Trichoviridine metabolite

A few natural products with oxirane rings fused to five-membered rings are known. These include the antibiotic methylenomycin-A (82) (79H(13)353, 79JOC4210,80JA3904, 81CC714) and the truly remarkable fungal metabolite trichoviridine (83), which appears to be the first example of an isocyanide epoxide (76CPB832). 

In studies directed towaids the synthesis of the fungal isonitrile antibiotic isonitrin B (103), a cy-clopentanoid metabolite related to trichoviridine (104), various trialkylsilyl enol ethers were irradiated with propionaldehyde to produce equimolar amounts of stereoisomeric bicyclic oxetanes (105). The corresponding silyl dienol ethers, however, gave little oxetane product owing to preferential diene photopolymerization. The use of vinyl epoxide derivatives such as (106), however, offers a possible access to the epoxycyclopentanoid system with simultaneous control of the face selectivity of the photoaddition by the epoxide moiety. 

Some fungal species produce cyclopentenyl isocyanides, for example trichoviridin (166), which are known to be biosynthesised from tyrosine by cleavage of the aromatic ring. Despite much experimental study, the biosynthetic origin of the isocyanide carbon into the cyclopentenyl diene isocyanide acid (167) and related metabolites remains elusive [101-103], Notably the standard C j-tetrahydrofolate precursors such as methionine, formate, glycine or serine do not provide the source of this carbon, nor is cyanide incorporated into the isocyanide moiety [101-103], In summary, other than one terrestrial cyanophyte, the marine environment appears so far unique in accessing cyanide for isocyanide biosynthesis. 

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