No abstract

No abstract

The structure of the free lipid A from Rhodomicrobium vannielii ATCC 17100 was elucidated. It consists of a central β‐1′,6‐linked glucosamine disaccharide which is not substituted by phosphate. About 30% of the disaccharide molecules are substituted with mannopyranose in β‐1,4′‐linkage to the non‐reducing glucosamine. The reducing glucosamine can be directly reduced with NaBH4, indicating either that this glucosamine is not substituted at C1 or its substituent has been removed during the preparation of free lipid A or is removed during reduction with NaBH4. The following formula shows the ‘backbone’ structure of the free lipid A from Rm. vannielii ATCC 17100: β‐Manp(1→4)‐β‐GlcpN(1→6)GlcpN. 3‐(R)‐Hydroxyhexadecanoic acid is linked to the amino group of the reducing glucosamine. The residue at the amino group of the non‐reducing glucosamine has not been identified. The hydroxyl groups of the central disaccharide are acylated with 3‐(tetradecanoyloxy)‐tetradecanoic acid, 3‐hydroxytetradecanoic acid, Δ14‐ docosenoic acid (Δ14‐C22:1) and acetyl groups. The hydroxyl groups of the mannose are not substituted.

No abstract

The α‐and β‐forms of permethylated 1,3‐, 1,4‐ and 1,6‐linked N‐acetylglucosaminyl‐N‐acetylglucosaminitol disaccharides have been analysed directly (without hydrolysis or further modifications) by combined gas‐liquid chromatography mass spectrometry. Gas‐liquid chromatography facilitated the separation of the α‐ and β‐isomers of each disaccharide pair. In every case, the respective α‐form was slower than the β‐form. While, additionally, the α‐ and β‐forms of the 1,6‐linked glucosamine disaccharide could be separated from those of the 1,3‐ and 1,4‐linked disaccharides, the α‐ and β‐forms of the latter two could not be resolved from each other with the liquid phases used. All three disaccharides could be readily differentiated and characterized by mass spectrometry, however. Specific fragments for each glucosamine disaccharide could be defined. Therefore, combined gas‐liquid chromatography mass spectrometry allowed an unequivocal determination of the anomeric configuration and the position of the glycosidic linkage in the glucosamine disaccharides.