Two new proanthocyanidin trimers isolated from Cistus incanus L. demonstrate potent anti-inflammatory activity and selectivity to cyclooxygenase isoenzymes inhibition

Two new proanthocyanidin trimers have been isolated from Cistus incanus herb; gallocatechin-(4α→6)-gallocatechin-(4α→8)-gallocatechin (compound 1) and epigallocatechin-3-O-gallate-(4ß→8)-epigallocatechin-3-O-gallate-(4ß→8)-gallocatechin (compound 2). The structures were determined on the basis of 1D- and 2D-NMR (HSQC, HMBC) of their peracetylated derivatives, MALDI-TOF-MS and by acid-catalysed degradation with phloroglucinol. A more abundant proanthocyanidin oligomer was also isolated, purified and its chemical constitution studied by ¹³C-NMR and phloroglucinol degradation. The mean molecular weight of the polymer was estimated to be about 7 to 8 flavan-3-ol-units with a ratio of procyanidin : prodelphinidin units at 1:5, some of which are derivatised by gallic acid. Water extract and higher oligomeric proanthocyanidin fractions of C. incanus significantly inhibited TPA-induced oedema when applied topically at doses of 0.5 and 1 mg/ear in mice. Furthermore, the extracts and the pure compounds inhibited COX-1 and COX-2 activities. In addition, compound 2 exhibited an IC₅₀ of 4.5 μM against COX-2 indicating its high selectivity towards COX-2.