There is an urgent need to develop new antimicrobial agents due to increasing bacterial resistance to therapeutically used drugs. Most methicillin-resistent Staphylococcus aureus (MRSA) strains are resistent not only to b-lactams, but also to most other antimicrobial agents.1) Penicillin resistance among Streptococcus pneumoniae strains is widely accepted as a global problem. [2][3][4][5] Bacteria have developed several strategies for escaping the lethal action of b-lactams. It may be expected that specific circumstance will make one the more effective stragegy than the other. 6) Much effort has been devoted to the discovery of drugs which would not be cleaved by b-lactamases of pathogenic strains and which have suitable physicochemical and pharmacodynamic profiles. 7,8) The modifications of b-lactam antibiotics could not keep pace with the development of resistance in the pathogenic microorganisms, so that numerous bacteria, among them multidrug resistant Staphylococcus strains, can no longer be treated with the currently available b-lactam antibiotics. 1,9,10) Besides the modification of existing antibiotics by chemical or biochemical methods the coupling of presently used antibiotics with other bioactive compounds or components from them which are not in use till now is a promising way to generate novel molecules with improved therapeutic properties.Laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2), classically considered a hydroquinone oxidizing enzyme, is able to oligomerize molecules. Up to now main application fields of this enzyme are waste detoxification, textile dye transformation, biosensors and diagnostic application, where the capability to catalyze polymerization reactions is used. 11-13)Recently we reported about our synthetic results on coupling reactions with laccase.14-17) Now we have employed laccase to achieve derivatisation of b-lactam antibiotics and to couple them with derivatives of 2,5-dihydroxybenzoic acid. These derivatives are structurally related to the ganomycins, a new chemical class of antibacterial compounds 18) and to other antibacterial active isolates 19,20) therefore interesting as coupling partner for b-lactams using laccase as initiator of the reaction to produce novel hybridantibiotics by biotransformation.The use of laccase for the derivatisation of antibiotics is limited to a few examples including the phenolic oxidation of 7-(4-hydroxyphenylacetamido)cephalosporinic acid, 21) the dimerization of penicillin X 22) and the oxidative coupling of hydroquinone and mithramicine. 23) In the examples realized to date, the sought object of enhancement of the bioactive effect has not been achieved. 21-23)The aim of this study was (i) to investigate whether laccase can be used for the synthesis of novel penicillins by heteromolecular coupling of two different compounds, (ii) to characterize the products of the reaction, and (iii) to analyze the biological activity of the novel penicillins. Results and DiscussionBiotransformation of Amoxicillin and Ampicillin by Laccase of Tr...

We examined the pathway by which the fungicide biphenyl is metabolized in the imperfect fungus Paecilomyces lilacinus. The initial oxidation yielded the three monohydroxylated biphenyls. Further hydroxylation occurred on the first and the second aromatic ring systems, resulting in the formation of five di-and trihydroxylated metabolites. The fungus could cleave the aromatic structures, resulting in the transformation of biphenyl via ortho-substituted dihydroxybiphenyl to six-ring fission products. All compounds were characterized by gas chromatography-mass spectroscopy and proton nuclear magnetic resonance spectroscopy. These compounds include 2-hydroxy-4-phenylmuconic acid and 2-hydroxy-4-(4-hydroxyphenyl)-muconic acid, which were produced from 3,4-dihydroxybiphenyl and further transformed to the corresponding lactones 4-phenyl-2-pyrone-6-carboxylic acid and 4-(4-hydroxyphenyl)-2-pyrone-6-carboxylic acid, which accumulated in large amounts. Two additional ring cleavage products were identified as (5-oxo-3-phenyl-2,5-dihydrofuran-2-yl)-acetic acid and [5-oxo-3-(4-hydroxyphenyl)-2,5-dihydrofuran-2-yl]-acetic acid. We found that P. lilacinus has a high transformation capacity for biphenyl, which could explain this organism's tolerance to this fungicide.

The ability of the imperfect soil fungus Paecilomyces lilacinus to transform the environmental pollutant dibenzofuran was investigated. Transformation of dibenzofuran and related derivatives lead to 14 products, which were identified by UV spectroscopy, mass spectrometry, and proton nuclear magnetic resonance spectroscopy. Biotransformation was initiated by two separate hydroxylation steps, leading to the accumulation of 4-monohydroxylated and 4-dihydroxylateddibenzofurans. Hydroxylation at both aromatic rings produced 2,7-dihydroxydibenzofuran, 3,7-dihydroxydibenzofuran, and 2,8-dihydroxydibenzofuran. Further oxidation yields ring cleavage of dibenzofuran, which has not been described before for filamentous fungi. The ring fission products were identified as benzo[ b]furo[3,2-d]-2-pyrone-6-carboxylic acid and [2-(1-carboxy-methylidene)-benzofuran-3-ylidene]-hydroxy-acetic acid and its derivatives hydroxylated at carbon 7 and 8 at the non-cleaved ring. Other metabolites were riboside-conjugates of 2-hydroxydibenzofuran and 3-hydroxydibenzofuran. The results showed that P. lilacinus transforms the hydrophobic compound dibenzofuran by phase I/phase II reactions to produce hydroxylated products and excretable sugar conjugates.

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