Okadaic acid (OA) and dinophysistoxins (DTXs) are a group of polyethers known to sometimes contaminate filter-feeding shellfish that cause symptoms classified as diarrhetic shellfish poisoning. The algae Dinophysis acuta is one pro-genitor of okadaic acid, DTX-1 and 2, and is found in coastal waters of Norway. The chemistry of the algal toxins is of particular importance, as testing methods are becoming more specific towards particular structures.DTX-2 for analysis by NMR was obtained through four isolation experiments. The isolated toxin will become standard reference material as set forth by EU s BIOTOX program. DTX-2 from these experiments was used in NMR analyses for full assignment of the molecule in two deuterated solvents (CDCl3 and CD3OD).Concurrent analysis of DTX-1 by NMR in three different solvents (CDCl3, CD3OD, and CD3CN) was also undertaken, and the second objective for this thesis was to critically review 1H and 13C NMR assignments reported in the literature for DTX-1 and DTX-2. The literature presents confusing information concerning the molecular structures of DTX-1 and DTX-2 and implies that they have the same configuration at C-35.Analyses of the NMR data obtained for DTX-1 and DTX-2 determined that the C-35 methyl group is equatorially oriented (35R-) in DTX-1, but axially oriented (35S-) in DTX-2.The isolation procedures initiated a demand for quantifying small amounts of algal toxin. A method for quantifying ìg amounts of compound using NMR, without compromising the integrity of the isolated products, was therefore successfully developed.