A known theonellapeptolide Ie, previously reported in other research group, was isolated from the methanolic extract of the Philippine sponge Theonella swinhoei. The planar structure of this compound was determined on the basis of NMR methods including HMBC and selective HMBC experiments. This is fast and efficient for the dereplication of natural products compared with the MS studies of fragments obtained from complete and partial hydrolysis. The sequence of thirteen amino acids including six N-methyl amino acids in the compound was clearly determined from correlations of extensive HMBC experiments.