One-carbon fragment

The one-carbon fragment is ethyl formate. This reaction is important as a method of control since it occurs only on one side of the carbonyl group that is it is regioselective. The reason is that this product can itself enohse in... 

Cleavage of Carbon—Carbon Bonds. Under appropriate conditions, the propanoid side chain in lignin maybe mptured to form three-, two-, or one-carbon fragments. This carbon—carbon fragmentation occurs in a variety of laboratory treatments and technical processes such as in bleaching of chemical pulps with CI2, CIO2, and O2, in microbial degradation (15), and in photooxidation (16). 

Condensed Pyrroles. Pyrroles can be condensed to compounds containing two, three, or four pyrrole nuclei. These are important ia synthetic routes to the tetrapyrroHc porphyrins, corroles, and bile pigments and to the tripyrroHc prodigiosias. The pyrrole nuclei are joiaed by either a one-carbon fragment or direct pyrrole—pyrrole bond. 

D, 2 or the two one-carbon fragments in type D,3, are idenjiicalpin these cases there are thus only two, not three, reagents. Actually all known syntheses pertaining to group D satisfy this condition. This requirement also explains why no example for a fourth imaginable type D,4, for the two imaginable four-component syntheses E,1 and... 

Cyclization of C3N4 Fragments with Two One-Carbon Fragments. 363... 

Folic acid Coenzyme in transfer of one-carbon fragments Megaloblastic anemia... 

B,2 Cobalamin Coenzyme in transfer of one-carbon fragments and metabolism of folic acid Pernicious anemia = megaloblastic anemia with degeneration of the spinal cord... 

Tetrahydrofolate can carry one-carbon fragments attached to N-5 (formyl, formimino, or methyl groups), N-10 (formyl group), or bridging N-5 to N-10 (methylene or methenyl groups). 5-Formyl-tetrahydrofolate is more stable than folate and is therefore used pharma-... 

The major point of entry for one-carbon fragments into substimted folates is methylene tetrahydrofolate (Figure 45-16), which is formed by the reaction of glycine, serine, and choHne with tetrahydrofolate. Serine is the most important source of substituted folates for biosynthetic reactions, and the activity of serine hy-... 

The methylation of deoxyuridine monophosphate (dUMP) to thymidine monophosphate (TMP), catalyzed by thymidylate synthase, is essential for the synthesis of DNA. The one-carbon fragment of methy-lene-tetrahydrofolate is reduced to a methyl group with release of dihydrofolate, which is then reduced back to tetrahydrofolate by dihydrofolate reductase. Thymidylate synthase and dihydrofolate reductase are especially active in tissues with a high rate of cell division. Methotrexate, an analog of 10-methyl-tetrahydrofolate, inhibits dihydrofolate reductase and has been exploited as an anticancer drug. The dihydrofolate reductases of some bacteria and parasites differ from the human enzyme inhibitors of these enzymes can be used as antibacterial drugs, eg, trimethoprim, and anti-malarial drugs, eg, pyrimethamine. 

Function To donate methyl groups to phospholipid, biogenic amines, thymidine, and amino acid biosynthesis To provide one-carbon fragments at the level of formaldehyde and formic acid for purine and pyrimidine biosynthesis Location Most everywhere... 

Connections One-carbon fragments in from serine, glycine, formate, and histidine... 

One-carbon fragments out from SAM, formyl-THF, methylene-THF, and methyl-THF Regulation At individual enzyme level... 

The structural features shown in parentheses or brackets represent the structure of the one-carbon fragment attached to the N5 and N10 of tetrahydrofolate. The bonds to carbon are as shown, but for simplicity all the bonds to N may not be shown. 

Group-transfer reactions often involve vitamins3, which humans need to have in then-diet, since we are incapable of realizing their synthesis. These include nicotinamide (derived from the vitamin nicotinic acid) and riboflavin (vitamin B2) derivatives, required for electron transfer reactions, biotin for the transfer of C02, pantothenate for acyl group transfer, thiamine (vitamin as thiamine pyrophosphate) for transfer of aldehyde groups and folic acid (as tetrahydrofolate) for exchange of one-carbon fragments. Lipoic acid (not a vitamin) is both an acyl and an electron carrier. In addition, vitamins such as pyridoxine (vitamin B6, as pyridoxal phosphate), vitamin B12 and vitamin C (ascorbic acid) participate as cofactors in an important number of metabolic reactions. 

The number of vitamin B 12-dependent reactions is not large. Most of these involve rearrangements of the carbon skeletons of metabolites. Such reactions are important in linking some aspects of fatty acid metabolism to the citric acid cycle. In another form, a vitamin Bi2-derived coenzyme is involved, along with folic acid coenzymes, in the metabolism of one-carbon fragments, including the biosynthesis of methionine. 

Folic acid is a coenzyme involved in the metabolism of one-carbon fragments the methyl, hydroxymethyl, and formyl groups. An inadequate intake of folic acid during pregnancy can result in spina bifida. 

Folic acid the vitamin precursor to a family of coenzymes involved with the metabolism of one-carbon fragments. 

Tetrahydrofolate receives one-carbon fragments from donors such as serine, glycine, and histidine and transfers them to intermediates in the synthesis of amino acids, purines, and thymine—a pyrimidine found in DNA. ... 

The coenzyme forms of folic acid are derivatives of tetrahydrofolic acid, FH4. See Fig. 7. Folic acid functions as a coenzyme in enzyme reactions which involve the transfer of one-carbon fragments at various levels of... 

One-carbon fragments in various oxidation stales are (I) formyl l—CHO) (2) hydroxymethyl l-CHiOH) and (3) methyl t-CHj). The coenzyme forms of folie acid have one of these groups attached to either the 5-N or 10-N of telrahydrofolic acid. One folic acid... 

There are two ionic modes of bond formation where one carbon fragment is nucleophilic (e rich) and the other is electrophilic (e poor). There is one free-radical mode in which each fragment has a single unpaired electron which becomes... 

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