Abstract-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.THE POLYCYLIC carboxylic acids monensin (Ia)' and nigericin (IVa)2 are members of a newly recognized family of biologically active compounds produced by Streptomy~es.~ Their structures have been determined recently by X-ray ~rystallography.4*~ Independent investigation by chemical and spectroscopic methods provided corroborative result^.^*^*^ In this study the mass spectra of monensin, nigericin and several derivatives thereof were determined. This paper presents an interpretation of the mass spectral data and their application to the structure elucidation of two minor factors, IIa (factor B) and IIIa (factor C ) , formed along with monensin by the micro~rganism.~.~
Monensin and Related FactorsThe mass spectrum (high-mass region) of monensin (Ia) is shown in Fig. 1. The molecular ion has not been observed for the free acid (Mol. wt. 670, C36H6201J. The first peak occurs at m/e 634 (C36H5809)T and is due to the loss of two molecules of
A study of the rates of addition of trifluoroacetic acid to terminally substituted 1-alkenes was carried out for alkenes having chains of four to eleven carbon atoms.Among several inductive substituents examined, the cyano and trifluoroacetoxy groups were notable in giving significant rate depressions for all alkenes in the series, including the 11-substituted 1-undecenes. The more remote of these substituents are several carbon atoms farther removed from the reaction site than substituents previously observed to produce measurable inductive effects in aliphatic compounds. The rates of reaction are remarkably well correlated by the assumption that the substituent effect is attenuated by a constant factor per methylene group, although our attenuation factor (0.65) represents an unusually small attenuation with increasing distance. 5-Methoxy-l-pentene and, more notably, 5halo-l-pentenes show deviations from the expected inductive effects attributable to substituent participation. Oxygen-and nitrogen-containing substituents show marked enhancement of inductive effects, attributable to hydrogen bonding of the substituent to trifluoroacetic acid. In order to assess the effect of substituents in systems of semirigid or rigid geometry we studied the addition of trifluoroacetic acid to several 4-vinylcyclohexanemethyl derivatives and bicyclo[4.3.0]non-3-en-8-yl derivatives. Rate effects similar to those found in the aliphatic series were observed, indicating that large rate effects are in fact characteristic of substituents which are remote from the reaction site.
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