The marine endophytic fungus Coniothyrium cereale produces the structurally unusual polyketide-type alkaloids (-)-cereolactam (1) and (-)-cereoaldomine (3), incorporating a lactam and an imine functionality, respectively, as well as the related metabolite (-)-trypethelone (2). Compounds 1 and 3 showed selective inhibition of human leukocyte elastase with IC50 values of 9.28 and 3.01 μM, respectively. Compound 2 was found to be inhibitory toward Mycobacterium phlei, Staphylococcus aureus, and Escherichia coli and also cytotoxic against mouse fibroblast cells (IC50=7.5 μM).