W0309

Unusual Hydrogen Bonding in Quinoline Carboxylic Acid Compounds. Amy A. Narducci*, Gudrun A. Trescher*, R. Curtis Haltiwanger*, Jeffrey M. Axten⁺, Robert A. Daines⁺, and William D. Kingsbury⁺, Depts. of Physical and Structural Chemistry* and Medicinal Chemistry⁺, SmithKline Beecham Pharmaceuticals, P.O. Box 1539, King of Prussia, PA 19406

Three quinoline carboxylic acid compounds (Fig. 1.) have been synthesized and studied by single crystal x-ray diffraction techniques: 1-(6-Chloro-benzo[1,3]dioxol-5-ylmethyl)-6-(2,6-dichloro-benzyloxy)-4-oxo-1,4-dihydro-quinoline-2-carboxylic acid (1), 1-Ethyl-6-methoxy-4-oxo-1,4-dihydro-quinoline-2-carboxylic acid (2), and 6-Allyloxy-1-ethyl-4-hydoxy-1,4-dihydro-quinoline-2-carboxylic acid (3). Structural analyses of these materials show them to form unexpected hydrogen bonding contacts. Instead of forming typical carboxylic acid dimers, these compounds share hydrogen atoms between the carboxylate and quinoline oxygen atoms, forming an infinite hydrogen bond network. For 1 and 2 the resultant solid-state structures are an average of acid and hydroxyl tautomers. In the case of 3, the hydrogen atom lies much closer to the quinoline oxygen, suggesting that this compound exists solely as the hydroxyl form.