Quebecol, a novel phenolic compound isolated from Canadian maple syrup

Abstract

The province of Quebec in Canada leads the world’s production of maple syrup, a natural sweetener obtained by thermal evaporation of sap collected from maple (Acer) species. As part of our laboratory’s detailed chemical investigation of Canadian maple syrup, a novel phenolic compound, 2,3,3-tri-(3-methoxy-4-hydroxyphenyl)-1-propanol, assigned the common name of quebecol, was obtained. Quebecol was isolated using a combination of chromatographic methods and identified by detailed 1D and 2D nuclear magnetic resonance (NMR) and mass spectral (MS) analyses. Liquid chromatography mass spectral (LC-MS) analyses revealed that quebecol is not originally present in maple sap. This observation, as well as the lack of a feasible biosynthetic pathway to explain its origin, suggests that quebecol is formed during the processing and/or extraction of maple syrup. Thus, the identification and biological evaluation of non-natural, process-derived compounds in maple syrup are warranted since such molecules may contribute towards the biological activities reported for this natural sweetener.

Introduction

Maple syrup is the largest commercially produced and consumed natural product which is obtained entirely from the sap of deciduous trees. It is produced by thermal evaporation of the colourless watery sap collected from maple (Acer) species in the spring months when freeze/thaw cycles cause the sweet sap to rise and flow from taps made in the tree trunk. Maple sap is boiled to concentrate the sugar and approximately 40 L of the sap is required to produce 1 L of the rich 66° Brix syrup (Perkins & van den Berg, 2009). Apart from sucrose which is its predominant sugar, the natural tree sap contains minerals, oligosaccharides, amino acids, polyphenols, and phytohormones (Ball, 2007, Davison and Young, 1973, Perkins and van den Berg, 2009, Potter and Fagerson, 1992). During the intensive heating process required to transform the sap into syrup, a complex cocktail of both native phenolics (originally present in the xylem sap) and derived compounds (formed through chemical reactions during processing) ultimately ends up in maple syrup (Ball, 2007). This is interesting from a human health perspective considering that phenolics have attracted significant research attention for their potential roles in human health promotion and disease prevention (Shahidi & Ho, 2005).

Canada and the United States are the only two countries that commercially produce maple syrup in the world. Canada’s production accounts for more than 80% of the world’s supply of maple syrup with the province of Quebec leading this production with ca. 91% (Ontario Ministry of Agriculture Food & Rural Affairs). Apart from its cultural significance, maple syrup production is thus of great economic importance to the north-eastern region of North America.

Given the worldwide popularity and consumption of this natural sweetener, chemical identification of maple syrup constituents is of great scientific interest. Moreover, published studies have shown that maple syrup extracts have antioxidant, antimutagenic, and human cancer cell antiproliferative properties (Legault et al., 2010, Theirault et al., 2006). To this end, our laboratory has embarked on a collaborative project to comprehensively identify the chemical constituents in maple syrup from Canada (Li & Seeram, 2010). In that study, we isolated 23 naturally derived phenolics belonging to lignan, coumarin, stilbene, and phenolic acid sub-classes in maple syrup. Here, we report the isolation and structural elucidation of a novel process-derived phenolic compound from the Canadian maple syrup which has been assigned the common name of quebecol.