I. Ariziridinomitosene Synthesis and DNA Binding Properties.
An aziridinomitosene, a compound related to the clinically used anticancer agent mitomycin C, has recently been shown to form DNA interstrand cross-links under non-reductive conditions. The occurrence of the cross-link is significant for two reasons. First, mitomycin C prohibits cell proliferation via the formation of rare interstrand DNA cross-links. Second, aziridinomitosenes were previously thought to be responsible solely for formation of less toxic DNA monoadducts. Several factors may facilitate this previously unobserved cytotoxic event, including the presence of additional electrophilic sites on the quinone ring at C-6 and C-7. Evidence suggests that the C-1 and C-10 electrophilic sites are key to cross-link formation, as is the case with mitomycin C, but the molecular structure of the cross-link is not known. The mechanism of DNA cross-linking by the synthetic aziridinomitosene is hypothesized to involve monoalkylation of DNA at C-1 followed by nucleophilic attack at C-6 or C-7 of the quinone ring, which in turn activates C-10 for a second alkylation of DNA. Our current research efforts aim to identify the molecular structure of the DNA-aziridinomitosene interstrand cross-link, determine the role of the four electrophilic sites, and investigate the physical properties required to induce cross-link formation. Specifically, we are currently preparing relevant mitosene analogs, characterizing mitosenes with respect to physical properties, and are conducting in vitro assessments of DNA alkylation by mitosene derivatives.
II. Synthetic and Computational Investigations of Electrocyclization and Cycloaddition Reactions of Azomethine Ylides.
Electrocyclization and cycloaddition of azomethine ylides and azaallyl anions offer potential for regio- and stereocontrolled formation of azacycles. Thus, these reactive intermediates have been investigated computationally. Specifically, we have studied the properties of conjugated azomethine ylide and azaallyl anion systems that are theoretically capable of undergoing disrotatory electrocyclization due to their six pi electrons. As ring closure is dependent on the geometry of the intermediates, a computational study of conformer energies and interconversion energy barriers has been conducted. Initial studies suggest that intermediates substituted at the four position favor the U-geometry required for electrocyclization. Further calculations indicate that added steric hindrance at this position gives increased bias toward the U conformer while simultaneously lowering the activation energy required for electrocyclization. Related studies have examined the structural properties that facilitate spontaneous ring opening of 4-oxazolines to produce stabilized azomethine ylides.