Application of mass spectrometry to the structural investigation of 9,19-cyclosterols and triterpenes

Tetracyclic triterpenes containing the 9,19-cyclo-function undergo two diagnostically significant fission reactions on electron impact. The first is due to the loss of the side chain (R) to give a peak at M– R. The other involves cleavage of the 9–10, 9–19, and 5–6 linkages with rearrangement of one hydrogen atom and with charge retention with rings C and D. Consideration of the mass spectral fragmentation can thus yield valuable information on the substitution pattern of 9,19-cyclosterols and triterpenoids.