L-Threuronic acid

L-dihydroxy-succinic acid (L(dexiro)-tartaric acid, CXIII). This result establishes the position of the double bond between C4 and C5 and demonstrates that C4 carries only one hydrogen atom while C5 has attached to it the enolic hydroxyl group. Treatment of the enol CXI with ethereal diazomethane gives 5-methyl-A4-D-glucosaccharo-3,6-lactone methyl ester (CXIY) which upon further methylation with silver oxide and methyl iodide yields 2,5-dimethyl-A4-D-glucosaccharo-3,6-lactone methyl ester (CXV). When the latter is subjected to ozonolysis there is formed oxalic acid and 3-methyl-L-threuronic acid (CXVI). Oxidation of this aldehydic acid (CXYI) with bromine gives rise to a monomethyl derivative (CXVII) of L-ilireo-dihydroxy-succinic acid. 

Treatment of 720a with methanol provides in 75% yield the crystalline monomethyl tartrate 721 which is converted in 75% yield to the crystalline acid chloride 722 with thionyl chloride. Rosenmimd reduction of 722 in xylene at 130-135 °C affords the crystalline methyl diacetyl-L-threuronate (723) in 65-70% yield [216] (Scheme 158). 

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