Two new cytotoxic spermidine derivatives isolated from the Pacific soft coral Sinularia brongersmai have been identified as CH~(CR~)~-C(CH~)ECH-CO-NH(CH~)~-N(CH~)- (CH~)I,-N(CH~)~ and its dihydro analog by spectral methods combined with chemical conversions. Acid hydrolysis of the saturated amide followed by esterification yielded methyl 3-methyldodecanoate.