[88-75-5]  · C6H5NO3  · o-Nitrophenol  · (MW 139.12)

(preparation of active esters for peptide synthesis1)

Physical Data: mp 45 °C; bp 216 °C; pKa 7.23 (at 25 °C).

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.

Preparation of Active Esters for Peptide Synthesis.

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

1. Bodanszky, M.; Funk, K. W.; Fink, M. L. JOC 1973, 38, 3565; Bodanszky, M.; Kondo, M.; Yang Lin, C.; Sigler, G. F. JOC 1974, 39, 444.

Alan Armstrong

University of Bath, UK

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