Remarkable Chichibabin-type cyclotrimerisation of 3-nitrotyrosine, tyrosine and phenylalanine to 3,5-diphenylpyridine derivatives induced by hypochlorous acid

Reaction of 3-nitrotyrosine with HOCl in aq. phosphate buffer (pH 7.4) leads to a mixt. of extractable products, including 3,5-bis(4-hydroxy-3-nitrophenyl)pyridine (15% isolated yield) and 3,5-bis(4-hydroxy-3-nitrophenyl)-2-[(4-hydroxy-3-nitrophenyl)methyl]pyridine (3%) arising by a Chichibabin-like pyridine synthesis via N-chloro imine intermediates. Under the same conditions, phenylalanine gives 3,5-diphenylpyridine in 9% isolated yield, while tyrosine leads to 3,5-bis(4-hydroxyphenyl)pyridine (3%) and 3-(3-chloro-4-hydroxyphenyl)-5-(4-hydroxyphenyl)pyridine (3%).