On the Ground State Energy Hypersurface of Blepharismins and Oxyblepharismins

Summary.

 AM1 calculations on blepharismins and oxyblepharismins, which are related photosensory pigments of certain protists, revealed that the accessory substituents of the natural pigments do not lead to a change of the tautomerism and conformational states of the fundamental systems. The valence tautomerism possible in principle for the blepharismins yielding a cycloheptatriene–norcaradiene system was found to reside completely on the side of the cycloheptatriene. With respect to proton tautomerism, the strong predominance of the meso-type 7,15- and 7,14-dioxo tautomers was established in both series. Whereas the conformation of the fundamental condensed aromatic ring system of the oxyblepharismins remains comparable to that of hypericin, the conformational situation of the blepharismins was found to be unique with the phenyl group in an endo-position and dihedral twisting at the unperturbed bay-site only.