Glyoxylic acid, »-butyl ester

Glyoxal-sodium bisulfite, 30, 86 Glyoxylic acid, w-butyl ester, 35, 18 ethyl ester, diethyl acetal, 35, 59 Grignard reaction, addition to ethyl sec-butylidenecyanoacetate, 35, 7 allylmagnesium bromide with of,(3-di-bromoethyl ethyl ether, 36, 61 allylmagnesium chloride with a,/3-di-bromoethyl ethyl ether, 36, 63 ethylmagnesium bromide with tin tetrachloride, 36, 86... 

Transmetalation of the ( )-0-Li-enolate derived from the stabase -protected glycine ethyl ester (11) with 1.1 equiv of (1) affords the chiral Ti enolate (12), which adds with high re selectivity to various aldehydes. By mild acidic cleavage of the silyl protecting group, the primary product (13) can be transformed to various Af-derivatives (14) of D-t/treo-a-amino-p-hydroxy acids in 45-66% yield and with excellent enantio- and syn(threo) selectivity (97-99%) (eq 3). An exception with lower enantioselectivity is glyoxylic ester (ethyl ester 78% ee t-butyl ester 87% ee). 

Identification of the diacid butyl esters was conducted by comparing the GC retention times with those of authentic standards. Mass spectra of the organic compounds were also obtained with a GC/MS (ThermoQuest, Trace MS) using a similar GC condition. Duphcate analyses of several filter samples showed that the analytical errors for major diacids were within 10%. Spiked experiments using authentic standards (oxalic, malonic, succinic and adipic acids) in quartz filter showed that recoveries were 77% for oxalic acid and better than 86% for other diacids. Recoveries of glyoxylic acid, pyruvic acid, and methylglyoxal were 88, 72, and 47, respectively (Kawamura and Yasui, in preparation). The procedural blanks showed that contamination levels of the diacids during the analysis were less than 5% of the sample. The data reported here are corrected for the procedural blanks, but not for recoveries. 

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