Trehalose, acylation

Disaccharides to have been examined are two D-ribofuranosyl-D-ribitols produced from two bacterial capsular polysaccharides, and several aa-trehalose derivatives prepared as model bacterial cord factors [F.D. cationization with cesium iodide gave intense (M + Cs) ions]. The same group of workers have also reported on this method applied to the natural cord factor of Corynebacterium diphtheriae, and they found at least 22 species differing in the chain lengths of the two trehalose acyl substituents. A further report describes the determination of the sites of substitution of the acyl groups.Daunosamine-containing disaccharides have been examined by negative ion, positive ion, chemical ionization, and electron-impact methods. 

Improved selective acylation of 4,6 4, 6 -di-0-benzylidene-a,a-trehalose was achieved in acetone by the following method, in which a gentle liberation of -acyl-imidazole occurs on the conversion of benzotriazolyl-iV-oxytris(dimethylamino)phos-phonium hexafluorophosphate with the carboxylic acid in the presence of triethylamine and addition of imidazole 1199 ... 

If the acylation is carried out in CH3CN, DMF, or HMPA, 2,2 -diester is formed along with the trehalose 2-ester. 

However, a search for similar products in field isolates of M. tuberculosis proved fruitless. The work instead focused on a family of simple acylated trehaloses first reported by Minnikin et al.61 The structures of these acylated trehaloses were elucidated by a combination of GC-MS and H-13C-NMR spectrometry.68... 

PDMS of native LOS-I showed a [M + Na]+ ion at m/z 1823, confirming the presence of one of each of C15, C15 OH, and C25 fatty acids per molecule of LOS and fragment ions of mlz 245.6, 477.3, 706.9, 993.9, and 1282.4 supported the evidence for the structure of LOS-I, showing that the fatty acids are present on the terminal 2-O-methyl-glucose of the trehalose unit. Similarly, for the LOS from the unknown Mycobacterium, the location of the acyl functions was confirmed by using PDMS. Thus, a combination of alkylation and degradation techniques and PDMS may be used simultaneously to establish the nature and position of the acyl functions on the lipo-oligosaccharides. 

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. 

The purification procedure of 6,6 -esters of OMf-trehalose from Coryne-bacterium diphtheria has been modified and the products were analysed by m.s. of the permethylated derivative.The constituent fatty acids have been extensively examined and the detailed structure of the major acids have been confirmed by a variety of techniques. Novel glycolipids in the cord factor fraction from C. diphtheria were a 6,6 -bis(3-oxo-acyl)-o a -D-trehalose and a 6, 6 -mixed ester of aa-trehalose with the 3-oxo-acyl group and a corynomycolic acid. The metabolic implications of these structural studies suggest that condensation of the common fatty acids by a Claisen-like process via the oxo-ester pathway may not be the only pathway for the synthesis of the cord factors. 

In the permethylatlon analysis of trehalose glycolipids such as cord factor and 6- -mycolyl-a,a-trehalose, various standard reagents proved unsatisfactory due to ester cleavage, but the method of Ciucanu and Kerek (Vol.18, p.50 powdered NaOH-Mel-DMSO) gave excellent results, only lower acyl groups such as acetyl being cleaved. 6,6 -Di- -methyl-a,a-trehalose was obtained from the... 

The reaction of D-glucose diethyl dhhioacetal with addic acetone fiimished the two diacetonides 6 and 7 in the ratio 3 1 thdr structures which were proposed thirty years ago without proof (P.A.J. Gorin, Can. J. Chem., 1965, 43, 2078) have now been firmly established with the help of extensive n.m.r. spectroscopic analysis. Experimental details fi)r the one-pot preparation of l,2-0-isopropylidene-a-l> xylofiiranose in 80% yield fiom D-xylose have beoi published/ 2, 3 4,6 ,4, 6 -Tri-0-cyclohcxylidene-(X,a -trehalose was an important synthetic precursor of mycobacterial 2,3-di-O-acyl derivatives of oc,a -trehalose in connection with this preparation the lohe 7iidenation, isopropylidenation, and ethylidenation of this disaccharide by use of ethoj rcydohexane, 2-methoxypropene, and acetaldehyde, respectively, in acidic media have been studied in some detail/... 

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