Colored Dimeric Alkaloids from the Barks of <i>Erythrina variegata</i> and Their Neuroprotective Effects

Abstract

Five dimeric <i>Erythrina</i> alkaloids, named erythrivarines J-N, were isolated from the barks of <i>Erythrina variegata</i> L. (Fabaceae). The erythrivarines J-L featured a 6/6/5/6/6/5/6/6/6 ring system and super conjugated double bond systems, causing intense color from blue to wine red, while erythrivarines M-N looked orange. The structures of the isolated compounds were elucidated by 1D and 2D NMR experiments combined with MS and confirmed by the X-ray crystal diffraction technique. The performed bioassay using HEI-OC-1 cells revealed neuroprotective properties of erythrivarine N against the hearing loss causing antibiotics, neomycin.