Cord-factor

Asselineau, J., H, Bloch and E. Lederer Synthesis of Cord-Factor active... 

The chemical synthesis of derivatives and emalogs has long coimnanded much interest, as such compounds are required for the study of structure—activity relationships in the action of trehalases (23,28), may serve as substitutes for 51 in the synthesis of cord-factor analogs to be used as probes in the field of mycobacterial biochemistry (29, 30), and could possibly prove to possess interesting properties as enzyme inhibitors or antibiotic agents. 

Bacteria also contain a very rich variety of glycolipids with unusual structures. Lipid A13 is the site of attachement of the 0-specific chain of Gram (-) bacteria, which constitutes the antigenic lipopolysaccharide [87]. Other members of this family can be quoted, for example glycosyl glycerophospholipids in which the carbohydrate and glycerol moieties are linked by a phosphodiester bond (e.g. GPI anchor 14) [88] or carbohydrate esters (e.g. cord-factor of mycobacteria 15). 

S. Bottle and I. A. Jenkins, Improved synthesis of cord factor analogues, J. Chem. Soc., Chem. Commun. (1984) 385. 

I. D. Jenkins and M. B. Goren, Improved synthesis of cord factor analogues via the Mitsunobu reaction, Chem. Phys. Lipids, 41 (1986) 225-235. 

Lederer E (1976) Cord factor and related trehalose esters. Chem Phys Lipids 16 91-106... 

As concerns the chemistry of these glycolipids, they contain either an eater linkage between the sugar moiety and the lipid moiety, as in cord factor and in wax D of Mycobacteria, or they are glycosides of phenolic alcohols (as in mycoside B) or of inositol (as in the phosphoglycolipids), or they can be linked to the carboxyl group of D-alanine (as in mycoside C). 

The lipid moiety of the glycolipids under consideration is either composed of branched-chain fatty acids (for example, mycolic acids in cord factor and in wax D) or can be a wax formed by the union of a phenolic alcohol with branched-chain fatty acids of the mycocerosic acid type, as in mycosides A and B. In the phosphoglycolipids, simple normal fatty acids have been found, accompanied by some methyl branched acids. 

Four principal types of glycolipid will be considered in the present review (1) cord factor (2) wax D (3) type-specific mycosides and (4) phosphoglycolipids. All recent work on these compounds is a development of the excellent work of Anderson and his school, published between 1926 and 1946. 

The purification and isolation of cord factor was greatly facilitated by its particular delayed toxicity for mice (upon repeated injections of microgram quantities). For detailed reviews on cord factor, see Refs. 25 and 26. 

Isolation of Cord Factor.—In Bloch s first paper, it had been shown that a petroleum-ether treatment of living bacteria extracts a crude lipid having the particular toxicity of cord factor. As the yield in these extractions was rather low, other lipid fractions extracted from whole bacilli were examined and it was found that cord factor is present in preparations of wax C and wax D —principally, however, in the former. 

Pure cord-factor was finally isolated by repeated chromatography on magnesium silicate, silicic acid, and silica gel. From the H37 Rv strain and from BCG, cord factor was obtained as a colorless wax, melting at about 40°, [ ]d -f 30°. 

Chemical Structure of Cord Factor.—A first important clue to the... 

In order to determine which of the hydroxyl groups of trehalose are es-terified with mycolic acid, cord factor was methylated and the methylated cord-factor was then saponified the hexa-O-methyltrehalose thus obtained was hydrolyzed by dilute acid, and from this, a tri-O-methyl-D-glucose resulted which gave only one spot on paper chromatograms this proved that cord factor is symmetrical, that is, that, on each D-glucose moiety, the mycolic acid is esterified with the same-numbered hydroxyl group. 

A painstaking chromatographic and infrared study of the tri-O-methyl-D-glucose obtained from methylated cord-factor then showed that it was... 

Some of these compounds had a certain degree of cord-factor toxicity ... 

As soon as structure (4) was certain for cord factor, efforts were made to prepare 6,6 -diesters of trehalose with mycolic acids, so as to confirm struc-... 

Four methods of synthesis of cord factor and its analogs have been developed. 

The deacetylation of this product with sodium methoxide or hydroxyl-amine (mycolic acid esters react very slowly with hydroxylamine) gives, in rather low yield, a 6,6 -di-0-(3-hydroxy-x-methoxymycolanoyl)trehalose, m.p. 40-42°, [a]D -f 132°, CissHsvoOi 10 CH2 (9b), with an infrared spectrum identical with that of the natural cord-factor the biological activity of this compound was indistinguishable from that of natural cord-factor. ... 

By using a natural mycolic acid (from the strain Test) and Bredereck s compound (10), a 2,3,4,2, 3, 4 -hexa-0-acetyl-6,6 -di-0-mycoloyltre-halose (11), C198H378O23 10 CH2, m.p. 39°, [ ]d -1-44°, was obtained in 90 % yield. Deacetylation with hydroxylamine gave a 6,6 -di-0-mycoloyltre-halose, m.p. 39-40°, [a]n -f33°, having all the physical and biological properties of natural cord-factor. ... 

Variations of the Structure of Natural Cord-factor in Different Strains. —It is known that different strains frequently contain a different assortment of mycolic acids. Thus, it is not astonishing that cord factor of different strains sometimes contains different mycolic acids. It was found that cord factor of a streptomycin-resistant strain of H37-Rv and of the BCG strain contains a methoxyl-free 3, x-dihydroxymycolanoic acid C87H174O4 5 CHj, whereas the virulent, human strain Br vannes contains a cord factor wherein the mycolic acid is a 3-hydroxy-x-methoxy-mycolanoic acid C88H176O4 5 CH2. 

A toxic lipid isolated by Spitznagel and Dubos by extraction of Mycobacteria with monochlorobenzene has been shown to contain cord factor as the only active compound. ... 

Kato and coworkers have made an extensive study of the mechanism of action of cord factor (see p. 210) and have found a significant decrease of the activity of the succinic and malic dehydrogenase systems of the liver of mice, about twenty-four hours after intraperitoneal injection of 0.1 mg. This finding seems to be related to the work of Martin and coworkers, who reported a decrease of succinic dehydrogenase activity in the kidneys of tuberculous guinea-pigs. 

Later, Kato and coworkers found that the injection of cord factor also decreased the activity of some other diphosphopyridine nucleotide -linked dehydrogenases in mouse liver (such as lactic and a-glycerophosphoric dehydrogenase). The decreased enzymic activity was restored by homogenizing the liver of mice (treated with cord factor) with the sucrose extract of normal mouse-liver. The metabolic lesion caused by the injection of cord factor was assumed to be a decrease of a soluble factor affecting the activity of the succinic dehydrogenase system of mouse liver. 

Bloch has found that crude preparations of cord factor show inhibitory effects on the migration of leucocytes. 

The chemistry of cord factor, a toxic lipid of virulent or attenuated Mycobacteria has already been described in detail (see p. 210). It has also been mentioned that at least part of this biological activity can be explained by the action of cord factor on dehydrogenases dependent on diphospho-pyridine nucleotide as described by Kato and coworkers (see p. 231). 

The toxicity of cord factor is of a delayed type five to ten micrograms kill adult mice within 5 to 8 days after injection. Repeated small doses are more toxic than a single large one. The cause of death is unknown extensive pulmonary hemorrhages are the most conspicuous symptom. ... 

A single injection of cord factor, which by itself has no lasting deleterious effects, causes tuberculous infections to progress more rapidly than they otherwise would thus, mice receiving an injection of cord factor prior to infection die sooner than controls their lungs, livers, and spleens contain a greater number of viable tubercle bacilli than do the organs of control animals. 

The enhancing effect of cord factor on murine tuberculosis seems to be specific injections of mycolic acid or of bacterial-wax fractions other than cord factor do not influence the course of experimental tuberculosis. Infections of mice by gram-negative bacteria are not affected by injections of cord factor. ... 

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