N-Hydroxy compounds such as 1-hydroxybenzotriazole hydrate (HOBt) or 1-hydroxy-7-azabenzotriazole (HOAt) have traditionally been used in amide coupling reactions to suppress side reactions and minimise racemisation, the latter challenge being a key one in peptide synthesis. However, racemisation can still be an issue with either additive.
A recent change in the UN classification of HOBt resulting in more restrictive shipping regulations has led to interest in the lesser known alternative, 2-hydroxypyridine-N-oxide (HOPO).
2-Hydroxypyridine N-oxide is less frequently known by several other names: 2-hydroxypyridine 1-oxide, 2-pyridinol N-oxide, 2-Pyridinol 1-oxide, 1-hydroxypyridine-2-one, 1-hydroxy-2-pyridone and 1-hydroxy-2(1H)-pyridinone, 2-HPNO.
The major use for HOPO is in amide bond synthesis. A simple and efficient, biphasic (CH2Cl2 or EtOAc with water, 1:1) coupling protocol with EDC has been described, yielding di- or tri-peptides with low levels of racemisation, Scheme 1.5 HOPO had been previously used in a stepwise process via the initial formation of esters from activated amino acids (for example acid chlorides).
Research or further manufacturing use only, not for food or drug use.