Racemization and Epimerization

Racemization and epimerization.

In recent reports (I ) the term racemization is used inappropriately. It is stated in both reports that Lisoleucine racemizes to D-alloisoleucine. This reaction is epimerization, not racemization. Racemization of L-iSOleucine results in the formation of DLisoleucine. As stated in Eliel (2): "'racemization is the process of producing a racemic modification starting with one of the pure enantiome...

Amino acids in fossil corals: racemization (epimerization) reactions and their implications for diagenetic models and geochronological studies*

Thirty-eight fossil coral samples of known age from late Pleistocene uplifted reef terraces have been analyzed for amino acid composition and for the degree of racemization of selected amino acids. Particular attention has been given to the epimerization (racemization about the cc-carbon) of isoleucine. The D/L ratios observed in many of these samples do not conform to the concept of increaqing...

Epimerization and stereochemistry of avoparcin.

The epimerization of avoparcin entities is discussed in some detail. The absolute stereochemistry of avoparcin is now known since the N-methyl terminal amino acid of the aglycone has been isolated and shown to exhibit negative optical rotation and hence has the R-configuration. The same amino acid has been isolated from an epimerized solution of avoparcin and found to have positive rotation and...

Amino Acid Racemization

Epimerization of erythromycin derivatives.

Dirithromycin (3) isomerizes upon dissolution in different solvents. From X-ray analysis of V-T 108, an analogue of dirithromycin, and comparative 1H and 13C NMR, and MS data, the isomer of dirithromycin was confirmed to be the C-16-(S)-epimer. The ratio of the two epimers at equilibrium conditions was approximately 8:2 (R/S) in methanol at room temperature.