Chemical profiling and characterisation of anthraquinone-based polyphenols as biocolourants from Cortinarius semisanguineus

Abstract

Anthraquinone dyes are known for their significant colour (brightness of shade in the red, blue and green areas) and light fastness properties compared with other synthetic dyes (such as azo-based dyes). However, challenging multi-step synthesis of anthraquinones and limited access to fewer substituents result in insufficient reactivity, hindering their wider industrial applications. Therefore, seeking highly substituted anthraquinone-based colourants from natural sources is gaining interest among researchers. Notably, certain species of Dermocybe mushrooms are recognised for their red gills rich in anthraquinone colourants, which have been studied. However, limited knowledge of the chemotaxonomic characteristics of their species and molecular structure hinders wide use of their commercial applications. Our study screened extraction methods for their selectivity towards specific anthraquinone types, such as glycosidic vs non-glycosidic, or those with carboxylic acid groups vs those without. In our observation, a sequential extraction strategy, starting with aqueous buffer extract followed by acetone extract, selectively yielded carboxylic acid-containing anthraquinones and non-carboxylic acid-containing anthraquinones, respectively. We carried out a detailed analysis of anthraquinone-based colourants in Cortinarius semisanguineus, comparing MS1-MS2 profiles with two other species of the Dermocybe fungus group (Cortinarius sanguineus and Cortinarius ominosus), highlighting key interspecies differences in expressing certain anthraquinones or regioisomers. This study led to the structural identification of eleven natural anthraquinones and their glycosidic forms among these species. The carboxylic anthraquinones identified and characterised by their fragmentation pattern using MS1-MS2 profiles include dermolutein, dermorubin, chlorodermorubin, endocrocin and chlorodermolutein, while the non-carboxylic anthraquinones, primarily from the acetone extract, were dermoglaucin, emodin and dermocybin.