Direct resolution of enantiomers of (RS)-ketorolac was achieved by thin-layer chromatography on silica gel plates using enantiomerically pure L-tryptophan, L-valine, L-methionine, and L-histidine as chiral additive in the stationary phase. The solvent system (acetonitrile, methanol water, and chloroform) with different ratios was successful in resolving the enantiomers. Spots were detected by use of iodine vapor. The detection limit was 0.4 µg mL−1 for each enantiomer of (RS)-ketorolac. The native enantiomers were isolated and characterized.
Authors:G. Meyer, A. Osterholz, and H. Hundeshagen
Radio high pressure liquid chromatography (radio-HPLC) is the method of choice for quality control of radiopharmaceuticals
labelled with short lived isotopes. Our preparations of “no carrier added”11C-labelled palmitic acid and L-methionine are both designed to end with a HPLC separation on either silica gel or C-18 reversed
phase material. Since the crude reaction mixtures contain milligram amounts of inactive substrate materials, both separations
must be carried out at preparative scale. Nevertheless they are performed in less than 10 min. The most critical factor for
the separation of11C-palmitic acid from the main by-product pentadecane is the solvent composition: while the11C-L-methionine separation is especially sensitive to pH variations.
Authors:Franco Cataldo, Pietro Ragni, Susana Iglesias-Groth, and Arturo Manchado
The sulphur-containing proteinaceous amino acids l-cysteine, l-cystine and l-methionine were irradiated in the solid state to a dose of 3.2 MGy. This dose corresponds to that delivered by radionuclide
decay in a timescale of 1.05 × 109 years to the organic matter buried at a depth >20 m in comets and asteroids. The purity of the sulphur-containing amino acids
was studied by differential scanning calorimetry (DSC) before and after the solid state radiolysis and the preservation of
the chirality after the radiolysis was studied by chirooptical methods (optical rotatory dispersion, ORD) and by FT-IR spectroscopy.
Although the high radiation dose of 3.2 MGy delivered, all the amino acids studied show a high radiation resistance. The best
radiation resistance was offered by l-cysteine. The radiolysis of l-cysteine leads to the formation of l-cystine. The radiation resistance of l-methionine is not at the level of l-cysteine but also l-methionine is able to survive the dose of 3.2 MGy. Furthermore in all cases examined the preservation of chirality after
radiolysis was clearly observed by the ORD spectroscopy although a certain level of radioracemization was measured in all
cases. The radioracemization is minimal in the case of l-cysteine and is more pronounced in the case of l-methionine. In conclusion, the study shows that the sulphur-containing amino acids can survive for 1.05 × 109 years and, after extrapolation of the data, even to the age of the Solar System i.e. to 4.6 × 109 years.
Authors:Debasis Das, Animesh Sahana, Raja Saha, Pijush Kundu, and Subrata Laskar
A new ligand has been synthesized by anchoring anthracene to l
-methionine. The ligand enables easy identification of amino acids on thin-layer chromatography plates by developing distinguishable colors. This paper deals with the detailed synthesis, characterization, and application of the new ligand. Estimation of binding constants of this new ligand with different amino acids are also reported. A theoretical calculation (
) has been performed to investigate interaction of the ligand with the amino acid.
The method developed for the determination of the optical purity of L-selenomethionine-75Se is based on the conversion of the mixture of L-and D-amino acids into the diastereoisomeric derivatives by reaction with
(−)-camphorsulphonyl chloride. The diastereoisomeric derivatives are separated by means of thin layer chromatography. From
the ratio of the radioactivities of the two spots on the chromatogram, the optical purity is calculated, and given in % D.
For a sample of L-methionine-14C the following value was found: 0.53±0.05 (S.D. of mean, n=7). For a sample of DL-methionine-14C the percentage of D found, was: 48.5±0.5 (S. D. of mean, n=7). Of 30 different samples of L-selenomethionine-75Se the percentages of D-isomer were determined in duplicate. From the 30 differences between duplicates the S. D. of a single
measurement is calculated to be 0.2.