Methyl-1,2-dimethoxy succinate

When methyl a-L-sorboside was methylated and the resulting penta-methyl derivative was hydrolyzed, a tetramethyl-L-sorbose was obtained. Oxidation of the latter with nitric acid gave dextrorotatory dimethoxy-succinic acid126 (LVII), from which fact it became evident that a normal pyranoside structure is present in the methyl a-L-sorboside, since this dimethoxysuccinic acid could only have arisen if carbons 4 and 5 were methylated. From a comparison of the rate of hydrolysis of ethyl a-L-sorboside126 with the methyl a-derivative the authors assumed that it... 

In a continuation of earlier128 studies on methylated derivatives of methyl L-sorboside, Khouvine and Arragon129 were able to isolate xylo-trimethoxyglutaric acid (LVI), as well as the dextrorotatory dimethoxy-succinic acid (LVII), by oxidation of either sirupy tetramethyl-L-sorbose (LV) or the methyl L-sorboside. The formation of either acid indicates the pyranoside ring in the original compounds. 

They then prepared the completely methylated derivatives of adeno-gine . and guanosine by simultaneous deacetylation and methylation of the acetylated nucleosides. In this way, trimethyl-iV-methyl adenosine and trimethyl-A -methyl guanosine were formed, and isolated as the hydrochlorides. On hydrolysis of the adenosine derivative by means of dilute hydrochloric acid, 6-iV-methyladenine and trimethyl-D-ribo-furanose were isolated. The same trimethyl sugar was isolated from the methylated guanosine and was identified in each case by oxidation, first to trimethyl-7-D-ribonolactone and then to meso-dimethoxy succinic acid. It follows that the sugar component has the furanose ring-structure. 

The ring structure of the ribose residue was ascertained" in the same general manner as for adenosine and guanosine. Triacetyl-dihydrouridine was prepared by the hydrogenation of triacetyl-uridine. On simultaneous deacetylation and methylation this was transformed to the fully methylated dihydro-uridine. By simultaneous hydrolysis and oxidation of this product, with hydrobromic acid and bromine, trimethyl -D-ribonolactone was formed, its identity being confirmed by oxidation to meso-dimethoxy-succinic acid. It follows that the ribose component has the furanose ring structure, and that uridine is 3 -D-ribofuranosyl-uracil. 

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