Chemistry of naphthazarin derivatives. 8. Determination of structures of substituted 2-hydroxy-6(7)-methoxynaphthazarins and 7(8)-hydroxypyranonaphthazarins by IR spectroscopy

A set of substituted 2-hydroxy-6(7)-methoxynaphthazarins and 7(8)-hydroxypyranonaphthazarins were synthesized. The IR spectra of 2-hydroxy-6-methoxynaphthazarins and 7-hydroxypyranonaphthazarins, on the one hand, and of 2-hydroxy-7-methoxynaphthazarins and 8-hydroxypyranonaphthazarins, on the other hand, have the characteristic nonoverlapping intervals of stretching vibration frequencies of the -hydroxy groups. These regularities confirm the structures of cristazarin and 6-methylcristazarin, which are metabolites of lichen Cladonia cristatella.     

Chemistry of naphthazarin derivatives. 7. Determination of structures of substituted 2,6(7)-dihydroxynaphthazarins by UV and IR spectroscopy

A set of substituted 2,6- and 2,7-dihydroxynaphthazarins were synthesized. The difference in the UV spectra of alkaline alcoholic solutions of 2,6- and 2,7-dihydroxynaphthazarins allows the reliable differentiation of the structures of these compounds. The IR spectra of 2,6- and 2,7-dihydroxynaphthazarins have characteristic nonoverlapping intervals of stretching vibration frequencies of the -hydroxy groups. Based on these spectral regularities, the data on cuculoquinone, which has been isolated previously from lichen Cetraria cucullata and has been identified as 7,7"-bis(3-ethyl-2,5,6,8-tetrahydroxynaphthalene-1,4-dione), were revised and the structure of 6,6"-bis(3-ethyl-2,5,7,8-tetrahydroxynaphthalene-1,4-dione) was assigned to this compound.     

The chemistry of naphthazarin derivatives

In water-containing organic solvents 2-oxo-2,3-dihydronaphthoquinone derivatives are hydrated to give the corresponding 2,2-dihydroxy-2,3-dihydronaphthoquinones. The hydration is reversible; in some cases, a keto-gem-diol equilibrium is established. The susceptibility of 2-oxo-2,3-dihydronaphthoquinone derivatives for hydration depends on the donor-acceptor properties of substituents at C(3), C(6), and C(7), on whether or not hydroxy groups are present at C(5) and C(8), and on the organic solvent basicity. For Part 5, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 3, pp. 465–470, March, 2000.