Abstract: The aim of the invention to provide a less complex method for the production of A-ring aromatized acetyl minocyclines of the formula (I), wherein R1 to R5=acetyl and/or H, which can also be used on an industrial scale, is achieved in that minocycline hydrochloride is reacted with acetanhydride in the presence of a proton catcher, the reaction product is subjected to chromatographic filtration using a carrier material and an eluant, the eluant is distilled off, and the product is subsequently cleaned by recrystallization.

Abstract: The invention relates to a method for determining the concentration of asymmetric dimethylarginine (ADMA) simultaneously with arginine and with symmetric dimethylarginine (SDMA) in biological samples by means of HPLC-MS-MS. The sample preparation consists exclusively of adding a solution of isotope-labeled internal standards (13C6-arginine and D6-ADMA) and of adding a mixture consisting of acetonitrile/propionic acid/trifluoroacetic acid for precipitating high-molecular proteins, the quantity and composition being realized in such a manner that a bringing of the sample composition in line with the composition of the mobile phase in the HPLC separation is achieved without requiring a derivitization or extraction of the analytes.

Abstract: The invention relates to a method for determining the concentration of asymmetric dimethylarginine (ADMA) simultaneously with arginine and with symmetric dimethylarginine (SDMA) in biological samples by means of HPLC-MS-MS. The sample preparation consists exclusively of adding a solution of isotope-labeled internal standards (13C6-argininc and D6-ADMA) and of adding a mixture consisting of acetonitrile/propionic acid/trifluoroacetic acid for precipitating high-molecular proteins, the quantity and composition being realized in such a manner that a bringing of the sample composition in line with the composition of the mobile phase in the HPLC separation is achieved without requiring a derivitization or extraction of the analytes.