(2R∗, 3S∗, 4S∗, 2″R∗, 3″S∗)-Guibourtinidol-(4α→8)-catechin, a biflavanoid procyanidin of the proguibourtinidin group from Senna macranthera: its relative stereochemistry and conformation. Issue 5 (28th March 2015)