Figure 6.
Structures of two possible rotamers of 1a and 2a. A steric clash arises when H7 is oriented towards the hydroxyl group in the co-planar conformation of the pterin and dithiolene units. Pterin rotation around the C6–Cα bond produces a more stable conformation due to possible formation of an intramolecular N5···H–O hydrogen bond (highlighted in blue).