Involved in the biosynthesis of wybutosine, a hyper modified guanosine with a tricyclic base located at position 37 of eukaryotic phenylalanine tRNA (tRNA(Phe)) that contributes to maintenance of the translational reading frame. Catalyzes the condensation of N- methylguanine with 2 carbon atoms from pyruvate to form the tricyclic 4-demethylwyosine, an intermediate in wybutosine biosynthesis. . This is the function of TYW1 (tRNA-yW synthesizing protein 1 homolog, Ensembl gene identifier ENSG00000198874).