Coibamide A is a methyl-stabilized cyclic depsipeptide with a lariat side chain that was isolated from a marine cyanobacterium as part of an International Cooperative Biodiversity Groups program based in Panama. Previous testing of this potent and selective growth-inhibitory agent in the National Cancer Institute (NCI) in vitro 60 human cell line panel revealed a "COMPARE-negative" profile indicative of a unique mechanism of action. Presented herein is a collection of studies characterizing the mechanism of action of coibamide A and cataloguing the cytotoxicities of putative coibamide A and related structures from efforts at its total synthesis. We report that coibamide A induces apoptotic and non-apoptotic cell death in human U87-MG and NCI-SF-295 glioblastoma cells, respectively, which can occur independently of a rapid and sustained mTOR-independent autophagic response. Loss of cell viability from coibamide A exposure was concentration-dependent and time-sensitive, characterized by extensive cytoplasmic vacuolization and an absence of apoptotic morphology and DNA fragmentation prior to cell rounding and detachment from the substratum. Coibamide A also induces a cytostatic effect mediated by a G1 phase specific cell cycle arrest and inhibits glioma cell invasion but not migration. Lastly, structure activity relationships suggest that linearization, loss of N-methylation and disjoining of the cyclic and side chain structures of coibamide A are not well-tolerated modifications to retain activity.