Mass spectrometry ring cleavage

Mass spectrometry indicated this metabolite has undergone oxidative cleavage of the imidazole ring. 

Anthramycin.—Anthramycin (85) is formed from tryptophan and tyrosine.76 Utilization of the latter amino-acid is with cleavage of the aromatic ring. New results confirm earlier ones76 that C-l of (85) derives from C-3 of tyrosine and without loss of the protons at C-3.77 It has also been shown that N-10 of anthramycin (85) has its origin in the indole nitrogen of tryptophan.78 The experiment which gave this result involved incorporation of h- indole-lsN 1-tryptophan and of DL-[l-uCltyrosine into (85) and analysis essentially by 13C n.m.r. and mass spectrometry [C-l of tyrosine (84) is the source of C-l 1 in (85)1. 

The mass spectrometry of oxazole compounds has been reviewed by Traldi ef al. <1980H(14)847>. The main fragmentation pathway for most oxazole rings is shown in Scheme 1. Radical cation formation is followed by cleavage of the 0-C(2) bond, and then sequential loss of CO and HCN or nitrile <19920MS317>. 

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