Rhamnopyranose isolation

The same compounds isolated by Brigl and coworkers,9 who started from 2,3,4,5,6,7-hexa-O-benzoyl-D-gZt/cero-D-gaZacto-heptononitriIe, were obtained from the ammonolysis of 1,2,3,4,6-penta-O-benzoyl-a-D-mannose,19 namely, a mixture of l,l-bis(benzamido)-l-deoxy-D-mannitol (12) and N-benzoyl-D-mannopyranosylamine (13). Likewise, 1,2,3,4-tetra-O-benzoyl-L-rhamnopyranose,10 having the same steric relationship at the asymmetric carbon atoms as the perbenzoate of D-mannose, also afforded an N-benzoyl-L-rhamnopyranosylamine directly. 

Many polysaccharides contain L-rhamnose as a constituent, and various methylated L-rhamnoses have therefore been isolated by the hydrolysis of methylated gums and mucilages. For example, trimethyl-L-rhamnopyranose has been isolated from methylated gum arabic86 and from the methylated polysaccharide from the somatic portion of the cells of Mycobacterium tuberculosis,26 and in both these polysaccharides L-rham-nopyranose residues evidently occupy terminal positions in the molecule. 

Trimethyl-L-rhamnopyranose has been isolated from methylated gum arabic on hydrolysis, and from the specific somatic polysaccharide of M. tvbercubsis.tb This derivative was originally prepared either by the direct methylation of the free sugar or of the methyl pyranoside, followed by hydrolysis.67 Oxidation gave L-arabo-trimethoxyglutaric acid. 

Five different crystalline products were separated and characterized from the reaction mixture obtained from the condensation of L-rhamnose with paraformaldehyde. None of the products isolated corresponded to the acetal isolated earlier by Lobry de Bruyn and Alberda van Ekenstein. The expected 1,2 3,5-di-0-methylene-a-L-rhamnofuranose was identified on graded hydrolysis, this gave the 3,5-0-methylene acetal. However, the possibility of the 3,4-0-methylene-L-rhamnopyranose structure was not eliminated. The main product was 3,4-0-(oxidodimethylene)-L-rhamnose a smaller yield of 2,3-0-(oxidodimethylene)-a-L-rhamnose was obtained. 

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