Colchicine is formed by para-para phenol coupling from autumnaline

Article abstract of DOI:10.1016/S0040-4039(97)10011-9

In order to distinguish between ortho-para and para-para phenol coupling in colchicine biosynthesis, [[3'-O¹⁴CH₃]autumnaline was converted to [¹⁴C]colchicine in seeds of Colchicum autumnale and the product was then selectively demethylated by a bacterium that exclusively demethylates C-3 of colchicine. The retention of the radioactive label in 3-demethylcolchicine indicates that biosynthesis proceeds through para-para coupling.