Fallacinol

[1] A few years later Asano and Yosio Arata further purified the crude material from this lichen, ultimately obtaining an orange-yellow compound with a molecular formula of C16H12O6.

[2] In 1949, T. R. Seshadri and S. Subramanian published their investigations into the chemistry of Teloschistes flavicans,[3] a lichen from which they isolated an orange substance they named teloschistin, and which had a structural formula identical to that of fallacin proposed by Asano and Arata years earlier.

[5] In an early chemical examination of the lichen Teloschistes flavicans, Friedrich Wilhelm Zopf identified two substances: physcion (now known more commonly as parietin) with a melting point (m.p.)

[6] The presence of another compound with a higher melting point posed a purification challenge, which was resolved by employing petroleum ether and chloroform for sequential extraction.

They confirmed its molecular formula as C16H12O6 and identified it as a hydroxyl derivative of parietin, lacking specific hydroxy groupings that would typically cause fluorescence or colour changes in acidic conditions.

[7] The research also noted the slower-than-expected reaction rates during oxidation, suggesting a distinctive reactivity pattern for fallacinol, possibly due to its additional hydroxyl group.

Similar to parietin, it produces a reddish-brown colour with alcoholic ferric chloride and yields a deep orange-red solution with concentrated sulfuric acid, which appears eosin-like in thin layers.

To early researchers, these properties suggested that fallacinol was structurally similar to parietin but with an additional oxygen atom, inferred to be a hydroxyl group, based on its higher melting point and reduced solubility.

The sparing solubility of its potassium salt and its insolubility in aqueous sodium carbonate suggested a methoxyl group placement consistent with other known compounds like parietin and erythroglaucin.

This reduced form can be prepared by treating fallacinol with zinc dust in boiling acetic acid, yielding lemon-yellow prismatic crystals with a melting point of 249–250 °C.

[9][10] In a study exploring lichen compounds for COVID-19 therapeutics, fallacinol demonstrated the highest binding energy against SARS-CoV-2's spike protein, suggesting its potential as an inhibitor of virus growth.

The process involves the conversion of parietin diacetate to an ω-bromo derivative via N-bromosuccinimide in the presence of benzoyl peroxide, a technique also applied to various anthraquinones and related compounds.

[15] Fallacinol is a common secondary metabolite in the lichen genus Teloschistes, typically occurring in smaller amounts alongside parietin and other related compounds like fallacinal and emodin.

Reynoutria japonica (Japanese knotweed) is one of the few plants known to contain fallacinol.