Photoaffinity bevirimat analogs. (A) Structures of bevirimat and the photoaffinity analogs. (B) Detail of mass spectra showing ion mass corresponding to the C-28 analog crosslinked to a synthetic peptide spanning the CA-SP1 region. Red and blue traces are spectra derived from the crosslinking reaction performed in 50% TFE or pure water, respectively. The theoretical monoisotopic mass of the synthetic peptide/C-28 analog adduct is 3302.79: monoisotopic mass of peptide + monoisotopic mass of C-28 - mass of N2 gas + mass of proton = 2460.29 + 869.5 - 28 + 1 = 3302.79 Da, which is in good agreement with the monoisotopic mass of the ion shown.