Orcinol depsidones

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. 

Colensoic acid, from Stereocaulon colensoi, was assigned structure (285) by Fox, Klein, and Huneck (7 7). This has been confirmed by Djura and Sargent (102) by a synthesis in which the diphenyl ether linkage was 

The structure of grayanic acid (351) has been confirmed by synthesis 101). It co-occurs with the ring-opened diphenyl ether congrayanic acid (352) in the lichen Gymnoderma melacarpum 47). Interestingly the dibenzo-furan melacarpic acid (353), a product of carbon-carbon oxidative coupling, also occurs in this lichen. 

Elix(772) and Yosioka and his co-workers 163) have reported the isolation and structural elucidation of the O-methylphysodic acid (359) from Hypogymnia billardieri and H.vittata, where it co-occurs with physodic acid (295). In this connection Elix developed the useful technique of treating the mixture of lichen acids with phenyldiazomethane, which 

Chester, and Elix (75) have isolated the new depsidones conorlobaridone (371) and conloxodin (372) from Xanthoparmelia xantho-sorediata where they co-occur with the known depsidones norlobaridone (373) and loxodin (374). The structures (371) and (372) followed from a study of their mass and H-n.m.r. spectra. Foo and his co-workers isolated the lactols norlobariol (375) 140) and loxodinol (376) 139) from 

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

Culberson CF, Nash TH, Johnson A (1979) 3a-Hydroxybarbatic acid, a new depside in chemo-syndromes of some Xanthoparmeliae with (3-orcinol depsides. Bryologist 82 154-156 Culberson CF, Culberson WL, Johnson A (1981) A standardized TLC analysis of 3-orcinol depsidones. Bryologist 84 16-29... 

Elix JA, Yu J (1993) New lichen (3-orcinol depsidones and their congenors. J Hattori Bot Lab 74 317-323 Elix JA, Ferguson BA, Sargent MV (1974) The structure of alectoronic acid and related lichen metabolites. Aust J Chem 27 2403-2411... 

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... 

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... 

New p-Orcinol Depsidones from Xanthoparmelia quintaria and a Thelometra Species. Phytochem. 17, 1192 (1978). 

O Donovan, D. G., G. Roberts, and M. F. Keogh Structure of the P-Orcinol Depsidones, Connorstictic and Consalazinic Acids. Phytochem. 19, 2497 (1980). Ollis, W. D. Personal Communication. 

A 10-25% aqueous solution ofpotassium hydroxide is used as the reagent. The solution is stable, but etches glass vessels slowly. Quinonoid lichen pigments (anthraquinones, naphthoquinones, terphenylquinones) give a positive dark red to violet K test, whereas pulvinic-agid derivatives, xanthones, and usnic acids do not respond. Some depsides (e.g., atranorin, thamnolic acid) and many /5-orcinol depsidones exhibit yellow to red colors with K. 

Phenylenediamine reacts with aromatic aldehydes, giving yellow to red Schiff bases (Fig. lb). Most -orcinol depsidones, as well as some -orcinol depsides, give a positive PD test. Aromatic diamines other than p-phenyl-enediamine also react with aromatic aldehydes. Asahina (1934) found that benzidin gives less intensely colored reaction products thanp-phenylenedia-mine. Santesson (1966) compared some diamine reagents and suggested the use of o-dianisidine (OD) as a PD substitue. o-Dianisidine is more sensitive, more stable, and more toxic than PD, but not as corrosive. The color reactions obtained with OD are not always identical with those of PD. 

The use of a few different solvents in succession will often effect a certain degree of separation of the constituents. The series benzene-ethyl ether-acetone is commonly used. Most lichen substances will appear in benzene and ether extracts, but certain compounds (e.g., erythrin, thamnolic acid, /3-orcinol depsidones) will only be extracted by acetone. Polyols (erythritol, arabinitol, mannitol, etc.) are usually found in the acetone extract, but saccharides (especially polysaccharides) have to be extracted with alcoholic solvents or water after prior removal of other constituents (cf. Lindberg et al., 1953 Lewis and Smith, 1967). 

Many /5-orcinol depsidones discolor and decompose slowly without melting at temperatures above 240°-250° C, the decomposition being dependent upon the heating rate. For physodalic acid a decomposition range of 230°-260° C has been given, for salazinic acid 260°-280° C, and for fumarpro-tocetraric acid 245°-260°C. Presence of the solvent of crystallization may alter the mp drastically. Alectoronic acid (from benzene) melts at 193° C,... 

Elix JA, Lumbsch HT, Wardlaw JH (1995) Conhypoprotocetraric Acid, a New Lichen P-Orcinol Depsidone. Aust J Chem 48 1479... 

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