Chemical-ionization mass spectrometry of lincomycin and clindamycin

Abstract

The chemical-ionization (ci) mass spectra of the carbohydrate antibiotic lincomycin ( 1), its 7( S)-chloro analog clindamycin ( 2), and its N-deacylated derivative methyl 1-thiolincosaminide ( 3), produced with isobutane or ammonia as the reagent gas, display in each instance the protonated molecular-ion as the most abundant species. Only a few fragment-ions are observed, and these arise largely from low-energy, nonskeletal cleavage-reactions of the major ion, or through thermal breakdown of the original molecule; characteristic differences in the patterns of charge capture are observed as a function of the reagent gas. The spectra contrast sharply with those obtained by electron-impact (ei) mass spectrometry, wherein extreme fragmentation occurs and few prominent fragments of high mass are observed. The ci-ms technique offers considerable potential as a micro method for determining the purity of antibiotics, for analyzing them in admixture, and for monitoring reactions performed by chemical or biochemical methods to effect structural modification of antibiotics.