Observations on the mass spectrometry of monensin and related compounds

Monensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali‐metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.