Carboxylic acids absolute configuration determination

The enantiomeric composition and absolute configuration of a-deuteriated primary carboxylic acids can be determined by H- and 2H-NMR analysis of the corresponding esters of methyl (S)-mandelate71 72. 

Yabuuchi T, Kusumi T. Phenylglycine methyl ester, a useful tool for absolute configuration determination of various chiral carboxylic acids. J. Org. Chem. 2000 65 397 04. 

R=(CH2)2NMe with chiral centres only at the N atoms has been obtained with an optical purity of 88.55 by resolution with (+)-canphor-3-carboxylic acid and its absolute configuration determined. 

The absolute configuration of naturally occurring 5(-)-azetidine-2-carboxylic acid has been established (73CL5), and the DL form has been resolved (69JHC993). ORD and CD curves have been determined for 2-methylazetidine and an octant rule has been proposed for the N-chloro- and N-cyano-2-methylazetidines (74T39). 

In order to obtain more information on the reaction intermediate, the stereochemical course of the reaction was investigated. The absolute configuration of the product from a-methyl-a-phenylmalonic acid was unambiguously determined to be R, based on the sign of specific rotation. Then, which carboxyl group remains in the propionic acid and which is released as carbon dioxide To solve this problem we have to distinguish between two prochiral carboxyl... 

Starting from the Michael adducts of (4R,5S)-4,5-diphenyloxazolidine-2-one (100) onto chlorospiropentylideneacetates 2 c (102c-Bn and 102c-Me) and juggling with the set of transformation discussed above, the spiropentane amino-carboxylic acids 207,208 and 213 were also prepared either in racemic (208) or enantiomerically pure (207, 213) forms, the absolute configurations of which were determined on the basis of X-ray crystal structure analysis of the precursor... 

Azetidine-2-carboxylic acid (2) like proline gives an intense blue color with sodium nitroprusside in 10% acetaldehyde solution in the presence of sodium carbonate. 98,99 Upon usual acid hydrolysis (6M HC1, 110 °C, 24 h or more) as required for amino acid analysis, azetidine-2-carboxylic acid is completely decomposed, yielding mainly homoserine lactone, as well as other ninhydrin-positive compounds. 87,89,99 To enable an accurate quantification of this imino acid, azetidine-2-carboxylic acid peptides should be hydrolyzed by alkali (5M barium hydroxide, at 100 °C for 18 h 89 or 2 M sodium hydroxide at 110°C for 22h 100 ). There are extensive NMR spectroscopic data available 100-104 and the absolute configurations of A-acetyl-L-azetidine-2-carboxylic acid 105 and A-terf-butoxycarbonyl-L-azetidine-2-car-boxylic acid 106 have been determined by X-ray analysis. 

J. P. Kamerling, M. Duran, et al., Determination of the absolute configuration of some biologically important urinary 2-hydroxydi-carboxylic acids by capillary gas-liquid chromatography, J. Chromatogr., 222 276-283 (1981). 

Determinations of absolute configurations of trans-cyclopropane-l,2-dicarboxylic acids on the basis of a definite Cotton effect seem to be possible for carboxylic acid thioamides. In these molecules, such as 123a and 123b, there is a Cotton effect near 330 nm which results from the (n, n ) excitation of the thioamide chromophore . In the... 

The absolute configuration of samandaridine was determined by partial synthesis (11). Condensation of iV-acetylsamandarone (XVIII) with glyoxylic acid yields a mixture of the two carboxylic acids XIX and XX. Reduction of the former, first with sodium borohydride and then catalytically generates samandaric acid (XXI), which on boiling with dilute mineral acid lactonizes to samandaridine (XVII). 

We have recently developed chiral carboxylic acids as novel molecular tools useful for enantioresolution and simultaneous determination of the absolute configuration of various alcohols. These chiral molecular tools are very powerful for the facile preparation of enantiomers with 100% ee and also for the absolute configurational assignment. Methods using these chiral tools have been successfully applied to various compounds, and their methodologies and applications are explained throughout this chapter. 

Fig. 9.1 Enantioresolution and determination of absolute configuration of alcohols using chiral carboxylic acids [5-8],...

We have discovered that this novel carboxylic acid, MaNP acid 3, is also effective for enantioresolution and simultaneous determination of the absolute configuration of various secondary alcohols by the H NMR anisotropy method [41-52, 56-58]. The results obtained by the H NMR anisotropy mefhod are, of course, consistent wifh those by the X-ray method. Therefore, the methods of CSDP and MaNP acids are useful as complementary molecular tools, as discussed in fhis chapter. 

The additional signals in the H NMR spectrum indicated that the esteri-fying unit was l,2-dihydro-l-methyl-2,7-naphthyridine-4-carboxylic acid (69), and this was confirmed by methanolysis to afford the methyl ester of 69 and tetrahydrocantleyine (16). The absolute configuration of the methyl group at 1 on the 1,2-dihydronaphthyridine unit could not be determined due to rapid aerial oxidation to 70. Hence the structure of scaevodimerine A was deduced to be 71 (69). 

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