Analyzing the X-ray structures available on the protein databank (www.pdb.org/pdb) for CYP2A6 complexed with the natural substrate (coumarin, PDB entry 1Z10) and with a linear psoralen inhibitor (xanthotoxin, PDB entry 1Z11), it was found that both compounds bind in a similar manner, and that the carbonyl group of the coumarin moiety interacts very closely with Asn297 [34]. The only observed difference was in the type of interactions nearby the iron atom from the heme cofactor. In the natural substrate, the position 7 of the coumarin ring is very close to this centre (3.09 Å), thus favoring the hydroxylation reaction in this position. In the psoralen, it is the oxygen from the furan group that comes closer to this centre (3.25 Å). This result indicates that the inhibitory power of the psoralen may be related to the chelation of the oxygen from the furan ring with the iron from the heme, possibly resulting in the inactivation of the enzyme.
The molecular docking studies performed with compounds 1, 3e6 show that the binding poses of some of the compounds are very similar to those that are represented on Fig. 1, while others differ significantly (Fig. 2).