Sterol metabolism—XLV. Differentiation among monohydroxylated cholesterol derivatives by chromatography and mass spectrometry

Abstract

Twenty monohydroxylated cholesterol derivatives have been characterized by high performance liquid column chromatography and by chemical ionization (CI) mass spectrometry. With ammonia as reagent gas four ions are formed: an ammonium adduct [M + NH 4] +, a substitution ion [M + NH 3-OH] + and elimination ions [M-OH] + and [M-H 2O-OH] +]. Thermally stable stenediols exhibit [M + NH 4] + as principal ion, less stable allylic or tertiary alcohol derivatives the elimination ions [M-OH] + or [M-H 2O-OH] +. With methane or isobutane as reagent gas monohydroxylated cholesterols yield five ions: the protonated molecular ion [M + H] +, molecular ion[M] +, hydride abstraction ion [M-H] +, and elimination ions [M-H 2O + H] + and [M-2H 2O + H] +, the principal ion uniformly being the [M-H 2 + H] + ion. Methane CI mass spectra of trimethylsilyl ether derivatives of the side-chain hydroxycholesterols exhibit unique fragmentation ions [C nH 2nOSi(CH 3) 3] + derived from α-cleavages diagnostic of the site of side-chain hydroxylation.