New spirocyclic sesquiterpenes from the marine sponge Geodia exigua

Three new spirocyclic sesquiterpenes designated exiguamide (), exicarbamate () and exigurin (), together with (−)-10-epi-axisonitrile-3 (), have been isolated from the marine sponge Geodia exigua. All four compounds possess the spiro[4.5]decene skeleton and their structures were determined on the basis of spectroscopic data. The structure of was confirmed by X-ray crystallographic analysis and the absolute configuration was determined by applying the modified Mosherʹs method on its amine derivative. Exiguamide () inhibited cell fate specification during sea urchin embryogenesis at a minimum inhibitory concentration of 0.4 μM.