Table 2. Selected dihedral angles (in degrees) for the BP-1 and BP-2 complexes.
Angle* | BP-1 | BP-2 |
---|---|---|
χ | 219.5 | 268.1 |
α′ | 156.8 | -85.1 |
β′ | 107.0 | -47.2 |
N6-C10-C9-O9 | 37.4 | 66.2 |
O9-C9-C8-O8 | -54.4 | -57.6 |
O8-C8-C7-O7 | -84.8 | -83.4 |
In both BP-1 and BP-2, the partially saturated ring assumes a distorted half-chair conformation. In BP-1, the C10-N6 bond linking the hydrocarbon to the base makes an angle of ≈50° with the plane of the aromatic rings, corresponding to an orientation for this bond that is about midway between axial and equatorial; whereas, in BP-2, this bond is pseudoequatorial and makes an ≈25° angle with the aromatic system. In both structures, the 7- and 8-hydroxyl groups are close to pseudoequatorial, and the 9-hydroxyl group is pseudoaxial. This orientation of the 9-hydroxyl group closely resembles that proposed in the NMR solution structure of a DNA duplex containing a cis opened (10R) BP tetrahydroepoxide dA adduct (PDB accession code 1N8C, Fig. 3A) that lacked the 7- and 8-hydroxyl groups on the tetrahydro ring (6).
Angles are defined as follows: χ = O4′-C1′-N9-C4; α′ = N1-C6-N6-C10(BP); β′ = C6-N6-C10(BP)-C9(BP).