A database study of nonbonded intramolecular sulfur-nucleophile contacts.

A search of the Cambridge Structural Database (1991, version 4.5) was performed to investigate nonbonded intramolecular 1,4 S...O close contacts of the kind seen in the thiazole nucleoside tiazofurin and other classes of compounds. The search yielded 362 structures with 1,4 S...O connectivity. S...O distances in 70% of these structures were less than the sum of the sulfur and oxygen van der Waals radii. Findings indicate that 1,4 S...O close contacts are common and so probably result from intramolecular interactions rather than from external crystal packing forces. A structure containing a sulfur atom in a conjugated ring system is more likely to exhibit 1,4 S...O close contacts than a structure containing a sulfur atom in an unconjugated and/or acyclic environment. Sulfur-nitrogen contacts were also investigated and were found to show similar properties. These results are consistent with findings from previous quantum-chemical-based studies performed on model fragments [Burling & Goldstein (1992). J. Am. Chem. Soc. 114, 2313-2320].