3-0-Methylorsellinate

In similar types of reactions orsellinic acid (Fig. 74) and 3-methylorsellinic acid (Fig. 73) are built. 

Aspergillus Jlaviceps normally produces 5-methylorsellinic acid 3.24) and its transformation product flavipin 3.25). A cell-free enzyme preparation used [ " CH3]methionine for formation of the aromatic metabolite [in this case, 5,6-dimethylresorcinol, as 3.24)] without addition of any poly-)8-keto-acyl-CoA acceptor. So this substrate was already enzyme bound. Various products derivable from 3.21) were obtained on hydrolysis of the enzyme complex thus indicating 3.21) to be the substrate for methylation (Scheme 3.5) [22]. This is a second piece of evidence for methylation occurring before release of the completed polyketide from the synthetase complex. 

A mono-oxygenase is also implicated in the biosynthesis of fungal tropolones, e.g. stipitatonic acid (3.52). Ring expansion of an aromatic ring could, as in colchicine biosynthesis, account for the formation of the tropolone ring (Section 6.3.7). This is strongly supported by the appropriate specific incorporation of labelled 3-methylorsellinic acid (3.51) into stipitatonic acid (3.52), and 02... 

Di-O-methylorsellinic acid, 2,4-Dimethoxy-6-methylbenzoic acid (2,4-Di-O-methylorsellinsaure, 2,4-Dimethoxy-6-methylbenzoesaure)... 

Ethyl 3-methylorsellinate, Ethyl P-orcinolcarboxylate, Ethyl 2,4-dihydroxy-... 

Methyl 3-chloro-di-O-methylorsellinate, Methyl 2,4-dimethoxy-3-chloro-6-methyl-benzoate (3-Chlor-di-O-methylorseUinsauremethylester, 2,4-Dimethoxy-3-chlor-6-methylbenzoesauremethylester)... 

Evernia prunastri has proved to be a particularly rich source of lichen compounds and extraction and g.c. — m.s. studies have revealed the presence of orcinol (99) 268, 269), 3-methoxy-5-methylphenol (100) 144), 3,5-dimethoxytoluene (101) 144), 2-chloro-3,5-dimethoxytoluene (102) 144), phenol 144), thymol 144), 2-chloro-3-methoxy-5-methylphenol (103) 144), methyl salicylate 144), methyl 4-O-methylorsellinate (90) 268, 269), and methyl (3-orcinolcarboxylate (104) (255). Rhizonic acid (105) has been isolated from Parmelia subnuda 215). 

Several groups of characteristic polyketides occur in lichens. Biosyntheti-cally they are closely related, being derived mainly from 6-alkyl-or 6-( -keto) alkyl-2,4-dihydroxybenzoic acids which further vary in their details of extra ring substituents (Table I). /3-Orsellinic acid units are not so widespread as fungal metabolites. The only report of such a recognized depside component in a free-living fungus concerns the occurrence, biosynthesis, and metabolism of 3-methylorsellinic acid (R = CHg) in Penicillium stipi-tatum (Scott et aL, 1971). 

O-Demethylbarbatic acid Diifractaic acid Evernic acid Lecanoric acid 4-0-Methylorsellinic acid Orsellinic acid Ergochrome AA Phytotoxin 667)... 

Takenaka S, Ojima N, Seto S (1972) The Isolation of 2,4-Dihydroxy-3,6-dimethylbenzoic Acid (3-Methylorsellinic Acid) from a Culture of Aspergillus terreus. J Chem Soc Chem Comm 391... 

The same research group has also re-investigated the biosynthesis of puberulonic (37) and puberulic acid (38) in P. aurantio-virens (NRRL 2138) and have shown that C-9 of (37) is derived from acetate. A common biosynthetic route has been suggested for the fungal tropolones (35)—(38), although attempts to demonstrate the conversion of stipitatonic acid (35) or 3-methylorsellinic acid (33) into puberulonic acid (37) were unsuccessful. ... 

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