(+)- and (−)-Spiroreticulatine, A Pair of Unusual Spiro Bisheterocyclic Quinoline-imidazole Alkaloids from the South China Sea Sponge <i>Fascaplysinopsis reticulata</i>

A pair of novel bisheterocyclic quinoline-imidazole alkaloids, (+)- and (−)-spiroreticulatine (1), were isolated from the South China Sea sponge Fascaplysinopsis reticulata. The structures and absolute configurations were elucidated by comprehensive spectroscopic analysis, single-crystal X-ray diffraction, and quantum chemical calculation methods. Spiroreticulatine is the first example of a sponge-derived natural spiro quinoline-imidazole alkaloid that may derive from tryptophan and 1,3-dimethylurea. Compound 1 showed inhibitory activity on IL-2 production but inactive against normal tumor cell lines.