Natural products usnic acid

Isolation and Characterization of an Optically Active Natural Product Usnic Acid... 

When the enol ring is adjacent to a cyclic moiety, then it is possible to achieve very short hydrogen bonds, as in the structure of usnic acid, a natural product found in lichens. A low-temperature X-ray diffraction analysis of this compound showed two enol moieties, one in which a carbon-carbon bond of the enol was part of a cyclohexenone ring, and this had... 

Strategies based on biogenetic pathways which apply only to natural products as in, for instance, usnic acid, tropinone, thebaine, strychnine, steroids etc. 

Many photobleaching herbicides act by inhibiting the enzyme protoporphyrinogen oxidase (Protox), which catalyzes the last step in common between chlorophyll and heme biosynthesis. Usnic acid shares some structural features in common with these herbicides, such as the diphenyl ether scaffolding. The inhibitory activity of (-)-usnic acid on Protox was similar to that of the herbicide, acifluorfen, (I50 ca. 3 pM). However, these compounds did not displace acifluorfen from its binding site on Protox (data not shown), indicating that this natural product interacts with Protox differently than other photobleaching inhibitors. 

The Phytotoxic Lichen Metabolite, Usnic Acid, Is A Potent Inhibitor of Plant P-Hydroxyphenylpyruvate Dioxygenase. Romagni, J. G. Meazza, G. Nanayakkara, N. P. D. Dayan, F. E. Natural Products Utilization Research Unit, USDA/ARS, University of Mississippi, Lafayette, MS, USA. FEES Lett. (2000), 480(2,3), 301-305. 

Natural products provide interesting opportunities for measuring opfical activity. An excellent example is the lichen metabolite, usnic acid, which can be easily isolated from its native source,"01d Man s Beard"lichens, as... 

Racemic (equimolar amounts of each enantiomer) usnic acid has been resolved (separated into the individual enantiomers) through preparation and separation of the diastereomeric (-) brucine salts. This procedure was the route followed to obtain an authentic synthetic sample for comparison with the natural material. The separation was required because the dimerization step in the synthesis, which was carried out in the absence of enzymatic, or other chiral, influence, gave a racemic product. 

Qnnamaldehyde s formation from shikimic add utilizes one of only two biogenetic routes in nature that lead to the aromatized benzene ring (the other pathway is found in the acetogenins and produces secondary metabolites like usnic acid see Experiment [llA]).The shikimic acid route contributes to a class of metabolites called the phenylpropanes (Ph—C3), of which cinnamaldehyde is one of a limited number of simple end products. Another close relative is, for example, eugenol from oil of cloves. 

Huneck S, Schmidt J (1980) Lichen substances-126. Mass spectroscopy of natural products - 10. Comparative positive and negative ion mass spectroscopy of usnic acid and related compounds. Biomed Mass Spectrom 7 301-308... 

Kinrade WTB, Ahmadjian V (1970) The effect of usnic acid on the physiology of two cultured species of the lichen alga Trebouxia Puym. Lichenologist 4 234-247 Kjaer A, Kjaer D (1982) Synthesis of benzylchromones and benzoxanthones related to natural products. Acta Chem Scand B 36 417-419... 

Taguchi, H., Sankawa, U., and Shibata, S. (1969a). Biosynthesis of natural products. VI. Biosynthesis of usnic acid in lichens. (1). A general scheme of biosynthesis of usnic acid. Chem. Pharm. Bull. 17, 2054. 

Huneck S, Schmidt J (1980) Lichen Substances. 126. Mass Spectroscopy of Natural Products. 10. Comparative Positive and Negative Ion Mass Spectroscopy of Usnic Acid and Related Compounds. Biomed Mass Spectr 7 301... 

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