Usnic

Usnic acid (2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyldibenzofuran-l,3(2//,9b//)-dione)... 

A molecule which is not itself symmetrical may still be cleavable to identical precursors. Examples of such cases are carpanone (123)34a n j usnic acid. h... 

Preservatives which are based on natural ingredients or nature identical are small in numbers and these are gaining the attention of marketers. The ones I am aware of are - Grapefruit Seed extracts and Usnic Acid distributed by Paroxite, Neem seed oil... 

Table 1 Experiment 2. Guided isolation and identification of potential allelochemicals from Cladonia foliacea. O, fraction O P, fraction P UA, usnic acid ca, caulonema ch, chloronema sb, side branches. Protonemal system from shoots after 21 days in culture tested against three fractions from C. foliacea thallus and in control Mohr medium. The observations represent means calculated from about 300 protonemata for each species. P. squarrosa is the species least affected, while 7. flavovirens is the most affected by lichen fractions. 

Not all neomycin salts, however, possess advantages such as a reduced toxicity. In fact, the orotic acid(1,2,3,6-tetrahydro-2,6-dioxo-4-pyrimidine carboxylic acid) salt was reported to have a greater toxicity than neomycin itself74f75. some uncertainty of this fact is apparent as other authors have reported the two compounds to be of a similar toxicity 6. The salt of neomycin with usnic acid(an antibacterial substance found in lichens) has been reported to have less antibacterial activity than the neomycin used in the preparation of the salt. 

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... 

More recent examples of biomimetic synthesis are the syntheses of thebaine [11] and usnic acid [12], as well as strychnine [13], morphine alkaloids [11] [14] and a great number of terpenic compounds [15]. On the other hand, hypothetic prebiotic considerations may also simplify tremendously the synthetic plans. Such is the case, for example, of the work of Eschenmoser on vitamin B12 who, after synthesising it in collaboration with Woodward by a linear sequence of almost fifty steps [16], investigated the prebiotic origen of this complex molecule. The experimental work undertaken in this direction demonstrates that the amount of "external instruction" required for "self-assembling" the different structural elements present in this molecule is surprisingly small. This fact could eventually lead to a very simple synthesis of vitamin Bj2 starting from a-amino nitriles which would involve only a few steps [17]. 

Much more subtle are those molecules which exhibit only potential symmetry. Usnic acid (21), for instance, which does not exhibit any kind of symmetry, can be synthesised in two steps by the unsymmetrical coupling of two molecules of the same phenoxy radical 19 (Scheme 4.4) [17], which is prepared from readily accessible starting materials 13 and 14. 

Bertz [5] has drawn the attention to the relationship existing between the concept of potential symmetry and the symmetry present in the corresponding "synthesis tree" (or "synthesis graph") [18]. In the abovementioned synthesis of usnic acid both branches of the synthesis tree are identical, and collapse into a single path, a fact that is most easily visualised by comparing synthetic trees for labelled (a) and unlabelled (b) usnic acid (see Diagram 4.1). 

Synthesis graph for a) labelled and b) unlabelled usnic acid according to... 

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

The scope of the present work is limited, to some extent, by the choice and particular interest of the authors. The chemistry of reduced dibenzo-furans has received attention only where it impinges on the synthesis of the fully aromatic derivatives consequently, the chemistry of usnic acid, which... 

Threats to orceins, orcinol, picrolichenic acid, usnic acid, and other metabolites not shown in Table 16.2.5.1, reflect the sensitivity of lichens to environmental pollution worldwide (Huneck 1999). 

Usnea diffracta Dill, ex Adans. U. longissima Acharius Lao Jium Xiu Song Lo (whole plant) Barbaric acid, usnic acid, diffractaic acid, ramalic acid, lichenin.54 Treat throat discharges, malaria, headache, cough, a detoxicant. 

N.A. Lobelia pulmonaria L. d-Usnic acid, thamnolic, polysaccharides, anthraquinones.154 Stimulate immune system, antitumor, cancer. 

---