Lactic acid labeled with

Write bond-line three-dimensional formulas for the starting compound, the product, and all of the intermediates in a synthesis similar to the one just given that relates the configuration of (-)-glyceraldehyde with (-l-)-lactic acid. Label each compound with its proper (R) or (S) and (-I-) or (-) designation. 

The earlier work of Miller (35), Outright (37), and Brady (5) on nonmedicated implants provided an excellent basis for further studies on specific controlled release formulations such as the determination of the biodegradation rates of lactide/glycolide drug-loaded microspheres (38). Those studies were done with l c-iabeled polymers produced from DL-lactic acid and glycolide. The final formulations tested in rats were microspheres loaded with H-labeled steroid and polymer as the matrix. The microspheres were administered intramuscularly and animals were serially sacrificed over a period of about a year. 

Kimura and coworkers have also developed hybrid-type polymersomes composed of polysarcosine-b-PLA ( lactosomes ) [242-243]. The lactosomes are fully biodegradable due to the equipped metabolic pathway for sarcosine and lactic acid. Hence, the lactosome is preferred for in vivo applications rather than for in vitro studies. Indeed, they have demonstrated a potential utility of lactosomes as a contrast agent for in vivo liver tumor imaging [243]. Lactosomes labeled with indocyanine green showed high escape ability from RES, were found to be stable in... 

You can tiy working the other way, from the configurational label to the structure. Take lactic acid as an example. Lactic acid is produced by bacterial action on milk it s also produced in your muscles when they have to work with an insufficient supply of oxygen, such as during bursts of vigorous exercise. Lactic acid produced by fermentation is often racemic, though certain species of bacteria produce solely (R)-lactic acid. On the other hand, lactic acid produced by anaerobic respiration in muscles has the S configuration. 

On standing in alkali in the laboratory, prephenic acid rearranges to 4-hydroxyphenyl-lactic acid with specific incorporation of deuterium label as shown. Suggest a mechanism, being careful to draw realistic conformations. 

Chiral methyl chiral lactic acid (5). This labeled molecule, useful for study of stereospecificity of enzymic reactions, has been prepared in a way that allows for synthesis of all 12 possible isomers. One key step is the stereospecific debromination of 1, accomplished by conversion to the vinyl-palladium cr-complex 2 followed by cleavage with CF3COOT to give the tritium-labeled 3. The next step is the catalytic deuteration of 3, accomplished with a rhodium(I) catalyst complexed with the ligands norbornadiene and (R)-l,2-bis(diphenylphosphino)propane. This reaction gives 4 with an optical purity of 81%. The product is hydolyzed to 5, which is obtained optically pure by cr3rstallization. 

Compounds labeled with 20-min half-lived carbon-11 were first intro- duced into biomedical research over 40 years ago (1-6). Before the discovery of carbon-14, compounds such as propionic acid (3) and lactic acid (2) labeled with carbon-11 were synthesized and utilized in biochemical research. After the introduction of carbon-14 as a biomedical tracer, interest in the shorter-lived carbon-11 decreased, and only in the past decade has there been renewed interest in labeling compounds with carbon-11 as well as with other short-lived positron-emitters such as oxygen-15, nitrogen-13, and fluorine-18. 

Step 6 is the final step in the cellulose-to-lactic acid cascade, involving the isomerization of the 2-keto-hemi-acetal (here pyruvic aldehyde hydrate) into a 2-hydroxy-carboxyhc acid. This reaction is known to proceed in basic media following a Cannizzaro reaction with 1,2-hydride shift [111], Under mild conditions, Lewis acids are able to catalyze this vital step, which can also be seen as an Meerwein-Ponndorf-Verley reduction reaction mechanism. The 1,2-hydride shift has been demonstrated with deuterium labeled solvents [110, 112], Attack of the solvent molecule (water or alcohol) on pymvic aldehyde (step 5) and the hydride shift (step 6) might occur in a concerted mechanism, but the presence of the hemiacetal in ethanol has been demonstrated for pyruvic aldehyde with chromatography by Li et al. [113] andfor4-methoxyethylglyoxal with in situ CNMRby Dusselier et al. (see Sect. 7) [114]. 

Pyruvate can be labeled either in the carboxylic (Hwang et al. 1986 Takahashi et al. 1990) or in the 3-position (Bjurling et al. 1988 Ropchan and Barrio 1984 Cohen et al. 1980). Pyruvate is a versatile compound for further transformations to aromatic amino acids and to lactic acid (Kloster and Laufer 1980 Bjurling and Langstrbm 1989 Cohen et al. 1980). Some aliphatic amino acids have been labeled with R C employing enzymatic and combined chemo-enzymatic methods (Antoni et al. 1997, 2001 Barrio et al. 1982b Cohen et al. 1982 Kaneko et al. 1999 Svard et al. 1990) as exemplified in Pig. 41.31 and 41.32. 

Figures. Comparative blood circulation time (A) and liver uptake (B) after injection of 11 In-labeled nanospheres in the tail vein of BALB/c mice. The nanospheres were prepared from PLGA (0), PEG5K-PLGA45K (O). PEG5K-PLGA25K (x), and PEG5K-PLGA20K (A) pol5Tners, with a lactic acid glycolic acid molar ratio in PLGA of 3 1.

The degradation of PLA by hydrolytic scission of ester linkages yields lactic acids. Lactic acid is a natural product associated with muscular construction in animals and humans, which can be decomposed by the body s normal metabolic pathways. In the body, lactic acid is converted to pyruvic acid and enters the tricarboxylic acid cycle to yield carbon dioxide and water. Using carbon-labeled PLA, no significant amount of accumulation of degradation products... 

The general procedure used in these studies is to trace-label samples of the protein with H-FDNB at several pH-values in the presence of N-acetyl-histidine or imidazole lactic acid as internal standard. The reaction mixture is then made chemically homogeneous by fully reacting with unlabelled or " C-FDNB. In the case of proteins containing more than one histidine residue, peptides are isolated so than an unequivocal assignment of parameters can be made. For proteins containing a solitary histidine residue, imidazolyl-DNP-histidine is isolated after acid hydrolysis. The internal standard is purified separately and the data from scintillation counting is substituted into Equations (1) or (2) to derive rate constants. 

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