Alkylation reactions biosynthesis

Figure 22.7 The biosynthesis of indolmycin from indolylpyruvate occurs through a pathway that includes an alkylation reaction of a short-lived enolate ion intermediate.

Some sugar residues in bacterial polysaccharides are etherified with lactic acid. The biosynthesis of these involves C)-alkylation, by reaction with enol-pyruvate phosphate, to an enol ether (34) of pyruvic acid, followed by reduction to the (R) or (5) form of the lactic acid ether (35). The enol ether may also react in a different manner, giving a cyclic acetal (36) of pyruvic acid. 

Experiments have been carried out to mimic the reactions of model systems for coenzyme F430 that is involved in the terminal step in the biosynthesis of methane, and that is able to dechlorinate CCI4 successively to CHCI3 and CH2CI2 (Krone et al. 1989). Nickel(I) isobacteriochlorin anion was generated electrolytically and used to examine the reactions with alkyl halides in dimethylformamide (Helvenston and Castro 1992). The three classes of reaction were the same as those observed with Fe(II) deuteroporphyrin IX that have already been noted. 

Transfer of a phosphocholine residue to the free OH group gives rise to phosphatidylcholine (lecithin enzyme l-alkyl-2-acetyl-glycerolcholine phosphotransferase 2.7.8.16). The phosphocholine residue is derived from the precursor CDP-choline (see p. 110). Phos-phatidylethanolamine is similarly formed from CDP-ethanolamine and DAG. By contrast, phosphatidylserine is derived from phosphatidylethanolamine by an exchange of the amino alcohol. Further reactions serve to interconvert the phospholipids—e.g., phosphatidylserine can be converted into phosphatidylethanolamine by decarboxylation, and the latter can then be converted into phosphatidylcholine by methylation with S-adenosyl methionine (not shown see also p. 409). The biosynthesis of phosphatidylino-sitol starts from phosphatidate rather than DAG. 

Reaction type 6C (Table 10-1) occurs during the biosynthesis of leucine and valine (Fig. 24-17). The rearrangement is often compared with the nonenzy-matic acid-catalyzed pinacol-pinacolone rearrangement in which a similar shift of an alkyl group takes place (Eq. 13-57). The enzyme-catalyzed rearrangement... 

H,6H-Purine, l,7-dimethyl-6-oxo-UV spectra, 5, 517 7H,8H-Purine, 8-oxo-UV spectra, 5, 517 Purinecarboxamides reactions, 5, 550, 551 Purinecarboxylic adds reactions, 5, 550 Purine-6-carboxylic acids synthesis, 5, 593 Purine-8-carboxylic acids synthesis, 5, 593 Purine nucleotides biosynthesis, 1, 87-88 Purine[9,8-a]quinolines, 5, 566 Purines, 5, 499-605 aldehydes reactions, 5, 549 synthesis, 5, 593 alkylation, 5, 505, 528-538 amination, 5, 541-542 anions... 

In ergosterol biosynthesis, side chain alkylation of lanosterol normally takes place to build 24-methylenedihydrolanosterol, which itself is then the substrate for demethylation reactions at and C. The C -demethylation has been studied in detail. It is an oxidative demethylation catalyzed by a cytochrome P -system. The first step involved in this reaction is the hydroxylation of the Cj -methy1-group to form the C -hydroxymethyl derivative. A second hydroxylation and loss of water lead to the C -formyl intermediate, which is hydroxylized a third time to form the corresponding carboxylic acid. Decarboxylation does not directly take place, but proceeds instead by abstraction of a proton from C, followed by elimination and formation of a A 4-double bond. The NADPH-dependent reduction of the A14 -double bond finishes the demethylation reaction. Subsequently, demethylation at has to take place twice, followed by a dehydrogenation reaction in A" -position and isomerization from A8 to A7 and A24(28) to A22. respectively. 

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