Linkers disulfide-based reduction

An interesting linker is based on bis(4-hydroxyphenyl)disulfide 3 (Scheme 9.9). Both MPEG and the carbohydrate are linked as ethers, and for removal from MPEG, the linker s disulfide bond is reductively split by propanedithiol. The carbohydrate is freed as a glycoside of 4-hydroxyphenylmercaptan.38... 

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. 

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