Two new sulfur-containing amides, entadamide A (1) and entadamide B (2), isolated from the seeds of Entada phaseoloides, were synthesized by the addition reaction of methanethiol to propiolic acid (5) followed by condensation with ethanolamine by the use of dicyclohexylcarbadiimide. These compounds inhibited the 5-lipoxygenase activity of RBL-1 cells at 10^-4 g/ml. This finding suggests that entadamides A and B may be examples of a new type of anti-inflammatory drug.