2-Hydroxy- 5-nitrobenzyl

Hydroxy-5-nitrobenzyl bromide [772-33-8] M 232.0, m 147", pK st -8.0. Crystd from benzene or benzene/ligroin. 

Horton, H. R. Koshland, D. E. Jr. A highly reactive coloured reagent with selectivity for the tryptophan residue in proteins 2-hydroxy-5-nitrobenzyl bromide. J. Amer. Chem. Soc. 1965, 87, 1126-1132. 

Mole, J. E. Horton, H. R. A kinetic analysis of the enhanced catalytic efficiency of papain modified by 2-hydroxy-5-nitrobenzylation. Biochemistry 1973, 12, 5278-5285. 

The 2-hydroxy-5-nitrobenzyl chloride begins to separate as a solid about one hour after the beginning of the reaction. At the end the mixture is cooled in ice for one hour whereby more crystals separate, after which the acid liquors are either filtered or decanted from the crystals (Note 6). The 2-hydroxy-s-nitro-benzyl chloride is purified by recrystallization from 125 cc. of hot benzene (Note 7). The yield is 46 g. (69 per cent of the theoretical amount based on />-nitrophenol) of a white product melting at 129-130°. 

The solid material should be air-dried for several hours or, better, overnight to remove all water before recrystallizing from hot benzene. The chlorine atom is very labile and hydrolyzes easily to form 2-hydroxy-5-nitrobenzyl alcohol. 

Hydroxy-5-nitrobenzyl chloride can also be prepared from 2-hydroxy-s-nitrobenzyl alcohol by passing hydrogen chloride into an alcoholic solution at 70 20 for two hours. In this case the yield of chloride is almost quantitative. The foregoing detailed procedure has been arrived at from that given in German Patent 13 2,4 7 5.3... 

HYDROXY-5-NITROBENZYL CHLORIDE (Toluene, a-Chloro-2-hydroxy-5-nitro-)... 

The polar 1,4-cycloaddition of alkenes with 2-hydroxy-5-nitrobenzyl chloride in the presence of tin(IV) chloride yields 6-nitrochromans (69TL5279). The quinone methide, which is protonated under these conditions, undergoes stereospecific syn addition of the alkene. Although in most cases the reaction is regiospecific, ds-pent-2-ene yields a mixture of isomers. 

Effect of 1.0 M 2-hydroxy-5-nitrobenzyl bromide (HNBB) on bubble production in buffered agarose gels (0.3% w/w, 0.27 ml) containing distilled water. (Taken from ref. 231.)... 

Loudon GM, Portsmouth D, Lukton A, Koshland DE Jr. The chemistry of the modification of tryptophan with 2-hydroxy-5-nitrobenzyl bromide. J. Am. Chem. Soc. 1969 91 2792-2794. 

One common way to modify tryptophan residues occurs through the addition of 2-hydroxy-5-nitrobenzyl bromide (HNB). Also known as Koshland s reagent (68), this compound first alkylates the 3-position of the ring and eventually leads to the formation of a product mixture through subsequent intramolecular cyclization pathways. Fig. 6c. This reagent exhibits good tryptophan selectivity, although some levels of... 

Tyrosine Tryptophan Serine Aspartic Acid Glutamic Acid T etranitromethane Chloramine T iV-Bromosuccinimide 2-Hydroxy-5-nitrobenzyl bromide Diisopropylfluorophosphate Halomethyl ketones Carbodiimides Trimethyl oxonium fluoroborate Isoxazolium salts Chloramine T also modifies histidines and methionines... 

To facilitate aminoacylation of A -(2-hydroxybenzyl)annino acids or -peptide derivatives via O—> N acyl migration various related nitro derivatives were proposed,among which the A -(2-hydroxy-6-nitrobenzyl) and A -(2-hydroxy-5-nitrobenzyl) proved significantly more reactive in this context than the Hmb anoino acid residues. Incorporation of these protecting groups is performed by reductive alkylation as for the Hmb derivatives and removal of the N -protecting group is readily achieved by mild photolysis at 366 nm for 3 hours. 

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