The mass spectra of formycin, formycin B and showdomycin carbon linked nucleoside antibiotics

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Abstract
The mass spectra of the nucleoside antibiotics formycin (I), formycin B (II) and their heterocyclic aglycons (7‐aminopyrazolo[4,3‐d]pyrimidine and pyrazolo[4,3‐d]‐7‐pyrimidone) have been studied utilizing high resolution mass spectroscopy. The major electron‐impact fragmentation pattern exhibited by the heterocyclic aglycons can be explained by the initial expulsion of hydrogen cyanide followed by decarbonylation or by loss of a second mole of hydrogen cyanide. There is a striking difference in the fragmentation pattern of these nucleoside antibiotics where the glycoside linkage is a C‐C bond as compared to nucleosides possessing a C‐N bond linkage. The base peak observed for formycin and formycin B occurred at B + 30 in direct contrast to the usual nucleosides where the B + 1 or B + 2 normally occurs as the predominant peak. This pattern suggests that such a carbon linked nucleoside should be readily identified by this means. The mass spectrum of showdomycin (3‐β‐D‐ribofuranosylmaleimide, III) was also determined and found to exhibit a similar parent peak at B + 30. This base + 30 peak has been assigned to the aglycon plus a protonated formyl group which results from fragmentation of the sugar. Mass spectrometry should prove very useful in the future structural elucidation of carbon linked nucleoside derivatives since these features (B + 30 and M‐103) may be considered diagnostic.

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