626-64-2

4-Hydroxypyridine, available from pyridylpyridinium chloride hydrochloride, is the substrate for diodone and its n-propyl ester, propyliodone. 4-Hydroxypyridine (4-HP) is a non-nucleophilic analog of the product phenol found to bind specifically to and stabilize the aminoacrylate intermediate. When 4-HP is added to Tyrosine phenol-lyase (TPL) reactions, an absorption peak at 340 nm is observed. The formation of the 340 nm peak correlates with the decay of the quinonoid intermediate peak at 505 nm, with a clean isosbestic point, and the observed rate constants show an inverse dependence on the concentration of 4-HP. These results confirm that the observed peak at 340 nm is due to the formation of the amino acrylate intermediate[1-2].

Beige crystalline powder

ChEBI: A monohydroxypyridine that is pyridine in which the hydrogen at position 4 has been replaced by a hydroxy group.

Under standard reaction conditions, 10 equivalents of CuSO4-5H2O (0.049 g, 0.2 mmol) were mixed with 6.7 mol% EA (20 mg) in methanol, followed by the addition of 2 mmol of pyridine-4-boronic acid. The reaction mixture was placed in a preheated oil bath, maintained at 60 °C with continuous stirring and the reaction was carried out at atmospheric pressure. The progress of the reaction was monitored by TLC and after completion of the reaction, the mixture was washed twice with hot ethyl acetate to remove unreacted reactants and by-products. After removal of hot ethyl acetate by evaporation, the crude product was purified by column chromatography on silica gel (260 mesh) with an eluent ratio of petroleum ether:ethyl acetate (25:75). The recovered catalyst could be used directly in the next round of reaction. The structure of the final product 4-hydroxypyridine was confirmed by 1H NMR and 13C NMR spectra.

Crystallise 4-pyridone from H2O or wet CHCl3 as the monohydrate. It loses H2O on drying in vacuo over H2SO4. Store it over KOH because it is hygroscopic.[Beilstein 21 III/IV 446, 21/7 V 152.]

[1] Yates, F. S. “2.09 – Pyridines and their Benzo Derivatives: (vi) Applications.”Comprehensive Heterocyclic Chemistry 2 (1984): 511-524.
[1] Robert S Phillips, Olivia Bauer. “Characterization of aminoacrylate intermediates of pyridoxal-5’-phosphate dependent enzymes.” Methods in enzymology 685 (2023): 199–224.