Clionamide, the major metabolite of the burrowing sponge C. celata, was isolated. The structure of clionamide was shown to be (2S)-N-((1E)-5,6,7-trihydroxystyr-1-yl)-2-amino-3-(6-bromoindol-3-yl)propionamide by spectral analysis and by interconversion to its tetracetyl derivative 2. The structure of 2 was determined from spectral data and extensive chemical degradation and was confirmed by the synthesis of its ultimate hydrogenation product, N-(5,6,7-triacetoxypheneth-1-yl)-2-acetamido-3-(indol-3-yl)propionamide.