P-Orcinol

Oakmoss. Extracts of oakmoss are extensively used in perfumery to furnisli parts of the notes of the fougnre or chypre type. The first step in the preparation of an oakmoss extract is treatment of the Hchen Evemiaprunastri (L.) Ach., collected from oak trees mainly in southern and central Europe, with a hydrocarbon solvent to obtain a concrete. The concrete is then further processed by solvent extraction or distillation to more usable products, of which absolutes are the most versatile for perfumery use. A definitive analysis of oakmoss volatiles was performed in 1975 (52). The principal constituents of a Yugoslav oakmoss are shown in Table 15 (53). A number of phenoHc compounds are responsible for the total odor impression. Of these, methyl P-orcinol carboxylate is the most characteristic of oakmoss. 

Constituent of Hcemotomma ccccineum. Needles from AcOH. M.p. 172-3°. Depside with p-orcinol carboxj lic acid methyl ester is atranorin, q.v. 

P-Orcinol depsidones All lichen substances Aromatic aldehydes... 

Deriv Dibromo-p-orcinol, mp 151-152 °C (EtOH-HjO), by bromination of P-orcinol with Brj in CSj... 

Blaser D, Gunzinger J, Stocklin-Evans H, Tabacchi R (1992) Structure of 2-methoxy methyl P-orcinol carboxylate (methyl 4-hydroxy-3,6-dimethylbenzoate). Acta Crystallogr C 48 1126-1127... 

Culberson CF, Culberson WL (1976) Chemosyndromic variation in lichens. Syst Bot 1 325-339 Culberson CF, Culberson WL (1978) P-Orcinol derivatives in lichens biogenetic evidence from Oropogon loxensis. Exp Mycol 2 245-247... 

Elix JA, Chester DO, Gaul KL, Parker JL, Wardlaw JH (1989a) The identification and synthesis of further lichen p-orcinol para-depsides. Aust J Chem 42 1191-1199... 

Chem Unserer Zeit 16 71-88 II. ibid. 16 116-123 Keogh MF (1976) 2 -0-Demethylpsoromic acid from Us-nea sp. Phytochemistry 15 1801 Keogh MF (1977) Malonprotocetraric acid from Parm-otrema conformatum. Phytochemistry 16 1102 Keogh MF (1978) New P-orcinol depsidones from Xanthoparmelia quintaria and a Thelotrema species. Phytochemistry 17 1192-1193 Keogh MF, Duran I (1977) A new fatty acid from Usnea meridensis. Phytochemistry 16 1605-1606 Keogh MF, Zurita ME (1977) a-(15-Hydroxyhexadecyl) itaconic acid from Usnea aliphatica. Phytochemistry 16 134-135... 

Sala T, Sargent MV (1981) Depsidone synthesis. Part 19. Some P-orcinol depsidones. J Chem Soc Perkin Trans 1 877-882... 

Sundholm EG, Huneck S (1981) C NMR-spectra of lichen depsides, depsidones and depsones. 2. Compounds of the P-orcinol series. Chem Scripta 18 233-236... 

The most common phenolic acid units derived by the acetate-polymalonate pathway and combined to form the characteristic lichen substances are of two types the orcinol-type units and p-orcinol-type units. While compounds formed from these two types of units are similar in many ways, differences in their structure and especially in their distributimi among the lichens suggest that the usual tendency to consider the orcinol and p-orcinol compounds separately probably has a biosynthetic justification. 

P-orcinol series The orcinol-type compounds discussed in the previous section form a closely related series of substances in which changes in the length and oxidation state of the 6-alkyl substituents are major sources of variation among phenolic units. The compounds synthesised by various combinations of these units show secondary modifications attributable to 0-methylation, chlorination, decarboxylation and lactonisation. The p-orcinol compounds may undergo all of the same secondary reactions, but the most common variation is in the oxidation state of the Cj substituents at the 3- and 6-positions of the phenolic acid units. 

Except in gangaleoidin, the A ring of all p-orcinol depsidones has either a 3-aldehydic substituent like the A ring of the para-depside atranorin or a... 

Synthesis of P-Orcinol para-Depsides, p-Orcinol me fl-Depsides,... 

Until recently only two mixed orcinol P-orcinol depsides were known, namely obtusatic acid (210) and norobtusatic acid (211), but now a further four such compounds have been reported. These include 2-0-methylobtusatic acid (212) present in Xanthoparmelia tucsonensis 45) and evernine (213) 253), 3 -methylevernic acid (214) 252) and methyl 3 -methyllecanorate (215) 252) all obtained from Evernia prunastri. 

Starting with appropriately substituted phenols, procedures identical to those used for the synthesis of /7am-orcinol depsides have been employed in the synthesis of natural P-orcinol /7am-depsides 130, 152, 251, 252)... 

In the ten years since the last review there has been a resurgence of interest in the chemistry of depsidones in terms of the detection (79), the isolation of new compounds and the total synthesis of these substances. The new work is discussed in the order of the above classification and of increasing structural complexity of the compounds. A methodical study and interpretation of the C-n.m.r. spectra of orcinol 311) and P-orcinol depsidones 312) has been reported by Sundholm and Huneck. 

The biogenetically simplest of the third class of depsidones, those in which one benzenoid ring is derived from orsellinic acid and one from P orcinol carboxylic acid, is nornotatic acid (293) (Scheme 55). T.l.c. evidence was presented by Culberson and Hale 82) for its occurrence in many lichens. They advanced structure (293) on the basis of the chromatographic... 

Depside in Chemosyndromes of some Xanthoparmeliae with P-Orcinol Depsides. Bryologist 82, 154 (1979). 

Synthesis of P-Orcinol Meta-depsides. Austral. J. Chem. 28, 2035 (1975). 

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