Total Synthesis of Hybocarpone, a Cytotoxic Naphthazarin Derivative from the Lichen Lecanora hybocarpa, and Related Compounds

The concise synthesis of the lichen-derived antitumor agent hybocarpone (1) and its analogs is described. A new synthetic approach is based on the direct oxidative dimerization of the available naphthazarin precursors in the formation of the binaphtho[2,3- b; 2,3- d]furantetraone structure. It was shown that the first step to tetrahydrofuran features is the bridging hindered S*, S* and R*, S* carbon-carbon bonds of the molecules, setting the relative configurations of the 5a S*,6a S*,12a S*,12b S* and 5a S*,6a R*,12a R*,12b S* diastereomers.

Total synthesis of hybocarpone, a cytotoxic naphthazarin derivative from the lichen Lecanora hybocarpa, and related compounds

The concise synthesis of the lichen-derived antitumor agent hybocarpone (1) and its analogs is described. A new synthetic approach is based on the direct oxidative dimerization of the available naphthazarin precursors in the formation of the binaphtho[2,3-b; 2,3-d]furantetraone structure. It was shown that the first step to tetrahydrofuran features is the bridging hindered S*,S* and R*,S* carbon-carbon bonds of the molecules, setting the relative configurations of the 5aS*,6aS*,12aS*,12bS* and 5aS*,6aR*,12aR*,12bS* diastereomers.

Oxirapentyns F-K from the marine-sediment-derived fungus Isaria felina KMM 4639

Six new highly oxygenated chromene derivatives, oxirapentyns F-K (2-7), one new polyketide (8), one new benzofurane (9), and two known cyclodepsipeptides, isoisariin B and isaridin E, were isolated from the lipophilic extract of the marine-derived fungus Isaria felina KMM 4639. The structures of compounds 2-9 were determined using spectroscopic methods. The relative configurations of compounds 2-7 were established through a combination of NOE data and spin coupling constants, and these results were confirmed by X-ray crystallographic analysis of 4. The absolute structures of all oxirapentyns were assumed based on their biogenetic relationship and confirmed using the modified Mosher's method on 2 and 7. Isariketide (8) showed moderate cytotoxicity toward HL-60 cells.

Concerning the Structure of Islandoquinone Isolated from the Lichen Cetraria islandica

An investigation of the oxidative coupling products of some substituted hydroxynaphthazarins led to a revision of the proposed structure of islandoquinone, previously isolated from the lichen Cetraria islandica, and yielding (7a S*,13a S*)-6,7a-diethyl-2,5,9,11,12,13a-hexahydroxy-7,14-dioxabenzo[ a]tetracene-1,4,8,13(7a H,13a H)-tetraone through X-ray diffraction analysis of its 2,11-dimethyl ether.

Concerning the structure of islandoquinone isolated from the lichen Cetraria islandica

An investigation of the oxidative coupling products of some substituted hydroxynaphthazarins led to a revision of the proposed structure of islandoquinone, previously isolated from the lichen Cetraria islandica, and yielding (7aS*, 13aS*)-6,7a-diethyl-2,5,9,11,12,13a-hexahydroxy-7, 4-dioxabenzo[a]tetracene-1,4,8,13(7aH, 13aH)-tetraone through X-ray diffraction analysis of its 2,11-dimethyl ether.

Disordering of the [NbOF5]2- complex anions in bis(glycinium) pentafluoridooxidoniobate(V) and bis(beta-alaninium) pentafluoridooxidoniobate(V) dihydrate

The title compounds, (C(2)H(6)NO(2))(2)[NbOF(5)], (I), and (C(3)H(8)NO(2))(2)[NbOF(5)].2H(2)O, (II), are built from isolated distorted octahedral [NbOF(5)](2-) complex anions, amino acid cations and water molecules [for (II)]. In the pentafluoridooxidoniobate(V) anions, the Nb and O atoms, and the F atoms in trans positions with respect to the O atoms, are disordered about an inversion centre for both structures. The Nb atoms are shifted from the inversion centres by distances of 0.1455 (1) and 0.1263 (2) A for (I) and (II), respectively. The Nb=O and Nb-F(trans) bond lengths are 1.7952 (3) and 2.0862 (3) A, respectively, for (I), and 1.8037 (7) and 2.0556 (7) A for (II). In the crystal structures, cations and water molecules [for (II)] are linked to the [NbOF(5)](2-) anions via hydrogen bonds. This study demonstrates the possibility of true geometry determination of disordered [NbOF(5)](2-) complex anions in centrosymmetric structures.