Isolation, identification and quantitation of hydroxycinnamic acid conjugates, potential platform chemicals, in the leaves and stems of Miscanthus x giganteus using LC-ESI-MS(n)

Miscanthus x giganteus is a source of platform chemicals and bioethanol through fermentation. Cinnamates in leaves and stems were analysed by LC-ESI-MS(n). Free phenols were extracted and separated chromatographically. More than 20 hydroxycinnamates were identified by UV and LC-ESI-MS(n). Comparative LC-MS studies on the leaf extract showed isomers of O-caffeoylquinic acid (3-CQA, 4-CQA and 5-CQA), O-feruloylquinic acid (3-FQA, 4-FQA and 5-FQA) and para-coumaroylquinic acid (3-pCoQA and 5-pCoQA). Excepting 3-pCoQA, all were also detected in stem. 5-CQA dominated in leaf: a mandelonitrile-caffeoylquinic acid dominated in stem. Three minor leaf components were distinguished by fragmentation patterns in a targetted MS2 experiment as dicaffeoylquinic acid isomers. Others (M(r) 516) were tentatively identified as hexosylcaffeoyl-quinates. Three positional isomers of O-caffeoylshikimic acid were minor components. p-Hydroxybenzaldehyde was also a major component in stem. This is the first report of the hydroxycinnamic acid profile of leaves and stems of M. x giganteus.