An ab initio computational molecular orbital study of the conformers of muconaldehyde, and the possible role of 2-formyl-2H-pyran in bringing about the conversion of a (Z,Z)-muconaldehyde structure into an (E,Z)-muconaldehyde structure
Journal Article
·
· Chemical Research in Toxicology
- Philadelphia College of Textiles and Science, PA (United States)
- Fox Chase Cancer Center, Philadelphia, PA (United States)
- Rutgers Univ., New Brunswick, NJ (United States)
To determine whether conformers of 2-formyl-2H-pyran (2F2HP) can serve as intermediates in the isomerization (Z,Z)-muconaldehyde {yields} (E,Z)-muconaldehyde - an essential step in the metabolic oxidation of benzene in which (E,E)-muconic acid is formed - we have carried out ab initio molecular orbital calculations at the MP2/6-31G* (frozen core, valence orbitals active) level with full geometry optimization at the RHF/6-31G* level. Taking account of the configuration about the carbon-carbon single bonds as well as that about the double bonds, the six conformers of (Z,Z)-muconaldehyde have been characterized, as well as the eight conformers of (E,Z)-muconaldehyde. Axial and equatorial conformers of 2F2HP have been identified, which exist in stable syn or anti forms depending on the relative position of the pyran and carbonyl O-atoms. Each step in the metabolic pathway is stereospecific. The initial ring opening in 2,3-epoxyoxepin gives (eZzZz)-muconaldehyde, which then undergoes ring closure to give anti-axial-2F2HP. Inversion of the ring gives anti-equatorial-2F2HP, which upon ring opening gives (zEzZz)-muconaldehyde. An alternative pathway links (zZzZz)-muconaldehyde with syn-axial-2F2HP, and syn-equatorial with (eEzZz)-muconaldehyde. Half-reaction times, taking into account the fractional representation of each reacting conformer in rapidly established equilibrium mixtures, suggest that the operative pathway is via step a, with little to choose between steps b and b{prime}.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 45253
- Journal Information:
- Chemical Research in Toxicology, Journal Name: Chemical Research in Toxicology Journal Issue: 4 Vol. 7; ISSN 0893-228X; ISSN CRTOEC
- Country of Publication:
- United States
- Language:
- English
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