[Show abstract][Hide abstract] ABSTRACT: Two polyketide metabolites, nhatrangins A (1) and B (2), were isolated from a Vietnamese collection of Lyngbya majuscula. These compounds are related to the aplysiatoxin series of metabolites, which have also been isolated from this species of marine cyanobacterium. The use of 900 MHz cryoprobe NMR allowed the elucidation of the 2D structure of 1 from approximately 0.3 mg of compound. LC-MS analysis was utilized to direct the isolation of additional material as well as the isolation of 2. Conformational analysis was completed using J-based coupling constant analysis and selective NOE experiments.