Sumatranins A–J: Lignans with Immunosuppressive Activity from Cleistanthus sumatranus

Chemical investigation of the twigs of Cleistanthus sumatranus (Phyllanthaceae) led to the isolation of 10 undescribed lignans, sumatranins A–J (1–10). Compounds 1–4 are unprecedented furopyran lignans characterized by a unique 2,3,3a,9a-tetrahydro-4H-furo[2,3-b]chromene heterotricyclic framework. Compounds 9 and 10 are rare 9′-nor-dibenzylbutane lignans. Structures were established based on analyses of spectroscopic data, X-ray crystallographic data, and experimental ECD spectra. Immunosuppressive assays revealed compounds 3 and 9 displayed moderate inhibitory effects with good selectivity indexes against LPS-induced B lymphocyte proliferation.