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 (By similarity). Catalyzes the condensation of N-methylguanine with 2 carbon atoms from pyruvate to form the tricyclic 4-demethylwyosine, an intermediate in wybutosine biosynthesis (By similarity). . This is the function of TYW1B (tRNA-yW synthesizing protein 1 homolog B, Ensembl gene identifier ENSG00000277149).