Glycolic acid absolute configuration

The absolute configuration was also established unequivocally for C-8 of naturally occurring pyrrolizidine bases.88 It was demonstrated in the course of the structural analysis of isoheliotridene (146), obtained by degradation of the alkaloid monocrotaline, that ozonolysis of this compound affords 2-acetylpyrrolidine-l-acetic acid (147).66 The (— )-methyl ester of this acid was condensed with methylmagnesium iodide to give (— )-l-(2-hydroxy-2-methylpropyl)-2-(l-hydroxy-l-methylethyl)pyrrolidine (148). The same glycol (148) was obtained... 

The proof of configuration just described relies on the assumption that there is the same relative stereochemistry for the hydrogen atoms in glycolic acid and lactic acid on formation of the enzyme-substrate complexes. The absolute configuration of the glycolate-2-d (22) prepared by reduction of glyoxylate-2-d (21) with glycolate dehydro-... 

To determine the absolute configuration of optically active organic compounds, there are two nonempirical methods. One is the Bijvoet method in the X-ray crystallographic structure analysis, which is based on the anomalous dispersion effect of heavy atoms. - The X-ray Bijvoet method has been extensively applied to various chiral organic compounds since Bijvoet first succeeded in determination of the absolute stereochemistry of tartaric acid in 1951. The second method is a newer one based on the circular dichroism (CD) spectroscopy. Harada and Nakanishi have developed the CD dibenzoate chirality rule, a powerful method for determination of the absolute configuration of glycols, which was later generalized as the CD exciton chirality method. 8 The absolute stereochemistry of various natural products has been determined by application of this nonempirical method. 

Fig. 9.7 (a) En antioresolution and determination of the absolute configuration of 2-(l-naphthyl)propane-l,2-diol (42). (b) ORTEP drawing of4-bromo-benzoate (S)-(-)-44, whose absolute configuration was determined by the heavy atom effect of the bromine atom, (c) Preparation of (S)-(+)-MaN P acid (3) from glycol (S)-(-)-42 [40]. 

The absolute configuration of the epoxide group of insect JHs was determined by spectroscopy and circular dichroism [29], In the first method, perchloric acid was used to catalyze the hydrolysis of the epoxide in the presence of H2180. The resulting v/c-diol was analyzed by mass spectroscopy and definitively demonstrated the 10/ , 115 chirality of the epoxide [30]. The chirality was confirmed by circular dichroism. The epoxide was hydrolyzed by sulfuric acid and tetrahydrofuran and the circular dichroism cotton effect of the resulting acyclic glycol was measured in the presence of tris(dipivaloylmethanato)praseodymium [31]. 

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