Abstract:
:Comparative X-ray crystallographic structure analyses have been carried out on seven cyclopenta[a]phenanthrenes, namely 15,16-dihydocyclopenta[a]phenanthren-17-one and its 2-, 6- and 12-methyl homologues (non-carcinogens) and the 7-and 11-methyl and 1,11-methano derivatives (carcinogens). All-valence-electron molecular-orbital calculations by the CNDO/2 method, using the crystallographic parameters, have also been executed. Charge distribution and the energies of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) have been calculated. With one exception all the molecules show only small deviations from planarity, the exception being the strongly carcinogenic 11-methyl-17-ketone in which the bay-region methyl group causes out-of-plane deformation of the benzo rings of 12.5 degrees. Among the other six compounds the two carcinogens are readily differentiated by high angle strain induced by a 7-methyl group or a 1,11-methano bridge. As expected, the HOMO's of these molecules to some extent reflect their ease of chemical oxidation at the 6,7-double bond; biological oxidation is less easy to correlate probably due to spatial restrictions at the active site within the mono-oxygenase.
journal_name
Carcinogenesisjournal_title
Carcinogenesisauthors
Clayton AF,Coombs MM,Henrick K,McPartlin M,Trotter Jdoi
10.1093/carcin/4.12.1569subject
Has Abstractpub_date
1983-12-01 00:00:00pages
1569-76issue
12eissn
0143-3334issn
1460-2180journal_volume
4pub_type
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