[88-75-5] · C6H5NO3 · o-Nitrophenol · (MW 139.12)
(preparation of active esters for peptide synthesis1)
Physical Data: mp 45 °C; bp 216 °C; pK
Solubility: sol ether, benzene; sparingly sol H2O.
Form Supplied in: yellow solid, commercially available.
Purification: crystallizes as yellow needles or prisms from ethanol or ether.
Handling, Storage, and Precautions: moderately toxic by inhalation and skin absorption.
Esters of o-nitrophenol, prepared by the 1,3-Dicyclohexylcarbodiimide coupling method, can be used in peptide synthesis (eq 1)1 in the same way as are the corresponding p-nitrophenyl esters (see p-Nitrophenol). o-Nitrophenol is less reactive than p-nitrophenol in the DCC coupling step; use of pyridine as solvent instead of ethyl acetate increases the nucleophilicity of the hydroxyl group and minimizes side reactions. In the aminolysis step, the o-nitrophenyl esters are more reactive than the p-isomers, and the reaction rates are less sensitive to changes in solvent or to steric hindrance. o-Nitrophenyl esters have been used in a stepwise synthesis of a nonapeptide in which all synthetic operations are performed in the same reaction vessel, without isolation of intermediates (
in situ peptide synthesis).1
University of Bath, UK