ELUCIDATION OF THE CONFORMATIONAL PROPERTIES OF N-FORMYLGLYCINE DITHIO ACID BY ABINITIO SCF-MO CALCULATIONS

Ab initio SCF-MO calculations were carried out for the molecule N-formylglycine dithio acid using STO-3G and 3-21G basis sets. Structures and energies of several conformations of this molecule determined by gradient geometry refinement are reported, and some conformationally dependent local geometry trends discussed. For conformations involving rotational isomerism about the NH-CH2 and CH2-C(=S) single bonds, the 3-21G results reveal the presence of three conformational states. These conformers are strikingly similar to those determined for glycine dithio esters by X-ray crystallographic and vibrational spectroscopic analyses. One conformer has a small NH-CH2-C-S(thiol) torsional angle and close N-to-S(thiol) atom contact. The calculations provide a description of this N...S nonbonded interaction which has implications for the structure and reactivity of enzyme-substrate complexes which incorporate a similar contact. However, no evidence is found for favorable N-to-S(thiono) interactions for the conformer which has a small NH-CH2-C=S torsional angle.