21 - Current Organic Chemistry, 2004, 8, 845-865 845...

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Current Organic Chemistry , 2004, 8, 845-865 845 1385-2728/04 $45.00+.00 © 2004 Bentham Science Publishers Ltd. Progress Toward Understanding the Nature and Function of C–H•••O Interactions Ronald K. Castellano* Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA Abstract: Recent studies confirm that C–H•••O hydrogen bonds have many, if not all , of the spectroscopic and physical earmarks of “traditional” H-bonds. Only more recently have we come to understand that these contacts are operative not only in protein-protein recognition, but enzyme-substrate interactions (with implications for drug design), biological and nonbiological transition state stabilization and have, in some circumstances, a strength and geometric predictability to make them useful in the construction of materials and supramolecular assemblies. Forays into each of these areas have come largely due to advances in computational protocols and spectroscopic instrumentation. This review discusses the most recent findings related to the nature (i.e. strength, geometrical preferences, and spectroscopic features) and function (i.e. in supramolecular design and synthesis, conformational control, enantioselective synthesis, and biology) of C–H•••O interactions in a variety of chemical and biological systems. An understanding of the key features of these interactions should promote their deployment in target areas like medicinal chemistry and materials science. Dedicated to Professor Jack D. Dunitz 1. INTRODUCTION Close contacts between relatively acidic C( α29 –H protons and amide carbonyl oxygens were detected in sheet-like arrangements of peptides as early as the 1940’s [1]. The potential structure- or function-serving roles of these contacts in secondary structures could in no way be formally assessed at this time largely due to technological limitations. Only more recently have we come to understand that weak, noncovalent interactions are operative not only in protein- protein recognition, but enzyme-substrate interactions (with implications for drug design), biological and nonbiological transition state stabilization and have, in some circum- stances, a strength and geometric predictability to make them useful in the construction of materials and assemblies. A recent X-ray crystal structure of human lysosomal aspartyl- glucosaminidase (Fig. 1 ) shows short C–H•••O contacts, together with conventional N–H•••O H-bonds, between adjacent β -strands — the structure is one of many that feature important C–H•••O interactions at protein interfaces (Section 3.4.3) [2]. This review focuses almost exclusively on the most recent literature in the area of C–H•••O interactions. It is in no way meant to be a treatise on H-bonding — for this the reader is referred to several excellent resources [3-8]. Additionally, nearly all of the early history regarding
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21 - Current Organic Chemistry, 2004, 8, 845-865 845...

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