| Abstract
| - We present the crystal structure of an acridine drug derivatized at carbon 9, [Nα-(9-acridinoyl)-tetraarginine], intercalated within the dodecamer [d(CGCGAATTCGCG)]2. The presence of a lateral chainat the central carbon 9 atom differentiates this compound from most acridine drugs hitherto studied, whichare usually derivatized at carbon 4. The DNA:drug interaction we observe differs from that observed inprevious studies, which primarily involves shorter, mainly hexameric sequences, in two importantregards: the acridine intercalates within an AA/TT base step, rather than within a CG/CG base step; andthe binding site is located at the center of the sequence, rather than at one end of the duplex. In addition,we observe a novel crystal packing arrangement, with six dodecamer duplexes and seven hydratedmagnesium ions in the asymmetric unit of a large (66.5 × 68.4 × 77.4 Å3) unit cell in space groupP212121. The duplexes are organized in layers parallel to the ab plane, with consecutive layers crossingeach other at right angles.
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