[mycofactocin precursor peptide]-C-terminal glycyl-N-{[2-(4-hydroxyphenyl)ethenyl]-3-methylbutanamide} + AH2 + S-adenosyl-L-methionine = [mycofactocin precursor peptide]-C-terminal glycyl-N-{5-[(4-hydroxyphenyl)methyl]-4,4-dimethyl-2-oxopyrrolidin-3-yl}acetamide + 5'-deoxyadenosine + L-methionine + A + H(+) — reaction