- such as boleti -, moulds and lichens produce a wide range of pigments made up of one or several units of pulvinic acid. In 1831, in the course of a study of the constituents of lichens, the French chemist and pharmacist Antoine Bebert discovered a compound named vulpinic acid, the first known naturally occurring methyl ester of pulvinic acid. More details about the structure of this pigment were disclosed in 1860 by the German chemists Franz Möller and Adolph Strecker. While trying to elucidate the structure of vulpinic acid, the German chemistAdolf Spiegel found in 1880 that the vulpinic acid could be saponified to a diacid. He named the resulting diacid pulvinic acid. The German chemist Jacob Volhard elucidated the constitution of pulvinic acid by synthesizing it through the basic hydrolysis of a corresponding dicyanocompound. In the process, he also obtained small amounts of a side-product. One year later Ludwig Claisen and Th. Ewan achieved the synthesis of this side-product and characterized it as the 5-benzylidene-4-hydroxy-3-phenylfuran-2-one. Claisen and Ewan described it as das der Pulvinsäure zu Grunde liegende Lacton : that was the origin of the name pulvinone.
Natural occurrence
It was a century after the synthesis of the first pulvinone that the wordpulvinone turned into a collective term. In 1973, Edwards and Gill isolated the first naturally occurring hydroxylated pulvinone derivative. This trihydroxylated pulvinone was found as one of the main pigments responsible for the yellow colour of the stem and caps of the European mushroom Larch Bolete. In the very same year 1973, Seto and coworkers also found hydroxylated pulvinones in cultures of the mouldAspergillus terreus. To insist on their origin - and thereby differentiate them from the hydroxylated pulvinones found in Suillus grevillei - Seto and coworkers named these compounds Aspulvinones. The aspulvinone terminology also incorporates a letter, indicating the order of chromatographic elution of these compounds. Like many other yellow pigments in fungi and lichens, pulvinones can be traced back from the pulvinic acid pathway. The pulvinonestructural unit is found in a number of natural products. All monomeric or oligomeric derivatives of the pulvinic acid contain the pulvinone structural element. So far, all naturally occurring pulvinone derivatives were found to be Z-configured.
Pharmacological properties
Rehse et al. showed the anti-coagulant activity of some pulvinones in rats.
At the beginning of the 80s, the companies ICI and Smith Kline & French patented a large number of derivatives of the vulpinic acid because of their anti-inflammatory, anti-fever and pain-killing properties. Yet vulpinic acid - as well as many of its derivatives - is a cytotoxic compound. Since pulvinones exhibit a lower cytotoxicity compared to vulpinic acid and its derivatives, Organon investigated the pharmaceutical potential of more than 100 pulvinones. To date, the results of these studies were not fully disclosed.
In 2005, the Wyeth company patented biphenyl-substituted pulvinones due to their promising activity against Gram-positive bacteria, including otherwiseresistant bacteria. However, pulvinone-based antibiotics were so far only patented for animal use.
Chemical properties
Pulvinone is a lactone, more precisely an intramolecularester of the trans-1,4-diphenyl-2,3-dihydroxy-1,3-butadiene-1-carboxylic acid, from which it can be prepared through removal of one equivalent of water: The central 5-membered ring core of pulvinone reveals a 4-hydroxy-butenolide structure. They are essentially found in their enol form, which exhibits acidic properties due to the relative lability of the hydroxylic proton. 4-hydroxy-butenolides such as pulvinones are therefore referred to as tetronic acids, and belong to the larger category of vinylogous acids.
Biosynthesis
The fungal biosynthesis starts from aromatic aminoacids such as phenylalanine and tyrosine; after oxydeamination to the corresponding arylpyruvic acid, the pulvinone skeleton is formed by a sequence of dimerisation, oxidative ring-cleavage and decarboxylation. , Pulvinic acids and Pulvinones.
Total synthesis
was the first to synthesise vulpinic acid, pulvinic acid and pulvinone. To date, 11 total syntheses of pulvinones were reported:
