One-carbon compound

We did not explicitly account for the number of carbon atoms because all compounds have the same number of carbons except EG. In the case of EG (Scheme 1), for each molecule of EG formed there is a corresponding one-carbon compound formed as well. 

The chemistry of the major processes of the petrochemical industry, including cracking, reforming, isomerization, and alkylation, is covered in Chapters 2, 4, and 5, respectively. The increasingly important Ci chemistry—that of one-carbon compounds (C02, CO, methane, and its derivatives)—is discussed in Chapter 3 (Synthesis from Ci sources). 

The active form of folic acid, tetrahydrofolic acid (THF), is produced from folate by dihydrofolate reductase in a two-step reaction requiring two moles of NADPH. The carbon unit carried by THF is bound to nitrogen N5 or N10, or to both N5 and N10. THF allows one-carbon compounds to be recognized and manipulated by biosynthetic enzymes. Figure 20.11 shows the structures of the various members of the THF family, and indicates the sources of the one-carbon units and the synthetic reactions in which the specific members participate. 

Now let us consider the synthesis of the monomeric units from which biopolymers are made. How can simple one-carbon compounds such as C02 and formic acid be incorporated into complex carbon compounds How can carbon chains grow in length or be shortened How are branched chains and rings formed ... 

Various bacteria and fungi are able to subsist on such one-carbon compounds as methane, methanol, methylamine, formaldehyde, and formate.192 197 Energy... 

Figure 17-15 One of the serine pathways for assimilation of one-carbon compounds.

From the foregoing you may anticipate that the chemistry of carbon compounds will be largely the chemistry of covalent compounds and will not at all resemble the chemistry of inorganic salts such as sodium chloride. You also may anticipate that the major differences in chemical and physical properties of organic compounds will arise from the nature of the other elements bonded to carbon. Thus methane is not expected to, nor does it have, the same chemistry as other one-carbon compounds such as methyllithium, CH3Li, or methyl fluoride, CH3F. 

In order to understand the bewildering variety of reactions involving tetrahydrofolate, it is essential to realize that in biological systems, one-carbon compounds may exist in five different oxidation states. The most reduced form is methane, CH4, and the most oxidized form is C02. In between these two extremes are methanol (CH3OH), formaldehyde (CH20), and formate (HCOO ). 

Question Are all the above one-carbon compounds involved in Ci metabolism ... 

Two reactions are of special interest thymidylate synthetase (Section 10.3.3) and remethylation of homocysteine to methionine (Section 10.3.4). This latter reaction is central to the control of the metabolism of one-carbon compounds and folate. 

The production of hydrocarbons from CH3OH was achieved for the first time when it was heated (<190°C) in phosphorus pentoxide, polyphos-phoric acid, or combinations thereof.127 About 200 hydrocarbons were obtained in ca. 36—39% yield. The discovery is remarkable because CH3OH does not form an alkene and yet must proceed from a one-carbon compound to multi-carbon units. Two interpretations of the reaction mechanism, based on either the five-co-ordinate carbon atom of Olah or carbene as intermediates, have been proposed.127... 

Nucleotides are synthesized by two types of metabolic pathways de novo synthesis and salvage pathways. The former refers to synthesis of purines and pyrimidines from precursor molecules the latter refers to the conversion of preformed purines and pyrimidines—derived from dietary sources, the surrounding medium, or nucleotide catabolism—to nucleotides, usually by addition of ribose-5-phosphate to the base. De novo synthesis of purines is based on the metabolism of one-carbon compounds. 

Methoxatin 267 is a bacterial co-enzyme that allows the oxidation of methane to more useful one-carbon compounds. The 1,2-dione in the middle ring is the powerhouse of the molecule and can be made from the simpler aromatic compound 268 by oxidation. Oxidative cyclisation of the Z-alkene 269 might give 268. 

TABLE 2.6 Oxidation Number of Carbon in One-Carbon Compounds ... 

---