Massetolides A-H (1-8), novel cyclic depsipeptides, and the known compound viscosin (9) have been isolated from cultures of two Pseudomonas sp. isolated from a marine alga and a marine tube worm, respectively. Massetolide A (1) and viscosin (9) exhibit in vitro antimicrobial activity against Mycobacterium tuberculosis and Mycobacterium avium-intracellulare. Precursor-directed biosynthesis has been used to generate unnatural massetolides 11-13 incorporating nonprotein amino acids.