Iodination modification agents

Directing the iodination reaction toward histidine residues in proteins, as opposed to principally tyrosine modification, is possible simply by increasing the pH of the lodobeads reaction from the manufacturer s recommended pH 7.0-8.2 (Tsomides et ai, 1991). No reducing agent is required to stop the iodination reaction as is the case with chloramine-T and other methods. 

The sequence of events following the reaction of metMb with hydrogen peroxide has also been investigated through the use of spin trapping agents. Initial studies of this type with 5,5-dimethylpyrroline N-oxide (DMPO) led to the identification of Y103 as the primary site of DMPO adduct formation, a modification that was blocked by specific iodination of this residue 187). The identity of the radical trapped in this reaction... 

In this section the first two approaches, modification of biliary contrast agents and iodination of nutritional lipids will be described. 

The basis for contrast agents derived from nutrional products was Intralipid, which had been prepared from phospholipids obtained from soy bean oil and egg yolk [86]. Intralipid was chemically modified by iodination into Intraiodol, which contained 50 mgl mbThe particles formed in the emulsion were mostly taken up by the hepatocytes and to a lesser extent by the RES [87,88]. Intraiodol was better tolerated than EOE-13 or its precursor, AG 60.99. The addition of cholesterol to Intraiodol resulted in NRI 757 with an iodine concentration of 42 mg mL b Further modifications by replacing the iodinated triglycerides of Intraiodol by ethiodized poppy seed oil and reducing the cholesterol content to... 

Perhaloalkanes serve as bromination or iodination agents in the radical decarbox-ylative halogenation of carboxylic acids. In an interesting modification of the Hunsdiecker-Bodin reaction Barton and coworkers have applied iV-hydroxypyridine-2-thione esters as nonelectrophilic intermediates for the decarboxylative bromination and iodination of primary, secondary and tertiary aliphatic and alicyclic592, as well as aroma-... 

Iodine-mediated oxidation has been applied in conjunction with 5-Xan, S-Tmob, S-Mmt, S-Trt, and 5-Acm protection (5, 8, 26-28, 38). Optimal solvents include ACOH-H2O (4 1), MeOH-HjO (4 1), and DMF-H2O (4 1) (39). The main caution with iodine is to avoid over-oxidation of the thiol functionality to the corresponding sulphonic acid, as well as to prevent or minimize modification of other sensitive amino acid side-chains (Tyr, Met, Trp) (5, 8, 38), It is advisable to monitor reactions, e.g. by HPLC once complete oxidation is verified, quenching should be carried out so as to lessen the extent of any possible side reactions. Other oxidizing agents, such as cyanogen iodide (97) or iV-iodosuccinimide (98), can be used. 

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