The Methyl Ethers of l-Arabinose

Since L-arabinose is a constituent unit of many natural products a number of methylated derivatives of this sugar have been isolated by the hydrolysis of methylated polysaccharides. Thus methylated peanut (Arachis hypogea) araban and sugar beet araban give trimethyl-L-arabofuranose, 2,3-dimethyl-L-arabinose and 2-methyl-L-arabinose in equal proportions.84 From methylated gum arabic trimethyl-L-arabo-furanose and 2,5-dimethyl-L-arabinose have been isolated.85 These same compounds have also been isolated from methylated cherry gum86 and methylated damson gum,87 whereas methylated mesquite gum88 affords 3,5-dimethyl- and 2,3,5-trimethyl-L-arabinose on hydrolysis. 

2-Methyl-L-arabinose has been isolated from the products of hydrolysis of methylated damson gum37 and the araban found associated with pectin.84 88 This sugar has been synthesized by the conversion of methyl /3-L-arabopyranoside to the 3,4-benzylidene derivative (XXIX) which on methylation gave methyl 2-methyl-3,4-benzylidene-/J-L-arabopyrano-side (XXX) from which the desired 2-methyl ether was obtained by hydrolysis.40 

Methyl-5-tosyl-L-arabofuranosides (a/3 mixture) (XXXI) on condensation with acetone containing hydrogen chloride gave the 1,2-iso-propylidene derivative (XXXII). Methylation gave 1,2-isopropylidene-3-methyl-5-tosyl-L-arabofuranose (XXXIII) from which the tosyl 

The constitution of the product followed from the facts that the derived amide gave a positive Weerman test and that the crystalline lactone underwent the characteristically slow hydrolysis of a furanolactone. 

3-Dimethyl-J arabinose (XXXVI) has been isolated from the products of hydrolysis of methylated araban94 and of methylated damson gum.97 It has been synthesized49 from methyl 5-trityl-L-arabofurano-sides (afi mixture) (XXXV) by methylation with methyl iodide and silver oxide followed by removal of the trityl group by means of hydrogen chloride in chloroform and hydrolysis of the methyl glycosides.  

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