FAST-ATOM-BOMBARDMENT MASS-SPECTRAL STUDY OF TETRACYCLINE ANTIBIOTICS

In the fast atom bombardment mass spectra of tetracyclines, ammonia elimination fragment ions, [M + H - NH3]+ and [M + H - NH3 - H2O]+, appeared with considerable abundances. A plausible mechanism for the loss of ammonia from [M + H]+ was discussed based on results by measurements on various types of tetracyclines and benzamides as the model compounds and B/E linked scanning. The results indicated that the loss of ammonia occurred in the carboxyamide moiety in the A ring and was accelerated by an ortho-hydroxy group. The same fragmentations were observed in the electrospray mass spectra of tetracyclines with a skimmer-capillary voltage differential of 150 V.