Of L-rhamnose

Figure 10.26 Short enzymatic synthesis of L-fucose and hydrophobic analogs, and of L-rhamnose, by aldolization-ketol isomerization, including kinetic resolution of racemic hydroxyaldehyde precursors.

Analysis of S23 showed that it is composed52 of residues of L-rhamnose (35), D-galactose (31), and D-glucose (32%). Some phosphorus (3%) was also found. Immunochemical studies indicated that the polymer contains terminal L-rhamnosyl groups. 

L-Rhamnose isomerase catalyzes the interconversion of L-rhamnose and L-rhamnulose. L-Rhamnose, a deoxy sugar, is found in bacteria and plants and it plays an essential role in many pathogenic bacteria. The pathway for the metabolism of this sugar does not exist in humans, and this makes enzymes of this pathway attractive targets for therapeutic intervention. " Rhamnose isomerase from E. coli is a tetramer of (/ /a)8-barrels similar to xylose... 

This enzyme [EC 5.3.1.14] catalyzes the interconversion of L-rhamnose and L-rhamnulose. 

The first benzoylated nitrile of an aldonic acid was prepared by Brigl, Muhlschlegel and Schinle by benzoylation of the n-manno-n- oZa-heptononitrile the hexabenzoyl derivative was obtained. A series of benzoylated nitriles has recently been prepared by Restelli de Labriola and Deulofeu by treatment of the oximes of L-rhamnose, D-glucose, D-galactose and D-mannose with benzoyl chloride and pyridine. They were the sole products and were obtained in high yields. 

A good separation of L-rhamnose, 2-acetamido-2-deoxy-D-glucose, D-glucose, and 2-amino-2-deoxy-D-glucose, eluted in that order, was obtained by Zeleznick80 on a small column packed with the highly cross-linked, dextran gel Sephadex G-25, with 62 15 25 (v/v) butyl alcohol-M acetic acid-water as the eluant however, the gel functioned more as a support for partition chromatography than as a molecular sieve. 

In addition, the isolation of 4(5)-ethylimidazole (23) from the reactions of L-rhamnose (see Table VI), L-fucose (6-deoxy-L-galactose), and 3-deoxy-L-glyceraldehyde (see Table IX) with aqueous ammonia, led Komoto and Tsuchida39 to believe that the 2-oxobutanal forming the 4(5)-ethylimidazole (23) arose from an aldol reaction of the 3-deoxy-L-glyceraldehyde (formed by dealdolization in the cases of L-rhamnose and L-fucose) with formaldehyde, with subsequent loss of water from the 4-deoxytetrose so formed. 

The comparative study of the n.m.r. spectra of L-rhamnose nucleosides 40a, 40b, and 44 and their 4 -keto derivatives 41a, 41b, and 45 revealed that the conformation changes from 4Ci to C4 on introduction of the carbonyl group.30... 

The L-rhamnulose 1-phosphate aldolase (RhuA EC 4.1.2.19) is found in the microbial degradation of L-rhamnose which, after conversion into the corresponding ketose 1-phosphate 44, is cleaved into 41 and L-lactaldehyde (l-16). The RhuA has been isolated from E. coli [336-339], and characterized as a metallo-protein [194,340,341]. Cloning was reported for the E. coli [342,343] and Salmonella typhimurium [344] genes, and construction of an efficient overexpression system [195,220] has set the stage for crystallization of the homotetrameric E. coli protein for the purposes of an X-ray structure analysis [345]. 

M. Bols, I. Lundt, and E. R. Ottosen, Preparation of 2-, 3-, and 4-deoxy derivatives of L-rhamnose, and derivatives of 2-azido-2-deoxy-L-rhamnose and 2,6-dideoxy-2-fluoro-L-glucose, for use in glycosylation reactions, Carbohydr. Res., 222 (1991) 141-149. 

Fig. 12. Lactonase reactions involved in ascorbate biosynthesis and degradation of L-rhamnose and D-xylose...

Yamase H, Zhao L, Liu H-W (2000) Engineering a hybrid sugar biosynthetic pathway production of L-rhamnose and its implication on dihydrostreptose biosynthesis. J Am Chem Soc 122 12397-12398... 

Pseudomonas aeruginosa, which is composed of L-rhamnose and ( —)-2-hydroxynonane-l-carboxylicacid. Although it is a glycoside of a j3-hydroxy ester, it was reported to be non-reducing to Fehling solution. 

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