiety of tetrahydrofolate, but it is not involved in one-carbon transfers instead it participates in oxidation reactions. We consider its mode of action when we discuss phenylalanine degradation (see Fig. 18-24). 

After removal of their amino groups, the carbon skeletons of amino acids undergo oxidation to compounds that can enter the citric acid cycle for oxidation to C02 and H20. The reactions of these pathways require a number of cofactors, including tetrahydrofolate and 5-adenosylmethionine in one-carbon transfer reactions and tetrahydrobiopterin in the oxidation of phenylalanine by phenylalanine hydroxylase. 

The amino acid and nucleotide biosynthetic pathways make repeated use of the biological cofactors pyridoxal phosphate, tetrahydrofolate, and A-adenosylmethionine. Pyridoxal phosphate is required for transamination reactions involving glutamate and for other amino acid transformations. One-carbon transfers require S-adenosyhnethionine and tetrahydrofolate. Glutamine amidotransferases catalyze reactions that incorporate nitrogen derived from glutamine. 

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