Mycolic acids from 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. ... 

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. 

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. ... 

The cord factor from Mycobacterium tuberculosum could be permethylated with methyl iodide and sodium hydride in a diethyl ether-dimethylformamide mixture in the presence of a molecular sieve.It was confirmed that the mycolic acids were esterified at the 6,6 positions of the aa-trehalose molecule. Using 4-palmitoyl-D-glucose as a model compound, it was verified that acyl migration did not occur in this system. 

An important example of a carbohydrate ester is the so-called cord factor from Mycobacteria spp. This contains an ester of the disaccharide, trehalose, with two molecules of a complex acid, mycolic acid. The latter is a general term embracing a whole series of fatty acids containing 60-90 carbons. They are hydroxy fatty acids which differ in their degree of unsaturation and chain branching (Section 1.9). In the example given in Fig. 2.6 the mycolic acid is the 60-carbon compound found in Mycobacterium smeg-matis. 

In addition to the wall-bound mycolic acids three other important lipids are loosely associated with the murein layer. The st of these is the cord factor , so called since it was associated with the formation of cords , parallel rows forming characteristic serpentine strands demonstrable when smears of liquid grown cultures of mycobacteria are examined under the microscope. The cord factor of M. tuberculosis can be readily extracted from viable bacteria with organic solvents and identified as trehalose-6,6 -dimycolate. The mycosides constitute the second group of readily extractable lipids, gycosidically linked to the para position of a phenol... 

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