D/L configuration

Problem 5.37 Glyceraldehyde can be converted to lactic acid by the two routes shown below. These results reveal an ambiguity in the assignment of relative d,l configuration. Explain. 

Figure 1.4 The D/L configurations of amino acids. Note that the carboxylic acid group must be drawn at the top and the R group at the bottom of the Fischer projection. Stereogenetic centres in the R group do not affect the D/L assignment...

Fig. 13 Direct comparison of the experimental Sc-L23 x-ray absorption spectra of Sc2 C84 (line+symbols) with a simulation (grey solid line) based upon an atomic multiplet model with an initial state composed of 61% d° and 39% d L configurations. For details,see Ref. [34]...

Fig. 14 Solid lines simulated Sc-L23 x-ray absorption spectra of trivalent Sc ions (d°) with an initial-state admixture of the indicated proportion of a d L configuration in the initial state. For details of the calculations, see Ref. [36], Line+symbols experimental Sc-L2 s x-ray absorption spectrum of Sc3N C8o...

Thus, description of a simple change of fatty acid at the primary position required frequent changes of configuration prefixes. Also, the R/S system, like the older D/L one, did not account for the stereospecificity of the acylglycerol derivatives toward lipases (phospholipase A2 in particular). Finally, nonrandom distribution of fatty acids in natural or synthetic enantiomeric acylglycerols could not be systematically correlated by reference to either the R/S or D/L configuration. 

However, its a-carboxylate is often amidated or linked to an additional amino acid and in Microbacterium lacticum y-D-Glu is replaced by f/rreo-S-hydroxy-D-glutamic acid (3-Hyg). Most variation is found in position 3. If m-DAP (D,L-configuration) is incorporated, the L center is found in the pentapeptide chain and the D center in the side chain. Positions 4 and 5 (D-Ala-D-Ala) were for a long time thought to be invariant. However, the incidence of bacterial resistance to vancomycin-type glycopeptide antibiotics which recognize specifically the A-acyl-D-Ala-D-Ala terminus led to the discovery that these resistant strains contain altered substituents at position 5 as indicated in Fig. 16b [194,195,196]. 

D-Ribose is a five carbon sugar contained in ribonucleosides, ribonucleotides, and their derivatives. (Note that D here refers to the D/L configuration, not "deoxy" as in deoxyribose)... 

Use Figure 23.2 as a guide to help you name the aldose shown. What is the D,L configuration at the highest numbered chirality center The R,S configuration What is its sign of rotation ... 

FIGURE 2.4 Example molecules showing d/l configurations according to Fischer projections along with their observed optical rotations. 

Seto H. Isolation of peniopyranines A, B, C and D. Agric Biol Chem 1973 37tZ415-2419. Seto H, Otake N, Yonehara H. The structures of pentopycanines A and C, two cytosine nucleosides with d-l configuration. Agric Biol Chem 1973 37 2421-2426. 

Nishida, Y., Bai, C., Ohrui, H., Meguro, H. (1994). A highly sensitive method to identify the D, L-configurations of monosaccharides based on (-)-TBMB carboxilic acid and EPLC. Journal of Carbohydrate Chemistry, 13, 1003-1008. 

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