Figure 1.

Classification of the 277 tetramic acids (TAs) from marine microorganisms into eight classes. Some examples of typical molecules belonging to these classes are illustrated: simple 3-acyl-tetramic acids (penicillenol A₁), 3-oligoenoyltetramic acids (tirandamycin A), 3-decalinoyltetramic acids (equisetin), 3-spirotetramic acids (pseurotin A), macrocyclic tetramic acids (from left to right, ikarugamycin, GKK1032A₂), N-acylated tetramic acids (symplostatin 4), α-cyclopiazonic acid (CPA)-type tetramic acids (α-cyclopiazonic acid), and other tetramic acids (vermelhotin). The main characteristics of each chemical class are highlighted in red.