C2 -endo-sugar pucker

The two others, XXX and XXXI, were created from hydrogen bonding theory. All nucleotide conformations in the motif were assigned C2 - and CJ-endo sugar pucker modes and the glycosylic torsion the syn and anti values. 

It can be seen that alkylation has changed the sugar-base conformation (distant from the site of alkylation) from anti (as in deoxyadenosine and in B-DNA) to syn (as in alkylated deoxyadenosine and in some bases in Z-DNA). The sugar puckers are either C2 -endo or C3 -endo. A second structural feature of great interest in these crystals is that the more planar anthracene portion of the PAH is stacked between adenine residues of other molecules throughout the crystal. The highly buckled region of the PAH does not take part... 

FIGURE 12.40. The conformations of furanose sugars, (a) Conformations of five-membered rings. When a line is drawn through C4 -01 -C1, the pucker is described by which atom in the five-membered ring is most out of this plane of the five-membered ring, (b) CZ -endo with C3 most out of the plane on the C5 side, (c) C2 -exo with C2 most out of the plane on the opposite side from C5, (d) C2 -endo with C2 most out of the plane on the C5 side, and (e) C3 -exo with C3 most out of the plane on the opposite side from C5. ... 

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