6‐Hydroxymethtryptoline is naturally occurring in mammalian urine: Identification by combined chiral capillary gas chromatography and high resolution mass spectrometry

The tricyclic indole derivative 6‐hydroxymethtryptoline (7‐hydroxy‐1‐methyltetrahydro‐β‐carboline) was identified as a normal constituent of human and cat urine. The identification was based on the correct retention time on a chiral capillary gas chromatographic column and on selected ion monitoring of the molecular ion with the mass spectrometer set at high resolving power (RP 10 000). The quantitation utilized a 13 C‐labeled analog as internal standard and demonstrated levels of 135 ± 35 and 174 ± 42 (pmol ml −1 , mean ±SEM) for the S(−) and R(+) enantiomers, respectively, in human urine. In cat urine, the levels were 203 ± 55 and 108 ± 44 (pmol ml −1 , mean ± SEM) for the S(−) and R(+) enantiomers, respectively. In human urine, the compound occurred predominantly in a conjugated form while in cat urine the free compound predominated. It was concluded that 6‐hydroxymethtryptoline is naturally occurring in mammalian urine and that it most likely constitutes a metabolite of endogenous methtryptoline (1‐methyltetrahydro‐β‐carboline).