The electrospray spectra (positive and negative ion MS1) of a synthetic peptide?related compound are clearly inconsistent with the “target” structure shown below (explain why). MS/MS spectra were obtained for both MH+ and [M?H]? molecular ions of the highest MW species detected in MS1 experiments. MS3 of a positive fragment ion at m/z 501 yielded only two fragments at m/z 473.1 and 178.9(data not shown). Based on these data, can you provide any advice/suggestion to a synthetic chemist who submitted the sample? What further MS experiments would you propose if you were unable to elucidate?
Has yours come through yet?