Transferring petrochemical methods to pharmacognosy: a novel screening system for oligomeric proanthocyanidins using Kendrick mass defect

Proanthocyanidins (PACs) are complex polyphenolic substances composed of flavan-3-ol building blocks, existing in numerous plants. They occur as oligomeric and polymeric PACs, depending on the degree of polymerisation (DP). Whereas analytical methodology for PACs with low DP is well established, analysis of higher oligomers and polymers is still challenging, since structural diversity of the polymer strands is increasing with higher DP. Typical modifications are related to building blocks with different hydroxylation pattern or to additional substitution e.g., galloylation. Furthermore, two types of interflavan linkages - B-type (4→6 or 4→8) or A-type (4→8/2→7) - are possible [1]. In this study, Kendrick Mass Defect (KMD), which is a common methodology to characterize hydrocarbon polymers in petrochemistry since the 1980’s, is transferred to PACs, based on LC-(+)ESI-qTOF-MS data obtained from extracts of model herbal material Tiliae flos, Crataegi folium cum flore and Wisteriae floribundae fructus. Catechin, the predominant flavan-3-ol unit in PACs, serves as a reference unit, instead of commonly used CH₂-blocks. With the help of a KMD-diagram extracts can be screened quickly for detailed PAC-composition. This method provides information regarding the different DP clusters within the extract as well as detailed composition of each DP cluster, especially in respect of building blocks. KMD-diagram of Tiliae flos revealed oligomeric A-type and B-type PACs composed of (epi)catechin units up to DP 8, which was affirmed by MS² fragments. In Wisteriae floribundae fructus PACs consisting of three different types of building blocks - (epi)afzelechin, (epi)catechin and (epi)gallocatechin - can be detected.

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• References

• 1 Neilson AP, O’Keefe SF, Bolling BW. High-molecular-weight proanthocyanidins in foods: overcoming analytical challenges in pursuit of novel dietary bioactive components. Annu Rev Food Sci Technol 2016; 7: 43-64