Studies on the Photodegradation of Thyroxine with Ultraviolet-light Irradiation : Identification of Degraded Products with Gaschromatograph-Mass Spectrometer

Abstract

Identification of photodegraded products of L-thyroxine (T₄) suffering ultraviolet-(UV)-light irradiation (sterilization lamp 20 W, λ_max 253.7 nm, radiation distance 40 cm) was carried out by gas chromatograph-mass spectrometer (GC-MS). N, O-Bis (trifluoroacetyl) methyl ester derivatives of authentic T₄ and its related compounds and UV-light irradiated T₄ samples were analyzed by GC-MS (JEOL JMS-D300 GC-MS and JEOL JMA-2000 Data Analysis System). Gas chromatography was carried out with a 1 m×2 mm column packed with 3% OV-17 and the temperature was programed from 100°C to 300°C with 10°C/MIN. Mass spectrometry was performed by electron impact ionization method at 70 eV. M⁺ was found to be measured in all compounds except L-tyrosine (Tyr) and the base peaks were shown at (M-113)⁺ for T₄, L-3, 5, 3'-triiodothyronine (T₃), L-diiodotyrosine (DIT), L-monoiodotyrosine (MIT), and at (M-184)⁺ for L-3, 3', 5'-triiodothyronine (3, 3', 5'-T₃), L-3, 5-diiodothyronine (T₂), L-3, 3'-diiodothyronine (3, 3'-T₂), L-3', 5'-diiodothyronine (3', 5'-T₂), L-3-monoiodothyronine HCl·H₂O (3-T₁), L-3'-monoiodothyronine (3'-T₁), L-thyronine (T), Tyr. Individual derivatives gave single symmetrical peaks without tailing on their mass chromatograms. From the results of authentic compounds and of UV-light irradiated samples in mass spectra and mass chromatogram, T₃, 3, 3', 5'-T₃, T₂, 3, 3'-T₂, 3', 5'-T₂, 3-T₁, 3'-T₁, T, DIT, MIT, and Tyr were identified as photodegraded compounds of UV irradiated thyroxine. We confirmed the degradated processes of thyroxine caused by UV-light irradiation. That is, the photodegradation liberated iodine at the first step and then cleaved the ether bond in the molecule, and finaly caused the liberation of α-phenyl ring on our experiment.