Indolizidine alkaloids with delta-opioid receptor binding affinity from the leaves of Elaeocarpus fuscoides

In the first chemical investigation of the Papua New Guinean plant Elaeocarpus fuscoides, one new indolizidine alkaloid, elaeocarpenine (1), and three known Alkaloids, isoelaeocarpicine (2), isoelaeocarpine (3), and elaeocarpine (4), were isolated from the leaves. Their structures were determined by 1D and 2D NMR spectroscopy. Since treatment of elaeocarpenine (1) with ammonia produced a 1:1 mixture of the diastereomers 3 and 4, we propose that elaeocarpenine (1) is the biogenetic precursor of isoelaeocarpine (3) and elaeocarpine (4). Compounds 1-4 demonstrated binding affinity for the human delta-opioid receptor with IC50 values of 2.7, 35.1, 13.6, and 86.4 microM, respectively.