Penicillic biosynthesis

Luckner M, Nover L Biosynthesis of the benzodiazepine and quinoline alkaloids of Penicil-lum cyclopium and Penicillum viridatum in Mothes K, Kurt H (eds) Biochemistry Physiology of Alkaloids. 4th Int Symp. Berlin, Aka-demie Verlag, 1969, pp 525-533. 

Penicillic acid (82 in Figure 17) is a toxic compound produced by many Penicillum and some Aspergillus species.166 It is biosynthesized from orsellinic acid through the pathway shown in Figure 17.167 A candidate of a gene encoding a PKS for penicillic acid biosynthesis was obtained from A. ochraceus 6t... 

The relationship between the biosynthesis of the penicillin and cephalosporin nuclei [127] is shown in Fig. 8.25. The common intermediate in the biosynthesis of penicillins and cephalosporins is isopenicillin N (IPN), which in Penicil-lium is converted into penicillin G by replacement of the L-2-aminoadipyl side-chain with externally supplied phenylacetic acid, mediated by IPN acyl transferase (IPN AcT). In the cephalosporin-producing Ammonium chrysogenum, IPN is subjected to an enzymatic ring expansion. 

Two interesting metabolites of Penicillium patulum are patulin and penicillic acid. Their biosynthesis involves the cleavage of an aromatic ring. These substances are mycotoxins and their activity in this context is discussed in Chapter 9. 

The salt-water culture of Aspergillus ochraceus separated from the Indo-Pacific sponge Jaspis coriacea has yielded two new chlorine containing polyketides, chlorocarolide A (183) and B (184). These compounds have an overall structural analogy to penicilic acid whose biosynthesis has been intensely studied. The structures and stereochemical features of the chlorocarolides were reported [214]. 

An example is provided by the biosynthesis of polivione (metabolite of Penicil-lium frequentans) which has been studied using C-, and 0-labeled precursors. Polivione, after incorporation of [l,2- C2]acetate, showed a labeling pattern, outlined in Figure 2.6, compatible with a polyketide origin. Upon incorporation of [1- C, l- 02]acetate, it showed isotopically shifted peaks in its NMR spectrum for C, C-7, and C-8a, demonstrating that was bonded to those carbons. The oxygens at C-1, C-6, and the carboxyl carbon were shown to be derived from 02 gas by the presence of isotopically shifted peaks in the NMR spectrum of these carbon atoms upon incorporation of this precursor (Figure 2.6) [4]. 

Zamir, L. O., The biosynthesis of patulin and penicillic acid, in The Biosynthesis of Mycotoxins (P. Steyn, ed.), 223-268, Academic Press, New York, 1980. 

The fungal metabolites patulin (10) and multicolic acid (79) are derived in nature via oxidative cleavages of polyketide derived aromatic intermediates a similar pathway has been established for the tetronic acid penicillic acid (185). By contrast, the biosynthesis of carolic acid (76a) which is found with dehydrocarolic acid (75) in P. charlesii, has been shown to occur from Krebs cycle intermediates. 

The biosynthesis of the fungal tetronic acids penicillic acid (185) and carolic acid (76 a), which are closely related structurally to patulin and multicolic acid, have also been studied extensively. Early work with " C-labelled precursors has clearly demonstrated the polyketide origin of penicillic acid, and also the intermediacy of orsellinic acid... 

The biosynthesis of the fungal tetronic acid carolic acid (76 a) in Penicillium charlesii is markedly different from that of patulin, multicolic acid and penicillic acid. Carbon-14 work has demonstrated that the carbon sub-unit C-3, C-4, C-9 in the acid is derived from a C-4-dicarboxylic acid such as succinate, whereas the remaining six carbons (C-1, C-2, C-5, C-6, C-7, C-8) are derived from two malonate units (C-5, C-6, C-7, C-8) and just one acetate unit (C-1, C-2) (Scheme 19) (775). It is proposed then that the biosynthesis of carolic acid proceeds from a C4-dicarboxylic acid first to either y-carboxymethyltetronic acid (196) or to carlosic acid (77 b) hydroxylation of carlosic acid then gives rise to carlic acid (77 a) which on decarboxylation produces carolic acid 176). 

Bentley, R., and J. G. Keil Tetronic Acid Biosynthesis in Molds II. Formation of Penicillic Acid in Penicillium cyclopium. J. Biol. Chem. 237, 867 (1962). 

Axberg,. K., and S. Gatenbeck Intermediates in the Penicillic Acid Biosynthesis in Penicillium cyclopium. Acta. Chem. Scand. B29, 749 (1975). 

Fig. 5- Biosynthesis of penicillic acid from orsellinic acid (Mosbach, I960 Bentley...

Birch, A. J., G. E. Blance, and H, Smith Studies in relation to biosynthesis. Part. XVIII. Penicillic acid. J. Chem. Soc. 1958a, 4582. 

The technique of tritium NMR was reported by Bloxsidge et at., (1971). The first application of this method in biosynthesis involved penicillic acid (Al-Rawi et at., 91A Elvidge et at., 1977). The triton has a spin of j, and its sensitivity to detection is even higher than the proton s. Bloxsidge et at. 

Whole-cell feeding experiments imply adding labeled putative precursors (radioactive or stable isotope label) to the whole organism, which is grown on a synthetic media. The products and intermediates are then isolated, purified, and analyzed by the various methods. This type of experiment enables one to propose a plausible biosynthetic pathway. Isolation and purification of the enzymes responsible for each step of the pathway enable verification at the enzymatic level. The in vitro conversion of a putative precursor by the pure enzyme to the product constitutes unambiguous proof of the biosynthetic reaction. The ultimate proof of a biosynthetic pathway depends, therefore, on the characterization of the enzymes involved in each step of the pathway. The only major drawback is that the procedure is extremely difficult, and the detailed enzymology for polyketide-derived eompounds deserves further study. The problems are (a) instability of the enzymes, (b) lack of reproducibility, and (c) variability of activity in different enzymatic preparations (some of these enzymes are membrane bound and easily deactivated by isolation). Despite the difficulties involved, some of the enzymes involved in the biosynthesis of patulin and penicillic acid have been partially purified and characterized. 

The biosynthesis of patulin, as well as that of penicillic acid, can be summarized as acetate aromatic compound -> product. In this section we will concentrate on the first step the origin of the aromatic precursor. 

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