Puberulonic acid

Natural products containing the tropoloid ring system are not limited to selected alkaloids of the family Liliaceae. Nootkatin and the thuja-plicins, which have been isolated from the family Cupressaceae, are substituted monocyclic tropolones. In addition, the mold metabolites stipitatic, puberulic, and puberulonic acids contain the tropolone ring. It is of interest, then, to consider the possible biogenetic pathways by which this ring system is constructed in nature. 

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. ... 

Bentley, R., and C. P. Thiessen Tropolone biosynthesis the enzymatic decarboxylation of stipitatonic and puberulonic acids. Nature 184, 552 (1959). 

The tropolone alkaloid of Liliaceae species, colchicine, is transformed by acetylation, alkaline cyclization, and dehydration into the tetracyclic pyrrolotropone acetyl anhydrocolchicine [77TL2977 83AX(C)1709]. When the dicarboxylic acid anhydride groups of puberulonic and stipitatonic acids (metabolites of Penicillium species) condense with o-phenylenediamine, another tetracyclic pyrrolotropone structure is formed (51JCS1139 59JCS2847). 

Among the tropolone compounds found in nature are four tropolone-carboxylic acids,obtained from mold cultures.Two ofthese,stipitatonicadd(CXIV,R = COOH) and stipitatic acid (CXIV, R = H) have been obtained from Penicillium stipitatum (Bentley and Thiessen, 1963). Puberulonic add (CXV, R = COOH) and puberulic acid (CXV, R = H) were obtained from P. aurantio-virens, P. puberulum and P.johan-nioli as well as from strains of the P. cyclopium-viridicatum series (sources quoted in this paper). The infrared spectrum of the sodium salt of the anhydride of stipitatonic... 

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