Iodination cross-linkers

Radiolabel 55 nmol of SASD using IODO-GEN (Pierce Chemical) and 40 j,Ci Na125I for 30 s. Do not use Chloramine-T, since termination of the iodination reaction with this reagent involves addition of a reducing agent that may cleave the disulfide bonds of the cross-linker. 

Iodination of the cross-linker may be done according to the procedures discussed in Chapter 8, Section 4, or similar to that described for SASD (this chapter, Section 3.2). 

The homobifunctional photoreactive BASED (Chapter 4, Section 5.1) has two photoreactive phenyl azide groups, each of which contains an activating hydroxyl. Radioiodination of the cross-linker can yield one or two iodine atoms on each ring, creating an intensely radioactive compound. Cross-links formed between two interacting molecules are reversible by disulfide reduction, thus allowing tractability of both components of the conjugate. 

Finally, the small amine-reactive and photoreactive cross-linker NHS-ASA (Chapter 5, Section 3.1) can be iodinated to provide a nondeavable radioactive conjugate. 

Reported applications of SASD involve modification of lipopolysaccharide (LPS) molecules and studying their interaction with albumin and an antibody directed against LPS (Wollenweber and Morrison, 1985), identification of the murine interleukin-3 receptor and an N-formyl peptide receptor (Sorenson et al., 1986), cross-linking of factor V and Va to iodinated peptides (Chattopadhyay et al., 1992), and a comparison of radiolabeling techniques for the cross-linker (Shephard et al., 1988). 

B Label the cross-linker radioactively (radioactive cross-linkers are available in retail, e.g., H-HSAB or I-Denny-Jaffe reagent from NEN, or other, such as NHS-ASA or SASD, are easy to iodinate). Treat the radioactive cross-linker with an excess of nonradioactive ligand. Separate the radioactive PAL from unchanged ligand. 

Azetidines are compounds of interest in the field of agricultural and pharmaceutical chemistry. They are also useful as monomers and cross-linkers in polymer industry. Due to ring strain associated with it, azetidines are also useful S5mthons in organic chemistry. The common methods for S5mthesis of azetidines are cyclizations of y-amino alcohols, y-amino halides, 3-amino allenes, reactions of 1,3-dielectrophiles with amines, metal-catalyzed cyclizations in diazocarbonyls, cycloaddition reactions, and reduction of 2-azetidinones. There are several reports in literature on the S5mthesis of azetidines in aqueous media. A diastereoselective synthesis of azetidines is reported by the reaction of azazirconacyclopentane derivatives with iodine followed by treatment with aqueous potassium carbonate [26]. 

The iodination of cross-linked polystyrene has been achieved using iodine under strongly acidic reaction conditions [55] or in the presence of thallium(III) acetate [61], but this reaction does not proceed as smoothly as the bromination. More electron-rich arenes, such as thiophenes [45,62-64], furans [46], purines [65], indoles [66], or phenols [67,68] are readily halogenated, even in the presence of oxidant-labile linkers (Figure 6.2). Polystyrene-bound thiophenes have also been iodinated by lithiation with LDA followed by treatment with iodine [64],... 

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