| abstract |
This invention relates to compounds having the following structure: wherein Y is O, X is O, bond α is absent and bond β is present, or Y is H, X is CH, bond α is present, and bond β is absent; atom Z is a carbon and bonds χ, δ and γ are present, or atom Z is a nitrogen and bonds χ, δ and γ are absent, or atom Z is a nitrogen and bonds χ and δ are present and γ is absent. R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are various substituents as described in the specification. |