Ellagitannins in antimycobacterial extracts of Combretum hartmannianum, a savannah woodland tree

Combretum hartmannianum Schweinf. (Combretaceae) is native to East Africa, growing naturally in woodland areas in Eritrea, Ethiopia, South Sudan and Sudan [1]. Various parts of this plant, including roots and stem are used traditionally in Africa against bacterial infections and their symptoms such as cough [2].
We have assessed the antimycobacterial activity of extracts of C. hartmannium against the TB model bacterium Mycobacterium smegmatis ATCC 14468 . The most promising growth inhibitory activity was observed for root extracts, such as a methanol soxhlet extract (IZ 31.5mm, MIC 312.5 µg/ml) and an ethyl acetate extract (MIC 1250 µg/ml). Cold methanol extracts of the stem bark and wood gave a MIC of 5000 µg/ml. Hexane and dichloromethane extracts of the stem wood and stem bark were devoid of activity. HPLC-DAD and UHPLC/QTOF-MS analysis of the ethyl acetate extract of the root resulted in the characterization of fifteen ellagitannins, among them punicalagin, castalagin, corilagin, tellimagrandin, terflavin B and S-flavogallonic acid, none of which have been identified before in C. hartmannianum. Six of the identified ellagitannins are unknown and NMR is needed to elucidate their molecular structures. Previously, flavogallonic acid dilactone and terchebulin have been identified in C. hartmannianum stem bark [3]. Our results indicate that roots of C. hartmannianum contain a high diversity and concentration of ellagitannins which could be potential agents against tuberculosis.