Identification of the major degradation products of 4-methoxy-2-(3-phenyl-2-propynyl)phenol formed by exposure to air and light.

Exposure of 4-methoxy-2-(3-phenyl-2-propynyl)phenol (CO/1828) to air and light (accelerated by temperature) yields 1-(2-hydroxy-5- methoxyphenyl)-3-phenylpropynone as the major degradation product. With extraction, this product rapidly degrades to 5-methoxyaurone and 6-methoxyflavone. In addition, a mixture of dimeric and heterodimeric compounds that are not fully identified was observed. These results indicate the formation of a reactive ortho-quinone methide as an unstable intermediate. This hypothesis is supported by evidence that the aurone slowly isomerizes into the flavone in control samples. Identification of compounds was accomplished with mass spectrometry, nuclear magnetic resonance spectrometry, UV-high-performance liquid chromatography, and comparison with authentic samples.