Two new dimeric compounds of the alternariol class, (±)-alternarlactones A (1) and B (2), were isolated along with 11 known compounds from the fungus Alternaria alternata P1210. Their structures were elucidated with the assistance of long-range HSQMBC to address inadequate cross-peaks in HMBC that result from the highly dense quaternary carbons, as well as theoretical calculations. All isolated altenuisol derivatives were screened for their antiparasitic activities, which provide a preliminary structure-activity relationship of this class of compounds against neglected tropical diseases.