Natural diaryl ethers
In this review, on the basis of an analysis of voluminous literature material on natural phenolic compounds belonging to various structural types, the interrelationship between the dimeric molecules formed as the result of the oxidative coupling of the corresponding monomeric compounds is considered.
Constituents of tabebuia guayacan—II
Abstract A unique oxalactone dibenzxanthone, guayin, has been isolated from the heartwood of T. guayacan and structurally identified. A biomimetic synthesis of the dihydro derivative of guayin, based upon the probable biosynthetic origin of guayin from the dibenzxanthene guayacanin, has been successfully achieved.
Molecular diversity of skin mucus lectins in fish.
Among lectins in the skin mucus of fish, primary structures of four different types of lectin have been determined. Congerin from the conger eel Conger myriaster and AJL-1 from the Japanese eel Anguilla japonica were identified as galectin, characterized by its specific binding to beta-galactoside. Eel has additionally a unique lectin, AJL-2, which has a highly conserved sequence of C-type lectins but displays Ca(2+)-independent activity. This is rational because the lectin exerts its function on the cutaneous surface, which is exposed to a Ca(2+) scarce environment when the eel is in fresh water. The third type lectin is pufflectin, a mannose specific lectin in the skin mucus of pufferfish Takifugu rubripes. This lectin showed no sequence similarity with any known animal lectins but, surprisingly, shares sequence homology with mannose-binding lectins of monocotyledonous plants. The fourth lectin was found in the ponyfish Leiognathus nuchalis and exhibits homology with rhamnose-binding lectins known in eggs of some fish species. These lectins, except ponyfish lectin, showed agglutination of certain bacteria. In addition, pufflectin was found to bind to a parasitic trematode, Heterobothrium okamotoi. Taken together, these results demonstrate that skin mucus lectins in fish have wide molecular diversity.