Selective synthesis of the resveratrol analogue 4, 4′-dihydroxy-trans-stilbene and stilbenoids modification by fungal peroxygenases. Issue 9 (17th April 2018) - Aranda, Carmen
Abstract : Different unspecific peroxygenases (UPOs) catalyze the hydroxylation or epoxidation of trans -stilbene and other stilbenoids yielding resveratrol analogs and other compounds. Abstract : This work gives first evidence that the unspecific peroxygenases (UPOs) from the basidiomycetes Agrocybe aegerita ( Aae UPO), Coprinopsis cinerea (r Cci UPO) and Marasmius rotula ( Mro UPO) are able to catalyze the regioselective hydroxylation of trans -stilbene to 4, 4′-dihydroxy- trans -stilbene (DHS), a resveratrol (RSV) analogue whose preventive effects on cancer invasion and metastasis have very recently been shown. Nearly complete transformation of substrate (yielding DHS) was achieved with the three enzymes tested, using H2 O2 as the only co-substrate, with Aae UPO showing exceptionally higher total turnover number (200 000) than Mro UPO (26 000) and r Cci UPO (1400). Kinetic studies demonstrated that Aae UPO was the most efficient enzyme catalyzing stilbene dihydroxylation with catalytic efficiencies ( k cat / K m ) one and two orders of magnitude higher than those of Mro UPO and r Cci UPO, so that 4-hydroxystilbene appears to be the best UPO substrate reported to date. In contrast, the peroxygenase from the ascomycete Chaetomium globosum ( Cgl UPO) failed to hydroxylate trans -stilbene at the aromatic ring and instead produced the trans -epoxide in the alkenyl moiety. In addition, stilbenoids such as pinosylvin (Pin) and RSV were tested as substrates for the enzymatic synthesis of RSV from Pin and oxyresveratrol (oxyRSV) from both RSV and Pin. Overall, lower conversion rates and regioselectivities compared with trans -stilbene were accomplished by three of the UPOs, and no conversion was observed with Cgl UPO. The highest amount of RSV (63% of products) and oxyRSV (78%) were again attained with Aae UPO. True peroxygenase activity was demonstrated by incorporation of 18 O from H2 18 O2 into the stilbene hydroxylation products. Differences in the number of phenylalanine residues at the heme access channels seems related to differences in aromatic hydroxylation activity, since they would facilitate substrate positioning by aromatic-aromatic interactions. The only ascomycete UPO tested (that of C. globosum ) turned out to have the most differing active site (distal side of heme cavity) and reactivity with stilbenes resulting in ethenyl epoxidation instead of aromatic hydroxylation. The above oxyfunctionalizations by fungal UPOs represent a novel and simple alternative to chemical synthesis for the production of DHS, RSV and oxyRSV.