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 intramoiecular 1,4 S...O close cont acts 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 th an the sum of the sulfur and oxygen van der Waals radii. Findings indi cate that 1,4 S...O close contacts are common and so probably result f rom intramolecular interactions rather than from external crystal pack ing 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 struc ture containing a sulfur atom in an unconjugated and/or acyclic enviro nment. 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 fragm ents [Burling & Goldstein (1992). J. Am. Chem. Soc. 114,2313-2320].